I have an old KIKUSUI scilloscope type COS5021O . It has a problem that the trace is very bright. I cannot reduce it with intensity control. If I rotate the intensity clockwise I hear a high frequency pitch. Any help will be greatly appreciated. Also can somebody has a schematic/service manual?
In other words, is the scope working normal except that the trace is very bright and does not respond to adjustment. If so, look at the adjustment circuit first.
Clean and lubricate the "pot". Check any capacitors for short. Then look into the CRT cathode circuit in general.
Then see if there is an inter-electrode short in the CRT.
With a CRT tester. Since you don't have access to one, measure and record the voltages found on the pins at the back of the tube relative to ground. Do not measure the high voltage at the side of the tube.
Report to us the data you have collected.
If you can, provide the CRT type, the "model number" of the CRT.
What have you checked so far?
Would you mind answering the questions I asked above?
Adjuster orange wire 5.0V DCbrown wire 3.5V DC.
Electromagnetic deflection coil:
The parataxis pellucid wire 152V DC and 153V DC.
The tow wier splice :green wire 44V DC and blue wire 98V DC
The CRT is the least-likely item to fail. After 12 years working with scopes as a test equipment and calibration tech, I've replaced maybe six CRTs, one with a defect from the factory in the scan expansion mesh and the other five with open heaters -- directly-heated cathodes on Tektronix 200-series scopes with little filament support and customers who treated them like footballs.
Check components in the interface between the sweep unblanking output and the CRT HV circuitry. A very few scope models have a basic bias adjustment; check yours for that.
Be very careful troubleshooting this problem as you'll be dealing with about 2KV in the HV circuit and maybe 10KV on the second anode (although with this problem, you'll not be messing around with that.