In reply to M1EYP:
I’ll try and get it on ASAP as I miss the server for it’s other uses. I’ve got a wedding tomorrow night and Jethro Tull on Monday plus other stuff over weekend. But at least the mains is back on and everything is running again (except the server with the poorly disk) :-o !
That’ll teach me not to use any old IEC (Wlat knows what they are now) mains lead in the 'scope. So I’m trying to fix the busted PSU from my SI/NS expedition and with the 'scope earthed (as it has the wrong IEC mains lead in it) when I put the 'scope probe earth on the -ve of the bridge capacitor there was a mighty flash bang crack and the lights went out. “Oh dear” I said and remembered the floating earth 'scope lead did a vanishing trick hence the wrong lead in the scope. I’ve just pushed 330VDC up the earth lead of the 'scope probe and into the earth circuit. The ELCB in the consumer unit didn’t like that and off went the mains.
No lights and my hand very close to the capacitors charged to 330VDC, move hands slowly whilst everyone in the house started moaning about no power. Of course the big torch was nowhere to be felt. Hrmph!
The PSU is a Lascar PSU130, a 0-30V 1A adjustable bench supply. I rang Lascar and asked for a circuit and they said “we don’t supply them”. I told the dude that my employers wont be buying their products in future then. Anyway, after puzzling for a while I can see there are 2 switched mode controllers in it. Oh the complexity to save on a big transformer and shunt regulator. It looks like there’s an SG6840 driving the main chopper FET producing the raw DC plus the volts for the LCD board. Then there’s a TL494 (the one in every PC PSU ever made) driving another chopper to produce the variable 0-30V. Apart from the opto feedback, everything is DC coupled meaning the fault could be anywhere.
Argh! I hate analogue stuff!
Anyway the mini DMM is fixed (blown fuse in mA circuit), the super lightweight BNC extension lead is next to be fixed. Then there’s the vacuum cleaner and then when I find some T2.5A fuses this nasty Lascar PSU.