Welcome to the forum!😃
I'd be very surprised if anybody had the schematic to the PSU.
Looking at the picture quickly I find eight aluminium electrolytics and three line filter caps that you could preventively swap for new parts.
That's not too bad. Just unsolder them one by one (after safely making sure there's no charge left in them!), write down their location, check their values and order replacements.

Good luck!👍

Bro I just took mine apart two days ago you're in luck. My findings were that only the Nippon Chemicon SXF series caps were leaking.

C12, C61, C41 470uf 25V (Your particular PSU seems to omit C61)
https://www.digikey.com/en/products/detail/ni … 1MPD1TD/4320914

C36, C37 4700uf 6.3V
https://www.digikey.com/en/products/detail/ni … J472MHD6/589458

Additionally, I chose to replace C29 (1000uf 25V) even though it was a Panasonic and still tested good.
https://www.digikey.com/en/products/detail/ni … 1E102MHD/589572

This thread may also come in handy for you, mainly for the reference images
https://forum.vcfed.org/index.php?threads/com … r-supply.44511/

I annotated your original image. The green checks are the caps I decided to leave alone. Red X is replace.

This is called deskpro/M series. PSU board is a service item and is a rare part now even there is lots of computers, and have not seen used or broken one on market for long time and I have documented the pin out for the motherboard, and yes you can use 20 pin ATX plug rewired without power on and 3.3V wires! Either use ATX or standard baby AT PSU rewired into ATX connector previously described.

There's no choice but repair and maintain remaining PSU board.

The stunky capacitors is described as rotten fish smell.

Cheers,

Thanks for the info 🙂

I dug into it today and taken all the caps out. Most of them I have in my capacitor stash, the 4700uF 6v3 I don't have in the tall thin type. They've definitely been leaking 😬 one of the caps left its entire leg behind during desoldering, so that's definitely dead 😝 I'll have to wait for Mouser to ship the missing caps to get back to 386'ing 🙂

How many capacitors to replace and do you have cheat sheet of capacitors?

Cheers,

pentiumspeed wrote on 2023-04-02, 00:21:

How many capacitors to replace and do you have cheat sheet of capacitors?

Cheers,

I removed 10 electrolytic caps and will replace 8. I've put a list of caps I removed and tested in my post. I put the main high voltage caps back in as they aren't leaking and are more or less spot on for ESR. Annoyingly, the reservoir caps on the +5V rail are strange thin types and the closest I've found are Panasonic FR0J472B. This PSU is so easy to work on that I don't mind leaving caps in that are 30+ years old, I know what to target if the supply starts to die 😝

C12, C29, C36, C37, C41 all must be replaced with low impedance caps, not general purpose

You did that ya?

maxtherabbit wrote on 2023-04-02, 14:02:

C12, C29, C36, C37, C41 all must be replaced with low impedance caps, not general purpose

You did that ya?

Yeah, all the capacitors I used have no more than 0.1R ESR as I primarily repair SMPS. I only use high quality brand name 10k hr+ 105C/135C (Nichicon, Panasonic) they cost $$$ but they last and my time isn't free.

I do realise a higher ESR will mean higher temperatures in the capacitors concerned and more power, more often, is needed to be sent across from the HV to LV side of the supply, that also increases heating, although it will still function perfectly well. "Recapping" an old SMPS with new caps will very often reduce the running temperature of the power supply and the computer by a few degrees Celsius. It will also improve the longevity of the components in the supply and the rest of the computer if the PSU shares the same air as the logic PCBs.

maniacminer wrote on 2023-04-01, 22:42:

Thanks for the info 🙂

I dug into it today and taken all the caps out. Most of them I have in my capacitor stash, the 4700uF 6v3 I don't have in the tall thin type. They've definitely been leaking 😬 one of the caps left its entire leg behind during desoldering, so that's definitely dead 😝 I'll have to wait for Mouser to ship the missing caps to get back to 386'ing 🙂

Your findings inspired me to go back and revisit mine. Sure enough both of the little 68uf nichicons were leaking. Pulled em out. Figures they'd be the PL series, those always leak

I'm glad I did not power up mine, till it gets recapped.

Cheers,

I did wonder why the fan in the PSU was running fast and noisy? The fan is a Nidec TA350DC model M33503-68 made in Japan. Looking around various data sheets, I get the impression that the fan is supposed to be temperature controlled and there is feedback to the PSU and the fan isn't just connected to the 12V rail like PCs of old. It'd be interesting to understand how this part of the circuit works. Looking into it a bit more, I see a 67F075 sat on a heatsink, I think this is the emergency override to make the fan go to full speed if the fan control circuitry fails?

Final caps arrived today and now I've put them in and reassembled the PSU. Now to ponder the choice of OS 🫣

Keep in mind for your OS choice that these machines are quite fast for what they are and punch above their weight, especially if you have the original QVision EISA VGA.

You can down volt the fan to 5V and see. Nearly all 12V fans will work at that voltage. If you find this too slow, would need a regulator to get 6V from 12V rail.

Cheers,

pentiumspeed wrote on 2023-04-07, 00:49:

You can down volt the fan to 5V and see. Nearly all 12V fans will work at that voltage. If you find this too slow, would need a regulator to get 6V from 12V rail.

Cheers,

Yeah the speed control has come back to life after the recap and now it runs much quieter. It is cooling the entire machine and nothing has a heat sink, so without airflow, the ICs get super hot 🥵

maxtherabbit wrote on 2023-04-06, 13:47:

Keep in mind for your OS choice that these machines are quite fast for what they are and punch above their weight, especially if you have the original QVision EISA VGA.

I've got 64MB RAM, a Cyrix FasMath and a CF SSD - it certainly moves along very sweetly for a 386. I'm thinking Windows NT 3.51 or Windows 95? It takes over a minute to count the RAM on boot 😝