+EEVblog You need to get a variac and set it to the line voltage as shown on your picture to verify that the line voltage drop did not cause those output voltages to dip.
What's not to love about analog oscilloscopes, that phosphor glow is just beautiful. You have to fix this one Dave. Also, I laughed when you said "reboot it" lol.
I can't believe your timing with uploading this video Dave. Last week I dragged out of mothballs from the back of the factory where I work the very same CRO. It had been sitting there for 15 years or so. It was put there long before I was employed there. It wasn't wrapped up or protected in any way so everything looked crusty, rust on the BNC's dirty to look at. It past the PAT so I turned it on. Boy was it ill, Problems with the main Time Base, Vertical problems. Not quite like what you were getting Dave but felt it would need a lot of work to put it right. The traces would initially jump around even if you breathed on the control knobs. After awhile things started to settle a bit but never really stabilised. I attached a spectrum analyser to it, an SA450B which was also dragged out of mothballs and it produced a reasonable trace. It was rather unstable though and was inconsistent if you changed a Time Base setting. The general condition and the time needed to sort it out were prohibitive, It unfortunately had to make an appointment to see it's maker. Judging by how old it was, it will probably meet them too. lol Nice video though, thanks for that.
HI Dave, I have a mint one of these that my best friend and TE aficionado Ken Eastep left me in his will. I was with him when he ordered and took delivery of it from HP in the late 70's. I always wondered if his wife knew what he paid for it (you could buy most of a new car for the price of a 1740A). The 1740A was designed to compete with the Tektronix 465. Somewhere I even have the HP shipping box. A great scope. Now that you have it working check the risetime of the scope using a fast rise source. Chances are by now it is marginal. Fix this by massaging the coaxial delay line. The plastisizer in the jacket of the coax reacts with the silver and causes issues. Moving it around will cure this ill. On your bridge rectifier failure I had one of them fail in the +8V supply of a Tek 475 in exactly the same fashion, so though rare now I know of two!! Great job on a classic analog scope! How about that flood gun scale illumination! Worked great for Polaroid pictures. P.S. Kenny would have loved your teardowns, repairs and videos and also would be right up to speed with current electronics development. He was born 30 years too soon!
At 33:00 when you started to apply the heat gun to the electronics, I noticed that when you were focusing on the big long caps the black multi-meter started to dip constantly. When you pointed the heat gun away from them the black multi-meter began to rise again. I would suggest applying more heat to that area and see how low it goes and to hopefully (or not) break it again.
Another common failure with the 1700 series is the gold interconnect headers that connect the various boards. They commonly develop hairline cracks and what looks like oxidation around the gold plaited pins, where they contact the solder. I have had positive results when the old solder is removed and the pins are cleaned, then re-soldered with new solder. The horizontal time-base pcb's flex a little when changing the time-base setting and this may be why it's more common on them. Most of the IC's are standard TTL parts with the exception of the (2) Horizontal ASIC's (Gold Plated), (2) White Ceramic ASIC's, one near the CRT and one on the bottom PCB under the vertical calibration shield. One other common chip prone to fail is the 14 pin DIP chip on the Focus/Intensity/Beam Finder PCB, (HP 1821-0002) which is a CA3045 Transistor Array.
Well, I don't know if you can see it, but it seems that all the rails are deriving their reference fron the +15V rail, so anything wrong with the 15V rail would logically effect all of them. The +15V is the only one deriving its own reference (U1 pins 3 and 4)
So it's likely either something loading down the +15 or the power supply itself. I'd start by measuring the current draw on it, also disconnecting its filter cap and temporarily connecting a new one in, just so you eliminate it as a problem. I've once replaced a sprague with intermittent internal shorts. And look out for tantalums.
I HAVE ONE OF THESE!! This is my first scope and as a matter of fact the only working one I have. I love this thing! Wish I could afford a digital scope but I have to settle with my school's equipment if I need that capability. Still a great piece of hardware for analyzing the signals I work with. So great to see a piece of equipment I own on the channel.
I have two TEK's, a 454, and a 465. The 465 I got off Ebay from a seller that professionally reconditions them. IIRC I paid under $400 for that one. I've had my 454 for 30 years now, I bought it from a former employer who was auctioning off outdated test equipment to the employees. I paid under $250 for it at time, and they threw in a viewing hood, several probes, and a scope cart!
Looks like a vertical deflection problem, when you adjusted the trace position the vertical collapsed. You might want to look at the vertical output stage with the two wires going to the deflection plates. Your right with the case off it can cool, and operate normally. You might want to tack on a thermal probe and put the case back on and watch the temp. From what they say on the net, the vertical seems to be a common fault. Maybe apply some new thermal paste and that might do the trick. Worth a shot Dave ...
+MichaelKingsfordGray That must be why the manual looks spot on to USAF tech manuals that I used back in the day. You could have only basic electrical and mechanical knowledge; read that kind of manual and know %85 of what the engineers that designed it knew. Not only were great for working on the equipment, duh, but they also helped you learn new concepts technology on the way!
recently found your vlog, I used to have 1 of these on my bench back at Marconi when I worked in service and cal, also repaired and cald many a hp unit among others, keep up the grt work, really enjoy your channel.
Quite interesting! Did you notice that not only did all of those rails drop at the same time, they dropped by *THE EXACT SAME PROPORTION*? Every single rail you measured changed by (-20.76±0.1)%. Unless the mains flickered (and I didn't see the lights dim), I don't see how they could all drop by the exact same amount unless they all reference one of the rails. Find that rail, and you'll find the problem quickly I'll wager.
I absolutely share your enthusiasm for that exemplary operating manual! I wish I had something that thorough for the Lecroy scope I've been playing with lately.
Just looking back through Dave's remarkable treasure of UA-cam videos... Noticed I commented six years ago.. I just had to say I had one of these and as I looked again was struck by how beautiful this thing was. Hope Dave still has it, or it went to a good home.
Hi Dave ! I've got a HP1715 200Mhz the same panel and chassis than 1740, i buyed it 4 years ago , and after cleaning all electromechanical parts it's working OK , but the multi PCBs switches of time base are a pain in the a** , once a year or so, i have to realign the knobs axis with the rotary switches and clean the contacs of the connectors between 3 daughters and mother board. Mine got PCB edge contacts, i've see that yours have a very better plastic connector between boards. TIP: Power supply is almost the same in both scopes and in the service manual says that the +15V regulator serves as reference to al other voltages in the low voltage PSU. i hope this helps.
Awesome video. I bought that same scope with a spare scope for parts for $70 Canadian about 8 months ago, it works great and I love it as well... Looking forward to seeing how you problem solve and deduce that sick puppy into a healthy puppy... Thanks for taking the time to make and share the vid. Thanks for all your videos, they are truly great.
Hi Dave, I had similar HP scope with similar issue. Mine had multimeter on top with 7-segment display, the meter can be used for time measurements on the signal itself or as normal meter with external leads. Anyway, mine also had this exact issue with the power supply rails. Sadly I did find what is the problem, because it occurrence rarely, but I remember that all supply rails are referenced from the +15V rail. So if the +15V rail is overloaded and the current limit kicks in, not only the +15V rail collapses but all rails are collapsing. The problem can be overload on the +15V rail or in the PSU itself. I didn't figure it out, but may be you will have better luck. I hope this helps. Cheers!
And out of all the comments, you had the most useful information that lead to the issue. Or at least explained why all the rails dropped together about the same percentage. Good work.
HP 1740A CRO from a dumpster? Bloody hell. You have one mighty fine dumpster in your locality. Mine only has old fish bones and other rubbish of the same type.
I used these scopes in 2 workshops for 15 years in the 70s and 80s and they were extremely reliable.I liked them so much that I bought one 20 years ago and it is still working in my garage. Always start with the simple things when fault finding.Always re-solder those joints even if they look good because you can't always see the microscopic cracks. It is a crime to throw away a scope such as this.
Picked one of these up for $40 a few years back. In excellent shape and works like it did 40 years ago. On/Off switch is a little dodgy at times due to wear. Not a fancy digital scope, but pretty advanced for its time.
I have two of these. one had a bad multiplier and the other had a bad ch 1 gain selector. So they became a box of spares and one bobby dazzler as well. I absolutely love this piece.
mr carlson's lab blows eevblog out of the water i love mr carlson! he explains everything clearly and fixes everything he gets!!! i suggest adding him to your youtube lineup
+Joe Schmoe You can't really compare them, they both deal with different beasts, I'm sure mr carlson has also times when he can't fix stuff, but we don't get to see those, I could be wrong though.
This thing is a beauty. I'm trying to restore a 25 meg scope from ~ the same era, but from the eastern block (Hungary), and that is... Only a few PCBs, miles of wiring (all white), super-hard to access parts - but at least the documentation is kinda good. I highly respect those engineers who designed your HP for the care, and also the ones who designed this hungarian scope, because they could tame chaos itself...
I have the older 1710A 150MHz. I replaced the horizontal output chip on one of the channels with more discreet components. DTL logic. I still use it. Good find! I had a Tektronics 555 Quad channel with different input modules on my bench in the US Navy and a surplus one in one of the repair shops I worked for. I used a few HP oscilloscopes in my career.
Hey, that looks almost like my 1741A except mine has storage capabilities. I agree with you on the font on the knobs, very hard to read the decimal point. I ended up using a marker to bold them. Mine just has a problem with the intensity pot being touchy. Glad to see you with an Analog scope.
That problem reminds me the issue with my old crusty AT&T monitor made in 1994. Vertical positioning failed, so I only saw a thin bright horizontal line instead of picture. Fortunately, I could repair it with resoldering the joints, which lead to the main coil on the tube.
This is very similar to my 1725A. Mine was very dirty inside from being used in a garage though. I had to use De-Oxit on all of the controls, both internal and external, and also re-solder several of the header pins that connect the boards together. I also use an HP X-Y monitor from the same era. That one had a problem with a couple of the small round bridge rectifiers getting flaky.
The small round 1A rectifiers were a common failure on these, they intermittently short and pull the transformer voltages down. I've repaired 20 - 30 of the 1700 series scopes over the years and many odd failure problems were caused by the rectifiers. The problem will happen more with the unit closed up due to the heat not getting out. I ended up adding heatsinks on top of the newly installed rectifiers to keep them cooler and haven't had any more problems since.
I own a HP 1741A. didnt come with the manual so thats my next step to do repairs on it. seems like it wants to work but some contacts are dirty and some caps have started to leak.
For what is worth the 122V rail was dropping when he heated the regulators, and as soon as he lifted the "heat gun" from them it started rising again, it was slow (ten mV at a time) but steady and repetable, so maybe... we have also to consider the thermal inertia of the heat sink, it's obvious that a problem to the LDO's/regulation transistors can't be caused by 30 seconds of 100°C heat gun since the shear mass of the heatsink is sucking so much heat away from the active devices
Great scope! I the 1742A in immaculate condition. Even came with the manual! Want to get a nice compact digital one, but this is fun to use and I have a big soft spot for the old analogue screens... Besides, haven't found much that I really NEEDED a digital one for yet.
From the photo the voltages all fell to about 80% of their normal values. This has to be transformer primary side and or the transformer itself. Maybe solder in test wires taken out of a closed case so monitoring can carry on whilst the unit warms up. Transformers can get very smelly if distressed. Beautiful bit of kit. RIP. HP.
Bad contact on the mains voltage selector, thereby dropping all secondary voltages at the same time? Or is there a common reference for all the rails (or just the the 5V rail being used as a reference for all the others), so when it drops, everything falls proportionally?
The way it was cutting in and out, is there any chance that there is thermal protection on the voltage regulators or power supply (perhaps sensing a common shared heatsink), or even a common current sense circuit on a shared rail (such as ground) momentarily shutting things down when the total current exceeds a programmed limit? In the case of current sensing, a capacitor is often used to average out brief switching surges, but if the capacitor dries out then it may no longer properly hold off reacting to a brief switching surge that is otherwise within acceptable limits. Just some quick initial thoughts.
Just a few thoughts. When the fault happened, 4 things were different, only one of which was mentioned ( the lid off) The other 3: A)It was upsidown, B)There was no signal being fed into the Device, C) any tension of the Mains cord was reversed due to its orientation. All rails dropped @ same time.. any corosion on that mains plug/filter? Lose Ground Lug? I duno.. im just tossin out ideas.
I suspect that mains transformer is dying (intermittent connection on the primary side). That would also explain that smell your friend was talking about.
thanks Dave. I bought Tektronix 455 for $50 us dollar to learn but i couldn't fight out what that Verneir knob did. I guess I have ways to go with electronics!
Hell, Dave. I think this is the same series of scope I was using back in the early '80s. It would work for about 15 mins, then start acting goofy. Power LED was flickering like this one. Turned out to be a cracked 1A bridge rectifier, on the side that wasn't visible. One of those small round ones. I see you've got about a half dozen of those in there. When it got warm, it would partially fail. Just something that might help? Keep on slugging! At the time, it was a really nice scope! Stu Oh, another P.S. Those stupid connectors that they used to connect the pwr tranny to the board are notoriously flaky as they age, especially with a decent amount of current thru it. (Remember having to cut those out of about 40 power supplies, and soldering the tranny right in. All issues went away. Even worse, 70's pinball machines used them for all the lighting. What a mess! stu.
+Christian Ivarsson I am a hoarder!! hehe, I use everything at some point, but i live in a country when you have to work really hard to find quality instruments, most of what you get here is crap, and customs are impossible, so when I have the chance, yeah, i hoard all i can :)
For a current project, where I reverse-engineered the serial interface for a really cheap multimeter, I went out and bought 4 of them. That totals to five handheld DMMs now, one scopemeter and one bench multimeter.
Awesome video! I calibrate Oscilloscopes! Well, it's one of the many things I test and calibrate. Nothing this old but I've worked on many HP and Agilent products. :)
I have a bwd 521 scope (one of my prized possessions, 100mhz, true dual trace, a million knobs on the front panel, love it.) that must be at least 30 years old, and has a few of these issues, hopefully this video will help equip me to fix it.
The HP Way. Make a contribution to science, technology and society with innovative and quality products *_:... that are worth more to the customer than it costs us to make."_* Dave Packard.
I still have the mil-spec version of that one (AN/USM-339)... Those plastic knobs are *extremely* brittle... be gentle on them, they *will* break with use.
Surprised it did anything at all after 35 years! Beautiful build quality, and that manual! They don't make them like this any more... As an aside, I wonder how much that cost back in 1980? Probably the equivalent of several houses :-)
Dave: I generally appreciate the trouble shooting videos you produce. On this one, you trouble shot using five DMM's. Yes, of course, you were demonstrating a problem with the power supply. Most troubleshooters are lucky to have two DMM's. May I suggest, troubleshooting on a level that does not rely on the sophisticated equipment you have on your bench?
Please follow up with another video when you actually fix this! Hate to say this, but maybe you have an issue with the power transformer? Maybe an intermittent short in one of the windings? (Blow your heat gun on the tranny!) A short in ANY of the windings of a transformer will be reflected in the others! This DOES seem like a thermal effect, especially since it ain't showing up with the covers off and the thing inverted! Build yourself a heat chamber (wrap a thermal blanket around the thing!) and see what happens. When I was working at Digital Equipment in the 70's I had a board that would always fail in my lab, but it worked fine across town at another facility. I kept bringing the assembly back there to trouble shoot an they always gave it a clean bill of health. Then I realized that their lab was warmer than mine, we had real good A/C in ours. So I blew a heat gun on the board while it was plugged into an extender card and it started working! The cold spray made it fail! Turned out to be a bad I/C with an inverse thermal problem.
Is it that simple to learn?I saw one like this one at the flea market and they wanted 20 bucks but it was missing the plug in cord. Is it worth it to buy it? the guy said that he will bring the cord tomorrow.Cheers
Been thinking some more about that voltage drop. From what I saw of the schematic, those were 723 type regulators that have current fold back. So a short on one output shouldn't load down the transformer enough to drop the input to the other regulators enough for them to drop low. If your mains dropped for a moment you should have seen your shop lights flicker and your video camera would have burped. So to me this sounds like a problem with the power transformer.
I've seen dozens of these lately on ebay for sale, one problem is the time div switch. HP put some lubricate grease inside them at the factory. after several years it dries up and switch gets sticky. The switch has to be taken apart and cleaned.
I would suspect the hybrid coil drive going short, It would explain the strange trace and may pull the rest of voltages lower or maybe main transformer leakage issue. GET THE FLIR out. Big Thumbs Up.
+Mike James I was hoping he would do that, I think if he did, he would have found the problem with the rectifiers (1A round ones) common problem with this series.
Don't forget that real old timers never used picoFarads either. It was micro micro farads or mmf! Also, those Sangamo caps look familiar. Sangamo is/was a US maker of capacitors back in the old days (like 1930's - 1960's??)
If you plan a looong term use of this.....always remember these silver mica capacitors/condensers....they´re known to be very cool stuff, but they´re also known for the "silver mica desease" where the silver just dissapears from the foil, leaving just the foil formed a new insulation....Old sophisticated tube stuff suffer from this sort of grown error a lot as these SMCs are used a lot inside them...
Theres no way an LED, even below .5 watts, could cause such an issue in a well shielded oscilloscope. The LED runs at about 3 volts, a xenon at ~300 volts i think.
Dave, I think you need more heat. Hairdryer for sure, will spread the heat around more evenly and have larger coverage so you can just hold it there for a minute or so and not have to wave the damn thing around. Seems like you weren't able to stay on any one spot for quite long enough with that butane jobby.
Dave, Try Ye olde tryed and tested method, tap those bloody board connectors with a plastic screwdriver handle :-D The solder cracks, also where the connector presses on the pin you will find a black mark, dodgy joint central. The psu chips look like uA/Lm723's., Check the voltage changeover switch. I have an old cossor and telequipment scopes, bad joint city :)
Check the transformer, primary side. I bet that winding insulation is failing. Probably from chaffing over the years from thermal expansion/contraction. If the the short was reducing the number of turns on the primary side, would that result in lower output voltages? Also, check the voltage selector switch and see if dicking with it can cause the same defects.
'Dry as a dead dingo's donga'.LMAO ......Gotta love the Australian vernacular. lol.....Great vids dude, very interesting and informative......Best Regards from UK....
That is the most realistic type of troubleshooting...the kind where it won't fail while you watch it.
+youbecha64 Yup, if I had a dollar for every time it's happened...
+EEVblog You need to get a variac and set it to the line voltage as shown on your picture to verify that the line voltage drop did not cause those output voltages to dip.
+youbecha64 In demoing, I call this the negative demo effect.
In programming, a bug that doesn’t appear when you try to debug is called a Heisenberg
What's not to love about analog oscilloscopes, that phosphor glow is just beautiful.
You have to fix this one Dave.
Also, I laughed when you said "reboot it" lol.
I can't believe your timing with uploading this video Dave.
Last week I dragged out of mothballs from the back of the factory where I work the very same CRO. It had been sitting there for 15 years or so. It was put there long before I was employed there.
It wasn't wrapped up or protected in any way so everything looked crusty, rust on the BNC's dirty to look at. It past the PAT so I turned it on.
Boy was it ill, Problems with the main Time Base, Vertical problems. Not quite like what you were getting Dave but felt it would need a lot of work to put it right.
The traces would initially jump around even if you breathed on the control knobs. After awhile things started to settle a bit but never really stabilised.
I attached a spectrum analyser to it, an SA450B which was also dragged out of mothballs and it produced a reasonable trace.
It was rather unstable though and was inconsistent if you changed a Time Base setting.
The general condition and the time needed to sort it out were prohibitive,
It unfortunately had to make an appointment to see it's maker.
Judging by how old it was, it will probably meet them too. lol
Nice video though, thanks for that.
HI Dave,
I have a mint one of these that my best friend and TE aficionado Ken Eastep left me in his will. I was with him when he ordered and took delivery of it from HP in the late 70's. I always wondered if his wife knew what he paid for it (you could buy most of a new car for the price of a 1740A). The 1740A was designed to compete with the Tektronix 465. Somewhere I even have the HP shipping box. A great scope. Now that you have it working check the risetime of the scope using a fast rise source. Chances are by now it is marginal. Fix this by massaging the coaxial delay line. The plastisizer in the jacket of the coax reacts with the silver and causes issues. Moving it around will cure this ill. On your bridge rectifier failure I had one of them fail in the +8V supply of a Tek 475 in exactly the same fashion, so though rare now I know of two!! Great job on a classic analog scope! How about that flood gun scale illumination! Worked great for Polaroid pictures.
P.S. Kenny would have loved your teardowns, repairs and videos and also would be right up to speed with current electronics development. He was born 30 years too soon!
1st golden rule, measure voltages, 2nd golden rule, clean the switches. 3rd golden rule suspect the capacitors.
+Andrew Hull .. and start with the PSU power plug and those inter-board connectors.
5:41 ... that folks is why HP went from three guys in a garage to a loved and trusted, massive multinational instrument company.
At 33:00 when you started to apply the heat gun to the electronics, I noticed that when you were focusing on the big long caps the black multi-meter started to dip constantly. When you pointed the heat gun away from them the black multi-meter began to rise again. I would suggest applying more heat to that area and see how low it goes and to hopefully (or not) break it again.
+DiFractal Didn't notice that, will have to have a look, thanks.
+DiFractal A couple of hundred millivolts only on a 120V line is nothing to worry about.
+EEVblog
1970s technology is nice, but when are you going to make the next Samsung LCD TV repair video and nail down that bloody fault?
+MrCapacitator Yeah, but if he continues to heat and it continues to drop down, something else may reach a drop out point.
+Ernst Stavro Blofeld That Samsung is busted. Like most Samsungs.
this is a great video. i like how even when ya dont fix it, its still an adventure learning. what a ripper piece of equipment.
Looks like one you will have to come back to. Love vintage test gear.
Another common failure with the 1700 series is the gold interconnect headers that connect the various boards. They commonly develop hairline cracks and what looks like oxidation around the gold plaited pins, where they contact the solder. I have had positive results when the old solder is removed and the pins are cleaned, then re-soldered with new solder. The horizontal time-base pcb's flex a little when changing the time-base setting and this may be why it's more common on them.
Most of the IC's are standard TTL parts with the exception of the (2) Horizontal ASIC's (Gold Plated), (2) White Ceramic ASIC's, one near the CRT and one on the bottom PCB under the vertical calibration shield.
One other common chip prone to fail is the 14 pin DIP chip on the Focus/Intensity/Beam Finder PCB, (HP 1821-0002) which is a CA3045 Transistor Array.
Well, I don't know if you can see it, but it seems that all the rails are deriving their reference fron the +15V rail, so anything wrong with the 15V rail would logically effect all of them. The +15V is the only one deriving its own reference (U1 pins 3 and 4)
So it's likely either something loading down the +15 or the power supply itself. I'd start by measuring the current draw on it, also disconnecting its filter cap and temporarily connecting a new one in, just so you eliminate it as a problem. I've once replaced a sprague with intermittent internal shorts. And look out for tantalums.
I HAVE ONE OF THESE!! This is my first scope and as a matter of fact the only working one I have. I love this thing! Wish I could afford a digital scope but I have to settle with my school's equipment if I need that capability. Still a great piece of hardware for analyzing the signals I work with. So great to see a piece of equipment I own on the channel.
28:30 - David, you continue to amaze. I love the 5-DVM setup!
I have two TEK's, a 454, and a 465. The 465 I got off Ebay from a seller that professionally reconditions them. IIRC I paid under $400 for that one. I've had my 454 for 30 years now, I bought it from a former employer who was auctioning off outdated test equipment to the employees. I paid under $250 for it at time, and they threw in a viewing hood, several probes, and a scope cart!
THANK GOD FOR THIS VIDEO I JUST GOT A 1740A FOR 5$, TYPED IT INTO UA-cam HOPING DAVE HAD A VIDEO ON THIS BEAST
LOL I just got one for $10 and some yard work, and it works! Got here same as you. Great guy Dave.
Looks like a vertical deflection problem, when you adjusted the trace position the vertical collapsed. You might want to look at the vertical output stage with the two wires going to the deflection plates. Your right with the case off it can cool, and operate normally. You might want to tack on a thermal probe and put the case back on and watch the temp. From what they say on the net, the
vertical seems to be a common fault. Maybe apply some new thermal paste and that might do the trick. Worth a shot Dave ...
The manual!! It is like an old style Aircraft Maintenance Manual!(believe it or not we still have those as a backup for old aircraft.)
That's pretty quality material for a 70's device. Metal Film resistors!!
+MichaelKingsfordGray That must be why the manual looks spot on to USAF tech manuals that I used back in the day. You could have only basic electrical and mechanical knowledge; read that kind of manual and know %85 of what the engineers that designed it knew. Not only were great for working on the equipment, duh, but they also helped you learn new concepts technology on the way!
@@Kryoclasm whoahh can you give an example link? That's interesting
I love these diagnostic videos Dave
That scope is honeetly the most beautiful piece of engineering I have ever laid eyes upon.
recently found your vlog, I used to have 1 of these on my bench back at Marconi when I worked in service and cal, also repaired and cald many a hp unit among others, keep up the grt work, really enjoy your channel.
Quite interesting!
Did you notice that not only did all of those rails drop at the same time, they dropped by *THE EXACT SAME PROPORTION*?
Every single rail you measured changed by (-20.76±0.1)%. Unless the mains flickered (and I didn't see the lights dim), I don't see how they could all drop by the exact same amount unless they all reference one of the rails.
Find that rail, and you'll find the problem quickly I'll wager.
+Falcrist
There all referenced to the 15v rail, that makes troubleshooting a problem sometimes.
I absolutely share your enthusiasm for that exemplary operating manual! I wish I had something that thorough for the Lecroy scope I've been playing with lately.
Just looking back through Dave's remarkable treasure of UA-cam videos... Noticed I commented six years ago..
I just had to say I had one of these and as I looked again was struck by how beautiful this thing was. Hope Dave still has it, or it went to a good home.
I just bought one today! Haven't put a funtion gen on it yet. Glad Dave worked on one.
Hi Dave ! I've got a HP1715 200Mhz the same panel and chassis than 1740, i buyed it 4 years ago , and after cleaning all electromechanical parts it's working OK , but the multi PCBs switches of time base are a pain in the a** , once a year or so, i have to realign the knobs axis with the rotary switches and clean the contacs of the connectors between 3 daughters and mother board. Mine got PCB edge contacts, i've see that yours have a very better plastic connector between boards.
TIP: Power supply is almost the same in both scopes and in the service manual says that the +15V regulator serves as reference to al other voltages in the low voltage PSU.
i hope this helps.
Awesome video. I bought that same scope with a spare scope for parts for $70 Canadian about 8 months ago, it works great and I love it as well... Looking forward to seeing how you problem solve and deduce that sick puppy into a healthy puppy... Thanks for taking the time to make and share the vid. Thanks for all your videos, they are truly great.
Hi Dave,
I had similar HP scope with similar issue. Mine had multimeter on top with 7-segment display, the meter can be used for time measurements on the signal itself or as normal meter with external leads. Anyway, mine also had this exact issue with the power supply rails. Sadly I did find what is the problem, because it occurrence rarely, but I remember that all supply rails are referenced from the +15V rail. So if the +15V rail is overloaded and the current limit kicks in, not only the +15V rail collapses but all rails are collapsing. The problem can be overload on the +15V rail or in the PSU itself. I didn't figure it out, but may be you will have better luck. I hope this helps. Cheers!
+Tsvetan Marinov That's good info, he can focus on the boards which use +15V.
And out of all the comments, you had the most useful information that lead to the issue. Or at least explained why all the rails dropped together about the same percentage. Good work.
just awesome how detailed the manuals were back then. makers expected their wares to last forever! :)
HP 1740A CRO from a dumpster? Bloody hell. You have one mighty fine dumpster in your locality. Mine only has old fish bones and other rubbish of the same type.
I noticed the reset light blanked out when the scope glitched and then started flickering when you had the crap jumping all over the place.
I used these scopes in 2 workshops for 15 years in the 70s and 80s and they were extremely reliable.I liked them so much that I bought one 20 years ago and it is still working in my garage. Always start with the simple things when fault finding.Always re-solder those joints even if they look good because you can't always see the microscopic cracks. It is a crime to throw away a scope such as this.
Picked one of these up for $40 a few years back. In excellent shape and works like it did 40 years ago. On/Off switch is a little dodgy at times due to wear.
Not a fancy digital scope, but pretty advanced for its time.
I have two of these. one had a bad multiplier and the other had a bad ch 1 gain selector. So they became a box of spares and one bobby dazzler as well. I absolutely love this piece.
mr carlson's lab blows eevblog out of the water i love mr carlson! he explains everything clearly and fixes everything he gets!!! i suggest adding him to your youtube lineup
+Joe Schmoe
You can't really compare them, they both deal with different beasts, I'm sure mr carlson has also times when he can't fix stuff, but we don't get to see those, I could be wrong though.
The scope has been in Australia so long the electrons are running backwards.
This thing is a beauty. I'm trying to restore a 25 meg scope from ~ the same era, but from the eastern block (Hungary), and that is...
Only a few PCBs, miles of wiring (all white), super-hard to access parts - but at least the documentation is kinda good. I highly respect those engineers who designed your HP for the care, and also the ones who designed this hungarian scope, because they could tame chaos itself...
Dave is the best at scoping it out!
I have the older 1710A 150MHz. I replaced the horizontal output chip on one of the channels with more discreet components. DTL logic. I still use it. Good find! I had a Tektronics 555 Quad channel with different input modules on my bench in the US Navy and a surplus one in one of the repair shops I worked for. I used a few HP oscilloscopes in my career.
Don't get fooled, those are high tech Mega Farad caps!
It must have been the southern hemisphere compensation chip that had blown. Once you turned it upside-down, it worked perfectly
Whenever you see old Sprague capacitors you should automatically assume they are bad - because they always are :)
I think you got the operative words right. Wow. And beautiful.
Hey, that looks almost like my 1741A except mine has storage capabilities. I agree with you on the font on the knobs, very hard to read the decimal point. I ended up using a marker to bold them.
Mine just has a problem with the intensity pot being touchy. Glad to see you with an Analog scope.
That problem reminds me the issue with my old crusty AT&T monitor made in 1994. Vertical positioning failed, so I only saw a thin bright horizontal line instead of picture. Fortunately, I could repair it with resoldering the joints, which lead to the main coil on the tube.
The inside of that scope is beautiful and so is the manual :)
This is very similar to my 1725A. Mine was very dirty inside from being used in a garage though. I had to use De-Oxit on all of the controls, both internal and external, and also re-solder several of the header pins that connect the boards together.
I also use an HP X-Y monitor from the same era. That one had a problem with a couple of the small round bridge rectifiers getting flaky.
The small round 1A rectifiers were a common failure on these, they intermittently short and pull the transformer voltages down. I've repaired 20 - 30 of the 1700 series scopes over the years and many odd failure problems were caused by the rectifiers. The problem will happen more with the unit closed up due to the heat not getting out. I ended up adding heatsinks on top of the newly installed rectifiers to keep them cooler and haven't had any more problems since.
"A couple" of multimeters....
I own a HP 1741A. didnt come with the manual so thats my next step to do repairs on it. seems like it wants to work but some contacts are dirty and some caps have started to leak.
You got the prototype of "Tennis for two" video game with lightning storm simulation option package, nice! :)
For what is worth the 122V rail was dropping when he heated the regulators, and as soon as he lifted the "heat gun" from them it started rising again, it was slow (ten mV at a time) but steady and repetable, so maybe...
we have also to consider the thermal inertia of the heat sink, it's obvious that a problem to the LDO's/regulation transistors can't be caused by 30 seconds of 100°C heat gun since the shear mass of the heatsink is sucking so much heat away from the active devices
Great scope! I the 1742A in immaculate condition. Even came with the manual! Want to get a nice compact digital one, but this is fun to use and I have a big soft spot for the old analogue screens... Besides, haven't found much that I really NEEDED a digital one for yet.
From the photo the voltages all fell to about 80% of their normal values. This has to be transformer primary side and or the transformer itself. Maybe solder in test wires taken out of a closed case so monitoring can carry on whilst the unit warms up. Transformers can get very smelly if distressed. Beautiful bit of kit. RIP. HP.
how about using your thermal camera if you think its a head problem?
That's what I was thinking. Maybe the camera could narrow down the places he might target with the heat gun.
+gamerpaddy Because you could be chasing countless red herrings.
+EEVblog They would be orangish-white herrings =P
Bad contact on the mains voltage selector, thereby dropping all secondary voltages at the same time? Or is there a common reference for all the rails (or just the the 5V rail being used as a reference for all the others), so when it drops, everything falls proportionally?
+Dave Curran Yes, primary side was my first thought and plan of attack in the 2nd video I have half shot. I won't spoil anything...
The way it was cutting in and out, is there any chance that there is thermal protection on the voltage regulators or power supply (perhaps sensing a common shared heatsink), or even a common current sense circuit on a shared rail (such as ground) momentarily shutting things down when the total current exceeds a programmed limit? In the case of current sensing, a capacitor is often used to average out brief switching surges, but if the capacitor dries out then it may no longer properly hold off reacting to a brief switching surge that is otherwise within acceptable limits. Just some quick initial thoughts.
It kinda looks like the trace going to the diode at 27:35 might be cracked at the base of the socketed can. Could just be the angle though.
Fiske Brothers Refining are still in business they are now Lubriplate Lubricants the oldest lubricant manufacturer in the USA.
Just a few thoughts. When the fault happened, 4 things were different, only one of which was mentioned ( the lid off) The other 3: A)It was upsidown, B)There was no signal being fed into the Device, C) any tension of the Mains cord was reversed due to its orientation. All rails dropped @ same time.. any corosion on that mains plug/filter? Lose Ground Lug? I duno.. im just tossin out ideas.
I suspect that mains transformer is dying (intermittent connection on the primary side). That would also explain that smell your friend was talking about.
thanks Dave. I bought Tektronix 455 for $50 us dollar to learn but i couldn't fight out what that Verneir knob did. I guess I have ways to go with electronics!
Hell, Dave. I think this is the same series of scope I was using back in the early '80s. It would work for about 15 mins, then start acting goofy. Power LED was flickering like this one. Turned out to be a cracked 1A bridge rectifier, on the side that wasn't visible. One of those small round ones. I see you've got about a half dozen of those in there. When it got warm, it would partially fail. Just something that might help? Keep on slugging! At the time, it was a really nice scope! Stu Oh, another P.S. Those stupid connectors that they used to connect the pwr tranny to the board are notoriously flaky as they age, especially with a decent amount of current thru it. (Remember having to cut those out of about 40 power supplies, and soldering the tranny right in. All issues went away. Even worse, 70's pinball machines used them for all the lighting. What a mess! stu.
Hell yeah two part movie length repair video :)
"A couple of multimeters" And here I sat thinking I'm a hoarder :D
+Christian Ivarsson He uses them, so it's not hoarding!
+Necessaryevil 86
I know. It was a joke. I use all of mine too but I don't have that many :)
+Christian Ivarsson I am a hoarder!! hehe, I use everything at some point, but i live in a country when you have to work really hard to find quality instruments, most of what you get here is crap, and customs are impossible, so when I have the chance, yeah, i hoard all i can :)
I know about the joke, I was kidding too!
For a current project, where I reverse-engineered the serial interface for a really cheap multimeter, I went out and bought 4 of them. That totals to five handheld DMMs now, one scopemeter and one bench multimeter.
Awesome video! I calibrate Oscilloscopes! Well, it's one of the many things I test and calibrate. Nothing this old but I've worked on many HP and Agilent products. :)
I have a bwd 521 scope (one of my prized possessions, 100mhz, true dual trace, a million knobs on the front panel, love it.) that must be at least 30 years old, and has a few of these issues, hopefully this video will help equip me to fix it.
The HP Way.
Make a contribution to science, technology and society with innovative and quality products
*_:... that are worth more to the customer than it costs us to make."_*
Dave Packard.
I bought mine new with H13 option in 1982 for 3800 dollars us. Sadly, the vertical hybrids failed and are unavailable.
I still have the mil-spec version of that one (AN/USM-339)... Those plastic knobs are *extremely* brittle... be gentle on them, they *will* break with use.
Isn't vintage electronics something to look at! By the way, jealous on your multimeter collection, Dave!
Surprised it did anything at all after 35 years! Beautiful build quality, and that manual! They don't make them like this any more... As an aside, I wonder how much that cost back in 1980? Probably the equivalent of several houses :-)
Dave: I generally appreciate the trouble shooting videos you produce. On this one, you trouble shot using five DMM's. Yes, of course, you were demonstrating a problem with the power supply. Most troubleshooters are lucky to have two DMM's. May I suggest, troubleshooting on a level that does not rely on the sophisticated equipment you have on your bench?
Lubriplate is still in business, the name is at least. No 105 engine assembly grease is a standard for mechanics.
Please follow up with another video when you actually fix this!
Hate to say this, but maybe you have an issue with the power transformer? Maybe an intermittent short in one of the windings? (Blow your heat gun on the tranny!) A short in ANY of the windings of a transformer will be reflected in the others!
This DOES seem like a thermal effect, especially since it ain't showing up with the covers off and the thing inverted! Build yourself a heat chamber (wrap a thermal blanket around the thing!) and see what happens.
When I was working at Digital Equipment in the 70's I had a board that would always fail in my lab, but it worked fine across town at another facility. I kept bringing the assembly back there to trouble shoot an they always gave it a clean bill of health. Then I realized that their lab was warmer than mine, we had real good A/C in ours. So I blew a heat gun on the board while it was plugged into an extender card and it started working! The cold spray made it fail! Turned out to be a bad I/C with an inverse thermal problem.
that manual was printed 1 month before I was born. I was born in September 1976. a "Bicentennial" baby :-P
Just pick one these up, 1741A with the storage feature. But both my verniers are not functioning like yours! Fun times...
I picked one them up recently nice scope but I need to clean it up and fix the pannels a nice scope!
"because well, everyone knows how to use a scope" I don't :(
+Sonic Orb Studios There is enough info in there to get you started!
I think he meant EE engineers by everyone. Since those scopes were mainly in big corporations back in the day.
learn. it will take you 5 minutes.
Is it that simple to learn?I saw one like this one at the flea market and they wanted 20 bucks but it was missing the plug in cord. Is it worth it to buy it? the guy said that he will bring the cord tomorrow.Cheers
I saw one of these HP 1740A at the flea market today and they wanted 20 bucks for it would it be worth buying?Cheers
Gosh, that's a BEAUTIFUL scope (aesthetically speaking). I like my Hameg but... Dang, I gotta get my hands on an old HP at some point.
The tiewraps may have been replaced when the chemicon capacitor was placed.
Don't give up !
A Hewlett Packard piece of equipment. Does that sound sexy or what.
Been thinking some more about that voltage drop. From what I saw of the schematic, those were 723 type regulators that have current fold back. So a short on one output shouldn't load down the transformer enough to drop the input to the other regulators enough for them to drop low. If your mains dropped for a moment you should have seen your shop lights flicker and your video camera would have burped. So to me this sounds like a problem with the power transformer.
With a Z axis input, this sucker would make a great vector arcade monitor!
I've seen dozens of these lately on ebay for sale, one problem is the time div switch. HP put some lubricate grease inside them at the factory. after several years it dries up and switch gets sticky. The switch has to be taken apart and cleaned.
I'm curious to know, was that display bezel that same color from the factory or has it aged to that color?
I would suspect the hybrid coil drive going short, It would explain the strange trace and may pull the rest of voltages lower or maybe main transformer leakage issue. GET THE FLIR out. Big Thumbs Up.
+Mike James
I was hoping he would do that, I think if he did, he would have found the problem with the rectifiers (1A round ones) common problem with this series.
7:20 "WOOOW look at this, FANTASTIC bedtime reading!" hahaha
just bought this beast here in denver , colorado usa
Don't forget that real old timers never used picoFarads either. It was micro micro farads or mmf! Also, those Sangamo caps look familiar. Sangamo is/was a US maker of capacitors back in the old days (like 1930's - 1960's??)
If you plan a looong term use of this.....always remember these silver mica capacitors/condensers....they´re known to be very cool stuff, but they´re also known for the "silver mica desease" where the silver just dissapears from the foil, leaving just the foil formed a new insulation....Old sophisticated tube stuff suffer from this sort of grown error a lot as these SMCs are used a lot inside them...
Was your flash on when you took the photo? Could the LED flash of the phone camera cause some sort of reset like xenon flash does to the Raspberry Pi?
+Rockey Nope, hardly ever use my flash.
Theres no way an LED, even below .5 watts, could cause such an issue in a well shielded oscilloscope. The LED runs at about 3 volts, a xenon at ~300 volts i think.
+EEVblog darn, see your response now... very weird that you captured the voltage dip then...
Dave, I think you need more heat. Hairdryer for sure, will spread the heat around more evenly and have larger coverage so you can just hold it there for a minute or so and not have to wave the damn thing around. Seems like you weren't able to stay on any one spot for quite long enough with that butane jobby.
Dave, Try Ye olde tryed and tested method, tap those bloody board connectors with a plastic screwdriver handle :-D
The solder cracks, also where the connector presses on the pin you will find a black mark, dodgy joint central.
The psu chips look like uA/Lm723's., Check the voltage changeover switch.
I have an old cossor and telequipment scopes, bad joint city :)
Check the transformer, primary side. I bet that winding insulation is failing. Probably from chaffing over the years from thermal expansion/contraction. If the the short was reducing the number of turns on the primary side, would that result in lower output voltages? Also, check the voltage selector switch and see if dicking with it can cause the same defects.
At 26:43, the way they have spaced those two wires is very reminiscent of ladder line, so perhaps a balanced transmission line?
+Ethan Poole
it is, that's the vertical differential signal from the vertical amplifiers.
Look on ebay for 3d-printed replacement for the 4 feet on the back panel. They also function as cord wrap. Similar feet on Tek scopes of that vintage.
'Dry as a dead dingo's donga'.LMAO ......Gotta love the Australian vernacular. lol.....Great vids dude, very interesting and informative......Best Regards from UK....
5300 mega farads! :D
Maybe power fluctuation and bad power supply capacitors causes the failure?
Wow this thing goes berserk like hell. xD Really funny and interesting these failure modes!
In this case would wrapping it in cellophane( clear plastic ) be appropriate here to trap in the heat.