Sun MDT distributor tester

69DodgeMan said
I don't think it is too terribly different than the later models. It is direct drive instead of a belt drive. The wiring is probably a little more "primitive" but I'll bet the basic concept of operation is very similar. I've a feeling that the power supply (I think its a high voltage supply) pictured at the top is not operating quite right. I think it is what was called a multi-vibrator type supply or sometimes referred to as a "chopper" type. The flash tube does "flash" part of the time, but then I'm thinking the HV supply drops and the tube stops firing?? Vacuum pump was inop when I got it just like everything else was. Got the vac pump working fine now, RPM meter responds to varying speeds but isn't 100% accurate.

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I had missed this. I don't know about Sun machines specifically, but the HV supply is commonly called a "vibrator" power supply. This makes "fake" ac by chopping DC. It works sort of like a buzzer with extra contacts. Two major types. One chops DC and feeds it through a transformer to step up/ down the voltage to desired level, then separate rectifier tube(s)/ selenium/ diodes rectify back to DC

The second type is called "synchronus". Again, the vibrator chops the dc, feeds it through the transformer, now the transformer goes back to separate contacts on the vibrator which now acts as a rectifier to "pick" the proper phase of the chopped signal and send that out as pulsating DC, to be filtered by a capacitor.

Hard to say what is wrong. Vibrators certainly went bad. If you don't care about internal "restore correct" you can buy various solid state inverter/ chopper/ switch mode/ "switching" supplies on egag. If you want to fix that one, start by looking for, and replacing, a filter cap maybe under the chassis. The "good news" is that at least one cap, pictured is an oil filled (rectangular can with ceramic insulators) and these almost never fail unless they leak. THAT is a problem with type of oil, as it can be a carcinogen