diyAudio - Pioneer GM-H100 repair

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Pioneer GM-H100 repair

Long story made short, received a “working” GM-H100 off of Ebay. Of course the damn thing wouldn’t even power up. I found the problem to be the 1.8K resistor in the turn on circuit. I’m guessing the person didn’t know how the remote turn on works with these amps and ended up blowing the resistor up. I now have it powered up and all the rails are good. However, I don’t have any audio. I started to drive a signal into the RCAs and trace it through the amp. There is a small board with the gain, bass boost, and frequency controls. This board has it’s +/-15V supply coming in, but no audio coming in. So, the problem has to be between the RCAs and this board. (See attached picture) Due to the very small components and multi-layer board I’m at a loss where the signal runs in this amp. Does anyone have the front end schematic for this amp so I can continue my trouble shooting? There can’t be much between the RCAs and this board. Thanks.

Email me if you want the service manual.

babin_perry@yahoo.com

Reinforce the connections on the 3-pin connector. They are a weak point.

Quote:

Originally Posted by Perry Babin (Post 2732367)

Email me if you want the service manual.

babin_perry@yahoo.com

Reinforce the connections on the 3-pin connector. They are a weak point.

I had to solder bridge the traces around that connector because they were broke. That and replacing the 1.8K resistor got it to turn on. E-mail sent. Thanks a million Perry.

Rgs, JLH

Thanks so much Perry. I will have no trouble tracing the signal through the amp now. Since there is no audio in either channel, I suspect IC851 could be the problem. I'll have to wait till I get home from work to test it. Thanks again.

Rgs, JLH

I think IC851 is shorted internally because I only get about half a voltage across pins 9 and 5. However, referenced to ground (pin 7 of the UPC494) both pins 9 and 5 of IC851 measure 11.8VDC. I checked the output of the Isolator Regulator and it appears to be fine.

I looked for the UPC4570 dual opamp (IC851) and only found MCM Electronics selling it. It appears to be on back order until tomorrow. I hope that is true, because I need some.

LG Electronics IC Upc4570 Dual OP Amp, NEC | LG Electronics

Is my trouble shooting process below.

Quote:

Well, I’m scratching my head right now. I applied a 2VAC signal into the RCAs and traced it up to pin 4 of the IC851 dual opamp. The signal does not come out of the opamp output pin 2. I placed my voltmeter across pins 1 and 5 to check the power supply voltage going to it. It measured about half a volt. Obviously this isn’t enough. So, I started to trace the supply voltage backwards to see why it wasn’t getting to IC851. I suspected the Isolator Regulator might have gone bad. Well it tested good. What the heck is going on? So, then I placed the black probe of my voltmeter on pin 7 of the UPC494 and checked the voltage at pin 8 of the UPC494. It was 13VDC. I then checked the voltage on the other side of L907. It was 12.9VDC. Then I checked the voltage at D909 and it was 12.4VDC. Then checked the voltage at the collector of Q917 and it was also 12.4VDC. I then moved to the emitter of Q917 and it measured 11.8VDC. This led me to pin 9 of IC851 which also measured 11.8VDC in reference to pin 7 of the UPC494. So, why isn’t this IC working? I then measured pin 5 and it was also 11.8VDC. Is this thing shorted internally?

If they dont have the IC in stock tommrow This place has them in stock ive placed orders from them before and the shipping is quick and ive never had problems hope this helps

B&D Enterprises - Electronic Components Distributor

Thanks Mike. I really apprciate that.

Quote:

Originally Posted by mike49504 (Post 2737339)

It appears that MCM Electronics has the UPC4570 opamps back in stock. However, I'm feeling very skeptical about their authenticity. You just normally don't find this opamp for anything less than $5 to $6 a piece. Also, a few years ago I ordered some 2SK147 J-FETs from them that were supposed to be BL rated. They ended up being total crap and did not come anywhere close to their specs. At this point I think I should listen to my gut instinct and buy from B&D instead of MCM. What do you guys think?

NEC IC 9-pin SIP Dual OP AMP Bipolar | Distributed By MCM

I have bought parts from B&D Ent. only a couple of times, mostly because they have had some harder to find parts but they have been exactly what they were supposed to be and with good service.

I have not bought from MCM in a very long time, so I have no opinion on them.