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Mac misadventures

tezza said:
I am curious about the power transistor though (see blog). Is the middle leg always regarded as the base and should should resistance between emitter and collector always be infinite when measured across the these pins when out of circuit?
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Oh, the pinout can definitely vary. Most of what I've come across are ECB or CBE configurations (or indeed the reverse depending how you look at it). Your Q3 (a BC406) is of the former type. If you screwed it to the bench, pins towards you, the order would be BCE from left to right.

BTW: I don't suppose you have a transitor test setting on your multimeter? I never realised I had one until I looked last night! There's an "hFE" setting on the dial and two rows of four holes for plugging in the transistor.
 
cosam said:
Oh, the pinout can definitely vary. Most of what I've come across are ECB or CBE configurations (or indeed the reverse depending how you look at it). Your Q3 (a BC406) is of the former type. If you screwed it to the bench, pins towards you, the order would be BCE from left to right.
Click to expand...

Ah. That would explain it. That original transistor was probably ok then, not faulty as I thought. Well, now I know. Thanks.

cosam said:
BTW: I don't suppose you have a transitor test setting on your multimeter? I never realised I had one until I looked last night! There's an "hFE" setting on the dial and two rows of four holes for plugging in the transistor.
Click to expand...

No, I don't but I am aware some meters have them. I have an el-chepo meter someone gave me as an Xmas present. It does the bare minimum really. But then, I never expected to be tinkering around with electronics.

I need a better one really.

Tez
 
I got a meter for my brother in law for about £6 (he didn't need anything special) I was surprised to note the "Buy one, get one free offer" on them so I got a spare meter with a diode-test setting for £3. and it seems pretty accurate. My "proper" meter is a decent one though.
I use the diode test (and continuity beep) a lot.
I'm sorry to have led you down the garden path with the transistor though, however I would have been looking at it at that point, but done a diode test & discounted it as OK!
 
No worries Nige. If I'd known that transistors could vary on the orientation of their pins, my resistance measurements would have also cleared the original one as OK.

In some ways it's good, because with all the associated smaller components checking out ok, it must have been the flyback which was faulty. So I can be satisfied I did all I could to diagnosis it, and fixing it would not be possible.

I don't have to feel guilty from it's accusing stare from the junk pile now. :)

Tez
 
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