OTB – Tektronix 453A

I picked up a broken Tektronix 453A scope from Craigslist. It had a few issues, however none of them were fatal for this unit. I initially checked the power supply voltages and they all seemed okay. After looking around a bit more and reading the service manual I found the primary sawtooth signal was basically missing a tooth. It was keeping the voltage high every other “tooth” and not dropping down. I hunted back and noticed the pulse which generates the saw tooth signal had the same problem all the way back to the source. 

Long and the short of it, I started to check the voltage levels in this section and found the +75v rail was around 65v. So I second checked the power supply voltages, and found over 8v of AC ripple on the 75V DC rail at the output of the power section. Well I replaced a few caps and all is good again…. Next time I need to check the power rails closer. 

Oh, the only thing I could not fix was the variable timebase for channel A. The detent position will not engage…. So it’s 99.9% fixed, but this one is a keeper for my bench.


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