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Sounds reasonable. Thanks!
juan
"Arfa Daily" <arfa.daily@xxxxxxxxxxxx> wrote in message
news:BwXSg.48505$WV2.11806@xxxxxxxxxxxxxxxxxxxxxxx
>
> "Juan Jimenez" <flybd5@xxxxxxxx> wrote in message
> news:451bec7e$0$19619$88260bb3@xxxxxxxxxxxxxxxxxxxx
>> Hi folks,
>>
>> Does anyone have a calibration/maint manual for a JDR Instruments model
>> 3500 o'scope? I bought it cheap for my son ($100), he is building his own
>> analog synth, and it works great, but the focus control no longer brings
>> the trace into focus when I turn it all the way to the right. I need to
>> adjust this but I don't have a manual.
>>
>> Detailed instructions will do as well.
>>
>> bd5 at
>> bd5 dot com
>>
>> Thanks!
>>
>>
>
> If it's not a problem with the tube itself, then likely one of the high
> value resistors in the chain which divides down the PDA voltage to the
> right level for the focus grid ( via the focus control ) will have gone
> high in value. In the absence of a set of schematics for it, I would
> follow the connections from either end of the focus control ( especially
> the clockwise end which is probably the higher voltage end ) back to
> wherever they go, and look for some big-ish high value resistors right
> there, and carefully check their values. If you find one that has changed
> substantially in value, make sure that you use a resistor with a high
> voltage specification to replace it with ( many readily available
> resistors are only rated for operation up to a couple of hundred volts )
>
> Arfa
>
>
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