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SA8500 only works on DBT

paultlaw said:
ÌF there is no buzz when i switch speakers on, i reinstall C16 and try again with speakers to on?

If the buzz comes back when i pop C16 back in what are the next steps?

I know i am moving a bit ahead but this morning i done a very quick check, no buzz from speakers. (To be confirmed properly whenever i get home from work as was rushing as usual)
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Yes, then reinstall C16 if no buzz.
I strongly suspect the buzz is gone, because it was there before when C16 was out. I suspect there was a solder whisker short, or a cold solder joint that was cleared while we were troubleshooting.
If it is back, pull C22 and see if it goes away, if still buzzes leave C22 out and lift one end of R28 and recheck.
 
Sorry @merlynski with the speakers on we have buzz with C24 in and speakers set to on.

"Post 235" - Not yet for C16, but please do put C24 back in and check for buzz at C32. If it has buzz lift one end of R28 and recheck.

I am really sorry but i think i am wrong there is buzz at C32 with C24 installed.
I will leave C24 in and pull one leg of R28 and recheck C32
 
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i have pulled one leg of R28 and rechecked and we still have buzz on C32.
So one leg of R28 is lifted, C16 is still not installed.
 
Can you test C22?
Pull C24 again, it should have been isolated when C22 and R28 were lifted.
Does the buzz go away with C24 out?

EDIT: more
 
C24 has been pulled, signal tracer to +C32 no buzz.

The amp still buzzes quite loudly if i turn the speakers on but i am assuming that is because i have the tone board sitting out and a bunch of components removed??
If i turn the tone control off the noise goes away with the speakers on. But with signal tracer only at +C32 there is no discernible buzzing with tone control on
 
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That is weird, because C22 and R28 are the only connections to C24.
I marked two green arrows and a green line on the attached image. Check for 0 Ω between the two arrows and follow the trace with the green lin and look for anything out of place or that should not be there, R28 is in a blue oval.
IMG_0001greenline.jpg
 
It's really hard to see but I scraped the trace a bit, there is a tiny little bump in the trace, can be felt with fingertip, I wonder is it worth bridging this? I don't want to get excited but have we struck gold maybe??? I'll try get a decent picture but it's very difficult
 
paultlaw said:
0.3 ohm is the result i got +C24 to C22
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Is this about the same resistance you get with the leads shorted to each other (lead resistance)?

paultlaw said:
It's really hard to see but I scraped the trace a bit, there is a tiny little bump in the trace, can be felt with fingertip, I wonder is it worth bridging this? I don't want to get excited but have we struck gold maybe??? I'll try get a decent picture but it's very difficult
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If there is a good connection from green arrows pad to pad the bump is not likely a cracked trace, but it won't hurt to bridge it with solder.
There has to be something in that area (C24 connections). With R28 lifted and C22 pulled having C24 in or out should not matter, but it does.
 
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