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That was interesting! I have a GFA-535 (not the II). I was setting the bias and slipped with the probe and shorted an output transistor. Now two of the output PNP pairs as well as the PNP that feeds that pair have shorted collector to emitter. I'm hoping you can answer a couple of questions about the transistors. Do I need to match the PNP to the NPN outputs on these when I select transistors to replace them with? Do I need to match the driver PNP transistor to it's NPN counterpart? Should I also replace the NPN transistors even though they test well? I bought a used Heathkit transistor curve tracer but I haven't began to figure out how to use it yet. I also have the Peak Atlas DCA75 for matching low current parts. Let me know what you think.

Excellent video I just stumbled upon and new subscriber here! I would’ve gone troubleshooting in a very similar fashion. I was impressed that the DC offset voltage was that low considering the age of the unit and the fact that it’s probably never been serviced. I have a 1978 year NAD integrated amp model 3060 that I love but it’s now pushing upwards of 80 mVDC DC offset which is way too high for any speakers that I don’t want to destroy. Haven’t got around to repairing it yet as this one is not really Repair friendly and is going to require major troubleshooting and parts replacement.

Clearly explained Eric. Thank you

This is one poorly designed unit, so many thermal problems.

stupid noob question, but why would the shunt resistance go UP when the voltage goes down? seems counterintuitive.THANK YOU FOR YOUR CHANNEL!

What are those lengths of plain bare wire on the board? I always wondered what they are, if they're resistors or just connectors of some sort.

I doubt the amplifier could have left the factory with that solder bridge. Surely if someone bought a brand new relatively high end amplifier and one of the channels weren't working, they'd have returned it. I have one of these amplifiers, and after a few years the volume knob developed some crackles. I took it back to the store and they fixed it right up, no questions asked. Gave me a C368 loaner while it was being worked on too (though I preferred the sound of the C356).

The person talking seems to be parroting vocal mannerisms from Mr. Carlson Lab..

If the power plug is non-polarized, is there a "suicide capacitor"?

Sehr gutes Video. Du gehörst zu einer aussterbenden Gattung. Experten auf diesem Gebiet werden immer weniger. Im Zeitalter der Wegwerfgesellschaften. Möchte nicht wissen wieviele geräte weggeschmissen werden die man hätte retten können!!👍👍👍🇩🇪

Hi Erik, new subscriber here I love your attention to detail

Have you tried holding components down with Blutak when testing?

I very much appreciate your presentation style, with an emphasis on information, observations, and your thought process and analysis, and most importantly, all this without the swagger and ego that I often hear on a number of other electronics channels. I'm an immediate subscriber. Thank you.

Hey Erik, thanks for the excellent video. Please forgive the negative comments about your speech, it is quite remarkable how people will criticise the stupidest things. Your content is excellent, please keep it up.

You talk too fast

Excellent diagnostic I look forward to viewing more of your content 😊

I thoroughly enjoyed this troubleshooting session. Good video!

So....the protection circuit section needs itself a....protection circuit section!

17:00 fun fact, the voltage drop from B-E is always slightly more than B-C. One way unknown transistors can be identified (at least for pinout).

110 volt is a joke... we got 240 and 380 volts.. try to touch that.. then you can sing high tones !!!

I am going to (go ahead and) leave a comment

Very common on this modell is a´few power resistors close to the regulators on the big heatsinks.

Is NAD a popular brand in US ?

At 9:43 we see the soft clipping warning immediately coming on, yet no comment on it, instead 45 minutes of stuff happen until, finally, faulty components in the soft clipping circuit are identified as the source of the problem...oh man...obviously the soft-clipping shouldn't come on while there is no input signal, why didn't you focus on that right from the beginning???

Is there discoloration on the underside or is it just lights/reflection? (At least three areas seems suspicious to me at 34:10)

Thank you. That was a very interesting piece of fault finding - quite a cascade of issues from that one solder bridge. Good spot with the suspiciously sized resistors too! Looking forward to seeing what happens when you run audio through in part 2.

Thank you for the video, I have similar unit, but I need convert that for transformer and fan point of view to 230V, So simple unit that not big job :) Do you have scema of or picture of that isolator part in your system?, it is not in scema but you note it.

👍👍👍

Eric, you commented that you had the same fix done on your Teac X-1000R. I have the same deck with the same problem. It would be great if you could do a similar video on that sometime. I imagine it is very similar to repair with the exception of two capstans. Yes? Comments?

I know I'm late to the party but, some 3d printed inserts for those battery holders seem like a good idea. If you're interested shoot me a message and I'll see what I can do to help.

07:00 - the curve is 45 degrees, as our resistor in circuit is 3.3 kOhm and it just so happens the LoZ function in a Fluke 289 is about 3 kOhm. Curve will be between 0 and 90 degrees from horisontal, with the ratio of the 3.3 kOhm and the DUT resistor. The 2.2 kOhm at 08:16 gives us 2.2 kOhm / 3.3 kOhm = 0.67, counting the pixels we go up 1 division and left 0.6-0.7 divisions 🙂 Disclaimer: as long as scales are identical for A&B, else we need to multiply that in.

Cool basic videos. I really enjoy your tech talks. If anybody wants to built a slightly more complicated version of this, check out Mr Carlson's Lab channel where he has a circuit for a "curve tracer", which is essentially what Erik has built here. You have a little more control than shown here, especially if you don't have a variac. I think it's behind his patreon paywall but well worth a couple of bucks. For those new to this, it think easier to have the Y scale going the other way. I think it may just be a function of your X/Y setup? (Y seems to be more positive going down on your scope, which always seems backwards to me).

Very nice video. I'm definitely going to try this. I apologize ahead of time for this question, I'm new to electronics. For in circuit testing, wouldn't you want to use the higher value resistor? I figure it would lower the voltage so as to not turn on other components. Or maybe it doesn't matter ? Thanks, definitely subscribing.

Wow, I hope my 555se i just ordered (2025 edition as I've been led to believe) doesn't go off the rails like this one. I'd hate to see the repair bill. Sorry you got a lemon.

Thank you very much. I have this same deck. I found it in a storage closet at the University. Its in good shape but probably hadn't seen the light of day for 20+ years. lol Pinch roller issue is exactly the same as you describe. Wish me luck. All the Best.

For such a nice looking Amp on the inside it surely is underpowered

I just replaced the RIFA capacitors on my Tektronix 2213a oscilloscope and replaced them with RIFAs. I'm glad to hear that the modern versions have been improved, it sets my mind at ease. Thanks.

My power amp and preamp have stamps with nicknames of those that worked on them

Great video, I have a Poton D540 and not sure how to carry out bios adjustment, unfortunatly you didnt show how to do this😭

Very informative! I have one of these paired with the GFP 555. It's a great sounding set up, but I know that it will need servicing down the road. Now I know how to replace out the caps and set the bias. THANK YOU!

Erik, when modifying a TrippLite (sp?) to truly be an isolation transformer, don't you also have to ensure that the ground isn't common to both primary & secondary sides? If you didn't disconnect the common ground, wouldn't the "ground" line going back into the electrical panel be directly connected to the primary's neutral, still able to cause a dangerous shock? Santa brought me a TrippLite "isolation" transformer a couple of years back that I want to modify to be a true isolation transfer for my bench (with Variac & bulb too).

Hi first of all I want to compliment you on your work. I have a Tascam mod. 34 that when I press stop the tape continues to unwind. Could you make a tutorial on how to calibrate the brakes. Thanks

Erik, I like your videos, very easy to watch, well explained, it’s a pleasure to follow your diagnosis. I have a question. I am interested in some overview of your lab and test gears. I like test equipment and I wonder which ones you are using.

Hello how are you. I have a 002a machine for a backup generator . It has gotten me through several power outages. You obviously understand how these work and understand electrical schematics. I would like to convert my 003a machine to 220v single phase and change the voltage regulator to a common sx460 avr. I was on the steel soldiers website and did get some help but never got it done. A fella named Craig Tull posted how he did it, and posted a schematic . Think you might be interested in taking a look at that? If i could do this with my 003a machine, i would like to do it to my 002a machine. Thanks, Scott

Hello and how are you. You obviously understand electrical schematics and how these machines work . I have a 002a that I use as my backup generator. It has gotten me through several power outages, 1 as long as a week. I also have a 003a. I would like to change this machine over to strictly 220 v single phase. I also would like to change the voltage regulator over to a common sx460 avr. Have you ever considered doing this ? I was on the Steel Soldiers website , I did get some help but I couldn't get it done. I don't understand electrical schematics either. There was a fella that once posted how to do this and posted a schematic too. His name was Craig Tull. Would you be interested in looking into this ? Thanks, Scott

I have this amp, bought in early 2000’s; I love it, paired with Klipsch Forte I speakers. No issues, so far.

can bulb be halogen ?

And I watched the output hz jumping between 59.4 to 64.3 with no rpm difference . I need a place to start

Well thats a good video ,but I'm still lost as to why 1 leg is lower than the other while in 120/240 single

Wonderful learning! ❤❤❤