I recently had a similar "problem" with a Schneider 386SX PC and its power supply. It did have a few damaged components, but after replacing them I was also seeing wild variations even with a dummy resistor and a hard disk drive attached to provide some load.

Eventually I connected the PSU to the board and the PC just worked. I was overthinking it. Doesn't necessarily mean that's the case here, but you can read all about it here and decide for yourself.

devius wrote on 2020-06-09, 16:42:

I recently had a similar "problem" with a Schneider 386SX PC and its power supply. It did have a few damaged components, but after replacing them I was also seeing wild variations even with a dummy resistor and a hard disk drive attached to provide some load.

Eventually I connected the PSU to the board and the PC just worked. I was overthinking it. Doesn't necessarily mean that's the case here, but you can read all about it here and decide for yourself.

First of all - WHAT A BEAUTY OF A SYSTEM.. for two times i had the chance to buy a schneider and it sleap though my fingers...thats why i bought this olivetti.. for revenge..

i had tough in just conect the board and press the power buttom, but i was afraid of burning the thing out.

let's see if someone gives me the pinout

Hi,

you should be able to find out the pinout by yourself. PCs of this era usually need +5V, +12V, -5V and -12V. All these voltages are found on the ISA-bus (pinout). To find out the pinout do a simple continuity check between power-supply connector and the power pins on ISA-bus.

With best regards,

Alex

That website is almost unreachable. I have grabbed an archived copy and uploaded it.
https://imgur.com/gallery/Ah8wnL5

..aaaand I got a description:

for Olivetti PCS 286
Grabbed this rusty computer from an office basement, proprietary-shape-and-connectors original power supply hopelessly shorted, luckily the only AT one I had fits quite nicely in its place (minus power switch, which I left out - oh, and if anyone ever has to do that, the absolutely misleading wire colors are: brown +5, black 0, missing pin -12, red +12, blue -5, white PG)

https://www.reddit.com/r/vintagecomputing/com … ivetti_pcs_286/

POWER SUPPLY PROBLEM SOLVED..

I've adapted another AT power supply. Take the cables i dont need out...easy.
Thanks for the TIP of using the ISA connector for solving the custom power supply connector.. Turns out is basiclly an P8 AT connector... (o, +5, +12, -12, -5 (this one absent)).

also take the time to modd the RTC chip

works great now... It posted fine... went to bios... changed the setup...

but... the computer bios options are few.. just the very, i mean, very basic. DATE, TIME, FDD capacity, RAM TEST SPEED, and the HDD option.. 20MB or 40MB.

Now. i have the conner CP0344- 40MB) but it doesnt get recognized... tried diferent cables, positions.. nothing... maybe the disk is faulty.

So what are my options now ?

the disk is IDE (almost certain)... not interely.
Any way of installing another IDE disk ? have two 270MB spares... ontrack disk manager ?, some bios modd ?

or the only way is XTIDE ?? (more expensive)..

It's such a really nice compact computer...

Hello all

I have one Olivetti PCS 286 that needed service. The problem was in the PSU and also in the mainboard.

Regarding the PSU, I've replaced the capacitors, the main transistor (PWM), some diodes and also the NTC. And after all I got in running again.

The problem in the mainboard was concearned with a faulty CMOS battery. I had to remove that one, and place a new one connected to an external battery (CR2032) so it can maintain the BIOS information after shutdown.

Last week I connected it and had some smoke inside. No more Olivetti 🙁 🙁

After some minor inspection I found an open fuse. It's now running again but it has another problem at BOOT: it says 1742 hard disk controller failed. I listen to a strange noise comming out from the HDD when PC tries to boot.

I might consider buy a new HDD or it's something in the mainboard ??

Cheers
Paul

Hello..

Yes.. is the error i'm getting out of my HDD..

Have you enter extended setup and specify the hdd40mb ? you have just two choices.

Don't discount the possibility that maybe you still have PSU problems... reason I say this is because I have a system I powered with a weak PSU and the HDD wasn't recognised, I was playing with it with a floppy, being an XT class, so it has plenty of things to run that fit on a floppy. Then finally I came across a PSU with adequate power and plugged it in and the HDD came to life. However if you are sure that new PSU provides greater than required power, then put it to the back of your mind for now.

Strange noises from HDD is never a good sign of it's health. Chances are some power driver that drives the HDD spindle or head position had internal short and that was the smoking part. These early PSUs don't take shorts well, can easily blow a fuse or even damage themselves.
Connect the HDD to a known good PSU (just the power), see if it spins up properly and if there is any weird noise. If there is, HDD is most likely toast. Since the mobo boots I would assume it survived just fine, mostly it uses 5V and the early HDD motors and coils usually run on 12V, so that would be the line that shorted.

The original Conner 40MB HDD is old... changes are it's toasted ... I've replaced the original power supply with a a new (still old) one, but the measurements here good.

The big problem is that the BIOS is locked to this specific brand and model... 40MB or 20MB.. you can't change anything... just the size... I´ve tried Ontrack overlay, and although the program setups the new HDD just fine, when rebooting, the overlay can't overlap itself over the BIOS... strange...

Usually we see a blue message from Ontrack in the beginning, but not with this PC and with this BIOS...

I don't have an XT-IDE board so, I have the PC running, but never past the initial setup. ... 🤣

I'd say an ST-351AX would probably work, it copes with the classic "Type 17" and several other non-native 40MB translations... trouble is, nobody got the memo about keeping this an insider secret and even though there should be a relative "lot" around, the prices getting asked for them are stupid.

Actually, I do have a Seagate 40MB, AT compatible drive, and I did try to boot from it...
but with no success.

You'd have to configure and format it on the system most likely, wouldn't boot if formatted under a different translation.