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453 Trigger Fixed!!

Bill
 

Well as my frequent threads have shown this problem was a real challenge for me. I have no experience with Oscilloscopes so most of my time was spent researching the basics before diving into the problem.

Symtoms
Trace on both channels but no trigger.

The problem was in the Trigger Pre-Amp section of the Partial A Sweep Board. Since I had lost the trigger for both A and B channels I looked for something common to both of them. This was 3 days ago. I decided on checking out the Trigger Preamp board at that time but found the voltages ok and no obvious signs of PCB or component damage. Having read here about pulling transistors and reinstalling them I gave it a try with no change. Well today I decided to look there again. Pulled the same transistors, Q404, Q413, Q414, and Q423, again thinking there may something I missed. Pulgged them in and reinserted a few times and tried it again. Both channels now were triggering as they should and the wave forms looked great. Since there was no change the first time I did it the oxidation must of needed additional cleaning. I was very careful both times to make sure they were installed correctly in the socket by following the trace to the components they connected to then using the ohm meter to verify it.

I learned a lot about my 453 while doing all the research and have a new respect for the Engineers who designed it and the people of assembled it.

Thanks to everyone for your feedback and patience!!

Bill