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Pioneer sx-680 with on bad VU and with STK-0040's

I messed up one of my discrete modules.:rant: The right channel peaks the VU meter. No transistor shorts as far as I can tell. Voltage measure ok and putting the old power packs back in will fix the problem. Having changed most of the caps seems to have fixed the skewed volume issue. Meters looks better the short time I’ve tested it.

Edit: reflowed all joints on the bad module and it came to life. Now on to installing them again.
 
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Thank you everyone who helped me!
I know way to little about this but the amp is powered up and has not exploded. Almost all capacitors are changed and discrete modules up and running. I’ll have to bias the thing tonight. There is sound from the amp:music:
Don’t know yet what kind of sound but it’s not awful.
Big thank you to everyone who has answered any of my questions
 
Amp is biased but not done. Sound is good except for some scraping in the left channel. Works better with the lid off, go figure. Something is causing the left channel to give is some sort of static scraping sound. Sometimes it goes away if the lid is off and the sound is alright. Maybe I have to reflow the solder on the left module as well. It’s a real pain to solder these modules in and out of the amp.

FC06EA72-1843-4F10-A976-26545B2B198D.jpeg

found a cold solder on C415 reflowing that one really made the left channel go wild. The meter keeps jumping all over and it’s just scraping and sounding generally crap. Right channel is excellent though.
Voltage to the modules seems to be stable so I’m thinking I messed up the left module as well.
 
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Sound is coming out of both channels. Good sound. My soldering skills are not the best. Gonna tend to the last capacitors when the arrive but for now I’m pretty pleased. Not to happy with the soldering in and out of the modules. I also have intermittent static/sparkling coming in sometimes so something is not working well. When it is working sound is good.
 
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Ok!
Nothing wrong with my modules. Soldered the original stks back in and the problem is the same. Good sound for a couple of songs and then the left meter goes bonkers. The sound goes with the meter. Scraping and sparkling.
Are the diodes the normal 400V 3A? Gonna order those and the missing caps and see if that helps. I’m worried I might have destroyed the amp. The voltage to the modules are ok. Steady and at levels. But the meter is now far right all the time.
 
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Something does not seem right with the meter pinned check the DC offset under this condition. When you are referring to parts you should specify where they’re being used, reference the schematics and the assembly that they are used on. It is always good to have some 1N4004 diode‘s on hand if you are servicing these Stereos
 
Thanks rcs16
I’ll check and I’ll also try to refer to parts as the appear in the schematic in the future.
Edit:
it’s a s/sg model and when measuring the fuses fus3 has about 28V over it. The fus4 is 0V. Where do I go from here?

Some additional metering gives me about +\- 30V on all pins in the left channel. I’m assuming this means my power pack is fried. Also my discrete modules in that case. What is Causing this to happen? Both the old module and the discrete one worked for about an hour with the discrete module and about 10 min with the old Darlington.
Switching the Darlingtons will not shift the problem. The left channel is still peaking with the right channel Darlington in there. So not a faulty power pack after all.
 
Do you know about troubleshooting the pre stages with the 3K ohm resistors?
Back to basics. Get the amp(s) working without the modules first.
Bench test each component in the amp. Resistors and diodes can be tested on the board. Transistors tested on the bench. Ceramic caps should be fine.
Double check all you solder connections. Make sure you installed the polarized components properly.
 
@zebulon1
Are you talking about replacing the packs with resistors? If so then yes I remember reading about that somewhere.

slowly, and i mean slowly, going through the schematic and writing down all the diodes, resistors and transistors I can find to have as many parts as possible and to get free shipping. Shipping alone would otherwise be as much as the parts so might as well buy 20$ worth of extra parts.
 
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Looks like I get a lot of time to ponder this. One of our cats needed to stay overnight at the vet. Could buy several amps for the cost of that stay. No parts or rather no anything for the rest of this month. I have good hopes for the cat though and that is the most important to me at the moment.
I just can’t justify not spending money on the cat as long as I have money left.

when it comes to the amp I’m gonna list all diodes and transistors and buy those when I can afford it. Also the resistors and caps in the power section and go from there.
 
I doubt that you need much $ worth of parts. Mouser offers USPS Global Priority Mail at $8.00 plus taxes and duty etc. Where are you located?
Follow Zeb's advise (Merlyn's test method), test out the channel using the 240 to 1k ohm resistors in place of the STK and verify it's operation first before you order any parts. We are talking the $ some people spend for a lunch and a beer, gas for the car, not vet bill expenses.
 
Rcs16
I’m in Sweden and can’t find any shipping under 20$. That’s why I usually order 50$ worth of parts since it’s the same price as 30$ of parts.
 
Got some resistors today. Put them in place to run the amp without the stk packs. It started fine but after a minute or so the needle started to peak on the left channel. It’s not 28V right now but it’s about 17V on fus3.
Voltages over the 8000uf caps c413 and c414 are 37V and -37V.
The resistors next to them r408 and r409 measure -37V on one side and 0V on the other. The second one is the same except it’s 37V on one side.

edit: all stk socket pins
Left
1 8-9V
2 -37V
3 22V
8 27V
9 37V
0 33

Right
1 -6V
2 -37V
3 0V
8 0V
9 37V
0 6V
 
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It's getting closer to being sorted.
Whats the voltages on pins one and 0 (zero) of the modules location on the main board?
Has it been recapped?
 
It's getting closer to being sorted.
Whats the voltages on pins one and 0 (zero) of the modules location on the main board?
Has it been recapped?
 
It has been completely recapped but for a couple of caps. They are coming with my next purchase.
It’s the two power caps and one 330uf just in front of the stk sockets that has not been changed.
Edited my previous post to include all pins.
 
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