Component identification

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weirdah

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Hi all,

I want to identify this component. This one came in a Olivetti 290SP PC (same as PC PRO 290SP) PSU.

It had several blown up components but I'm unable to identify this component in order to replace it.

It came in the holes marked as PTC1 as you can see in the last image.

Could you help me?


Thanks.
 

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Can you remove it from the lug terminal and see if there are any numbers/letters on it?
 
It's clearly marked as a positive temperature coefficient thermistor (PTC), obviously monitoring the temperature on the heat sink.

Why are you wanting to replace it?.
 
It was surrounded by oxidation and my guess was that this component was damaged, any chance to test it with a multimeter?

It has no letters or numbers on it.

I replaced some 1000uf 16v capacitors that were soaking with newer ones, but voltage is oscillating constantly and it is lower than expected.

Replacing this PSU with a newer one can be a pain in the ass because it has its own motherboard connector and tension distribution as well as I think they are diferent voltage distributions for disks connectors, so I would need to rewire a newer psu in order to use it.
 
It looks like the leads have corroded at the PCB level due to liquid contamination from something.

The thermistor itself is probably OK if you clean the leads up and solder a couple of bits of thin flexible wire to them. Bolt it back sideways so the rigid leads are clear of everything and use the flexible "tails" to re-make the original connections.

I'd check the leads on the other components on the heatsink plate and near to it - any traces of that corrosion could be partly shorting things and messing stuff up, though not having the thermistor in place is also likely forcing it to shut down.
 
weirdah said:
It was surrounded by oxidation and my guess was that this component was damaged, any chance to test it with a multimeter?
Click to expand...

Stick a meter on ohms across it, and then warm it up - the resistance should increase with heat, and decrease with cold, you don't have a prayer of identifying an unmarked thermistor.
 
that board has a lot of water damage on it, likely quite a few components on the board are bad.
 

Is it from a chemical lab? Or chemical processing for manufacturing? I haven't seen oxidation like that in some time.
Is it some type of drying rack heater plates or oven?
 
I add some photos to clarify the damage.

I don't know where did this liquid damage came from.
 

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At a quick guess some very corrosive gasses were released when the big green transformer split apart as it burned up inside.

JimB
 
But there's nothing corrosive in a switch-mode transformer - and while I noticed the split, I'm not sure if it's faulty or not, it might just be a crack in the plastic casing (or it could be duff).

Has a pet perhaps peed on it?.
 
I'm guessing this was powering something in a lab or manufacturing area but our OP did not answer the question from my last post. We'll see.
Sometimes, these things self-destruct when backside copper corrodes to make high-resistance connections or the heatsink/component interface corrodes to make high thermal resistance junction.
 
I don't know where the problem came from. I rescued the Olivetti 290SP and it was preety good except for the PSU, it had corrosion near the fan and near the heatsink, but heavy corrossion was surrounding the fan.

The fan is in the rear (exposed) part of the machine, so it could be anything, (as Nigel said it could be some pet's orine or some other thing, I'm gonna ask the previous owner if they have some animal that could be done that...
 

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I cannot answer if the machine was in some lab, or some other chemical exposed ambiance because I rescued it a few days ago. I'll try to get more info from the previous owner.
 
weirdah said:
Olivetti 290SP
Click to expand...

if it is such an old computer and used for a great number of years, and mostly in line with the fan blast, it could be as simple as the salty air from a coastal home or office.
 
It sure can be that, PC was located in a coastal town in Spain. In spanish coast there's an enviroment with with high levels of humidity.

I managed to stabilize voltage in first two 5v red cables in about 7v, orange one must be 12V and it exceeds voltage with 12,9v stable, grey wire must be -12v and I get 0,07v, yellow one must be -5v and shows 0,04v, the last white wire marked as RES shows 6,90v. At least I managet to get more stable values, but I'm worried about -5 and -12v specially. Any hint?
 
Last edited:
Forgot to mention molex voltages are consistant with above voltages, being orange 12,7v, blacks 0v and red 6,9v, on floppy side wires show the same power values: red 6,9v black 0v.

May about +2v in 5v line be a problem?
Any clue to mess with -12v and -5v lines? What do they control?
May the pc turn on with these voltages or it may cause damage to it?

Thanks.
 
What loads do you have on the rails?, a stabilised PSU as in a PC only regulates ONE of the rails (usually 5V), the rest rely simply on the turns ratio of the transformer. There's no way to regulate more than one rail in a single supply, so the most critical is chosen.

Sometimes there's a bit of partial feedback from other rails, simply as a bit of a safety factor in case they go excessively high.
 
I've read this:

"The original IBM PCs drew most of their power from two voltage rails: 5 volts and 12 volts. Their power supplies also provided -5 and -12 volts but those only delivered small amounts of power. They had a 5 volt rail because that was the voltage needed to power most of the standard silicon chips of the time. The 12 volt rail was used primarly to operate fans and floppy disk drive motors. The original PC PSU could deliver a maximum 63.5 watts most of which was on the 5 volt rail."

My PC is a 286 processor one, so voltages may be as they are described above, as they were not CD Rom drives to be powered at 12v. Am I right with this reference?

May almost 7v be a problem to the PC?I don't think so, but I don't want to fry my PC.


Thanks a lot!
 

I'll ask again, what loads do you have on the rails? - with no load 7V could easily be correct - you shouldn't run them without loads.
 
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