Another Indigo2 psu died...

marmotta

Member
Feb 22, 2021
60
6
8
Hi! This days I have tried to fix my 8002 Indigo2 psu. But is really diabolic! ...at first time I have some shutdowns on load, and randomly not power on. Changed the HV caps and the psu return to power on... but with not optimal voltages (11v instead of 12v) and I decided to replace all LV caps! I replaced all caps with good quality nichicon capacitors and now the psu does not turn on anymore! Why? The standby voltage is ok (5,1v) when I push the power button (or bridge the 5v to power on pin) it tries to start for one second and then off... it gain two or three volts on rail and return to standby 0,7v. What I can see for find the issue? I need to restore the original (leaked) caps?
 

Elf

Storybook
Feb 4, 2019
469
118
43
It's very hard to say why without interactively troubleshooting it on a bench, but perhaps one or more of the capacitors went in backwards? Or some solder joints or traces cracked during the process, something could have gotten too hot, etc. Or it could just be that the lower ESR of the new capacitors drew more current at start and triggered overcurrent protection?

Unfortunately I don't think it's possible to be conclusive about these things without either a lot of information or having it in front of you with a lot of tools.
 

weblacky

Member
Jan 13, 2020
91
23
8
Seattle, WA
What Elf what hinting at is more important than you may realize, while I've yet to get to the Indigo PSU's myself. I can say that an important, unwritten, rule when dealing with capacitors in a design and what they might have been used for (filtering vs oscillation). Installing "better quality" caps can often be bad in the wrong places. Tougher filter caps (ripple tolerance), yes, better caps everywhere....no. The caps that were chosen where chosen based on data sheets. To do the design justice, you need to take a look at the caps you removed (and their original locations). You need to try your best to decode the Manufacturer, and series (family) the caps came from. Then research the manufacturer's charts and looks for the series upgrades (you may need several generations of charts...on the Indy I'm doing...I've needed TWO generations of charts to track the lineage upgrade recommendations from then to present-day.

Your jobs is to MATCH the original cap specs...not exceed them. Remember this, you're not improving the PSU, you're repairing it. Use new caps, but use caps that are similar in spec to the originals (no matter how much you may feel otherwise).

More than likely it could be something else, but for the smaller caps you found just around...it's likely to do with what you chose to replace it. Find each cap's original series data sheets (or family at least)...then go from there.

Also, just a gut reaction, lower voltage on the output side is normally a symptom of either a resistor value on your feedback circuit drifting (especially when it's literally a 1v difference in your case, like the feedback was working, but offset). In the later case of the LV side, you likely used caps that were TOO low in ESR and may have triggered a protection mechanism due to excessively out of tolerance voltage (as hinted by Elf).
 
  • Like
Reactions: Elf

marmotta

Member
Feb 22, 2021
60
6
8
Ok! Thanks for yours suggestions, I can try to slowly restore old caps, because I no other chance... I’am out of experiments :)

The idea of caps specs is probably correct, in the past I have the same issue with LH and another brand (and spec) of capacitors. But I didn't think he was so picky :)
Suggest to start with small (47uf) caps or the big (6800) caps?

This is the patient ;-)
 

Attachments

weblacky

Member
Jan 13, 2020
91
23
8
Seattle, WA
You had low voltage but working before your LV side caps where changed. Suggest that. Then once it works again, research and carefully re-re-replace LV caps, then research slight low voltage symptoms if still present.
 

ghost180sx

Member
Dec 13, 2019
90
39
18
The Great White North
Don't forget that repair of any power supply takes a fair amount of knowledge, persistence and hard work! Don't give up. If you need help, just post more details of exactly what you did. There are a lot of extremely skilled people on this forum who have a lot of practice repairing and fixing all kinds of things, including power supplies!

Pics pics and more detail please :)
 
  • Like
Reactions: Elf

marmotta

Member
Feb 22, 2021
60
6
8
I cannot restore all old capacitors some are damaged and some are leaked...

I restored the two 470uf and changed the two 3300uf and one 2200uf with another models. No way, ok standby but when I powerup the fan try to turn and voltages try to up (all voltages) and on one second go all to zero. Same problem... :-(

How I can test if the problem is on LH or LV? From LH I have only 18,5v from the small connector, from bigger square connector I not have a voltage... I think the small connector is alimented from the small transformer and the other from the bigger, is LV which gives consent at the bigger to start? How? Can I force it?

Some pics
 

Attachments

Last edited:

marmotta

Member
Feb 22, 2021
60
6
8
Oh my god..... :-O

I have take another psu (8001 surely working), connected to my test motherboard (used for testing the 8002) and not work!!! The problem is on the Indigo2 motherboard... Is strange, I need to investigate more ;-)
 
  • Sad
Reactions: Elf

marmotta

Member
Feb 22, 2021
60
6
8
Sorry to hear that! It's worth noting that you can test the supplies independent of the motherboard. The information here should let you do so: https://forums.sgi.sh/index.php?threads/indigo-2-power-supply-basics.111/
Without motherboard is the best way, but I’m not sure I understand correctly (I not have a very good English). I need to terminate the backplane wires, bridge to standby and power on, bridge to standby and power good? And other sense?

The motherboard is a spare board, the rails are not in short... I would like to know what happened
 

Elf

Storybook
Feb 4, 2019
469
118
43
You would want to:
  • Put a reasonable load on at least 3.3, 5, and 12V rails, something that would draw a few amps
  • Terminate the graphics power connector (if it is an Indigo 2 Impact supply)
  • Connect the Run line to the +5V Standby power (if Indigo 2 Impact)
An Indigo 2 Impact power supply should come with a suitable terminator for the graphics power connector; it comes attached to the side of the power supply.
 

marmotta

Member
Feb 22, 2021
60
6
8
You would want to:
  • Put a reasonable load on at least 3.3, 5, and 12V rails, something that would draw a few amps
  • Terminate the graphics power connector (if it is an Indigo 2 Impact supply)
  • Connect the Run line to the +5V Standby power (if Indigo 2 Impact)
An Indigo 2 Impact power supply should come with a suitable terminator for the graphics power connector; it comes attached to the side of the power supply.
The power good it is not needed?

Edit: wrong question, the power good is needed by the motherboard, not the psu :)
 
Last edited:

marmotta

Member
Feb 22, 2021
60
6
8
I have connected the terminator, two resistor of 20ohm on 3,5 and 5v, connected a hdd on molex, bridged together 5v standby and power-on.... no sign of life :-( ...connected to motherboard tries to start, without motherboard not respond to power-on, what’s wrong?

For the motherboard: I have two identical ip22, all pin of two connector give me the same impedance, except the -12v (1200ohm on good motherboard, open circuit on not working motherboard). What is the -12v for?
 

weblacky

Member
Jan 13, 2020
91
23
8
Seattle, WA
I could be wrong, but I was recently told that negative voltages are often used for audio/speaker driving, also I noted that normally the negative voltage amperage rating on the PSUs are pretty small.

I think negative voltage is often used to drive the speaker elements for the sound output.
 

marmotta

Member
Feb 22, 2021
60
6
8
I could be wrong, but I was recently told that negative voltages are often used for audio/speaker driving, also I noted that normally the negative voltage amperage rating on the PSUs are pretty small.

I think negative voltage is often used to drive the speaker elements for the sound output.
The second I2 motherboard not have the audio board, can be this ;-)

But it does not explain why it does not start
 

marmotta

Member
Feb 22, 2021
60
6
8
My story continues... and I slowly going crazy!

The motherboard is ok! I have done some tests, both motherboards only work with a graphic board inserted on one slot! Why not start without graphic board??? This is very strange... for the test I have used a surely working 8001 psu, the not working 8002 psu is on the bench, and I can’t start it... with motherboard connected try to start, without motherboard don’t give signs of life.

I need a shaman :-D
 

marmotta

Member
Feb 22, 2021
60
6
8
Not exist a trick to determine if the problem is on LV or HV? The two (four) big hard cables starting from main transformer... what are they for? Main power supply for LV, or start switch?
 

weblacky

Member
Jan 13, 2020
91
23
8
Seattle, WA
No one has done that analysis yet, but I assumed the cables are extensions of the transformer windings themselves and connect the primary and secondary PSU sides to different boards (LV to HV PCB boards). I'd assume they are for the primary windings due to how thick they are. They also could be part of the feedback circuit but then they needn't be so thick. I think the two boards provide air gap isolation between the LV and HV functions and the thick lines are for the transformer bridging that board gap as the main chopper. But that's my theory, no proof of course.
 

Elf

Storybook
Feb 4, 2019
469
118
43
Indeed, the negative voltages are usually for audio purposes or similar things where an op-amp needs to drive things to both sides of 0V. I don't think a failure of the negative rail should affect anything significant about the system, but of course I have never tried it.

Just to confirm, the power supply does not start with the resistors, but does start with a motherboard with a graphics card connected? Sort of odd...
 

marmotta

Member
Feb 22, 2021
60
6
8
Indeed, the negative voltages are usually for audio purposes or similar things where an op-amp needs to drive things to both sides of 0V. I don't think a failure of the negative rail should affect anything significant about the system, but of course I have never tried it.

Just to confirm, the power supply does not start with the resistors, but does start with a motherboard with a graphics card connected? Sort of odd...
No, the good psu (8001) with any motherboard (at the end all motherboard are ok) work only with the graphic board on slot...

The psu I want to repair (8002) not work in any case... but, connected to the motherboard it try to start (raising of voltages then stop), on bench with resistor it not give any sign of life when I put the 5v on power-on.
 
Last edited:

About us

  • Silicon Graphics User Group (SGUG) is a community for users, developers, and admirers of Silicon Graphics (SGI) products. We aim to be a friendly hobbyist community for discussing all aspects of SGIs, including use, software development, the IRIX Operating System, and troubleshooting, as well as facilitating hardware exchange.

User Menu