[Repairing the PSU from an SGI Iris Indigo R3000]
In the last episode, I managed to extract one of the boards from the PSU and found it to be in superb condition. But what about the other, larger PCB? Although I could see parts of it “in-chassis”, I really needed to remove it to be able to inspect it fully, and to have any view at all of the non-component side.
Hey, removing the other, smaller board was pretty straightforward, so this should just take a jiffy, right?
Unscrewing the three screws that attached the board to its’ cylindrical standoffs was easy enough. The screws are crap, soft metal, perhaps aluminium? You have to be a bit careful not to knacker the screw-heads – gently, but firmly, does it!
However, in spite of doing so, the board would not move, neither slide-out nor lift, not even a bit. Dammit, there is another “attachment” that needs to be dealt with, on the outside of the chassis…
That darned hex-nut, and it’s location, is a royal pain. After 25 years, it has welded itself to the large solder-pad on the PCB.
I dug out my hex-driver sets, only to find that they were all Imperial rather than Metric, and this sucker needs a 4mm driver. A visit to the hardware store didn’t show up any as small as 4mm, not even rummaging through their behind-the-counter “special stash”. Fortunately, the local petrol-station has its’ own hardware tool shop, including precision tools, so I was able to pick up a set of hex-drivers that included a 4mm driver.
However, that didn’t actually help. This particular hex-bolt is sooooooo low-profile that any regular hex-driver just won’t grip it properly. The usual solution to that situation would be to apply a lot of downward pressure, but this damned bolt is made of some really cheap and nasty soft metal, and I nearly stripped it’s hexiness. Plenty of cursing ensued!
Given its’ location, getting even needlenose pliers or a needlenose wrench onto it just won’t fly – you can attach, but there just isn’t enough room to rotate it! There isn’t even enough room to saw-cut or file a straight slot into the head (to be able to get a flathead screwdriver to turn it).
All together now, loudly, with feeling: “Which zarking genius designed this damned arrangement?”
The only solution was to grind the head off the bolt, using a Dremmel fitted with a rather narrow-tip grinding head, being very careful not to wreck the underlying PCB…
Not too much scraped, considering the confined working-space, although some metal particles were scattered over the back of the board, which will thus need cleaning.
The remainder of the bolt (thread body still in the hole) still needed removing. Cue a naked junior-hacksaw blade and plenty of patience, to cut a slot in the barely-protruding top of the thread, to be able to get a small flat-head screwdriver onto it.
Even with the troublesome bolt removed, getting the board actually out of the chassis was still tricky, due to the 24-pin system-backplane connector. The fly leads to same are very short, and are very stiff thick wires. There isn’t enough room above the board to push that connector through its’ chassis-cutout without removing the board first, but you cannot do that as the connector is hard-attached to the board by such a short cable-harness. Time to pick yourself up by your bootstraps?
Also, that connector has active components attached to its’ backside, so using force wasn’t a sensible option.
A lot of wiggling back-and-forth, both pushing the connector from one side whilst simultaneously pulling from the other, all at the same time as pull-sliding the PCB out to make room, FINALLY got the danged thing out. Hooray!
Not Too Shabby
Most of this larger board and components looked in OK condition, albeit a little dusty in places.
Not too shabby, huh? Oh yes, spot the two huuuuuge capacitors lurking under the black plastic sheath – a reason for nervousness whilst trying to wrangle the board out of the chassis – those could give you a very major DC shock!
But Now, The Good News
But there was something a bit odd-looking in the middle of the board, next to the plug where the smaller board would attach.
The solder pads for component CR111 don’t look quite right, and is the PCB a bit discoloured there too? Time to take a look at the other side of the board underneath CR111…
WOW! The solder-mask on the underside of the board underneath CR111 looks like it has been heat-treated with a blow-torch!
These signs of damage are good news, I have likely found the reason why the PSU +12V rail is dead – CR111 has failed, and rather spectacularly.
Now for a little aside… on the ‘net, there are a few reports of people repairing ITT PEC4044B PSUs as used in the R4000 Indigo, but absolutely none regarding repairing the different PEC4044A used in the R3000 Indigo. Comparing my pictures with pictures of the 4044B internals, and in spite of the specification differences, it appears that the two PSUs use the exact same PCBs, just fitted with different capacitors/resistors/etc. In particular, http://forums.nekochan.net/viewtopic.php?f=3&t=16731963&p=7401329&hilit=Indigo+PSU#p7401329 shows what appears to be an identical fault to my 4044A, but on a 4044B, together with a mention that yet another person also found the same problem with CR111.
CR111 is famous!
OK, so three people out of several thousand isn’t what you would reasonably call compelling statistical evidence, but in 2017, its’ probably the best that can be achieved.
I’m guessing that CR111 in my PSU is also a 1N5352 15V zener diode, but before I dash off to digikey.co.uk, I will need to extract it from the PSU, to make sure.