I was not in the room when it shut down. There were no lights. So it seems next steps are to open it back up, check the fuses, inspect for obvious issues, then check voltages, perhaps per the service manual. I will perhaps start by looking at the TR 630-634 area. I do not have a DVM that can check capacitance (mine is a clamp meter), nor do I have a tool to check the condition of TRs. I will start with basics, and if I need to buy tools, I will buy them. Not gonna give up yet, but may pick up a good used Adcom 565 so I can evaluate the condition of my Technics turntable and Grado carts and listen to vinyl whilst I take my time with the C4. The sound I heard for about 20 minutes was promising and I hope to be successful. I took a course in analog back in college, right around the time I bought the C4. But I never designed a circuit or worked on a PCB. Thanks so much for the help.
Yamaha C4 Pre-Amp: Worth Refreshing/Repairing?
- Thread starter mahler9th
- Start date
Someones hosting a weekend BBQ...
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Glad I don't live in the Destin-Fort Walton Beach area anymore.Someones hosting a weekend BBQ...
OK. I connected to the DBT. The bulb comes up and stays dimly lit (75w). I measured the DC power on the jumpers leaving the power board. The +45 is measuring +31 and the -45 is measuring -30.1.
I also measured the + and - 30 volts and got +28.8, and -27.7. These voltages stayed steady after about 15 minutes.
Should I try to get it to shut down again and measure some DC voltages? Can I do this without damaging anything? or should I go after the diodes?
I also measured the + and - 30 volts and got +28.8, and -27.7. These voltages stayed steady after about 15 minutes.
Should I try to get it to shut down again and measure some DC voltages? Can I do this without damaging anything? or should I go after the diodes?
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Those transistors are working! You really don't need to test them. Just clean off the heatsink compound and replace with fresh compound. I guarantee they will test OK with your multimeter or any of the cheap testers on the market.
I take that back. It will help identify errors and typo's in the schematic and service manual.
There is an adjustment in the service manual to adjust as close to +/- 30vdc as possible. Step # 1 in the adjustment procedure. VR304 & Test points 7 and 8 are right behind the volume control.
Best to make adjustment without a dim bulb.
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Thanks. I figured the TRs are working just fine, but decided to ring them out anyway as a simple learning exercise. I re-installed them with the heat sinks attached to the board. There was a 1212 diode nearby so as a precaution, I replaced it with two 1N4148s in series. I fired it up and there is hum present on all input choices. This time it ran for about 20-30 minutes with the aux input fed by my iphone without shutting down at all. The left channel was weak/not really working.
I need the ECB voltages of TR630 thru 634.
Yes.
Okay... status update from the beginning.
Cleaned all switches and pots with Craig products.
From what I can see, the wafer switch contacts look pretty good.
My next step was to replace caps 519, 520 and 520. It was clear the glue and/or heat had damaged the leads on one of them because when I touched it, one of the leads broke.
I then went after the transistor on the small heat sink since it was just dangling and there was a lot of glue residue around its base. I removed it but damaged the pads. Reinstalled with a silicon pad and washer... may later go back and use paste instead if/when it makes sense. I used some automotive RTV to glue the sink to the board, and made some jumpers because of the damaged pads.
Then as a precaution I went ahead and changed out C313, with a Nichicon with the same specs.
Then I decided to go after the other two heat sinks. Removed them... this time being more careful and using solder wick, which seems easier than a suction device in my inexperienced hands. Still managed to damage pads so had to use a couple more jumpers. Again, used silly con pad and washer to insulate the TR from the sink since that is what I had on hand. Screwed both sinks to the board.
Then I decided to go after the nearby VD1212.
Fired it up and I had hum on all inputs and a weak channel. But she would not shut down after about 30 minutes of power on.
Before troubleshooting any further, I decided to replace all 1212's on that board as a precaution.
Then I fired it up and and presto, like magic she made music, but with hum present on all phono inputs.
I decided to go after the 1212's on the headphone board this am.
Next I will adjust the 30VDC and offset, then I measure some voltages and try to hunt down the phono input hum.
If I get that sorted, I will order and then replace caps for the headphone board, since the originals have signs of deterioration.
During one of my tests, the neck of the headphone jack broke off when I removed my plug. Old plastic. So I will eventually deal with that. Right now the hum has priority.
I will do some search here on AK to learn about potential causes of phono input hum, and study the schematic as well.
Cleaned all switches and pots with Craig products.
From what I can see, the wafer switch contacts look pretty good.
My next step was to replace caps 519, 520 and 520. It was clear the glue and/or heat had damaged the leads on one of them because when I touched it, one of the leads broke.
I then went after the transistor on the small heat sink since it was just dangling and there was a lot of glue residue around its base. I removed it but damaged the pads. Reinstalled with a silicon pad and washer... may later go back and use paste instead if/when it makes sense. I used some automotive RTV to glue the sink to the board, and made some jumpers because of the damaged pads.
Then as a precaution I went ahead and changed out C313, with a Nichicon with the same specs.
Then I decided to go after the other two heat sinks. Removed them... this time being more careful and using solder wick, which seems easier than a suction device in my inexperienced hands. Still managed to damage pads so had to use a couple more jumpers. Again, used silly con pad and washer to insulate the TR from the sink since that is what I had on hand. Screwed both sinks to the board.
Then I decided to go after the nearby VD1212.
Fired it up and I had hum on all inputs and a weak channel. But she would not shut down after about 30 minutes of power on.
Before troubleshooting any further, I decided to replace all 1212's on that board as a precaution.
Then I fired it up and and presto, like magic she made music, but with hum present on all phono inputs.
I decided to go after the 1212's on the headphone board this am.
Next I will adjust the 30VDC and offset, then I measure some voltages and try to hunt down the phono input hum.
If I get that sorted, I will order and then replace caps for the headphone board, since the originals have signs of deterioration.
During one of my tests, the neck of the headphone jack broke off when I removed my plug. Old plastic. So I will eventually deal with that. Right now the hum has priority.
I will do some search here on AK to learn about potential causes of phono input hum, and study the schematic as well.
Sorry for the confusion. After I changed the big caps, I tested it and left channel was weak. After about 25 minutes, it shut down. Then I pulled the TR on the small heat sink, cleaned up the glue, and reinstalled. After that it would not shut down on its own. So that shut down problem seems to have disappeared from that step. But left channel was still weak and I had hum on all inputs. Then I did the other steps and got sound from both channels and the only hum I got was on phono inputs. I just tried tried to set the 30vdc rail. Stuck at 37.7. Won't adjust down. Need to check that pot, and troubleshoot from there.
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