Arfa Daily wrote:
"Sylvia Else" wrote in message
u...
Ok, as I mentioned elsewhere in this thread, I managed to get the A/C
working again by replacing Q1 and the 8.2 ohm resistor.

Actually, I'd misread it, and when I looked more carefully, it realised it
was 6.2 ohm, as is the other one on the board with the same markings
(i.e., a not blown one). Nice standard value that.

So now I have to replace the resistor with a fusible, but sourcing a 6.2
ohm fusible is problematic.

The situation is not made any easier because if the switching transistor
fails by shorting out, then after it blows the fusible will have 340V
across it.

From the suppliers I now know about (thanks, Trevor), I can get a 0.5 watt
340V 4.7 ohm fusible. I propose to put it in series with a 1.5 ohm 1 watt
non-fusible. My reasoning is that the 1.5 ohm resistor will have only 1/3
the power dissipation, and will handle twice as much. Therefore the 4.7
ohm will go open circuit before the 1.5 ohm could get hot enough to be a
problem.

Does this stand up?

Sylvia.


Are you absolutely sure that it is definitely 6.2 ohms ? That is a *very*
odd value, particularly for a fusible type ... FWIW, I really don't think
that the circuit would give a damn if you replaced it with a 6.8 ohm, which
is a standard value. Did you actually measure the one that's ok with an
accurate low ohms meter, and get a reading of 6.2 ? Seems to me that a grey
band and a blue band might easily be misread one for the other, with some of
the banding paints I've seen used over the years. I find that it is often
very easy to misread red for orange or brown, especially if the resistor
runs warm in normal use.

Blue Red Gold Gold = 6.2 ohms, 5%. It is in the E24 series, but I've
certainly never seen one before.

When I made up an equivalent, my meter gave the same reading (allowing
for tolerance) for the equivalent as it does for the identical resistor
on the board.

So, yes, I'm pretty sure.

As for whether I could substitute a 6.8, maybe I could, though I'd have
trouble getting one that has a 350 volt rating. The only supplier I know
of that purports to have them doesn't give the rating. The suppliers
that give ratings don't carry that value.

If I understood the circuit better, I'd be more comfortable about
changing the value. The mere fact that an unusual value has been used
gives me pause - maybe it's the value that's required there. Even if
another value worked, I'd not know the ramifications.

Sylvia.