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!



--
Posted via a free Usenet account from http://www.teranews.com

"Juan Jimenez" wrote in message
.. .
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

Sounds reasonable. Thanks!

juan

"Arfa Daily" wrote in message
...

"Juan Jimenez" wrote in message
.. .
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





--
Posted via a free Usenet account from http://www.teranews.com

Juan Jimenez wrote:

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?