Re: Imac G5 PSU no power to 3845B



I've been messing with these old junkers for a bit. Q1 keeps on dying after a few days/weeks/months. I've done 10 or so of them, all the same issue again.
In your "on" case there is a 2V drop over CE and with 16V at the base that transistor should be saturated. It means that Q1 is dissipating a lot of power and will soon die again.
The 16V zener at the base will limit base voltage, D2 (E to B) will limit emitter voltage at 16V+0.6V. So a voltage higher than 16.5V at the collector will start to heat up Q1 and...