Collectors with ATs running on 230VAC mains may want to replace their EMI filter caps

[paul]

... before they let loose in a cloud of acrid smoke ...



My AT had not been run for about a year and has never been run on 230 VAC before. After setting the 115/230 switch correctly it booted and ran fine for about three minutes, then I heard what sounded like a loud grinding noise then a string of popping sounds. I thought it was a floppy disk drive seeking but it was accompanied by thick smoke pouring out of the fan and filling the room. I thought "that's not right," so pulled the power plug as quick as I could reach it, then thinking, "oh, crap, just what I need at 11pm, a house full of smoke."

Fortunately damage was confined to a small area and the rest of the PS looks fine. One of the line-to-ground (Y) caps was to blame and must have been arcing for several seconds. Oddly there is no line fuse in this design but it looks top-quality otherwise.



I might have to make up a line cord with an RCD (GFI) and fuse built-in.

 

[1ST1]

This is a serious thing. The power supply of my Triumph Adler Walkstation 386 laptop also burned partitially one day. Luckily the main 16A fuse of my house floor stopped it. Otherwise we might not have a house anymore... I have two more walkstations and olivetti laptop using the same powersupply now and before playing bigger with them I have to replace these EMI filter capacitors.

Warning: Don't use WIMA MP 3 250V~ - they are old and burn again. Better use WIMA X2 for 275V~. That's what I have now in my walkstation.

 

[Malc]

Quite a common problem with this old gear now, I've had it happen too many times, Snap crackle and pop and the room fills with smoke and stink, If i get a new machine the PSU gets pulled / cleaned out / checked and the X2 caps replaced with better quality parts if required, I don't wait for them to go pop anymore.

 

[paul]

Yes, 275VAC seems to be a prudent rating since our "230" is actually 235 to 245. The lack of a fuse on the AT supply is most disturbing and I will look at installing one. The house circuit breaker is 20A ... not going to help.

parts from Element14

 

[paul]

All done, a fuse holder installed on each side of the line.

 

[Chuck(G)]

I'd probably opt for a higher working voltage if it was my choice. After all, the 230V is the RMS value, while the peak value is about 325V (230/0.707).

But it's nice to see that it's working for you.

 

[1ST1]

Today at our classic computing meeting HomeCon in Hanau, Germany (near Frankfurt/M) was a guy who brought a very old portble color TV set. He used that for his Nintendo Entertainment System. And suddenly smoke came out of the TV set and all neighbour computers on the same electic line switched off with the fuse.

It was the same, EMI filters which burned down. He has soldered them out and the TV set worked again.

So be carefull, it's not only AT power supplys where this can happen.

 

[paul]

I'd probably opt for a higher working voltage if it was my choice. After all, the 230V is the RMS value, while the peak value is about 325V (230/0.707)
But it's nice to see that it's working for you.

Gee, Chuck, you're usually an unimpeachable fountain of knowledge! It's working for me because these are specifically IEC 60483-14 X and Y rated caps with a working voltage expressed as "VAC" line voltage, hence RMS.

 

[paul]

More pics for those who might want to make this simple mod ... I'm using T2.5 fuses which seem to be sufficient for 230 VAC, depending on how much you draw off the auxiliary IEC outlet. Also, rather than upgrading the caps in my entire collection I'm now powering all my old computers off a plug-in RCD (residual current detector) to catch Y-cap failures before they turn into a fireworks display.

Interestingly the caps on the main PCB are all original and still appear to be in good condition.

 

[Chuck(G)]

Gee, Chuck, you're usually an unimpeachable fountain of knowledge! It's working for me because these are specifically IEC 60483-14 X and Y rated caps with a working voltage expressed as "VAC" line voltage, hence RMS.

Okay, it wasn't clear from your description. Proceed and nevermind. That will teach me to comment before my first cuppa.

Line filter cap failures are legend among Rifa film caps here. Unfortunately, they were in very common use in the 80s.