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Old 17th Mar 2021, 11:33 am   #51
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,484
Default Re: The Transam Triton Personal Computer

For your dead switch-mode, here's something you can try. (Carefully) take it apart far enough so you can get to the pins of the high voltage electrolytics on the mains side, or if it is possible to do so to the + and - pins of the mains-side rectifier.

Either way, see what the DC voltage on the high voltage capacitors / output of the bridge is and if you still have a very high (300VDC + ) voltage sitting there a long time after the mains was last applied, that would point to a problem in the start-up chain, narrowing things down quite a bit.

If you do find this to be the case then needless to say you should use a suitable resistor, held in insulated pliers, to discharge the capacitors before looking around for the cause.

Typically there is a chain of 2-3 identical high value resistors in series on the high voltage side, one of those often goes open circuit. Also look for small electrolytics which were placed too close to heatsinks, high frequency transformers or other hot-running components. These usually end up being baked dry.
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