I love seeing different ways to do tasks and diagnose from other techs. Nice change of perspective, sometimes I find they way I was doing it for years wasn't the best way. Everyone has their set ways and preferences, not necessarily right or wrong.
I've seen similar problems with TVs from the 60's, particularly with RCA, G.E. and Sylvania among others They used phenolic boards and they are brittle and don't handle heat well (especially with vacuum tube sets). This was before popular use of glass/epoxy boards. I've also seen this type of boards in VCRs. WRT "flux removal", using a brush with alcohol doesn't actually "remove" the flux. It just dissolves it and spreads it around in a thin layer so it's not easily seen. Sometimes, attempts to dissolve flux can cause otherwise benign flux to become reactivated and become somewhat corrosive. I'd rather just leave it on the board undisturbed. It's not harmful. In current industry, most flux is water soluble for SMT and TH convection/wave solder and is sprayed off with DI water and ends up down a drain but in the "old days", it was typically just left on the board.
Tony, I can't tell you how much I've learned from you. I watch your videos for general information and enjoyment but I'm not tempted to try to repair. Yet, when you touched the heatsink, I said out loud before you, Bias and DC offset.... :) Thanks so much!
Thanks for the video Tony. Painstaking job. I had one of these for 25 years and it travelled around the world a few times. Great amp with heaps of current. Those tone switches (and the other pots) are a real problem and get noisy / faulty - sometimes cutting out one channel.. was very tricky to get the thing running properly. Eventually it just got too hard to get right again and I sold it to a guy who restores them for 100 bucks. Weighs a ton too!
Love the display of the insets in the videos. By stopping the video, it's possible to see everything without any jitter. Perhaps in time you can put them up in real time, during the session, and point to things with your cursor as you make the points?
Dude LoL, if you are getting jitter, you need to upgrade to a HDD recorder and look into the issue that you might be having with tracking on your VCR... I know what you are saying but I just pictured you using a VHS VCR to watch this LoL...
The problem is that I do my editing on the computer upstairs in the living room, while I actually record the video downstairs at the bench. Placing static images and talking over them at the editing computer is a bit too time consuming and I have to wait until it's quiet (that never happens around here) before I can record. So, this is the next best thing. ;)
I repaired (well, mostly, I actually need to go back in to fix a "pop" when the tone bypass is turned on) a Hitachi HA-4700 which is also from that era of early-mid 80s and it was the same, just about every solder joint was cracked. Had to retouch the entire board.
Hi Tony and all.. The PCB and components, pots,ribbon connectors and even the Bando transformers look exactly like the 1980's era Pioneer SA 720 /620 /520 range of amplifiers. Same problems as well. I enjoy your vids A LOT. Thanks.
I agree with your flux removal philosophy. Hey Tony. I was thinking when I saw the "Bubble Headed Booby" robot from Lost in Space. The funniest scene with the robot, I think, was when he was playing the guitar and singing a Cowboy song. Too funny! He is my 2nd favorite robot. My first place robot, of course was "Robbie" from Forbidden Planet. The guy who designed that form was a genius! Also, the best sci-fi movie ever made. My opinion. Looking forward to part 2!
You keep talking about how good these amps sound. I bought my HK 655 for the added power over my kenwood 6090, but I don't remember it sounding "better". I now have a kenwood KA7100 and am amazed at the sound compared to some more modern equipment. Now you got me wondering if it is better. But the KW is known to be more reliable so I am sticking with it for now. Great part one. Looking forward to part two.
It make perfect sense why the joints would crack with to big of holes on a single sided board. However, I find that on plated through hole boards it can be a real challenge to suck out of wick the solder if the holes are too tight. Especially on wave soldered boards.
Just found your channel. I like working on vintage HiFi equipment too so this is very interesting. I also make my own audio equipment just for fun. To help remove the CA glued knobs, use a CA debonder. Bob Smith Industries offer one called "Un-Cure". Sometimes soaking the joint with acetone works too.
Greetings: I have no first-hand experience with liquid flux because all of my soldering needs are covered with paste flux beyond core flux. When I need to do a lot of reflow, I first apply paste flux to sections that will allow me a comfortable amont of work area. Then I only need to keep my iron's tip clean to progress without having to adjust my solder length. It is my practice to use lacquer thinner to clean excess flux off the board even though the air quality folk would rather I didn't.
Why do I see Technics when I look at this amplifier... There's something about the styling of it... Tony, I really don't mind you doing it the same way each and every single time... I personally think that it's better that way, you see the same thing so many times that it becomes ingrained and forms a good habit... Visual inspection first, check power supply voltage, check for DC offset, check Capacitors for all possible failure modes ( I was kinda hoping that you would bring out the other LCR Bridge Meter which displays everything on the one screen, not just ESR and capacity but Drain (EPR) and Quality too...)... So basically I think that routine is always healthy because it keeps you from missing something important... Something that I see a lot of on UA-cam is people just replacing the obvious failed component but never really go looking for why it failed in the first place... I believe that transistors and diodes don't normally fail out of nothing! The cause is usually somewhere before or after... Regarding Capacitors though... I kinda don't like seeing people just checking capacity and ESR... I tend to think that high ESR becomes a real problem in the power supply section where speed is essential to filter out voltage ripple but EPR (Equivalent Parallel Resistance or drain or DC leakage ( seems to have many different names)) is a far worse fate than death... A capacitor with low EPR will pass DC and this usually results in death for the next component... I have been trying to raise awareness about low EPR and what it means in the comments section of other channels but people still think that ESR and a visual inspection is plenty... A capacitor with low EPR can display very good ESR and higher capacity! This is not a good Capacitor! They don't get better with time LoL... If the capacitors capacity has gone up, it's because it's leaking DC which will cause it to take longer to measure giving the impression that it has more capacity than what is printed on the side of it... This is why I personally prefer the other LCR Bridge Meter.. I went right out and got the newer version of yours which is black and has a built-in rechargeable battery via USB C which makes it even easier to use than your one... But they both work identical... Having all that information goodness all at the same time is far more functional than having to scroll through it... The DERR model that you used in this video is a great unit but you didn't scroll through the other details (on camera anyway), I'm wondering if the Capacitors that you tested were leaking DC? Because if they are very high ESR, they might not leak anything lol... Except for getting hot, expanding and leaking electrolyte! But low EPR Capacitor's don't get hot 🔥, everything else does!! Bypass capacitors will cause the transformer and rectifier to heat up or transistors and opamps! Coupling Capacitor's with low EPR will also destroy opamps and transistors and other semiconductors... I think that once the fundamental level of understanding is reached regarding the capacitor failure modes and what it all means, then we will all know what to look for to prevent a catastrophic failure down the road... I love Capacitors but the grief that they cause is a huge problem and not everyone really understands why! ESR is not enough to give you the full picture of what's happening and what's about to happen.... Apart from that.. spending time and talking while working can only be a good thing... Videos will take only as long as they need, not a minute more, not a minute less! You do what you do, I'ma be here watching...
TV's from the 90's were the worst, I spent so many hours resoldering cracked joint's just to find that the intermittence will reappear as soon as you slide the pcb on the bottom of the device, at least the 80's TV's had the pcb with the solder side oriented to the back of them, making it easier to resolder
Tony , it is best way your way , we like your long video , more longer better , don't lesson to other , if some don't like it just they can forward it or close it . simple as that.
Tony, Have you ever considered PCB Rivets for connectors on single sided PCBs? Sure seems like adding a solid mechanical thru hole would do good for these types of applications. Granted the rivet press is an expensive item, and doing it by hand is time consuming, but what ever. I've been thinking about using them myself and having a friend spin up the dies on a lathe, just use a plain ole cheap arbor press (something from Harbor Freight) to set the rivets.
Had my 655 in the trunk of my car when the cat burned up. The heat boiled the caps in the amp. Sounds like the burned up cat saved me a lot of future headache.
Thanks Tony, you know it seems problematic to have those rigid wire interconnecting cables - because of their rigidity they act like a fulcrum and overly stress the solder joints - I wonder if less rigid cables wouldnt have been a better design.
Hi I have a HARMAN KARDON HK6600, I have a pop when turning on the amp when the relay in the protective circuit kicks in and when turns off. In addition the speaker selector pops when turned to a different position. Other than this my amp works fine, have you run across this problem? I will try to resolder the the solder joints at the capacitor in the meantime and see if that helps
Sir, how do you clean the little push switches on the front fascia? Mine all make popping or scratching sounds when depressed. Also the volume and balance pots are scratchy. Otherwise the amp still works very well.
Great video:-) I was thinking about retouching the solder joints, would it be possible to use hot air? I am just thinking to make sure every joint has been reflown. Or maybe put it into a solder own?
@MARTIN PRECÁK Thank you a lot for your reply,! :-) I was just thinking that cleaning off the board, some new flux, and reheating would be like resoldering. Many of us do often use old solder rolls added some flux.-)
Just reheating it won't work. The best approach is to remove the old solder, clean the solder pad and apply fresh rosin core solder. In less critical applications, you can reflow the existing solder joint by adding some fresh rosin core solder or by adding some non-corrosive flux to the existing joint. Either way, the repaired joint should be smooth (no pits or cracks) and shiny, and should look conical, not dome shaped. Thanks for the comment!
These amps use standard bipolar transistors. Those VFET's are impossible to find these days, although they are supposed to be pretty reliable. Those amps are very rare as well. That's why you haven't seen one of those Sony VFET amps on my bench yet!
@@xraytonyb Yea..And the T0-92 small FETS for the line-amp stages are unobtanium also. I ended up redesigning a line-amp circuit and replaced them with low noise bi-polars after they ran flawlessly for 40 years ! The Sony boards were designed well easy to remove. My college roommate had an HK1000 cassette deck. That gear got a work out...:)
The flashing LED at startup indicates it is going through its startup routine, but I hear "boom" on the speakers when it stops flashing. I do not have it on my other amplifiers. Is it a failure or just a feature?
my brother had one of these after he graduated HS. Hours listening to this thing. 1987 I think? Thot very well of this unit. Not sure it was PM665....wonder if there was a 645 or 655? but the front looks almost identical. Never thot of them as 'high' end but the better end of the middle.
I worked in a factory where we mass produced electronic boards back in the 80s. Most of the components were mounted by a machine, hence the big holes and then they were wave soldered. EVERY BOARD had to be inspected and touched up by a crew of humans. I dont know if they ever got their ROI from the cost of that equipment, because the repair facility was always busy. SMH.
I see some test equip. 'under wraps' Coming soon ? Also, Playlists would be really good, when looking at you back vids. I've made a few of my own but I had to make some of them private to stop my channel looking like xray-cloney. I know you're busy so thanks anyway.
Hello! I have a PM655 Vxi, which gives me a problem. When I turn it on there is no sound, but a small "pop" is heard in the background on both speakers every 10 seconds repeatedly. When it has been like this for 20 minutes, the music starts playing. Sometimes it stops again, but the music comes back. The next day when I turn it on, I only have to heat it for 3 minutes for it to work well. No contact failure, I already reviewed all the soldering on the board. The fault is not in the preamp, because I disconnected the jumpers from the back that goes directly to the power stage, and it continues to give the same fault. Does anyone have an idea what could be wrong? Thanks.
I have a *Harman/Kardon* *AVR* *80* - It's a 5.1 with THX. It cost an extra $1,000 for the THX. Bought it in 1985, has never needed servicing! --- Sorry, with all those loose solder joints, I WOULDN'T power it up! What kind of Alcohol?
I have repaired old solder joints on computers by putting the mother boards in the oven at 200C. Can you do this with amplifier boards to avoid having to resolder joints.
Wouldn't really be a reliable repair, as there was not enough solder to begin with. Watch what happens when he touches one of the joints without adding solder, it wicks to the pad and there is virtually none holding the component in place.
I recently bought a HK 680, but the transformer emits a tremendous humming of the kind you can't hear in speakers. I also screwed with some bolts, even those transformers are similar (Bando, now closed). Do those make noise? Should I change it?
I have a HK690, and I have the same hum (mechanical vibrations) from time to time (not continuous), I think it depends on the power network... I learned to live with that......
Hi, after replacing the burnt transistor in the final stage of the amplifier,I checked back and I found varistor mv12ym (chain of diodes) which is burnt out. I can not find any replacement. Maybe you know any substitute. Amplifier PM 655Vxi, element D409, kindly please help me if yoy can.
What about upping the THD to something like 0.1 would that be in the local feedback? Couple of people told me nichicon capacitors are not very good not for sound quality
I don't think that you will notice a difference in sound quality with any brand of Capacitors... The main difference is in the working life... That reminds me of the people who say that they don't want to change Capacitors because they don't want to loose the sound that they are getting, well if you like listening to an amplifier in pain... It's going to die, but if you like that sound, there are ways to get the same sound without destroying an amplifier. People want a clean sounding Amplifier and don't realise how much they actually like distortion until they hear a dying amplifier... That's why they say that you shouldn't believe everything that you read on the internet....
This is screaming consumer grade. It's a fine unit but those bakelite single sided boards and all those plastic knobs covered in metal make your job so difficult.
This looks like a very time consuming repair. So much to go over and resolder. So many transistors that could be bad because of it as well. Brunt resistorsand out of tolerance e caps. There are a lot of things to check to get it working properly again for sure. At 18:25 in we have a good candidate for a speaker circuit breaker protection device for all speaker outputs. www.parts-express.com/Speaker-Circuit-Breaker-2.5A-200W-260-830
Tony, I really enjoyed this video. I was about to look for part 2 when I realized that you probably don't have it uploaded yet. Looking forward to it. I have a few questions. 1. On those switches...the plastic ones you said were quick to fail...is there a recorded MTBF on them that you know of? 2. Do those same switches contain a Wobblefram Actuator Seal ? 3. In the area where you replaced the Zener Diodes, did you check the value of the resistors there? Since I didn't see any of those raised above the board, I imagine you either didn't measure them or didn't replace them for some reason. 4. Do you really trust the filter capacitors in the power supplies enough to leave them in there? I would not trust them and would replace them, but that is just my own "knee jerk" reaction to capacitors in general. 5. Did I understand you correctly that the holes in that circuit board do not have a "feed-through" hole that connects the top and bottom of the board? Keep up the good work...and I am glad that you don't worry about the "gripes" you get. You can't please everyone, and you seem to have that under control so that it doesn't bother you.
THD < 0.08% is surprisingly high distortion for a high end amp. That said, I'm an amp designer, and by the time these amps have been through the various cost cutting measures and sourcing issues involved in mass manufacturing, maybe that's pretty typical? That said, my best designs are closer to 0.0001% at 20kHz, and aren't a lot more complex than my high-power designs which perform better than 0.001% THD. My first design, a guitar amp, where I didn't even care about the distortion ended up performing around 0.01% at 20kHz and 0.005 at 5kHz (the sweet spot). I think it's the difference between me having access to free simulation software to iron out the kinks, sweep for issues, and optimize things, (LTSpice is my favourite) and these older designers having to work things out the hard way.
Hello Tony, thanks for the video. I was wondering why you used the ksc2383 with the ksa916 instead of using the ksa1013. Is it because in this application they do not work as a complementary pair?. Anyhow, interesting and useful video. Thanks again
Hello! Does anyone know why one red light comes on on some models and two on others? The one that is always on is "High Current", but the one for "High Voltage" in my amplifier works fixed and in other equal amplifiers it is without light. Do you know what these lights mean? Thank you.
Found it... the "High Voltage" light is due to the switch on the back where it changes from 4Ω to 8Ω. What a way to call it, anyone would have thought anything else.
Any reason why there is no capacitive coupling for the output stage of this class AB amp ? Almost every class AB output stage uses capacitor coupling to prevent DC leakage into speakers
These amplifiers use a split power supply, with equal positive and negative rails. The center point of these amplifiers will be 0 volts at idle, if working properly. Amplifiers with single rail power supply will have the mid point set at a voltage roughly 1/2 the voltage of the supply. This is called offset. Single rail amplifiers, regardless of being class A or Class AB, will need some form of isolation (either a capacitor or transformer) to remove the DC offset from the speaker output. The design of the amp has everything to do with the offset. It is possible to design either class A or class AB with or without an offset, depending on how the power supply is configured.
@@xraytonyb - Thanks for thorough explanation, however I don't see a reason why not to use a coupling cap even for split power supply amps, as a precaution.
It wasn’t about cost. A direct coupled solid state amp was the thing back then. I think it actually started about 10 years before this amp. Eliminating the capacitor gave better sound.
I used superglue on the knobs, and to my disappointment it holds very well. Why disappointment? Because I glued one of the the damn things upside down :(
46:00 To little solder on each pads is the real issue here, not necessarily the size of the holes. To high speed on the boards when they pass trough the wave-solder would result in to little solder sticking to the pad. As you will notice the fix is to add more solder. There's really no need to remove the old solder. Clean it with IPA and resolder it will fix it. And BTW, not to much solder. You should see the leg of the component, not drown it in a big blob of solder. Btw those tracks shure has some odd shapes.
Argh, the best way to do this is replace the boards with some sturdier shit, and replace all parts. Then it's almost better to just build a new design as well. :(
For all the hype of HK, the fact is, they used crappy quality boards. Thin, brittle, oversized holes. Not exactly the quality one would expect from a supposedly high end audio company.
I appreciate your concern. I can assure you that I do not suffer from Parkinson's, nor essential tremors. My mother-in-law along with several other friends of mine do, however, suffer from this terrible disease. It can't be diagnosed by watching someone with shaky hands on a video. What I do suffer from is the inability to reach both hands around either side of a camera that is positioned in my face, holding the solder and the circuit board in one hand and the soldering iron in the other, all at an odd angle while trying to see what I'm doing through the progressive lenses in my glasses...all so that I can get a good camera view for you, without my hands and arms getting tired and shaking. ;)
The flashing LED at startup indicates it is going through its startup routine, but I hear "boom" on the speakers when it stops flashing. I do not have it on my other amplifiers. Is it a failure or just a feature?
The only thing I've found that superglue works on, reliably, 100%... is fingers
It's good to see one of these from out in the wild drop in for a tune up!
Great timing, I have a vxi I saved from the scrap heap that needs some work. Now I have a few things to keep an eye out for!
Well, you know Tony, there's so many people out there willing to tell you that their way is the only way it should be done. @ 21:45
Their way or the highway 🤣🤣
I've got a PM660 that when running right, really delivers. Those push buttons are a pain. Good stuff Tony, keep it up.
I love seeing different ways to do tasks and diagnose from other techs. Nice change of perspective, sometimes I find they way I was doing it for years wasn't the best way. Everyone has their set ways and preferences, not necessarily right or wrong.
A lovely adventure. Enjoyed, always something new to learn . Thanks, as always .
I've seen similar problems with TVs from the 60's, particularly with RCA, G.E. and Sylvania among others They used phenolic boards and they are brittle and don't handle heat well (especially with vacuum tube sets). This was before popular use of glass/epoxy boards. I've also seen this type of boards in VCRs.
WRT "flux removal", using a brush with alcohol doesn't actually "remove" the flux. It just dissolves it and spreads it around in a thin layer so it's not easily seen. Sometimes, attempts to dissolve flux can cause otherwise benign flux to become reactivated and become somewhat corrosive. I'd rather just leave it on the board undisturbed. It's not harmful.
In current industry, most flux is water soluble for SMT and TH convection/wave solder and is sprayed off with DI water and ends up down a drain but in the "old days", it was typically just left on the board.
Wow, your hands have the muscle memory of a surgeon, when soldering. Impressive. Not your first rodeo. Thanks for sharing.
Tony, I can't tell you how much I've learned from you. I watch your videos for general information and enjoyment but I'm not tempted to try to repair. Yet, when you touched the heatsink, I said out loud before you, Bias and DC offset.... :) Thanks so much!
Thanks for the video Tony. Painstaking job. I had one of these for 25 years and it travelled around the world a few times. Great amp with heaps of current. Those tone switches (and the other pots) are a real problem and get noisy / faulty - sometimes cutting out one channel.. was very tricky to get the thing running properly. Eventually it just got too hard to get right again and I sold it to a guy who restores them for 100 bucks. Weighs a ton too!
I have the same amplifier ready to be get serviced! great video.
Love the display of the insets in the videos. By stopping the video, it's possible to see everything without any jitter. Perhaps in time you can put them up in real time, during the session, and point to things with your cursor as you make the points?
Was thinking the same thing.
Dude LoL, if you are getting jitter, you need to upgrade to a HDD recorder and look into the issue that you might be having with tracking on your VCR...
I know what you are saying but I just pictured you using a VHS VCR to watch this LoL...
The problem is that I do my editing on the computer upstairs in the living room, while I actually record the video downstairs at the bench. Placing static images and talking over them at the editing computer is a bit too time consuming and I have to wait until it's quiet (that never happens around here) before I can record. So, this is the next best thing. ;)
I THANK YOU !! for Showing your work. It helps me learn how to fix my equipment.
Great Job
I have the PM655. Hooked up a DAC to it and JBL LX500. I love the sound!
Always liked HK gear, looking forward to this Tony!
Thank you for all videos and lessons! I really learn a lots new thinks from you video! Best regards from Romania!
Thanks a lot, I have this amp and I wanted to restore it, I just needed something like this great video!
I like your attitude!!! "You don't have to watch it." Awesome!
I repaired (well, mostly, I actually need to go back in to fix a "pop" when the tone bypass is turned on) a Hitachi HA-4700 which is also from that era of early-mid 80s and it was the same, just about every solder joint was cracked. Had to retouch the entire board.
Hi Tony and all.. The PCB and components, pots,ribbon connectors and even the Bando transformers look exactly like the 1980's era Pioneer SA 720 /620 /520 range of amplifiers. Same problems as well. I enjoy your vids A LOT. Thanks.
nasa quality
I agree with your flux removal philosophy.
Hey Tony. I was thinking when I saw the "Bubble Headed Booby" robot from Lost in Space. The funniest scene with the robot, I think, was when he was playing the guitar and singing a Cowboy song. Too funny! He is my 2nd favorite robot.
My first place robot, of course was "Robbie" from Forbidden Planet. The guy who designed that form was a genius! Also, the best sci-fi movie ever made. My opinion.
Looking forward to part 2!
All I can say is you have a LOT of courage powering this on after finding so many open solder joints!
You keep talking about how good these amps sound. I bought my HK 655 for the added power over my kenwood 6090, but I don't remember it sounding "better". I now have a kenwood KA7100 and am amazed at the sound compared to some more modern equipment. Now you got me wondering if it is better. But the KW is known to be more reliable so I am sticking with it for now. Great part one. Looking forward to part two.
HK PM665 has a lot more power
Look forward to next episode. Thank you.
It make perfect sense why the joints would crack with to big of holes on a single sided board. However, I find that on plated through hole boards it can be a real challenge to suck out of wick the solder if the holes are too tight. Especially on wave soldered boards.
The way YOU, make your videos is the best, nevermind the pros, WE are not pros, we try to learn!!!
Just found your channel. I like working on vintage HiFi equipment too so this is very interesting. I also make my own audio equipment just for fun.
To help remove the CA glued knobs, use a CA debonder. Bob Smith Industries offer one called "Un-Cure". Sometimes soaking the joint with acetone works too.
Good job👍 I call those cracked joint city🤣
Greetings:
I have no first-hand experience with liquid flux because all of my soldering needs are covered with paste flux beyond core flux. When I need to do a lot of reflow, I first apply paste flux to sections that will allow me a comfortable amont of work area. Then I only need to keep my iron's tip clean to progress without having to adjust my solder length. It is my practice to use lacquer thinner to clean excess flux off the board even though the air quality folk would rather I didn't.
Why do I see Technics when I look at this amplifier... There's something about the styling of it...
Tony, I really don't mind you doing it the same way each and every single time... I personally think that it's better that way, you see the same thing so many times that it becomes ingrained and forms a good habit...
Visual inspection first, check power supply voltage, check for DC offset, check Capacitors for all possible failure modes ( I was kinda hoping that you would bring out the other LCR Bridge Meter which displays everything on the one screen, not just ESR and capacity but Drain (EPR) and Quality too...)... So basically I think that routine is always healthy because it keeps you from missing something important...
Something that I see a lot of on UA-cam is people just replacing the obvious failed component but never really go looking for why it failed in the first place... I believe that transistors and diodes don't normally fail out of nothing! The cause is usually somewhere before or after...
Regarding Capacitors though... I kinda don't like seeing people just checking capacity and ESR... I tend to think that high ESR becomes a real problem in the power supply section where speed is essential to filter out voltage ripple but EPR (Equivalent Parallel Resistance or drain or DC leakage ( seems to have many different names)) is a far worse fate than death... A capacitor with low EPR will pass DC and this usually results in death for the next component... I have been trying to raise awareness about low EPR and what it means in the comments section of other channels but people still think that ESR and a visual inspection is plenty... A capacitor with low EPR can display very good ESR and higher capacity! This is not a good Capacitor! They don't get better with time LoL... If the capacitors capacity has gone up, it's because it's leaking DC which will cause it to take longer to measure giving the impression that it has more capacity than what is printed on the side of it...
This is why I personally prefer the other LCR Bridge Meter.. I went right out and got the newer version of yours which is black and has a built-in rechargeable battery via USB C which makes it even easier to use than your one... But they both work identical... Having all that information goodness all at the same time is far more functional than having to scroll through it... The DERR model that you used in this video is a great unit but you didn't scroll through the other details (on camera anyway), I'm wondering if the Capacitors that you tested were leaking DC? Because if they are very high ESR, they might not leak anything lol... Except for getting hot, expanding and leaking electrolyte! But low EPR Capacitor's don't get hot 🔥, everything else does!! Bypass capacitors will cause the transformer and rectifier to heat up or transistors and opamps! Coupling Capacitor's with low EPR will also destroy opamps and transistors and other semiconductors...
I think that once the fundamental level of understanding is reached regarding the capacitor failure modes and what it all means, then we will all know what to look for to prevent a catastrophic failure down the road...
I love Capacitors but the grief that they cause is a huge problem and not everyone really understands why! ESR is not enough to give you the full picture of what's happening and what's about to happen....
Apart from that.. spending time and talking while working can only be a good thing... Videos will take only as long as they need, not a minute more, not a minute less! You do what you do, I'ma be here watching...
TV's from the 90's were the worst, I spent so many hours resoldering cracked joint's just to find that the intermittence will reappear as soon as you slide the pcb on the bottom of the device, at least the 80's TV's had the pcb with the solder side oriented to the back of them, making it easier to resolder
Tony , it is best way your way , we like your long video , more longer better , don't lesson to other , if some don't like it just they can forward it or close it . simple as that.
These 1990s era HKs always remind me of the Lechmere Sunday paper ads of the day along with the AR speakers.
Tony,
Have you ever considered PCB Rivets for connectors on single sided PCBs? Sure seems like adding a solid mechanical thru hole would do good for these types of applications. Granted the rivet press is an expensive item, and doing it by hand is time consuming, but what ever. I've been thinking about using them myself and having a friend spin up the dies on a lathe, just use a plain ole cheap arbor press (something from Harbor Freight) to set the rivets.
Had my 655 in the trunk of my car when the cat burned up. The heat boiled the caps in the amp. Sounds like the burned up cat saved me a lot of future headache.
Dammit all !!
I really wanted to get a look at a 10000 rpm capacitor ! :)
Thanks Tony, you know it seems problematic to have those rigid wire interconnecting cables - because of their rigidity they act like a fulcrum and overly stress the solder joints - I wonder if less rigid cables wouldnt have been a better design.
9:10 - I wonder if the 150-watt/channel model is the same except for increased supply voltage?
28:45 - Could the DC offsets alone cause it to overheat? In that case, only one side of each heat-sink would be overheating.
So it's basically every circuit board needs to be completely re-soldered, to ensure future reliability.
So far, that's what I've noticed on this generation of HK gear.
Hi I have a HARMAN KARDON HK6600, I have a pop when turning on the amp when the relay in the protective circuit kicks in and when turns off. In addition the speaker selector pops when turned to a different position. Other than this my amp works fine, have you run across this problem? I will try to resolder the the solder joints at the capacitor in the meantime and see if that helps
Sir, how do you clean the little push switches on the front fascia? Mine all make popping or scratching sounds when depressed.
Also the volume and balance pots are scratchy.
Otherwise the amp still works very well.
Great video:-) I was thinking about retouching the solder joints, would it be possible to use hot air? I am just thinking to make sure every joint has been reflown. Or maybe put it into a solder own?
@MARTIN PRECÁK Thank you a lot for your reply,! :-)
I was just thinking that cleaning off the board, some new flux, and reheating would be like resoldering. Many of us do often use old solder rolls added some flux.-)
Just reheating it won't work. The best approach is to remove the old solder, clean the solder pad and apply fresh rosin core solder. In less critical applications, you can reflow the existing solder joint by adding some fresh rosin core solder or by adding some non-corrosive flux to the existing joint. Either way, the repaired joint should be smooth (no pits or cracks) and shiny, and should look conical, not dome shaped. Thanks for the comment!
Hopefuly HK doesn't use proprietary FETs or you might have an unobtainium issue..like Sony did on some of its high end stuff.
These amps use standard bipolar transistors. Those VFET's are impossible to find these days, although they are supposed to be pretty reliable. Those amps are very rare as well. That's why you haven't seen one of those Sony VFET amps on my bench yet!
@@xraytonyb Yea..And the T0-92 small FETS for the line-amp stages are unobtanium also. I ended up redesigning a line-amp circuit and replaced them with low noise bi-polars after they ran flawlessly for 40 years ! The Sony boards were designed well easy to remove. My college roommate had an HK1000 cassette deck. That gear got a work out...:)
The flashing LED at startup indicates it is going through its startup routine, but I hear "boom" on the speakers when it stops flashing. I do not have it on my other amplifiers. Is it a failure or just a feature?
my brother had one of these after he graduated HS. Hours listening to this thing. 1987 I think? Thot very well of this unit. Not sure it was PM665....wonder if there was a 645 or 655? but the front looks almost identical. Never thot of them as 'high' end but the better end of the middle.
There was a 645
I worked in a factory where we mass produced electronic boards back in the 80s. Most of the components were mounted by a machine, hence the big holes and then they were wave soldered. EVERY BOARD had to be inspected and touched up by a crew of humans. I dont know if they ever got their ROI from the cost of that equipment, because the repair facility was always busy. SMH.
Dear friend do you have any pioneer GR 777 ( not working) to sell ?
I see some test equip. 'under wraps' Coming soon ?
Also, Playlists would be really good, when looking at you back vids.
I've made a few of my own but I had to make some of them private
to stop my channel looking like xray-cloney.
I know you're busy so thanks anyway.
Kann man neue bei heutige Technik nicht neue Leiterplatten bestellen und somit den Verstärker sicher repariren?
Hello! I have a PM655 Vxi, which gives me a problem.
When I turn it on there is no sound, but a small "pop" is heard in the background on both speakers every 10 seconds repeatedly.
When it has been like this for 20 minutes, the music starts playing.
Sometimes it stops again, but the music comes back.
The next day when I turn it on, I only have to heat it for 3 minutes for it to work well.
No contact failure, I already reviewed all the soldering on the board.
The fault is not in the preamp, because I disconnected the jumpers from the back that goes directly to the power stage, and it continues to give the same fault.
Does anyone have an idea what could be wrong? Thanks.
I have a *Harman/Kardon* *AVR* *80* - It's a 5.1 with THX. It cost an extra $1,000 for the THX. Bought it in 1985, has never needed servicing!
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Sorry, with all those loose solder joints, I WOULDN'T power it up! What kind of Alcohol?
I have repaired old solder joints on computers by putting the mother boards in the oven at 200C. Can you do this with amplifier boards to avoid having to resolder joints.
Wouldn't really be a reliable repair, as there was not enough solder to begin with. Watch what happens when he touches one of the joints without adding solder, it wicks to the pad and there is virtually none holding the component in place.
I recently bought a HK 680, but the transformer emits a tremendous humming of the kind you can't hear in speakers. I also screwed with some bolts, even those transformers are similar (Bando, now closed). Do those make noise? Should I change it?
I have a HK690, and I have the same hum (mechanical vibrations) from time to time (not continuous), I think it depends on the power network...
I learned to live with that......
Hi, after replacing the burnt transistor in the final stage of the amplifier,I checked back and I found varistor mv12ym (chain of diodes) which is burnt out. I can not find any replacement. Maybe you know any substitute. Amplifier PM 655Vxi, element D409, kindly please help me if yoy can.
Where's part II ?
What about upping the THD to something like 0.1 would that be in the local feedback?
Couple of people told me nichicon capacitors are not very good not for sound quality
Nichicon FG are great caps
I don't think that you will notice a difference in sound quality with any brand of Capacitors... The main difference is in the working life... That reminds me of the people who say that they don't want to change Capacitors because they don't want to loose the sound that they are getting, well if you like listening to an amplifier in pain... It's going to die, but if you like that sound, there are ways to get the same sound without destroying an amplifier. People want a clean sounding Amplifier and don't realise how much they actually like distortion until they hear a dying amplifier...
That's why they say that you shouldn't believe everything that you read on the internet....
Excellent view Peter, true
@@PeterMilanovski no caps have a massive importance On Sound or the lack of them even
@@gime3steps thank you..
The technicians of our ilk and experience... are a dying breed. It's sad.
This is screaming consumer grade. It's a fine unit but those bakelite single sided boards and all those plastic knobs covered in metal make your job so difficult.
This looks like a very time consuming repair. So much to go over and resolder. So many transistors that could be bad because of it as well. Brunt resistorsand
out of tolerance e caps. There are a lot of things to check to get it working properly again for sure. At 18:25 in we have a good candidate for a speaker circuit
breaker protection device for all speaker outputs. www.parts-express.com/Speaker-Circuit-Breaker-2.5A-200W-260-830
Hi fi engine will not let me register. I need service manual for harmon kardon pm665. Can any one help? Thanks!
Tony,
I really enjoyed this video. I was about to look for part 2 when I realized that you probably don't have it uploaded yet. Looking forward to it.
I have a few questions.
1. On those switches...the plastic ones you said were quick to fail...is there a recorded MTBF on them that you know of?
2. Do those same switches contain a Wobblefram Actuator Seal ?
3. In the area where you replaced the Zener Diodes, did you check the value of the resistors there? Since I didn't see any of those raised above the board, I imagine you either didn't measure them or didn't replace them for some reason.
4. Do you really trust the filter capacitors in the power supplies enough to leave them in there? I would not trust them and would replace them, but that is just my own "knee jerk" reaction to capacitors in general.
5. Did I understand you correctly that the holes in that circuit board do not have a "feed-through" hole that connects the top and bottom of the board?
Keep up the good work...and I am glad that you don't worry about the "gripes" you get. You can't please everyone, and you seem to have that under control so that it doesn't bother you.
THD < 0.08% is surprisingly high distortion for a high end amp. That said, I'm an amp designer, and by the time these amps have been through the various cost cutting measures and sourcing issues involved in mass manufacturing, maybe that's pretty typical? That said, my best designs are closer to 0.0001% at 20kHz, and aren't a lot more complex than my high-power designs which perform better than 0.001% THD. My first design, a guitar amp, where I didn't even care about the distortion ended up performing around 0.01% at 20kHz and 0.005 at 5kHz (the sweet spot).
I think it's the difference between me having access to free simulation software to iron out the kinks, sweep for issues, and optimize things, (LTSpice is my favourite) and these older designers having to work things out the hard way.
Hello Tony, thanks for the video. I was wondering why you used the ksc2383 with the ksa916 instead of using the ksa1013. Is it because in this application they do not work as a complementary pair?. Anyhow, interesting and useful video. Thanks again
Hello! Does anyone know why one red light comes on on some models and two on others? The one that is always on is "High Current", but the one for "High Voltage" in my amplifier works fixed and in other equal amplifiers it is without light. Do you know what these lights mean? Thank you.
Found it... the "High Voltage" light is due to the switch on the back where it changes from 4Ω to 8Ω. What a way to call it, anyone would have thought anything else.
i mean, this Boards is mashining assambled, for a 0,6 mm Lead need a 0,8 mm Hole for Examble.
Hi Sir. Good day to you.
Jacky here. Can provide or share a service manual to me ? Thanks
nice i hate todays junk
Any reason why there is no capacitive coupling for the output stage of this class AB amp ?
Almost every class AB output stage uses capacitor coupling to prevent DC leakage into speakers
These amplifiers use a split power supply, with equal positive and negative rails. The center point of these amplifiers will be 0 volts at idle, if working properly. Amplifiers with single rail power supply will have the mid point set at a voltage roughly 1/2 the voltage of the supply. This is called offset. Single rail amplifiers, regardless of being class A or Class AB, will need some form of isolation (either a capacitor or transformer) to remove the DC offset from the speaker output. The design of the amp has everything to do with the offset. It is possible to design either class A or class AB with or without an offset, depending on how the power supply is configured.
@@xraytonyb - Thanks for thorough explanation, however I don't see a reason why not to use a coupling cap even for split power supply amps, as a precaution.
@@NICK-uy3nl The bean counters would not let you do this in a mass production.They don't sell precaution, they sell amps.
@@bob1842ra - I hear you. A 60V film capacitor would only cost 50 cents in high volumes x 100,000 amps = $50,000. The cost of BOM sure adds up fast!
It wasn’t about cost. A direct coupled solid state amp was the thing back then. I think it actually started about 10 years before this amp. Eliminating the capacitor gave better sound.
I used superglue on the knobs, and to my disappointment it holds very well. Why disappointment? Because I glued one of the the damn things upside down :(
46:00 To little solder on each pads is the real issue here, not necessarily the size of the holes.
To high speed on the boards when they pass trough the wave-solder would result in to little solder sticking to the pad.
As you will notice the fix is to add more solder. There's really no need to remove the old solder.
Clean it with IPA and resolder it will fix it. And BTW, not to much solder. You should see the leg of the component, not drown it in a big blob of solder.
Btw those tracks shure has some odd shapes.
Naw, it is the size of the hole.
Argh, the best way to do this is replace the boards with some sturdier shit, and replace all parts. Then it's almost better to just build a new design as well. :(
For all the hype of HK, the fact is, they used crappy quality boards. Thin, brittle, oversized holes. Not exactly the quality one would expect from a supposedly high end audio company.
and somehow I have two HK's that are over 30 years old and still kicking
@@joeygonzo I had this amp for 25 years and it travelled across the world. Awesome amp!
Your hands are shacking....it is better to see a doctor, this seems Parkinson's starting and should be controlled with medicine
I appreciate your concern. I can assure you that I do not suffer from Parkinson's, nor essential tremors. My mother-in-law along with several other friends of mine do, however, suffer from this terrible disease. It can't be diagnosed by watching someone with shaky hands on a video. What I do suffer from is the inability to reach both hands around either side of a camera that is positioned in my face, holding the solder and the circuit board in one hand and the soldering iron in the other, all at an odd angle while trying to see what I'm doing through the progressive lenses in my glasses...all so that I can get a good camera view for you, without my hands and arms getting tired and shaking. ;)
I clap my hands once, hard, to stop my hands "shaking" before I do any fine works. Try that!
I hope your not charged for that misdiagnosis.
Adrenaline rush.
The flashing LED at startup indicates it is going through its startup routine, but I hear "boom" on the speakers when it stops flashing. I do not have it on my other amplifiers. Is it a failure or just a feature?