Rolling wrote on 2023-04-07, 09:04:

Hi guys, […]
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Hi guys,

sorry for digging up the old thread, but i guess my problem is quite similar...

I'm trying to resurrect an Olivetti PCS 286 machine at the moment and the power supply stands in my way. The fuse was blown, i already changed the two Rifa/ Kemet 0.47 Uf caps and put in a new fuse. At least there's no explosion anymore. When turning on, i hear a click (but no fan) and can measure the following voltages (while connected to mobo with hdd) .

1° BROWN: +5.06V
2° BROWN: +5.06V
1° BLACK: GND
2° BLACK: GND
RED: -0.19V (shoud be +12V)
BLUE: -12.10V
WHITE: +5.06V (shoud be -5V)

RED and WHITE seem to be wrong, but i don't know if that's a problem created by capacitors or any other component. I just measured the bridge rectifier, which seems to be ok.

Maybe anyone has a hunch?

Your problem should be in the selected part of the psu pcb. You can post some pictures with yours and the selected area, front and rear, maybe i can assist you further.

Hi bogdan,

that's interesting! I always assumed there's an error in the input section of the psu, but i guess you're right - a problem in the output section makes more sense!

Here are some pictures of my psu:

Can you post a better picture of that area/check the solder joints ?

You're right! Those joints look definitely broken! Unbelievable... I checked the whole psu, but somehow never noticed the broken joints... 😒

I'll fix them and post an update tomorrow, wife ist calling ^^

I fixed the broken joints on the transistor and now i get a clean 12v signal on the red lane - very nice!

I'm still getting +5V on the white lane, but i assume that's ok as mentioned Re: Olivetti PCS86 won't start - PSU?. Curiously i'm getting -5V on the pin, which has no line connected:

I guess it's time to connect some peripheral devices to it and see if it boots up...

Glad to hear. The withe line should be power good signal, as stated. -5v is probably done by a regulator somewhere on the board, from the -12v line, so don't try to feed it externally.

Probably a bit off topic, but at the moment i only have this monochrome brother ct-1050 monitor, which i'ld like to use, to test the pcs 286.

As mentioned here https://archive.org/details/Olivetti-PCS-286-Headland, the olivetti pc shoud support monochrome monitors but sadly mine doesn't have a D-Sub 15 conncector, but a D-Sub 9 MDA connector. Is there any way to make an adapter for this?

Better solution would probably be to just get a display with vga output... ^^

Rolling wrote on 2023-04-08, 13:33:

D-Sub 15 conncector, but a D-Sub 9 MDA connector. Is there any way to make an adapter for this?

Better solution would probably be to just get a display with vga output... ^^

Yep, nailed it - there are some such adapters but they are for early multimode VGA monitors, not for making a VGA card run in MDA/Hercules mode, but if you have the correct card you can use it if you set the bios to "mono ext" I think!

Sounds interesting, maybe i'll have a look at this in the future.

Yesterday i found an older vga flatscreen monitor to test the pc. Can't really tell you how happy i am to see the little olivetti back in business! 😉

Now i'm waiting for an XTIDE-ROM to try to get a slightly bigger hard drive to work with the old italian! 😀

Thanks for your awesome help!!!