Re: Help needed identifying failed components

Wolfi <publicalfa-ng@xxxxxxxx> wrote in
news:J9Xji.2783$K73.128@xxxxxxxxxxxx:

Judging from the surrounding circuitry, which I further re-engineered
by now, I have to assume, that its value is most likely 1 Ohm at most,
perhaps even 0.1 Ohm, (even though 2 other people also looking at it
and both came up with gold being the center ring).
From a tap of the SMPS transformer, a HER303 diode, which shorted out
is
connected via a wire bridge with a ferrite core around it to this
little 7mm × 2mm fusible resistor, and from there feeding the CRT
cathode heaters with a negative 6.3V voltage. The heaters have a cold
resistance of some 5 Ohm and assuming that when hot, the resistance
increases by at least 50% to about 8 Ohms, then it still would mean
some 0.6W dissipation in the little R (with an assumed value of 1
Ohm). My guess is, that it isn't rated for more than 0.5 W, so it
would be already a bit tight. But on the other hand, it is no DC, it
still is a pulsing current, so it might be just fine and the above
rule of thumb calculation resulting to high anyway.
But I think it also quite surely eliminates the possibility for a 2
Ohm reading, so it has to be something like Brn-Blk_Gld => 1 0 ×0.1,
next Blk = dunno, and finally Red = 2% tolerance OR Blk = 1% tolerance
and the final Red = dunno.

Any other thoughts?


Agreed, 1 ohm is likely.

http://xtronics.com/kits/rcode.htm indicates a 'quality' band in place of
the other possibility for 5th band, temperature coefficient. In this case
it might mean 2% likely failure risk every 1000 hours for those resistors.

That page says 1% tolerance resistors have three value bands before the
multiplier. I think that's true even if the third is unused (black). As
yours has a multiplier as third band, it presumably can't be 1% tolerance,
but that doesn't explain why the tolerance band is black. :)

Maybe it's a thermistor with its own coding type? It might be designed to
limit the inrush current to a cold heater.
.

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