Should a N15 I.C. read short-circuit?

[Old Sparky]

The N15 is a small 2-terminal device, which I gather is an I.C. protector. I have come across one in the PSU of a Denon RCD-M35 Dab Hi-Fi which, in situ at any rate reads <1 ohm on an analogue meter. Is this correct? As far as I can tell the N15 is connected between the i/p pin of IC605 (a voltage regulator) and the junction of the centre tap of T601 secondary and the negative side of C635. These components are part of the standby circuit of the receiver, for which I don't have a diagram, but the fault is that it won't come out of standby unless the ribbon cable connecting the PSU to the amplifier PCB is disconnected.

[Refugee]

Is it in series with the transformer secondary?
If this is true it will be a self resetting fuse and the reading will then be correct.
Put power on the set and measure across it while it is warm and then it should read open circuit or go open circuit as the fault currant rises.

[Old Sparky]

I've now downloaded a manual for the RCD-M35, and you are correct, Refugee. It is a self-resetting fuse in series with the secondary of the standby transformer, so i can rule out the N15 as being anything to do with the fault! (More 'digging' to do I guess!)

[Refugee]

It may well be telling you that there is a short on the amplifier by the tripping action.

[Nick]

The ICP-N15 is a type of self-resetting fuse, much like a polyfuse, but as it's solid-state, it reacts faster and more predictably.

It could be that its out of spec and tripping too early, but frankly I'd look elsewhere first...

I'd start with the ribbon cable plugged it and check each of the various PSU rails to see if any are out of spec when plugged in vs. unplugged...

[Old Sparky]

I am a silly *********! The primary of the mains transformer was open circuit, probably due to a failed thermal fuse somewhere in the winding. Borrowing a similar, but larger transformer from a different DENON model proved that the various functions all work, and there is good quality sound from the CD player, though, for a reason I haven't yet established, no sound at all from the radio. I've been told by someone at Charles Hyde that the mains tranny is no longer available, so either a suitable substitute will have to be found, or the set is scrap. What I don't understand is why the lack of the main and supplementary DC supplies due to an o/c primary, should cause protection circuits to trip, and the standby/on LED to flash.

[Refugee]

It would be due to there being no regulator feedback from the main power supply.

[Old Sparky]

I fixed the fault by fitting a new thermal fuse, which I managed to push inside the windings, and the Denon has now been working perfectly for just over a month.

[AlanBeckett]

If I have any tricky faults on modernish gear I'm bringing it round to you OS.
Well done.

Alan