Electronic – Identify and replace a resistor


My APC UPS stopped working. I have had it for many years and it was serviced once by APC while in warranty and never opened again.

Now since it is not in warranty anymore I opened it and saw two very suspiciously looking resistors.

Suspected resistors

What are those? Any tutorial on how to replace them (for a non solder iron friend)?

Here other pictures:
Large area
Small area

After reading the comments I gave another detailed look at the board with magnifying lenses and the only other suspicious thing I found is a capacitor that looks like it was hand soldered into place. May be when it was serviced by APC. Notice it has glue attached which I think indicates it was previously flush to the board. The place in the board immediately below where it should be glued to still has a mark of the glue. It is very far from the resistors place.

hand soldered capacitor

The visual underneath the smoked traces does not look bad although lightly darker:

underneath the resistors

Best Answer

Those resistor appear to be 0805 package 200 Ω 1%. However, all that crud around the resistors is a bad sign. These things have apparently been too hot for a long time, although that still doesn't explain all the crud. Resistors don't leak corrosive stuff like that. It's also very suspicious that the capacitor to the right seems to have brown stuff on its solder miniscus at both ends. It looks like flux, but flux wouldn't end up there like that. I'm thinking that maybe the long term overheating helped along by humidity broke down organic compounds in maybe the solder mask or residual flux, although I haven't actually seen that before myself.

In any case, the verdict is the same. This unit is toast. Done. Kaput. Forgeddaboudit. Two resistors wouldn't just overheat on their own for no reason. The fact that they are dead, and took part of the surroundings with them in the process, looks more like a symptom than the root cause. Toss this mess and move on.