I took the Miniscope to the local technical institute where I used a variac to gradually build up the supply voltage to 240VAC to reform the caps, and see if any magic smoke was waiting to escape. I was working in a class with 3rd year apprentices and the instructor asked me to give a mini-presentation on what I was doing. They were all interested. I forgot to take photos.
Over a period of about 20 minutes, the voltage was gently eased up and absolutely nothing happened. I had the variac output in series with a 18R 10W resistor and an underated fuse. Only 200mA. At full supply voltage it drew about 130W which is too high.
The critical part is the transformer. This is sealed in a metal can, probably with transformer oil for cooling. If this blows, the Miniscope would probably be unfixable.
One of the potentiometers is seized solid and two others have high friction. They are 1/4" SS shafts with no flat. I suspect this was done to prevent damage by over turning the knobs. The set screws are BSW 1/8, 40TPI, but one screw was 38TPI and that was enough to strip the thread in the Bakelite knob. I am currently making some replacement set screws (can't buy them here). And I need to repair the striped thread.
Now that I know it can take 240VAC, I plan to run it at about 115VAC to go through and check that individual components are doing their job. Before I do that, I need to reverse engineer a circuit diagram. That will take a while because of the way the components are packed in.
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