Those resistors are Power MOSFET source resistors. Those resistors are
used to limit total power output.If those are burnt up, It is almost
sure that the Power MOSFET is shorted. Why the MOSFET is shorted?
many reasons, but most likely the PWM IC is shot to death,too.
It is a chain reaction that happened so it is not worth trying to fix.
Give it to some power supply repair guy, I am sure you can find them.
For them, if they do repair day and night, it is a easy repair and
they may have plenty of parts.
If the PWM IC is UC3844 or UC3845, I can send you couple. The MOSFET
may be a Japanese part but it can be substituted with IR or ON Semi
part. The Japanes part is usually starts with 2SK series while the
american part is usually starts with IRFxxx series.
So leave it to Power supply guy.


(Scott Dorsey) wrote in message ...
OCEANRADIO wrote:
Sorry this is so far from boatanchors, but who else could answer?
I acquired a Sony VAIO P4 computer from my usual source and it didn't light up
at all. Luckily, I found two burned up resistors in the power supply. I
substituted a spare power supply and the computer works fine, but the power
supply is outboard so I need to fix the original. So here's the problem: the
two little resistors R4 and R5 (1/2W) are marked brown, black, silver, gold.
The translates to me as .1 ohm. Is that possible?

Yes. They may have been there just to act as fuses, or they may have been
used as shunts for measuring current.

The two were in parallel (electrically and physically) and it looked as if
there was an arc between them that burned them both up. There shouldn't have
been any voltage between them, given that they were in electrical parallel, and
they shouldn't have overheated, I wouldn't think, with such low resistance.

They may well have overheated if they were in series with a dead short.
Before doing anything else, start checking power transistors.

Since I was raised on 6L6s and 807s, a .1 ohm resistor is a mystery to me. Can
anyone tell me if these really are .1 ohm resistors?

If you have a working supply, you can measure the ones in the good one and
find out, but I would not be surprised if they were. Draw out the schematic.
I bet they were being used either as current shunts or fuses and that you
have a switching transistor that is a dead short. When you find it, also
check whatever is driving the transistor base too.

It's just like working with 6L6es, just with lower values on everything.

If I ask a computer guy (of which there are many) the answer would be: buy a
new computer. That's why I'm posting the question here.

I'll tell you the opposite. You should buy an older computer. The Vaio is
much too new to be interesting. You need a PDP-8e like I've got.
--scott