Re: Mystery SMPS IC Follow Up

In article , Andrew Mawson writes

And the fault was . . . . . .

A short circuit capacitor across the 35v rail in the line oscillator circuit. Due to the high load the smps never started up

AWEM

In article , Andrew Mawson writes

Thanks Andrew, others have previously reported weird and unexpected failure modes in the past that I wouldn't have thought to test, hence my curiosity.

when in doubt change ALL the electrolytics.

I've had several where the output caps drop in value, but not had one where they've shorted out.

En el artículo , Andrew Gabriel escribió:

Yes, 'lytics usually go low ESR but I've never seen a shorted one. Had a shorted tantalum cap once, but that was many years ago.

Oddly recently I've had several go s/c so I really should have thought about it. I had two go s/c quite dramatically in a high power servo amplifier on my CNC lathe - 100 amp peak current jobby. They were on the pre-driver board and made a noise like a wire fuse blowing. Turned out they'd taken a pcb track with them vapourising the track. Cause was a short circuit in the 'H Bridge' power circuit - this is an integrated six transistor 'chunk' made by Fuji (6DI75AH-050) oddly rated at 75 amps.

AWEM