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Old 9th Apr 2021, 6:42 pm   #20
ortek_service
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Join Date: May 2018
Location: Northampton, Northamptonshire, UK.
Posts: 1,394
Default Re: Weir HSS100/4 PSU blowup

I presume the lamp was lighting a bit (although won't light much / drop very much when still operating cold) on this limiter. So this would have been dropping quite a few volts, even without you putting a load on the SMPSU - especially if the SMPSU's was running overloaded due to a fault in it.

I was only thinking of using the Variac to run the SMPSU without a load, initially.
- So normally there shouldn't be too much current drawn (even at lower voltages), and it probably wouldn't start to run until >90V anyway. And I suppose you could always switch-on above this, if it got too upset at rather low input voltages.


I couldn't remember if it died after < 1min running, with no load on it. As otherwise, if it did survive like this despite the aubile oscillation, then you may abler to run it quite a bit to do various tests.

I was thinking more of an output capacitor going short / breaking down, so causing an overload. But looks like you've ruled that out, by changing them all.
I also wondered if any output rectifier diodes may have gone s/c, as HF AC into the electrolytics is going to upset it a bit.


Maybe there's a relatively-cheap similar spec transistor, that would be good enough for just running off-load, that you could afford to loose a few. I suppose you could always cut the leads above the PCB and rejoin to those to save re-heating the tracks.
With CRT TV's and Monitors, I often tried using BU508A/D's I had a few of, before putting more expensive original type in there.
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