Author Topic: HP 1821A timebase plugin trigger light  (Read 241 times)

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Offline Totoro

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    • The Belfry
HP 1821A timebase plugin trigger light
« on: November 01, 2018, 09:47:29 pm »
Hello all,
I recently purchased two HP 181A oscilloscope mainframes each with the 1821A timebase. On of the 'scope had obviously been dropped hard which had turned the lower section, including plugins, into a parallelogram. But the other worked, sort of, and I was able to re-build a working unit from the two. (I like old 'scopes!)
However, there was still one problem. The trigger reset light didn't work. Testing indicated it was the neon bulb and swapping the switch/lamp from the other unit fixed that. But now I have a question regarding the behavior of that lamp. When I put the timebase in single-shot, the lamp goes on when I press reset and goes out when there is a trigger event. But in auto or normal mode, the lamp is on all of the time. I can kind of understand that for auto mode but even in normal with no trigger the lamp is on. I would expect that in the absence of a trigger, the lamp would be off, especially in normal trigger mode.
Does anyone know what is the correct behavior? The manual is not forthcoming or I have missed it.
Thanks for any help.
- Michael (aka Totoro)
 

Offline Totoro

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  • Posts: 5
  • Country: de
    • The Belfry
Re: HP 1821A timebase plugin trigger light
« Reply #1 on: November 01, 2018, 09:53:34 pm »
BTW, here's a photo. (This is before I replaced the reset switch/lamp.)
 


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