I have a Hung Chan 6502 20MHz cro that is proving rather difficult to repair. Apparently it is also known as a Protek 6502.
The fault is that the trace is only just visible with the brightness on full. This one has me baffled.
Any advice would be greatly appreciated.
Cheers,
Dan
I'm not at all familiar with that scope, but....... Do you have access to the crt cathode, aka Z axis, control? Maybe you have a link, jumper, or other Z axis option mis-set.
Do you have a schematic? Check the various voltages on the CRT. If you have a high-voltage probe, measure the accelerator voltage - carefully!
H. R.(Bob) Hofmann
Is the trace equal illumination over the whole trace or is there an X-axis gradation in the brightness of trace? Is the trace constant in brightness or wavering? Did it suddenly emerge as a problem or gradually over time? Is the trace of the correct geometry, X and Y sense, for a test signal input ? if it is correct then not an EHT problem
I would suspect leakage/failure in something in the blanking/un-blanking area (eg opto-coupler high R resistor) or a "sub bright" preset failure.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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