Identify diode/capacitor

Please help identify a suitable replacement

This blue disc does not have any wiring on it.

It is identified as a diode “D1” but sure looks like a capacitor and there are similar blue discs on the PCB that are identified as “C#”

A search of the Z symbol did not yield anything conclusive.


That would be a metal oxide varistor (MOV), used to provide over-voltage protection. In absence of a legible label, a reasonable guess at replacement could be made by selecting something that fits mechanically and has a “Maximum AC Volts” rating slightly higher than the nominal supply voltage plus 10%. For 120V applications, MOVs with max ACV ratings of 140 to 150 can be a good starting point.

The dark and crispy state shown is the typical failure mode, and there’s probably a 99% chance that the adjacent fuse is blown also, because it was put there to keep the MOV from setting the building on fire when it reaches its end of life. If the voltage ratings of downstream components permit, selection of an MOV with higher max ACV rating can extend that lifetime.


Thanks for the reply. MOV was right on target!.. And the fuse is blown.

Probably bad form but I removed the MOV and jumpered the fuse and tomorrow I’ll try to run it to see if the rest of the board works before replacing these. It got taken out by a power spike when utility transformer was reset.

Here’s the info I was able to get from the parts. Love the camera macro!

sgsct t 3.15a 15a 250v

This one is close but only 6.5a 39216300440 Littelfuse Inc. | Circuit Protection | DigiKey


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OK for temporary diagnostic purposes, but one should not leave a device connected to power in such a state or reassemble it in a manner that may tempt a person to resume normal use with the protective components absent.

RST 3.15-BULK would appear a reasonable replacement fuse.