PS board blown component

[notallbad]

Can anyone recommend a replacement? I'm guessing it just acts as a fuse, the PS is from a fruit machine and it says fused at 5a on the PS casing but I can't see a fuse anywhere on the board.

It was, I believe, an NTC thermistor but can't identify the spec rating as it has blown past recognition.



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This is what it connects to, the black 4 legged component on the heatsink (AC to DC) Rectifier (8K printed on it):



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[Khron]

Re: PS board blown component

Yep, the leg length and the circuit placement points towards a thermistor indeed.

Maybe / hopefully the fuse is in or near the mains input connector?

Edit: Since you're in the UK, aren't the fuses inside the mains plugs, in fact?

[notallbad]

Re: PS board blown component

Thanks for confirmation on what the component is, hopefully someone can identify the rating for a replacement..
Yes there is a fuse in the plug but expected to see a fuse on the board too.

[notallbad]

Re: PS board blown component

I have a 10S050M, would this suffice? It is rated at 5ohms.

It was removed from the 240V filter part of a PC power supply.

[notallbad]

Re: PS board blown component

Is it possible to just replace with a link wire just to get it working to test it out?

[Khron]

Re: PS board blown component

Many "gutless wonders" are built like that (well, if you can call that "built" ) ie. with nearly all the input filtering "skipped".

But for testing at least, an NTC from a PC power supply should do just fine (if not even permanently).

[PeteS in CA]

Re: PS board blown component

You should first use an ohm meter to check to see if there is a short in the circuit after the inrush thermistor. I've seen such thermistors desolder themselves and fall out of the circuit if somewhat overloaded (e.g. a 100% overload), but being blown apart suggests a much more massive overload. If the circuit is OK and you use a wire instead of another thermistor, the worst that could happen would be the fuse blowing (or possibly the breaker for that AC circuit).

With a capacitive input circuit (rectifiers followed by large electrolytic capacitors, rather than PFC after the rectifiers), at first turn on the initial current will basically be the initial voltage at turn-on divided by the ESR of the capacitors. In the UK, that could be as nasty as 336A with a nominal 240VAC line and 1 ohm of ESR. Wires and traces have a little resistance, and there's a bit of differential mode inductance in the wires and common mode inductors, but that won't alter the picture much. If your fuse is a fast-blow type, it probably will blow.