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Thank you for watching and the compliment. I did not notice the oil tubes to be honest. I'll have to take another look. I do have the remote for this deck as well.

Yes you are correct that the 50 ohm load of the terminator has the affect of attenuating the source signal about half because it is loading it. I was just mentioning that the adapters are not also pass through attenuators because such adapters also exist (termination plus attenuation).

@@EriksElectronicsWorkbench I was thinking about my comment in the shower. I reconsidered that maybe it's almost philosophical or dogmatic, whether one wants to view the signal point at the top of the 'outside' 50 ohm load as having been attenuated (because it would almost surely be a higher level if that load was not present in the signal path), or if one should view the division as part of the systematic signal transmission mechanism, because if one measures signal at the wire *just* before and *just* after the top of the 50 ohm load point, given our 'real' measurement device is very high impedance, the signal level at those two points will be virtually the same. Whereas that would not be true for a -10dB attenuating pass-through. Not sure any more.

@@ivolol When I'm using an RF signal generator (as is the case here) it is intended to operate into 50 ohms so I consider the 50 ohm terminated voltage the normal operating voltage. Terminating the generator is not normally considered attenuating the signal level (in the terms of what an attenuation pad does) even though as you mentioned the 50 ohm terminated voltage will be lower than the open voltage by design. When I'm working with RF signal levels I almost always use dBm which assumes 50 ohm termination on most RF test equipment.

Thanks for watching Eric. Hope your 2465B turns out well!

I was also wondering why the meter movement had the problem in the first place. But they are so delicate and made with such precision it takes very little to interfere.

Thanks for the compliment and glad you enjoyed the video. The Triplett 630NA is a quality, reliable, and accurate meter but I'm not a fan of the 30 volt battery they used. It has a unique internal construction but a bit tricky to work on.

Yes correct that is what was done.

@EriksElectronicsWorkbench my apologies, lol, I only saw how many other people made that same comment after I had published mine. You must be very patient.

​@@bobbybiggs4348 no worries, it's a valid point about the voltage. Thanks for taking time to watch.

Pure gold does not tarnish, but the contacts are not pure gold, they contain other alloys added to the gold and they do (or can) tarnish.

Happy to know you are enjoying the channel! Thanks for watching.

Thank you!

Sure you can. All it takes is a static charge on the gate terminal. You can easily build up 100's or 1000's of volts if you are not ESD protected. toshiba.semicon-storage.com/ap-en/semiconductor/knowledge/faq/mosfet/mos-is-sensitive-to-static-electricityhow-do-you-protect-mosfets.html

That's crazy!! I noticed the seller had another power supply listed as non working after I purchased mine. I almost bought it out of curiosity. Really unusual that these would have this modification that makes them unusable. Thanks for sharing what you found in yours.

@@EriksElectronicsWorkbench What really puzzles me is why someone would go through the trouble of desoldering the resistor, but take the easy approach and just cut the jumpers? That missing 1K resistor on my board looks as cleanly removed as it did on yours.

@@repairitlee I agree it is very odd mystery.

It does seem like a ground loop problem. Inside the GFA555II the input connector ground side first connects to a 100 ohm resistor and then to ground. Check that this resistor is not open. Disconnect input cables and measure with an ohm meter from the RCA outside shell to the amp's chassis. Should be 100 ohms for each input. If that test is ok a solution could be to use this device to break the ground loop www.parts-express.com/Rolls-HE18-Buzz-Off-Hum-Eliminator-Balanced-Unbalanced-Conve-245-1032?quantity=1&srsltid=AfmBOorTiJzXfjFAfwW-TlMsBcDu6nJ0eM6GrwB-6vSzVbY42MLK6McO

Erik - Thanks. Each side measures 100 ohms. I already tried the Rolls "Buzz Off" device and it didn't help. The amp hums with any source. I even bypassed the power distribution component and went straight out of my dedicated 20A outlet without improvement. I tried lifting the ground to no effect. It seems that the 555 introduces hum when amplifying any signal but it is quiet when the inputs are unplugged. Can you think of any other potential cause in the amp? The substitute power amp plays; no hum.

@@carlespy7470 unusual problem as hum if coming from within the amp is usually present all the time. Perhaps it is more of a distortion issue. Really the only way to test is to input a known good sinewave signal from a signal generator and then use an oscilloscope and probe starting at the input jack and move through the amplification stages until the noise is found. It could be a defective transistor but equally any other component failure could cause distortion so it is not really possible to say the cause without testing. Also check the power supply rails and make sure they are equal in DC value and very low ripple voltage. Also check the output bias setting.

Eric - thanks for the advice. I'll give all your suggestions a try. I do have the equipment but have limited expertise.

Thanks! Glad you are enjoying the channel.

Yes very versatile for testing. Although not completely arbitrary, this one can be set to do various transient output waveforms.

In theory yes but it is the result of more than one adjustment that affects the peak from centering precisely. Some span and bandwidth settings it centers perfectly and in any case you can use the marker readout and the frequency counter readout to obtain very accurate results.

Thanks! It's been a reliable power supply since the repair.

The voltage and current controls are done with 12bit DACs - Digital to Analog Converters. The microprocessor sends a 12 bit value to the DAC which represents the analog output value. The DAC converts the digital bits to an analog voltage. Series pass transistors driven by this voltage control the final output voltage and current. There are feedback loops for voltage, current, and other parameters but this is the basic idea.

@@EriksElectronicsWorkbench Oh I never thought about the use of DACs. It makes sense due to the pass regulator being voltage controlled.

Thank you for the compliment and I am happy to know you enjoyed the video and found it helpful.

I think you have the series 8 model. www.simpson260.com/260-8/simpson_260-8.htm For the problem of the meter pegging full scale on so many ranges I'd start by looking at the shunt resistors across the meter movement. If the resistors are open or out of calibration the meter will have too much current through it and read full scale. This page has all the 260 models listed and links to manuals www.simpson260.com/downloads/downloads.htm

Yes I was surprised there was not more damage.

750 VA which is 750 watts on purely resistive loads.

Thanks for the kind words and I'm glad you are enjoying the channel. I appreciate the feedback!

Happy to know you enjoyed the video! If the right arm is dropping the take up tension may be the problem. The green colored resistors I show in the top of the unit set the take up and back tension. But you shouldn't mess with them unless you read up first in the service manual. If the right arm drops all the way down but does not shut off the machine there is a problem with the switch or the switch cam. Also check for stuck mechanisms like in this video, quite common to happen, my X-1000R had a similar issue with stuck capstan arms. service manual is posted here museumofmagneticsoundrecording.org/images/R2R/TeacA3440ServiceManual.pdf

@ Thank you for your quick response! When the right arm drops the machine does shut off. The R-take up reel (facing front) just spins a little longer than the L-reel (facing front). The L-reel solenoid plunger pops back out when I press on it and the R-reel solenoid plunger doesn’t pop back out the way the L-reel does. It’s feels like there’s less force pushing back on the R-reel solenoid plunger. Would adjusting the back tension, as shown in the manual, push that plunger out the way it’s supposed to? Or is it a dirt problem or possibly both you think? I just want to see how far I can narrow it down since this is my first time getting into the back of my machine.

@@fegyo1729 The tension adjust resistors would not affect the brakes. The brakes should only be on when the deck is stopped (or stopping). The solenoid might be sticking. You can try cleaning the plunger with isopropyl alcohol. If the reel motor or brake solenoid is being powered too long or at the wrong time compared with the other reel motor there might be an electrical problem in the control circuit. As a reference in my video at the end you can see how the machine should move the tape.

I'm glad the videos on my channel are helpful for you. I appreciate the compliment. Thanks for taking time to watch!

Your fan must be running very quietly! Yes Sunon seems to have discontinued the part that Fluke used. I have not found any other manufacture that makes a drop in replacement that has the side exhaust but it seems you can replace with a traditional axial flow fan as the side exhaust is not super critical. Mouser and DigiKey have some fans that are very thin and can be made to work although the hole mounting is usually slightly different. The lubrication I did on the fan has held up and it is still running quietly so that seems to be a lasting fix.

Agree the two red posts are not the best idea when polarity connections matter. The power supply is well protected by a number of the pico fuses and yes agree they are rather inconveniently placed.

@@EriksElectronicsWorkbench I have to correct, I do have a 66312A and the white sticker on the PCB has an A printed on it. But all the bridges and resistors you mention are populated in my unit. Picofuses came in yesterday and the unit is now repaired. Despite its age and the little dim display, my unit is in great shape as all parameters from the test sheet in the user manual are in spec or right on the boudary. I'll calibrate the unit when my Solartron 7081 is back from calibration.

Glad you enjoyed the video and thanks for sharing your experience.

The photo I found online of an identical A1 board had the components installed. They are drawn on the schematics and component layout, just not on the silkscreen. Restoring them solved the problem.

www.keysight.com/us/en/product/66312A/40-watt-dynamic-measurement-dc-source-20v-2a.html# scroll down a bit and click resources, then service manual.

There are no documented options for this power supply modifying the voltage sensing or current control and I can't find any settings outside those covered in the user manual or service manual. But perhaps someone was trying to modify the unit or test it in a particular way.. hard to know for sure.

There are two current shunts, the low range is 72.0 ohms, the high range is 0.250 ohms. The 1.1K resistor is listed in the calibration procedure. You don't need to factor in the internal shunts resistance when calibrating.

Yep, my 34401A has both red collars !

Thanks! There are two 12 bit DACs, one for CV and one for CC modes. I'll try the calibration on the rear output just to be on the safe side but I agree it may not make much of a noticeable difference.

Interestingly the front panel has a 4-pole connector which theoretically would be usable for a sense connection closer to the output. But internally only a long twisted 2-pole wire runs from the switch on the rear to that connector. I could not find any additional sense solder points on the PCB. I am pretty sure that HP tried avoiding the additional pick-up of noise when running that set of wires along the whole inside of the unit. If you need more precision, you can setup the unit as shown in the calibration part of the unser manual, but you use Kelvin leads and move all calibration connections to the end of that lead. Explanation for beginners: You move the calibration pane to the connection of the system, not the front panel and rule out the losses over the wires. It is to be seen like Vector Network Analyzers where you run the TOSL calibration right there, where your unit under test is, so you do not measure RF parameters of the VNA connectors but the filter or whatever you designed and want to measure. I use the 66312 for testing PLL circuits as most of them run from 2V to 19V and then I use Kelvin leads to the rear connection.

@@uki352 I noticed the front panel connector has more pins than are used. Yes the kelvin leads as you describe can improve accuracy. Also it is possible to run the load on the front terminals and use the rear remote sense lines to the load and compensate for all voltage drops that way. Ultimately the internal 12bit DACs becomes the limiting factor in voltage and current accuracy.

They are. Two red ones was common with older equipment.

@pa1wbu this makes no sense but I suppose 👀

@@Irilia_neko Older 34401A multimeters (HP era) have all red terminals as well.

@@Irilia_neko My HP 34401A has all red terminals.

Thanks for the nice compliment!

Glad the video was helpful! On my unit's fan it is still functioning very quietly. In fact I just used it a day ago on a new video I'm working on. I don't think the air direction, radial or axial, is all that important just as long as the fan moves some air around inside the instrument. UA-cam channel Feedback Loop repaired a Scopemeter and used a replacement traditional fan. It fits close but not quite the same way but does appear to work.

Thank you very much for your attention and for the references given ✌️, I will proceed to adapt a fan, I suppose that in your case you noticed as soon as the noise started and the oil managed to form a film that kept the fan arrow in place, I recommend that each battery replacement, give your fan its maintenance; In my case they were company equipment that had financial problems and sold off their equipment, you know, as long as it works and turns on the rest does not matter ☹️ I notice that you are an expert: I wanted to ask you: notice that the equipment has dust inside between the display and the external protective mica, and these equipments investigating have many details You recommend right now that I am going to open it, and that it is at hand to remove the display and With compressed air from a can (sweeping and sideways technique) and a microfiber cloth clean and then assemble carefully and without bending anything; I tell you this because in the lot I acquired there was also a fluke 43 and when I opened it to change the battery I decided to clean it because it had a lot of dust particles and I regret it, it had horizontal black lines and investigating I know that the 120 series has problems with its display and the flat cable soldered with an adhesive and a hot bar and over time they failed, I was very careful but a slight movement when assembling it had to make the black lines come out. Do you think that these scopes have the same technology as the 120 series and the display could fail? Better not touch it!!!

@@jmacedo7 On my Scopemeter I removed the display assembly from the case and cleaned the inside of the case window. I did not attempt to do any disassembly on the display module, that could be risky. I have heard that the black and white displays are more prone to lines than the color display but I do not know how true that is. I have only owned the color display model and had no issues with lines.

Thanks! Definitely a nice addition on the bench.

Sorry I'm not taking in additional projects at this time as I have a backlog of projects waiting.

There may be a burr or irregularity on the shaft or inside the flywheel that is not allowing the shaft to move. It could also have old oil that has become hardened and is stuck. You might try carefully heating the shaft and flywheel center with a heatgun, not too excessive though. Yes the tapping sound is probably endplay on the shaft since the shaft does not protrude past the flywheel. You might try pushing the flywheel forward until it stops and then tap the shaft forward (towards front of machine) using a soft wooden dowel. But don't hit it with excessive force. That may free up the shaft.

That's sad news. I did not know.

Yes some switchers do need a minimum load or they can't regulate properly. The data sheet for this model says that for less than 1 volt regulated output you need at least 500 mA. So for typical use at higher voltages as marked on the modules a minimum load isn't needed. Certain types of ceramic surface mount caps are prone to failing from stress as it cracks them or damages the structure since they have no flexible leads. There are surface mount caps designed to take flexing stress probably not what was used here. Yes the Dynaload has a current sample output. I recently did a video on another Dynaload model that needed repair ..you may be interested in seeing that.

Glad you enjoyed it, thanks for watching!

I think the values are chosen for what makes the most useable attenuation range. 0.25 dB would require the two top T configuration resistors to be 719.51 milliOhms perhaps more difficult (or costly) to make such small value of resistance? Also going up to 255 dB is such a huge attenuation it is not useful at low RF levels. This attenuator is 1 watt max. As it is 130 dB is down to fraction of a microvolt.

You're welcome and thanks for watching!

It's normal for the GFA5500 to pop when powering off. There is no speaker protection relay so the speakers are connected to the output stage at all times. As the power supply rails collapse the amp becomes unstable and a short pulse of voltage is applied to the speakers. It is not damaging, and the voltage is less than what the speaker is subjected to when playing loud music.

@@EriksElectronicsWorkbench Thank you. Maybe I should clarify. The pop I referred to is more of a "whumph" (not loud but audible). The cone movement is quite noticeable and, as I mentioned, the event is only on one speaker. Your assessment is probably correct and there is nothing to worry about but I am going to sell this amp and do not want to pass on a faulty product. I'll see if there is a local expert on this amp. For now I am using a Schiit amp and I am very pleased with it. Much thanks!!!!!!

@@charlesclifton5896 I would check the amp for meeting rated output power, no distortion issues, etc and if all looks good then the turn off thump is not a concern and for whatever reason the one channel is just more prone to it. Agree good idea to have it tested to be on the safe side.