Hitachi V202 oscilloscope issues - diyAudio
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Old 3rd September 2003, 05:35 AM   #1
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Join Date: Jun 2002
Location: 3RS
Default Hitachi V202 oscilloscope issues

I have an old Hitachi V-202 20 Mhz oscilloscope.
During the rainy season we had a really bad day and some moisture condensed on the components. When I turned it on it blew some TO220 type power transistors on the main board. I replaced these. The display however seemed to loose intensity control . So I had to solder a 3.3M resistor in series with the control grid ( I think) and it now has a fixed acceptable brightness.

All other parts 'seem' to be OK. Does anyone have any idea what is happening ? I have a circuit diagram of the intensity control circuit which I will scan and post later. I did see a flash around the connector of the CRT when I opened it and turned it on ( at the time it failed). That must be responsible for the blown power transistors.
I am able to use the unit now though the intensity is fixed. It also lost its ability to have an external (Z) intensity control.
It used to be a good scope - still is ! I wish I could fix it again.
The slide switches for the ac/gnd/dc are very hard to operate and have poor contacts. Can I use any switch or should I get them as spares from Hitachi ?
What is the best contact cleaner that I can use ?
Thanks.
Ashok.
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