Standford Research DS345 Error

[SoundTech-LG]

I just now noticed your post.
I have taken a break from it, but yesterday I returned to it.
I am now concentrating once again on my original assumption the problem is in the output amp.
I found several open transistors, including the finals. I replaced them. I found more, and am taking another break from it. The lower board is not anywhere near as easy to work on as the top board. I will be back at it again. I am determined to not let this unit win the fight.

[bostonman]

You found several open transistors?

I'm assuming you mean a bunch were bad, however, this indicates the problem isn't with one or two components, but an entire group, correct?

[SoundTech-LG]

Yes...  mostly on the Positive Half of the diff amp ckt. NPNs, and the Finals of both halves of the single ended output. There may be more. best to find them all before powering up again.
Lots of work ahead. Might be a good idea to power from external +/- 15V supply measuring current.

[bostonman]

This is somewhat upsetting news. I didn’t realize several bad transistors were part of this failure. I thought it would be a single component.

[SoundTech-LG]

There could be considerable collateral damage in this ckt. as I mentioned, working on the bottom board is difficult. Getting close enough to it wearing magnification to see what you are doing is tough. Especially when almost half blind. Hopefully this round will have a better outcome using current limited, and display indicated, external supply for power.

[bostonman]

Due to the recent pieces of information regarding potential collateral damage and the amount of damaged transistors, maybe it's not worth the time to repair?

Are the bad transistors an indication someone plugged something into the output connector that shouldn't have been and blew up the whole input section?

[bostonman]

Did you ever get anywhere with this or give up?