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Tek 7104 readout problem


dd@...
 

I have a 7104 and now a 7103 that have the same readout problem. The
readout is not visible unless the intensity knob is turned CW to the
"pulsed" position and then pushed against the stop.

On the 7104, I found that the TP1925 voltage was at -6.3V in the full CW
position, and I could make the readout go on by pulling it to about -11V,
so I tacked in a couple of resistors to change the range of the readout
intensity control. (Note, another problem this scope has is that the A/B
intensity knob indicator lamps don't activate properly, but I have no idea
if that's related.)

I wasn't totally happy with the above hack, and now that I have a 7103
with the exact same problem, I would really like to find the underlying
cause... has anyone seen/fixed this?

Thanks...


L. Mark Pilant <n1vqw@...>
 

I haven't ever looked at a 7100 scope, but I did have a 7904
with a very dim readout. If you turned the trace intensity all
the way down and dimmed the lights, you could make out the
readout characters.

In my case, it turned out to be the Z-blanking board was way
out of calibration. I went through the calibration procedure
until I got the the blanking board. When I did the board, I
suddenly had the readout. (And everything still worked as well :-)

Going through the rest of the calibration procedures showed the
rest of the 'scope wasn't that far out of spec.

I hope this helps.

- Mark