Focus adjustment on JDR 3500 o'scope

[Juan Jimenez]

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!

 

[Arfa Daily]

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

 

[Juan Jimenez]

Sounds reasonable. Thanks!

juan

 

[Kurt Krueger]

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.

Does it have an astigmatism control? Is that working correctly?