Fried PSU Resistor Replacement?

[dexters_lab]

i picked up a small 3.5" HDD enclosure with a built in switching PSU a while ago, popped it open today to check it and found a very sad power resistor on the PSU... looks like it's been getting hot hot HOT!

The PSU does seem to work ok with it like that, it has a good stable +5 & +12v

what's the best course of action to replace? Try and remove it without it disintegrating and measure, replace with the closest spec?

[ElektroQuark]

I would replace it, yes, but measure it BEFORE trying to remove.

[jaromir]

Try to measure it as is, soldered into circuit. You may get distorted value, but better than nothing, if it disintegrates during removal.
Then, I'd cut the longer lead, to remove it from circuit from one side and measure it again - this should yield accurate value, but at risk of damaging the resistor. Use thin cutter, to avoid bending of the leads/resistor as much as possible.

Also, try to find out why the resistor was so much damaged. The new one will get as hot as this old. Maybe it's designed to run as hot, maybe something is wrong with the PSU - perhaps leaky capacitors?

[Gyro]

An SMPS with no less than three high wattage resistors complete with ceramic standoffs and glass fibre insulation on the Primary side?    [Edit: I think I can see a fourth].

That must be one really inefficient power supply design! You might want to give some consideration to replacing it with something better.

[dexters_lab]

it measures 72kohm in circuit but there is a capacitor charging somewhere.

i'll snip it out and see what it reads out to

the PSU is in a pretty tight enclosure, i doubt i'd find a replacement that would fit and in reality it's probably not worth spending much on it

[drussell]

Something doesn't make sense there...  You need to take a look at that part of the circuit and see what that resistor is actually supposed to be doing in there.   If it is currently 70k+ ohms, even constantly across 400 volts DC it would only be dissipating a couple watts.  If it really is that high, there is a good chance that resistor is already fried so who knows that the value is supposed to be. 

Is it in parallel with anything else?  If more than one of those resistors are parallel, maybe that one went down in value, took all the current and fried.  If it is across a transformer winding it may supposed to be providing damping for inductive kick or something, maybe a diode that is supposed to take most of the spike is open?  etc. etc...

Find out where that resistor actually is in the circuit and then we can possibly deduce what is actually going on.