:: Are your TIP41Cs TIP41Cs  ?

Definitely TIP41C's.


:: How old are the cores?

At least 5 years old.

:: What are they made of?

Ferrite.

:: Try swapping cores (whole inductors) between a good and a bad one

Tried this, it appears to solve the immediate problem, but not the cause or=
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possible prevention.



:: How hot are the cores getting. Are the cores in bad units getting
:: much hotter than in the good ones.

Not very hot, they certainly run much warmer than an 'in service' ballast=20
(though they all get hot in the field as witnessed by brown and twisted=20
plastic cases.

The transistors get very hot - unlike other ballasts (using TIP41C's and=20
2SC2655's) the transistors don't disintegrate, they just short between C=20
and B (when they die, but in the case of these malfunctioning units they=20
just shut down), however much smoke curls from the PCB tracks.

Colin
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cdb, colin@btech-online.co.uk on 16/02/2011
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