SGI: Hardware

The other night, my Indigo's power supply let out magic smoke while I was listening to a few mp3s on it and cleaning my room. Some how it kept running, but I flipped the switch to prevent any more damage. It was very upsetting since I really have come to love the thing; thankfully I had a spare PSU. Anyway, I pulled out the bad one and opened it up to look at the damage. It looks like one of the diodes (?) cracked or split open and shorted, causing the component and leads to melt and char a bit.

I think simply replacing the component would give it new life, at least for a few years, but I do not have an EE background -- I know these questions are difficult to answer but would replacing the component be enough? Or is this an indicator of a much bigger problem? What are common points of failures in Indigo power supplies?

Also, after some searching around on this forum, I came across a few very old threads where people mentioned fitting regular AT or ATX power supplies into the Indigo power supply chassis. I am very interested but the website they were referencing appears to be down. Does anyone have a copy of the guide by any chance? And can anyone vouch for this mod?

Thanks!

Depends on the component. Often caps go, and usually (unless they're the big main filter caps) they don't take anything out with them. Actives (semiconductors) going is much more unusual - you should take a look around and see what is up if it's really a diode that went.

Do you know about where in the supply "chain" the diode was? Since the computer went on running it (if it was really a diode) was probably in a lesser-used rail such as the -12V.

Check out to see if it might have been a tantalum "blasting cap" or a paper cap - these are often used as small filter/ground shunt caps and can fail spectacularly without much additional damage. The tants are either surface-mount boxes or the sort of capacitor that looks a little like a pillow.

I think this happened to me the other night too.

Was testing things out and quite excited to have built a keyboard converter. I had stepped away and came back to "the smell" but things were still running and the fan had evacuated the scent pretty well so I couldn't tell what cooked. It wasn't until later I decided it was probably an old electrolytic cap in the power supply.

I haven't verified what failed, but caps get dry and fail, so if that's what it is just replace it, and probably the ones that are similar.

I have no idea where in the supply "chain" the diode was since I don't know anything about electronics. I don't know how familiar you are with the inside of an Indigo 9430812-A power supply but the component that failed is located on the main board, underneath the daughter board, and just below the "Caution: For continued protection against risk of fire..." warning. It may be component CR108. The component itself is cylindrical, black, with a silver band on one end. It has 5352B NT or 5852B NT printed on it; the B may be a 6.


Granted, I had my music playing a little loud but I didn't hear a pop that I would expect with a failed cap. I can't seem to find anything charred except for the component described above which looks more like it fried in-place than exploded.

BTW, is it possible this may have been caused by the fact I have the original PM2 heatsink on my R4400 150MHz? I really ought to take the time to replace it with a PM1 heatsink.


Bummer, man :[ Indigos are some seriously cool machines; saddens me to hear of any of these guys failing.

Definitely a diode. Diodes tend to fail spectacularly for one of two reasons: excessive reverse voltage and excessive current, and in both cases the overload needs to be significant for there to be anything noticeable.

Look very carefully at the caps in that section of the PSU to see if one has failed. A large cap shorting can drag a diode with it easily before going open-circuit, whereas the small caps generally don't need too much juice to burn out a connector wire.

Most PSUs use the diodes in a bridge configuration, so provided that there is enough filter capacitance available it will still look like it's working, but something went bad. Go over that area with a flashlight and magnifying glass.

A big diode near a fuse rating is probably in the main (~320V) section before the choppers/regulators.

The diode that failed is also in close proximity to a cluster of four fairly large caps. Granted, I haven't ripped apart the PSU yet, but there doesn't seem to be anything obviously wrong with them. Could you please tell me a little more about what things I should be looking for?

I think it's time to dust off my copy of the Art of Electronics book

Also, a big thanks for your help so far. I really appreciate it :]

It might be worthwhile to post a picture of the damage. I wouldn't be too surprised if somebody here could tell you exactly what failed just from that.

Agreed. Unfortunately, I don't have a decent digital camera, but I may be able to borrow one. I'll try and get some pictures up by tonight.

Update: Pics aren't happening this weekend; too many things going on.

Hmm capacitors have a tendency to 'bulge' near the top when they reach the end of their lives.
Look for any such signs and replace them. If need be, replace them all.

The big ones in PSUs can also leak around the bottom without appearing bulged, so look for evidence of something getting on the board around the cap.