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enon97
May 22nd, 2014, 11:44 AM
Hi all.

I have an old Olivetti PCS 286 and when I plug it, then I turn it on and then, the fuse "explodes".

How can I solve the problem?

(You have a lot of pictures here in my Dropbox: https://www.dropbox.com/sh/j5dmnoryhtcbw5o/RpdKVgxzRd)

Thank you and bye.

Stone
May 22nd, 2014, 12:29 PM
Find the short and fix it.

Simone2013
May 23rd, 2014, 08:01 AM
Wonderful machine! I had two of them with CMOS battery gone...
I suggest you (as i was thinking to do it myself) to replace the PSU with another that will fit in it, checking the voltages & ampere... the original PSU is very noisy...

Chuck(G)
May 23rd, 2014, 08:59 AM
I have a hunch, looking at those photos. Test the RIFA 0.47 uF capacitors near the fuse (those square plastic things). They usually explode when they go bad, but not always--they can sometimes blow the line fuse instead.

enon97
May 23rd, 2014, 09:34 AM
Find the short and fix it.

That's exactly the problem. I can't find the short because I don't have the scheme of the power supply, so I can't reapir it for myselft.

enon97
May 23rd, 2014, 09:36 AM
Wonderful machine! I had two of them with CMOS battery gone...
I suggest you (as i was thinking to do it myself) to replace the PSU with another that will fit in it, checking the voltages & ampere... the original PSU is very noisy...

Nah, I don't wanna modify this machine, all original. (If a fuse is gone, obiusly I am not going to repair it ;) ) I think the power supply isn't standard.

enon97
May 23rd, 2014, 09:37 AM
I have a hunch, looking at those photos. Test the RIFA 0.47 uF capacitors near the fuse (those square plastic things). They usually explode when they go bad, but not always--they can sometimes blow the line fuse instead.

I'll test it on weekend, so in Monday I'll answer you.

enon97
May 23rd, 2014, 10:26 AM
I have a hunch, looking at those photos. Test the RIFA 0.47 uF capacitors near the fuse (those square plastic things). They usually explode when they go bad, but not always--they can sometimes blow the line fuse instead.

Aparently, these RIFA 0.47 uF capacitors work well both. I don't have the exact item for test them, but I have a polymer, apparently, these capacitors chargue and unchargue well but I can't give you exact values.

Thanks.

pstmg
May 25th, 2014, 12:44 PM
Hello everyone

i have the same problem with the psu. What could it be the problem ?? Capacitors??

Another question is: where can i locate the cmos batery?? as I remember when it was working, the initial machine diagnostics used to halt on that item....


Thank you
Paulo

enon97
May 26th, 2014, 09:23 AM
So?

Any ideas?

Chuck(G)
May 26th, 2014, 09:57 AM
That blue thing in your photos is an MOV - metal-oxide varistor. Its role in life is to absorb short-term surges in line voltage. The PSU will run without it.

The trick is to localize the problem. Instead of blowing fuses and depleting your pocketbook, try substituting a large (say 100 W) incandescent lamp temporarily for the fuse. Use appropriate care to avoid shocking yourself.

Turn the system on--if the lamp glows at nearly full brightness, the problem is probably on the line side of the PSU and not on the load side. To verify, unplug the PSU from the mainboard. If the short remains, the fault is definitely in the PSU.

So what can go wrong in a SMPSU? The primary side usually has a bridge rectifier to convert AC to DC--a shorted diode there can cause problems. There's also a higher-voltage electrolytic capacitor to provide filtering--a short there can create problems. There's a power transistor (sometimes two) that drives the transformer--if it shorts, you have problems.

enon97
May 26th, 2014, 10:08 AM
What? What blue thing? The thing that says "NTC 33" is an NTC Thermistor.

I don't know what thing you mean...

I already connected the PSU without the motherborad, I know the short is on the PSU.

SMPSU?

I'll try to translate that "The primary side usually has a bridge rectifier to convert AC to DC--a shorted diode there can cause problems. There's also a higher-voltage electrolytic capacitor to provide filtering--a short there can create problems. There's a power transistor (sometimes two) that drives the transformer--if it shorts, you have problems." to Spanish, but it seems difficult. If you could say that, in an easier way maybe?

Thanks and Bye.