A mystery resistor...

Thread Starter

RoverAllOver

Joined Jan 23, 2024
3
Hello folks, I'm trying to fix an ATX power supply, among other problems it has a blow resistor with markings that don't make sense to any of the calculators I've tried.
I'm reading it as red, red, silver, gold, green.
It is a large resistor (15.5mm) on the high voltage circuit.

Here is a huge picture - can anyone help me with the resistance and wattage values?
Thanks for any help. mystery resistor .jpg
 

Thread Starter

RoverAllOver

Joined Jan 23, 2024
3
Thanks for the reply.
Yes I'm working on that, I've found a blown fuse and the resistor so far.
There was a loose piece of uninsulated copper wire in the case which may be the root cause.
I'm going to check the large transistors and diodes as well, so far everything looks good.
 

sagor

Joined Mar 10, 2019
912
While it seems badly "cooked", it might still be close to the original value. Lift one leg and measure it....
If it is a really low value, most ohm meters will simply show a zero reading, or close to it.
 

WBahn

Joined Mar 31, 2012
30,066
Red - 2
Red - 2
Silver - x0.01
Gold - 5% tolerance
Green -- Something else.

The green might indicate a few things -- often either a reliability rating or a temperature coefficient. If it's a tempco, it would be 20 ppm/K. Not sure whether green is every used as a reliability band, but if it were, it would probably be a failure rate of 1 ppm/1000 hrs, I can't imagine a resistor being used in an ATX power supply having a reliability band (this is almost never used on commercial resistors, it is part of a military specification), so it's almost certainly a tempco.

So 0.22 Ω, ±5%, 20 ppm/K

Not a guarantee, but highly likely.
 

Thread Starter

RoverAllOver

Joined Jan 23, 2024
3
Thanks for the replies, I was worried about using the 3rd band as the multiplier, getting that wrong would not go well I think.
I found a blown S30D60C "Schottky Barrier Chip" and big MOSFET on the PSU as well, so it has a fair few problems.
The piece of naked loose wire was near the S30D60C, maybe that caused a cascade failure.
I've ordered all the parts now, let's see how it goes.
 
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