Resistor end-cap corrosion? Ohms reading way high...

[roger2]

This little 3mm has something going on around its end cap. Nominal resistance is 10k ohm. But I get high, and inconsistent, readings on my LCR, it shows 60k one time, 200k another time.

What is this corrosion? Is this a known failure mode?

This resistor is from a RCA MPA-120, an STK amp from 1987. There are a lot of these little 3mm resistors in it. And a few of them are showing similar corrosion...or whatever that is. But the end caps on most of them appear clean.

Anybody seen this before, or have any knowledge to share?

 

[roger2]

It is possible that this is carbon the film disintegrating, or liquefying, and running out the end?

 

[davidsrsb]

Carbon film does not liquify
The coating flakes off like this when overloaded

 

[ticknpop]

The end cap attaching the leads to resistor body has come loose.

 

[wg_ski]

Yeah, the connection from the end cap to resistor element is compromised. Might have been initiated by an overload, or it might just be a cheap resistor. Somebody saving .05 cents on each BOM item to save a dime or two on each amp. If it is just a cheap resistor, there will be more in there that will go eventually.

 

[roger2]

Thanks everyone!

Cheap resistors makes sense. This resistor had -61V on it continuously, connected directly to a pin on a large STK4046. So I am guessing that is a stressful position compared to others, and why this one was the first to fail.

I have two of these amps. I carefully inspected both and found about a dozen showing similar signs. The compromised resistors across both amps were showing up in similar positions.

So my to-do list just got longer, lol

 

[NareshBrd]

Replace them with the next higher wattage rating, just as insurance, provided there is space on the PCB.