2N6308 NPN Power Transistor

[sigma7]

A pair of 2N6308 are used as Q1 & Q2 on the main board in the "DataPower" variant of the Lisa Power Supply, often referred to as the "1.8A" PSU due to the rating label.

This component does sometimes fail, but is not often a problem.

These transistors drive the rectified mains power through the primary side of the main transformer in a push-pull manner, controlled by the SG3524 on the daughterboard.

[TorZidan]

If I remember correctly, a continuity measurement across two of their leads (forgot which ones) when they are soldered onto the board shows "a short", whereas, in fact, the transistors are fine. This is a major confusion when testing them. Sorry, I have forgotten more details about this. I hope you can provide the details.

[sigma7]

measurement across two of their leads (forgot which ones) when they are soldered onto the board shows "a short", whereas, in fact, the transistors are fine. This is a major confusion when testing them.

Yes, that's a good point. In the DataPower PSU, the base drive for each of Q1 and Q2 comes from pulse transformers, with a winding connected between base and emitter. When attempting to check the b-e junction it looks like a short in both directions.