Shugart 851 power problem

"Richard Erlacher" <edick(a)idcomm.com> wrote: Hi I agree with Dick, it sure sounds like a switcher. The small transformer and the high voltage warning on the heat sink are good indicators. I still think it is a problem in the supply some place. I once had a similar problem in a switcher for a monitor. I never did track it down to the exact part that was causing trouble. My excuse was that I didn't have the schematic and besides, I did a hack to get it to work. I found that I could get it to power up if I disconnected the filament of the tube until it brought the power up. I put an extra push button on it and my younger brother inherited it later. All in all, it had about 6 years life instead of 1.5. It wasn't a recommended fix but it got me by. I'm surely not that proud, only indicating the options that one could take. In switchers, the filter capacitors on the output side run real close to their limits as far as power dissipation. This isn't as much a problem on linears. Try tacking an additional capacitor on the output filter of the 24 volt. If it is what I think it is, the voltage is coming up too fast, triggering a current shutdown. The reason it restarts after cycling is that there is a little charge left on the load caps and that reduces the power on surge. Look for the rectifiers on the output of the transformer, that is where the capacitors are. Dwight