My Gould OS300 osciliscope seems to have an intensity issue, when I first switch it on its fine. The trace intensity can be brighten or lowered no issue, however after ten minutes or so it seems to go very dull and is difficult to see. When it is at this stage turning the intensity pot changes the brightness but not to a level that you can see the trace clearly in fact its very faint.
Any ideas what thus might be?
Any ideas what thus might be?
Would have to see a circuit but it could be something as simple as a failing cap or resistor going high somewhere on the intensity control. If the EHT were falling (which would dim the brightness) then normally the trace would "go bigger" as well because the tube becomes easier to scan.
I'm just having a look at one now...
You need to check the -/+ 11 volt suplies comparing faulty against non faulty conditions. There are two intensity controls, a preset and the user one. Compare what is going on around there. Also there is a thick film resistor module RN720... again any problem with that could cause the issue.
Also check what is going on around T701 and T702. They call it a bright up amplifier. See what happens to the voltage on TR702 collector when the fault occurs.
You need to check the -/+ 11 volt suplies comparing faulty against non faulty conditions. There are two intensity controls, a preset and the user one. Compare what is going on around there. Also there is a thick film resistor module RN720... again any problem with that could cause the issue.
Also check what is going on around T701 and T702. They call it a bright up amplifier. See what happens to the voltage on TR702 collector when the fault occurs.
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