Thanks Maciej. I'll be surprised if the manufacturer has records of what they used for the chopper in power supplies 30 years ago - who knows if their design has changed between then and now. I'll be even more suprised if they will talk to me about it but I guess it's worth a try.

Thanks again Maciej. I've bit the bullet and unsoldered most of the electrolytic capacitors and other components that seem to be in trouble. When I got the chopper transistor out, I found that if I hold it at exactly the right angle to the light, I can see that there are faint markings on it after all and it turns out to be an IRFPE50 HEXFET. I was wrong about the cracked RIFAs not being mains filters too, they are actually across L-E and N-E and they seem to have between a few hundred kOhms and a few MOhms leakage too. The driver transistor looks like it might be ok.

from the right direction too and/or techniques used to take fingerprints

On Thu, Feb 03, 2022 at 06:06:10PM +0000, Peter Coghlan via cctalk wrote: Does that PSU have a PWM controller IC, or is it built entirely from discretes? If there is an IC driving the chopper transistor then you may be able to get some clues about the likely characteristics of the transistor from the IC datasheet. Is it definitely a FET? Some, particularly older, designs used bipolar transistors there. As you say there is a fairly high likelihood that other components on the primary side will have blown up as well so you might be looking at a fairly extensive repair. Are there any other obscure, unmarked devices or is this the only one? p.

What's a "Mean-Well module"? I somehow find myself imagining: "I put a new module in my router. It blew up. At least it meant well" :-) (My IGS has the rather heavy and over-engineered divider shelf with the main board underneath and the fan and power supply above.) Regards, Peter Coghlan Jonathan Chapman via cctalk wrote: > With that much carnage, I'd probably drop a Mean-Well module in there. I > > believe there would be enough room for one or two in the IGS I have > > (taller white box, divider "shelf" over the mainboard, I don't know if > > there was a lower profile model). > > Thanks, > > Jonathan > > ------- Original Message ------- > > On Saturday, February 5th, 2022 at 09:17, Phil Blundell via cctalk cctalk at classiccmp.org wrote: > > > On Thu, Feb 03, 2022 at 06:06:10PM +0000, Peter Coghlan via cctalk wrote: > > > > > Today I finally managed to check it out. The ceramic F4A mains input fuse > > > > > > beside the power switch on the back panel had blown. When I opened it up, > > > > > > I found a POWER-ONE MAP80-4000 power supply. The main chopper transistor > > > > > > labelled Q1 on the PCB is almost a dead short. It is a large plastic > > > > > > packaged FET mounted on a piece of aluminium which is in turn screwed to > > > > > > the case for heatsinking. Unfortunately, there are no markings on it so > > > > > > I have no idea what to replace it with :-( > > > > > > As Q1 is shorted across all three terminals, whatever drives it may be > > > > > > damaged too :-( > > > > Does that PSU have a PWM controller IC, or is it built entirely from discretes? > > > > If there is an IC driving the chopper transistor then you may be able to get > > > > some clues about the likely characteristics of the transistor from the IC > > > > datasheet. Is it definitely a FET? Some, particularly older, designs used > > > > bipolar transistors there. > > > > As you say there is a fairly high likelihood that other components on the > > > > primary side will have blown up as well so you might be looking at a fairly > > > > extensive repair. Are there any other obscure, unmarked devices or is this > > > > the only one? > > > > p.