Anyone come across a transistor "D 8050" ? The logo is just a small star. That is followed by a "D", then below that "8050". My first thought was 2S - D8050, but that turns up no data, except the usual component search engine dead ends and non-existent data sheets. It's a standard TO92 D-line plastic package, and the board has its pins marked as E-B-C. There is another transistor of the same type on the board, and it reads as a conventional NPN small signal transistor, so shouldn't be a problem to substitute. It would just be nice to know what its ratings are.
In case it helps, its in the SMPS of a Wharfedale monitor speaker. It is in the supply circuitry of the controller IC. The PSU is working ok - almost. It had suffered a burn-up around the leg of a cap strapped across the switching transformer somewhere. The resulting carbonised board had tracked across to another print track, and taken that out, along with a zener that was connected to that track. When the burn-up and tracking was all sorted, the PSU came up ok, and all seemed to be well until it was connected to the amplifier. With no signal, you could hear the woofer bumping quite fast. Like quiet motorboating. If you 'scoped the rails, you could see them all 'bouncing' a couple of volts. Turns out that the control IC is starting and stopping in bursts. It looks as though the startup supply is getting the IC going, but the sustain supplsy from the switching transformer is not then taking over. The bad transistor appears to be part of the regulator for this supply. The zener that had blown was connected directly to the base of this transistor, so it all seems to fit. If nobody knows any different, I think I will try an MPSA42 in there. They have a good voltage and current rating, and the right pinout.
Arfa