SGI: Hardware

Hi, I am new here and glad seeing a lot of information for sgi.

I brought an indigo 4000 which I saw 25 years ago and had never thought I could own one at that time.

For the last a few days. It did work till login screen after repairing the tod problem.

But suddenly, while from the login screen, it went dead. Every time fliping the power switch, just heard a bad chirp. the fan run but stoped in about 3 seconds. The led on the CPU board was green for a split of second.

Tried everything but just no luck until found a ceramic capacitor on the graphic card is cracked. May be not the reason but took it out. Measured the resistance between remaining pad is about 8 ohm.

Keeping trying till now. It seems improving itself by removing both hdds from the bay as the led now stay longer. It was green and then yellow. And most importantly, there is a usual chime.

However, the power shut off just after the chime. During this time, the 5 and 12 volt from 4 pins of molex connector on the top unused sled was valid and stable.

I am guessing the post detected something and decided shut down the power supply. Or it is indeed the powe supply was over heating and shutdown by itself?

Thanks for your time.

You can continue troubleshooting by removing the graphic card and see if it stays powered on for a longer period.

But the most likely scenario is that the power supply needs an overhaul. We just had a thread with tips on how to recap a R4000 Power Supply: viewtopic.php?f=3&t=16731963

Try to read through it and check f.i. if the zener diode C111 needs repair. Better still, get someone to recap that PSU.

Can you make a picture of the damaged cap on the graphic board?

Thanks.

No, the duration will be shorter and no chime without presence of graphic card.

The capacitor is c660.

Today's trial reveals that the power supply is okay.

The m/c now is complaining the SCSI has or cable error.

One thing from this incident that the power supply can work stand alone without pluging into the m/c as long as there is a small load on the 5v rail.

All voltage of 5 , 12 and -12 are correct and fan will run.

I have determined 22 over 24 pins function but 2 still unknown to me, which I believe is something like power good and power on.

It seems by default the power on is true, which might refer this function as power off from m/c.

If I understand properly the PSU is shutting down, correct? If so then that means that something is either going wrong in the PSU (voltages off), there's something drawing too much power in the computer and tripping the protect circuit, or the PSU can't put out the needed power. What exactly was "todays trial?" Yes, SMPSUs need a load on the main rail, but if the PSU is failing you might as well fix it now to support the load you need rather than trying to halfway hack something that kind of works. Try pulling all boards but the backplane and seeing how it runs with several disk drives for load. Indigo does not have soft power, so that won't be an issue.

The psu and machine is working now. I had now found anything wrong or changed anything.

The only possible reason is the harder that push the power cord the more dislodge of psu from the machine's receptacle. Once push the psu from the front side. Everything seems fine so far.

Dalplex wrote: Tried everything but just no luck until found a ceramic capacitor on the graphic card is cracked. May be not the reason but took it out.

[image was posted lower down]

No. There is a + mark on the silkscreen, and ceramic capacitors are never polarized. That was a tantalum capacitor that did auto da fé. It should be cleaned because the soot in the area can short out the power rails, which may be causing your problem.

Well. There is a r3000 board on sale right now on Xbay.

Although it has different destination but my understanding the capacitor is ceramic.

You do get surface-mount Tantalum capacitors and they are bi-polar, so they do tend to blow if they placed with the incorrect polarity across them!

Surface-mount Tantalum caps look very similar to the ceramic ones, but their cases are usually made of plastic.

The DEC AlphaStation 255 has a common fault, in that there is a Tantalum capacitor in the circuitry for the PS2 mouse port that tends to burn up, just like the one you've pictured. On later motherboards for the 255, the cap was placed the opposite way around, therefore it appears that the original silkscreen on the motherboard was incorrect, leading to the polarity across these caps being reversed and therefore causing them to blow.

To fix my AlphaStation, I simply placed another tantalum cap of the same value in that position, with the correct orientation. (opposite to the silkscreen on the motherboard)

I am not saying that the cap in question is placed incorrectly on the board that you have photographed, but these can be replaced rather easily.
Its easier to repair SMT technology than you think. If you have the right tools at your disposal. (hot air pencil)

My did my first SMT repair on the R12K 400Mhz CPU module for my O2.

To my horror, some of the ceramic caps on the module were cracked when I received it. The seller was dishonest and had removed the heatsink from the chip, probably to take a look at it and had replaced the securing bracket the wrong way around, when he re-assembled it! The securing bracket placed stress on a few large caps at the back of the CPU module and cracked them as a result!

I took a chance and used some of the ceramic caps off a spare R10K O2 module that I had lying around and I managed to repair the module in this way.

Now it works perfectly!

It is good to know this. may be my old experience was not updated as I always thought they are coming with either yellow or black colour.