Ampeg B100R again...

[g1]

maybe I should swap back the first (replacement) IC1?

Yes, please try it.
Also, can you attach that photo from post #74 ?
imgur does not work for lots of people running outdated computers like me.

[mtlbasslad]

Yes, please try it.
Also, can you attach that photo from post #74 ?
imgur does not work for lots of people running outdated computers like me.

Um, apparently no way for people running outdated brains like me to attach that photo LOL It's just a picture of the guts to show what I'm dealing with. I found it with Google 'Ampeg B100R images'
I'll try swapping IC1 & let you know.

[mtlbasslad]

Interesting... just found a post from June 2011 by member SYSDOA "melting bridge recto" with lots of interesting info from R.G. & Enzo.

Recommendation is never run the amp without output devices as drivers will try to do the work & won't. But that is what I have been doing...

Hmmm...

[g1]

Um, apparently no way for people running outdated brains like me to attach that photo LOL It's just a picture of the guts to show what I'm dealing with.

If it's just a google image and not your unit, no worries.
For future reference, when you post, there should be an 'upload attachments' button below the text area, that is probably the simplest way of attaching anything.

[g1]

Interesting... just found a post from June 2011 by member SYSDOA "melting bridge recto" with lots of interesting info from R.G. & Enzo.

Recommendation is never run the amp without output devices as drivers will try to do the work & won't. But that is what I have been doing...

Hmmm...

It can't do any work as long as there is no load connected. I was more concerned with DC correction which is why I had you disconnect that feedback resistor earlier (R35). As that made no difference it should not be a problem running with no outputs.

[glebert]

With IC1 & 2 out Pin14 reads -0.14V... not sure I understand the logic, but sure I don't understand much.

With no ICs in the voltage there should be zero (or very close to it) if the resistors and connections to the +/- 16V nodes are working right. It seems like they are. Therefore when you have IC1 in/IC2 out the voltage offset at the point has to be being caused by IC1.

[Enzo]

They can't do any work with no load, but who guarantees no load. I never assume. How many times has someone reported even after warnings not to, they got the variac up to 100v before it started smoking...again. I wouldn't doubt seeing, "yeah I worked without a load, but I connected a speaker - just for a second - to see if the loud hum was gone."

[g1]

Normally I would not recommend it (running with output transistors removed). But this was a special case where several sets of outputs had been blown. The whole point of running it with them removed was to find the cause of them blowing without blowing more.
And that cause has been tracked down to DC at IC1 pin14 (with 0V at both inputs for that IC section).

[mtlbasslad]

OK I get the 'no load' thing I think... no danger of connecting a speaker here, I promise!

I swapped IC1 for the original replacement but no change - still +9VDC at TP4 (IC1 Pin 14...
Have I somehow fried both new IC1's? Time to order more? Probably too late to ask Santa - & not sure I've been a good enough boy...

[mtlbasslad]

I hope everyone had a pleasant Christmas & New Year... very quiet here as we are under a 10pm to 5am curfew.

Lots of time to spend staring at my sick amp - I did swap in a shiny new IC1 (& yes g1 Digi-Key is a better deal) but this made no difference. Obviously I'm missing something when I study the traces...

[g1]

It's been a while, so we should retrace a few steps. Is this single or double sided board?

(Recap: Output transistors are removed and no load is applied.
IC1 pin14 output is going to 9VDC with approx. zero VDC at input pins 12 & 13. With IC removed, pin14 goes to zero VDC.)

Disconnect one end each of R35, R36, and R37. What is DC at pins 12, 13, and 14 ?

[mtlbasslad]

@g1 Thanks for hanging in there. I'm a bit slow responding, snow removal & groceries got in the way...
It's a single sided board. Going to try to post some pics.
A bit confused if I should lift R35 R36 & R37 all at once or one at a time - & test with IC1 & IC2 in or out?

[g1]

A bit confused if I should lift R35 R36 & R37 all at once or one at a time - & test with IC1 & IC2 in or out?

Test with all 3 resistors lifted and IC's installed.

[mtlbasslad]

Got it, thanks! Like the pictures?

[g1]

Yes, the pictures are helpful. More close up well lit shots of the trace side for IC's 1 & 2 would also help.