Ampeg B100R again...

[mtlbasslad]

Well, that was interesting,
With R35 R36 & R37 snipped IC1 Pin 12 & 13 read 0V Pin 14 was flipping from -14 to +14 ?? settled on +14V...
R35 was one which I had previously snipped & re-soldered... but this time I clipped it to death - not enough lead left to re-solder. Only 220K I have in stock is 1 watt - I can probably work that in...
Not sure I can get any better pics of the trace side IC's, with a magnifying glass it looks um, messy with flux...
I'm a carpenter - maybe I should stick to my trade.
A bit discouraged...

[g1]

I bet my carpentry looks worse than your soldering.

With R35 R36 & R37 snipped IC1 Pin 12 & 13 read 0V Pin 14 was flipping from -14 to +14 ?? settled on +14V...

Do you have a 100K or something (value not critical) you can solder across C23 ? Then see if pin14 is still flipping or goes to zero VDC.
Also with that resistor still in place measure resistance from pin12 and pin13 to ground.

[mtlbasslad]

Thanks for the encouragement, but I haven't seen your carpentry LOL.

Found a 100K (1 watt) & managed to squeeze the leads under C23 on the component side, quick dab of solder and...
With power off & measured to ground
Pin 12 is 33K Pin 13 starts in megohm range but settles at 70K in 30 secs.
Power on Pin 14 starts at -9 but flips to +9 after a few secs.

I actually managed this without messing up the board any more... I hope.

[g1]

Check resistance to ground from each side of R34. Then from each side of C23 to ground, with your 100K still attached.

[mtlbasslad]

Arrgh, I had foolishly pulled the 100K - put it back in...

Resistance to ground R34 3.2K & 0.2 C23 3.2K & 70K

I really have to order a 1/4 watt resistor assortment - these 1 watters (great in old tube amps) are really to huge for this job.
Wish i had wifi to the shop, dressing & undressing to run back & forth to the computer in the house at least is giving me some exercise LOL. Yeah, I know if I had a smartphone....

Sidebar - temps here on a rollercoaster from -25 to +2, great for our already crappy roads...

[g1]

Arrgh, I had foolishly pulled the 100K - put it back in...

Resistance to ground R34 3.2K & 0.2 C23 3.2K & 70K

This is with R35 still disconnected, yes? Something seems fishy with that 70K reading from IC1 pin13 to ground. With the 100K tacked across C23, the reading should be 100K + 3.3K (R34) for about 103K. Remove the 100K and lift one end of C23. What resistance do you measure from IC1 pin13 to ground?

A close up of the traces & repair under IC1 would still be helpful.

[mtlbasslad]

Ah, no R35 having been destroyed I put a new 1 watt 220K in...
So not doing anything until I'm more clear. Hesitate to lift C23 but if I must - it sits about 2mm from the board so I'd have to remove all the jumpers, pull the board & unsolder from back side. Any testing after that means reversing that process...
Next time board is out I'll try for more pics, meanwhile awaiting clarification. Recap - R35 & 100K across C23 are both in place

1/4 watt resistor kit on the way

[g1]

Ah, no R35 having been destroyed I put a new 1 watt 220K in...

If R35 is connected, then the 70K reading is correct. But not sure when it was re-connected? I think post #93 it was not, but post #95 it was?

Anyway, no ideas at the moment, maybe pics will give some insight. If there is a lot of flux at the IC socket connections, maybe try some isopropyl and an old toothbrush for cleanup.

[mtlbasslad]

If R35 is connected, then the 70K reading is correct. But not sure when it was re-connected? I think post #93 it was not, but post #95 it was?

Anyway, no ideas at the moment, maybe pics will give some insight. If there is a lot of flux at the IC socket connections, maybe try some isopropyl and an old toothbrush for cleanup.

Correct you are. Will leave everything in place as is & attempt cleanup & pics

[mtlbasslad]

After looking up the 220 page manual for my Canon digital camera I figured out how to take close-ups (macro) so here we go - PC board porn...

First pic is 'look what I found' only alcohol in stock was Vodka - for internal use only - but this might do...
Second & third pics are of IC1 (TL074) 4th is IC2 (5532)

A buddy lent me an 'Optivisor' gadget & with that I checked every connection around IC1 & IC2 for any shorts to adjoining traces or anything else I could think of - all seems good.
So still floundering here...

[mtlbasslad]

For anyone following this thread - problem has been solved thanks to g1. Fried IC's...

[g1]

I'll add that trying to run the unit with the output transistors removed was an error, my bad.
IC1 has no DC path from output to input without the entire feedback loop running. C24 from pin14 to 13 needs a DC path in parallel. With the outputs removed or R35 disconnected, there is no DC feedback and the IC section just acts as a comparator and puts out DC.
Somewhere along the line, replacing the IC's 1 & 2 fixed the problem, but we got on a wild goose chase trying to solve a test induced error.