Olivetti PCS86 won't start - PSU?

Discussion about old PC hardware.

Olivetti PCS86 won't start - PSU?

Postby mjnman » 2019-3-05 @ 08:24

Some days ago when I powered on the Olivetti PCS86 didn't work with strange screen below:

Image

some days before worked!!!
I tried to open the old computer but I didn't see any strange things.
After several power on broke the fuse on power supply.
Maybe a problem on some capacitor or component on power supply?
please please please, I would like to repair because I would like to use this old style 8086 (NEC V30) computer :(

Image

Image

Image
mjnman
Newbie
 
Posts: 29
Joined: 2017-2-07 @ 10:11

Re: Olivetti PCS86 won't start - PSU?

Postby sf78 » 2019-3-05 @ 09:49

You have two Rifa/ Kemet 0.47 Uf caps that need to be replaced ASAP! Their case will most likely crack soon and spew out oily substance that will smell like burning plastic.
sf78
Oldbie
 
Posts: 552
Joined: 2014-10-16 @ 15:05
Location: Finland

Re: Olivetti PCS86 won't start - PSU?

Postby treeman » 2019-3-05 @ 10:20

wondering what all that white stuff is, maybye some paste from the factory or maybye something less healthy
treeman
Member
 
Posts: 335
Joined: 2017-8-16 @ 11:05
Location: Australia, Melbourne

Re: Olivetti PCS86 won't start - PSU?

Postby mjnman » 2019-3-05 @ 10:29

ok thanks very much. I will try to replace the caps asap and I'll update :kiss:

P.S. I don't know what is it the white stuff
mjnman
Newbie
 
Posts: 29
Joined: 2017-2-07 @ 10:11

Re: Olivetti PCS86 won't start - PSU?

Postby Deunan » 2019-3-05 @ 12:20

That white stuff might be a side effect of the factory solder flux cleaning process, or it could be a spill from one of the electrolytic caps. One or more - sometimes an old capacitor will appear to work when powered after a long time being unused but then it will quickly fail after that.
In any case, try to remove it. Use a nylon brush and water - if it doesn't easily go away with scrubbing in water than it's flux residue and not an issue, leave it be. If if does go away, clean (and dry) the whole PCB.

Also, replace that big orange 100uF if you can. Preferably use 105C rated cap as a replacement. Inspect the rest too. Sometimes electrolytic caps fail not by venting but rather by spilling down - this usually leaves residue and corrosion around the pins. The rubber "cork" at the pin side might be visibly bulged too.

If (after cleaning and drying) you replace the fuse and it blows right away you have a secondary issue, like shorted switching transistor(s) and/or the bridge rectifier.
Deunan
Newbie
 
Posts: 86
Joined: 2018-5-29 @ 12:32

Re: Olivetti PCS86 won't start - PSU?

Postby mjnman » 2019-3-11 @ 11:26

Hi guys...I replaced the 0.47 Uf caps and big orange 100uF. Every time that poweron the computer the fuse break down :-/

Image

I don't know why...I didn't see any corrosion or strange caps
mjnman
Newbie
 
Posts: 29
Joined: 2017-2-07 @ 10:11

Re: Olivetti PCS86 won't start - PSU?

Postby Deunan » 2019-3-11 @ 11:41

Desolder the bridge rectifier and T3 transistor and check for shorts. Usually both will require replacing.
There is a small chance it's actually one of those 2 grey capacitors near the ones you've replaced, so maybe start with those. And rather than waste fuses (and risk further PCB damage) just test the resistance on input leads - anything close to single ohms is a short somewhere.
Deunan
Newbie
 
Posts: 86
Joined: 2018-5-29 @ 12:32

Re: Olivetti PCS86 won't start - PSU?

Postby mjnman » 2019-3-13 @ 12:15

Forgive my ignorance, what is the bridge rectifier? ...next days I'm going to try to replace the two grey capacitors. I tried to verify with the tester a shorts between two fuse poles but seems to be detached. I can try to measuring a current but I'm worried there are to much amps and risk further board damage.
mjnman
Newbie
 
Posts: 29
Joined: 2017-2-07 @ 10:11

Re: Olivetti PCS86 won't start - PSU?

Postby Deunan » 2019-3-13 @ 13:25

It's that black box below the red capacitor. Here's a helpful wiki on how it works: https://en.wikipedia.org/wiki/Diode_bridge
If you want to test for short before you desolder anything:

- put in a new fuse (for this any fuse will do so long it's not burned out)
- test resistance on the mains input pins

DO NOT actually connect it to the mains. And if it was recently, let it sit for 10min to discharge the main capacitor. EDIT: This test assumes there is no external switch that you've unplugged. If there is, it has to be connected (and turned on) to test.

If you find the input shorted, remove the rectifier and test again. No short now means you don't have to touch the grey capacitors and that rectifier has to be replaced. But as Ive mentioned earlier - if the bridge rectifier is faulty (shorted or open) then so is T3 transistor probably.
Deunan
Newbie
 
Posts: 86
Joined: 2018-5-29 @ 12:32

Re: Olivetti PCS86 won't start - PSU?

Postby mjnman » 2019-3-13 @ 14:29

Thank you. It's a B380C2000/1500
mjnman
Newbie
 
Posts: 29
Joined: 2017-2-07 @ 10:11

Re: Olivetti PCS86 won't start - PSU?

Postby 386_junkie » 2019-3-13 @ 15:46

Without shadow of a doubt there is a short somewhere. I'm guessing maybe at the bridge or across your triac's/transistors. Most caps fail open circuit as the dielectric dries up creating a bigger separation distance between the anode and cathode... or, the cap just spills it's guts to leave yet another gap between the anode / cathode contacts.

I'd definitely change the caps anyways since you have the thing open, though once you confirm a short... i'd be right on the bridge and switching transistor / triacs.

I hope you get this going again... I have much respect for anyone who resists impermanence with vintage retro hardware by physically repairing / refurbing hardware.
User avatar
386_junkie
Oldbie
 
Posts: 968
Joined: 2014-4-15 @ 20:02

Re: Olivetti PCS86 won't start - PSU?

Postby mjnman » 2019-3-13 @ 19:14

With the tester I found continuity between "R" input and fuse. Tomorrow I think to have more time and I'm going to remove the ridge rectifier and retry and so on with other components
mjnman
Newbie
 
Posts: 29
Joined: 2017-2-07 @ 10:11

Re: Olivetti PCS86 won't start - PSU?

Postby 386_junkie » 2019-3-13 @ 21:10

mjnman wrote:With the tester I found continuity between "R" input and fuse. Tomorrow I think to have more time and I'm going to remove the ridge rectifier and retry and so on with other components


Bridge rectifiers at first are tricky to test, but when you how it makes more sense.

You will have 4 pins; lets call them...1, 2, 3, and 4! :D

What you are looking for from a healthy rectifier is continuity one way, but then not the other way... i.e. pin 1 to 2, but not pin 2 to 1... and so on.

Testing: -

1 to 2, and 2 to 1
1 to 3, and 3 to 1
1 to 4, and 4 to 1

2 to 3, and 3 to 2
2 to 4, and 4 to 2

3 to 4, and 4 to 3

Best way I do it is make a table of all results, all in... you should normally find four directions have continuity and four at infinity (or at maybe have some resistance which all should be similar to each other)... if there is any which are odd, or have continuity in both directions i.e. 1 to 2, and 2 to 1 example only... then you will have found your short.
User avatar
386_junkie
Oldbie
 
Posts: 968
Joined: 2014-4-15 @ 20:02

Re: Olivetti PCS86 won't start - PSU?

Postby mongaccio » 2019-3-14 @ 18:54

I have on too, and i did repair it 2 years ago. I did replace the faulty ?BU508? (can't really remember well) switching transistor, and came back to life.
Later i've accidentally shorted GND with either the 5v or 12v line near the Motherboard connector while measuring voltages,and *Puff* fuse blew up.

Cause? BU508 was shorted again. Replaced fuse and said transistor,and my poor old PCS 86 came back to life ..again..

I came to the conclusion that Olivetti Pcs86 power supplies are really 'sensitive', and have no efficient short ciruit protections, excluding that fuse.

Now, regarding your problem.

In your specific case, if you can find and solve your PSU problem,(there surely is a shorted component!) switch it on without anything attached.When the PSU works again, i'll recommend to check if something on the motherboard, or isa addon cards, is shorted.
I fear that a short circuit on Mobo or eventual cards can cause cascade damage to that PSU (like it happened to me)

Here's a pic of my Pc,taken minutes ago, still working perfectly. Reading your comments, i will surely check/replace those Rifa Caps, they are encased in a particular resin that cracks with age.
pcs861.jpg
mongaccio
Newbie
 
Posts: 51
Joined: 2016-5-09 @ 21:59
Location: Italy


Return to General Old Hardware

Who is online

Users browsing this forum: Anonymous Coward, cyclone3d, gdjacobs, Google [Bot], krcroft, Speedsalat, sunaiac and 12 guests