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Unknown Part Identification - Help Needed

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ednspace:
I am attempting to repair an older piece of equipment and have found what looks like a damaged component. There are two identical sections on this circuit board and each have this component. The component designators on the board start with R and all other normal looking resistors on the board also start with R.

The one I think is good measures 25K and the one I think is damaged measures around 5K. They are light yellow discs and measure approximately one inch across and are very thin, around .065" They each have two legs. The good one appears to have the marking 40/3 and appears to be newer and to have been changed before. Both were wrapped in a heavy piece of heatshrink and dated 91/01/07 with a marker.

If I heat the good one up the resistance drops but not dramatically 25K to around 16K when too hot to touch. These components are part of an output power transistor circuit and they each have a diode in a TO16 package bent over and siliconed down to the top of these discs. The discs were mounted flat against the PCB. I assume the diodes are some type of thermal protection and are also found siliconed down to some power resistors on the same board.

I would appreciate any help identifying and finding suitable replacements for these components,
thanks for your time,
ED

Could these be some older style NTC inrush limiters or what???
The bright one with the visible markings measures 25K
The darker one that appears damaged measures 5K

ArthurDent:
It looks and sounds like an MOV, metal oxide varistor. used for overvoltage protection. The leads are soft soldered onto the metal plating on each side of the disc and when they overheat, you may see the beads of solder ooze out near the leads and the coating discolors or burns off. The numbers may be a voltage rating but unless you know the circuit they are used in, you can't figure out what you need as a replacement. Here's a photo of one.

ednspace:
Thanks for the feedback.
I think a MOV is likely. I wonder if there is a way I could test the good one.
It might also be possible to trace out a small section if this circuit to see what's going on.
What would the numbers 40/3 mean if I assume that it is a MOV?

The legs soldered on to a metal disc and oozing out when overheated statement appears to be dead on.

TimNJ:
I'm not sure what it is, but I'm having a hard time believing its an MOV. An MOV should be effectively open circuit, if it's good. I would imagine 5-10Megohm DC resistance Also, seems unlikely than an MOV would be used in an output circuit.

Another thought I had was that it's a 40nF capacitor, which would typically be marked "403". Maybe this manufacturer split the 3 off. But still, shoudn't be measuring 15KOhm on a ceramic disc capacitor, if it's good.

My third guess is a PPTC re-settable fuse. Maybe 40V blocking rating, 3A trip or hold current. But again, resistance measurement doesn't seem to make sense unless they are both damaged.

SeanB:
Disk thermistors, probably used there to do temperature compensation, and along with the diode are designed to make the output stage stable with temperature, as the bias voltage on the output stage is going to change with temperature, so this does an equal change for the bias voltage. Probably a 25k one, and replaceable with another of similar size and temperature coefficient.

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