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Tektronix 475A lost trigger


Jan 6, 2010
Jan 6, 2010

I just bought a Tektronix 475A from a fine man who calibrates scopes, he set it up and showed it to me working before I purchased it. I got home, turned it on and was showing the calibration square wave to my son when the trigger light blinked off, the screen went blank, then the trigger light blinked back on with both traces back, clear and strong. This happened a few times, then the screen went blank and trigger light off, and the scope has not triggered since. It worked for about 4 minutes at home.

I spoke to the seller, who generously offered to take it back and return my money, but I would prefer, if possible, to get it working. I saw a thread here about the same issue from 2004, and it appeared to be an pre-amp IC that is no longer available.

I can't yet post links, so here is part of the the link:

tektronix-475a-trigger-does-not-work-t39525. html

I have not found a copy of the service manual to begin my own tests, if anyone has a copy and could send it to me I would be grateful.

The seller had me remove the cover and adjust a pot on the trigger board, and press on each of the transistors to ensure they are seated properly, but that did not fix the problem.

Any ideas on what to do next?