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?
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.
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 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.
Tnx,
John
K4XC

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
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

OCEANRADIO ) writes:
Sorry this is so far from boatanchors, but who else could answer?

Do some searching before posting, you're just lazy.

sci.electronics.repair is the newsgroup you want.

The "FAQ" for that newsgroup, almost multiple books about the repair of e
electronic devices, is at http://www.repairfaq.org


At the very least, rec.radio.amateur.equipment might have been at least
slightly more appropriate than a newsgroup which is supposed to be
about old radio equipment.

Michael VE2BVW

OCEANRADIO wrote:
snip
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?
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.
snip

The arc path across two parallel resistors sounds like the result of a
lightning strike.

"The Art of Electronics" by Horowitz and Hill (2nd edn. 1989, Cambridge
Univ. Press) has a good write-up on computer power supplies, and has the
complete schematic for typical one (an old Tandy design).

73,
Ed Knobloch

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

OCEANRADIO wrote:
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.

Nope, we'll tell you the smart thing to do: buy a new power supply. If you
can't find an ATX supply for $20, then you probably shouldn't be playing
with electricity anyway. Why not just tell your buddy who sold it to you
that it was DOA and he owes you a new PS?

My wife's computer with a 200 watt ATX power supply went south. Cost to
replace the ps was over $60 just for the unit. Reason was that it fitted
into a small case. I got a new ATX case with a 350 watt power supply for
$50. Had to remove all the stuff from the old computer case and put them
into the new case but she now has more power capacity with better cooling.
Bill N3TVU
" wrote in message
...
OCEANRADIO wrote:
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.

Nope, we'll tell you the smart thing to do: buy a new power supply. If
you
can't find an ATX supply for $20, then you probably shouldn't be playing
with electricity anyway. Why not just tell your buddy who sold it to you
that it was DOA and he owes you a new PS?

My PSU story goes like this...Mine got zapped during a storm (yes, right
thru an APC UPS). I found a bad diode and a resistor that had cooked
over the years. Didn't fix.
Went to the local computer dealer and paid $29 for a new "500 watt"
unit. The damn thing was so light compared to the older 200 watter
you'd almost swear it was an empty box!
Now you can't listen to a radio anywhere in the house cuz this piece of
cheap chinese crap radiates so much rf hash. I'd rather fix the old one
but getting the machine back running was the goal at the time.
Oh, and the mounting screws didn't match up either.
Buyer beware.

-Bill M



MaryAnne Olsen wrote:
My wife's computer with a 200 watt ATX power supply went south. Cost to
replace the ps was over $60 just for the unit. Reason was that it fitted
into a small case. I got a new ATX case with a 350 watt power supply for
$50. Had to remove all the stuff from the old computer case and put them
into the new case but she now has more power capacity with better cooling.
Bill N3TVU
" wrote in message
...

OCEANRADIO wrote:

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.

Nope, we'll tell you the smart thing to do: buy a new power supply. If

you

can't find an ATX supply for $20, then you probably shouldn't be playing
with electricity anyway. Why not just tell your buddy who sold it to you
that it was DOA and he owes you a new PS?