Re: Tektronix 475


On Sun, Aug 9, 2020 at 02:45 AM, <tenareze32@...> wrote:

I am wondering if there is a way of testing it without extensive disassembly.

I went ahead anyway and the HT was OK, it lit up a neon bulb through a 22MΩ resistor.
Are you talking about the HV (-2450V) or the HV multiplier (PDA) voltage output?
Checking either (HV and PDA voltage) the way you did it is not a good indication of functionality: Since a neon bulb needs only a few hundred volts to light and less than a mA or so to stay lit, that is not an indicative test.
There are two easy tests for the PDA:
1. Often, with relatively low air humidity (!), a very slight crackling may be heard immediately after switching the 'scope on after it's been off for a while and approaching the screen immediately after switching on sometimes causes the same sound, unless your 'scope has the EMC screen in front of the CRT.
2. Switch the 'scope off and pull the two parts of the high voltage cable apart at the connector in the pink wire. If all is well, this is not without risk of shock; use gloves if you can. Be especially careful to keep the ends away from any electronics or you'll zap them, again, if all is well... Approach the chassis with the protruding metal end of the CRT cable. You should see and hear a discharge with a spark length of at least 3 mm. Be aware that usually, not all charge is gone after the one spark.


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