> That is absolutely the classic circuit. I assume the AC terminals of the > bridge > rectifier come from the mains input, possibly via fuse,switch,filter. > > To understand it, draw the bridge as 4 separate diodes. Now assume the triac > is > turned off (open-crcuit) and it's just a standard bridge rectifier circuit. > Then > consider the triac turned on (effectively shorted). You have the classic half- > wave voltage doubler using the 2 capacitors and 2 of the diodes. The other > 2 diodes end > up in parallel with the capacitors (remember the triac acts a short circuit > now) > and are always reverse-biased so don't do anything. > > For 230V mains input, I would expect the triac to be turned off. So it's a > full > wave rectifier with 230V AC in. Giving around 325V out. > > I suspect those capacitors! >
I have now managed, after a bit of a struggle, to replace to two big rectifier output smoothing capacitors. The DMM shows about 325V output now, so I think this side of the problem is fixed. However, the PSU still does not work. The first time I tried the new caps the PSU fans twitched for a fraction of second, but I did not have any other load attached. Now they don't move at all. Could the earlier defect with the rectifier output have caused any other damage? Regards Rob
