Pioneer SA-9800 hum after Recap (Help!)

So I had a bit of time last night and checked things over:

Power Supply
d1-4 all checked ok ( around 450) btw. i'm using UF4004 as Mouser didn't have 1n4004 in stock.
Then q3 tested out of circuit fine and so went back in.
Next q1 tested out of circuit probably 5x because I thought that I was doing it wrong, but no, it was open. But this part is only a month old, new from Mouser?

Anyways, I looked though the parts bucket and found the original 2sc1735 that was in there and it tested ok, so I put it back in. Powered up, relay click, and guess what? no hum. So the obvious question, should I leave this in or try to order another ksc2690 to replace it?

As for the 'Pop'. As soon as I turn the power switch on, the indicator shows no illuminated bars telling me that the hum is gone. (I also tested to confirm with headphones) But before the relay had even clicked I saw the left channel spiking to the max position maybe twice, then the relay clicks and it stopped for a moment. I played some music through it (vol. very low) and got about 30 sec. in when it started again. I noticed that not every time the indicator spiked there was an audible pop, only about every other time. So like I say I got about 1 min. in and about 3 pops and the last one triggered the relay into protection.

Thoughts?

thanks again for everything thus far.

pops in just one channel isn't likely the regulated power supply which is shared between the two channels.

Check the popping channel for sneaky hidden cracked solder joints, some don't show up (even with a BRIGHT light and a magnifier) until you take a sharp probe and PUSH on the wire in the joint. (ask me how I know - my bench is BRIGHT and my eyes are good close up.)

Q7, Q8, Q11, Q12 depending upon channel - they run hot and crystallize the solder that holds them. Sometimes you will see a color change in the board material. It's a design issue.

Resolder BOTH channels - because there are others just itching to crack.

OHHH, ouch, Q9 and Q10 are 2sa726 transistors, they are EVIL. use 512-KSA992FBU's to replace them.

markthefixer said:

pops in just one channel isn't likely the regulated power supply which is shared between the two channels.

Check the popping channel for sneaky hidden cracked solder joints, some don't show up (even with a BRIGHT light and a magnifier) until you take a sharp probe and PUSH on the wire in the joint. (ask me how I know - my bench is BRIGHT and my eyes are good close up.)

Q7, Q8, Q11, Q12 depending upon channel - they run hot and crystallize the solder that holds them. Sometimes you will see a color change in the board material. It's a design issue.

Resolder BOTH channels - because there are others just itching to crack.

OHHH, ouch, Q9 and Q10 are 2sa726 transistors, they are EVIL. use 512-KSA992FBU's to replace them.

Click to expand...

Ok, I'll take them out and check them.
Although, I'd be surprised to find anything wrong with them because Q7- Q12 on both amp boards were just replaced.

This is the parts list I used( all were replaced)
Amp Left
gwh-129 Q7 2SA912 TO-92L Replace with 512-KSA1220AYS TO-126
gwh-129 Q9 2SA726S Replace with 512-KSA992FBU
gwh-129 Q11 2SC1885 TO-92L Replace with 512-KSC2690AYS TO-126

Amp Right
gwh-130 Q8 2SA912 TO-92L Replace with 512-KSA1220AYS TO-126
gwh-130 Q10 2SA726S Replace with 512-KSA992FBU
gwh-130 Q12 2SC1885 TO-92L Replace with 512-KSC2690AYS TO-126

I'll also try and resolder all connections. Is reflowing the solder good enough? or do you recommend solderwicking the old stuff out and using new solder?

Ok, thanks for reminding me that those parts are new. (really, not sarcasm)

A dab of new solder will mix in ok. Old stuff can stay, dab will have flux which will help.

Were the trimpots replaced at the same time? 3x per channel.

hmmm, sockets are new, hot and noisy transistors replaced.

Those locations are just the start, sometimes the wave solder "went light" during manufacturing and fractured joints turn up in the oddest locations.

Tell you what, try running it a bit with the pre-out / power amp in jacks separated to see if the pop is coming from something else in the preamp circuit. You did check whether or not it happened on different inputs?

And occasionally check the +52v AWR-194 pins 3 & 4 regulated DC voltage just on general terms.

i just looked - did the list cover the fact that the mc / phono amp has at least 6 2sa726 transistors, q9, q10, q23. q24, q25, q26 ?

Were the trimpots replaced at the same time? 3x per channel.

Yes


Those locations are just the start, sometimes the wave solder "went light" during manufacturing and fractured joints turn up in the oddest locations.

So I took your advice and resoldered the Filter board - GWS-176 and Left Amp Board - GWH-129 (ALL) Then went around looking for any bent or out of place wires, or any wires touching things that maybe they shouldn't. This one seemed suspect to me.( See Picture) Could the wires insulation just be old and passing through to the ground post? Anyways after having moved it clear of touching the ground I haven't had any problems.
So put it together and guess what, it stopped, for the time being and hopefully it stays that way.

Tell you what, try running it a bit with the pre-out / power amp in jacks separated to see if the pop is coming from something else in the preamp circuit. You did check whether or not it happened on different inputs?

This was interesting because when I slowly slid the jumpers in and moved them around it would happen and then another move and it would stop. So that would seem to indicate this is the problem, no? Maybe a bad connection and its so close its arcing? So I used some Deoxit and put them back in and it seems to be working. Will wait and see.

And occasionally check the +52v AWR-194 pins 3 & 4 regulated DC voltage just on general terms.

So these are the new voltages after:
pins 1&2: -51.4, should be -52v, regulated
pins 3&4: +52.9, should be +52v, regulated
pins 5&6: +32.1, should be +32v, regulated
pin 7: +18.9, should be +18v, regulated, provides power for display circuit
pin 8: 0v, ground
pin 9: raw, -53.6, unregulated
pins 10&11: -31.6, should be -32v, regulated
pin 12: raw, +50.3, unregulated
pin 13: raw, +69.2, unregulated
pin 14: 0v, ground
pin 15: raw, -72.2, unregulated
pin 16: +6.4vac
pin 17: +57.6vac
pin 18: +55.5vac
pin 30: +57.2
pin 31: +57.2

i just looked - did the list cover the fact that the mc / phono amp has at least 6 2sa726 transistors, q9, q10, q23. q24, q25, q26 ?[/QUOTE]

Nope, didn't change those.

So seems problem solved(knock on wood). Thanks for your help and advise.

Oh, by the way. I found some 2sk34 locally here, and they seem to be legit NOS.

:thmbsp: