Electronic – In its former, pre-burnt-out life, was this thing a capacitor

identification

I've a problem with a ventilation system that stopped working shortly after power-on. I've pulled out what I believe is the power supply board and I can see an obvious problem, but I'm not entirely sure what the component is near the center that set on fire. Physically it seems virtually identical to a blue disc-shaped, two-legged one on the far left of the board between U4 and U3. That component is labelled C15, and the burnt out one is labelled RV1. Is there any hope of identifying the damaged one or do I need a manufacturer schematic to know the specifics (E.g. capacitance)?

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And a closeup with flash:

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Edit: couple of additionals

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Edit2: my neighbour has an identical unit. I was able to photo his board without disturbing it, alas no markings:

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Best Answer

It almost certainly was an MOV, Metal Oxide Varistor, a type of transient suppressor. It is on the AC side of a bridge rectifier, next to wires marked Line and Neutral, and next to an AC-rated film capacitor (the yellow box) that is part of the power line input noise filter. All of this points to primary-side protection.

In the center photo, the signal path is from the input wires, left through the fuse, up to the first layer of capacitors (both line-to-line and line-to-earth), right through common mode choke L1, then through another layer of capacitors, then down through the bridge rectifier.

If the supply is a universal-input type, then the MOV is rated for something in the 270-300 Vac range. The physical size determines how large a transient it can absorb. You can get approximately the same protection by matching its diameter.