Compaq Proliant 1500 PSU - unknown pins? \ VOGONS

Compaq Proliant 1500 PSU - unknown pins?

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First post, by scruit

Posted on 2022-04-09, 14:25

scruit Offline

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Compaq Proliant 1500 from the mid 90's. The PSU fires up and a green light appears on the backplane, but no POST / no video / nothing on POST card.

The first thing I did was test the pins from the PSU and I see most pins are labelled quite clearly and I have verified all those voltages.

There are 4 pins on the PSU that I don't recognize from their silkscreen labels. I was hoping someone here would know?

Pin labels that I know and check out ok:
"5" = 5.1v
"N5" = -5.0v
"12" = 12.0v
"N12" = -12.0v
"3" = 3.4v
"G" = Ground

Pin labels that I don't recognize:
"3RS" / Pink wire. Reads as 3.8v while PSU is powered but not connected to backplane, and 3.4v when connected.
"5RS" / Red wire. Reads as 5.2v when not connected, 5.1v when connected.
"PG" / White wire. Reads as 5.2v when not connected, 4.8v when connected.
"SD" / Purple wire. Reads as 0v either way.

Other info:
- The server has an actual power switch on the front, not a momentary. I thought one of these might be a standby/soft power but there's no buttons on the case for that.
- The intrusion protection is bypassed (microswitch that interrupts the power at the power switch if the case is open)
- It worked when I stored it

Reply 1 of 6, by Horun

Posted on 2022-04-09, 14:32

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3RS in Pink is most likely +3V AUX, PG is Power Good, 5RS is most likely +5V AUX, SD could be Standby/ON.
How many total pins in the PSU connector or is it two PSU connectors ?

Hate posting a reply and then have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. Stuff: https://archive.org/details/@horun

Reply 2 of 6, by OSkar000

Posted on 2022-04-09, 14:33

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My guess is that RS is "remote sense" and PG is "power good".

I dont have any good idea what SD stands for.

Have you tried removing all cards except for the cpu board?

Reply 3 of 6, by scruit

Posted on 2022-04-09, 15:18

scruit Offline

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Horun wrote on 2022-04-09, 14:32:

3RS in Pink is most likely +3V AUX, PG is Power Good, 5RS is most likely +5V AUX, SD could be Standby/ON.
How many total pins in the PSU connector or is it two PSU connectors ?

Thank you for your response.

I've been looking through other psu schematics and I believe you may be correct on PG and xRS. I woudl therefore expect the healthy behavior to be that 3rs and 5rs match the 3 and 5 rails while powered on and PG goes high shortly after the PSU powers on. I'll check for that.

For SD, this PC doesn't have a soft power switch or similar. All the rails are powered all the time when the big clunky power switch on the front is turned on. So that remains a mystery.

Reply 4 of 6, by scruit

Posted on 2022-04-09, 15:23

scruit Offline

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OSkar000 wrote on 2022-04-09, 14:33:

My guess is that RS is "remote sense" and PG is "power good".

I dont have any good idea what SD stands for.

Have you tried removing all cards except for the cpu board?

Thank you for your response.

I have just the backplane, psu and cpu daughterboard connected. Oscilloscope readings show weird stuff... Like the ISA slot address lines go from an 82374 EISA controller, through a F543 Octal Bus Transceiver. On the input from (from the eisa controller) the lines look good (square signal 0v-5v) but the outputs to the ISA slots are held high. Either something is pulling those lines high or the latch enable signal is not being interpreted correctly.

Also, I don't get a clock signal at the bios rom or video gpu, but I DO at the the PCI and ISA slots.

Reply 5 of 6, by scruit

Posted on 2022-04-12, 11:16

scruit Offline

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Follow-up.:

I gave the PSU a once-over internally, checking for leaking capacitors etc. Didn't expect a problem given the rails appear to be good.

I noted that powering the PSU back on afterwards, not plugged in to the backplane, it started up then shut off after a second. Rechecked connections, same thing. I suspect the 5RS and 3RS are giving it feedback that all it good, and that it shut down when it didn't see any juice on the those Remote Sense wires.

Reply 6 of 6, by pentiumspeed

Posted on 2022-04-12, 17:59

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PSU needs some load.

Cheers,

Great Northern aka Canada.

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