Love when the fault reveals itself

ubergeeknz

Member
2018-08-31 12:32 pm
When you power something on and viola, fault found (well, one of them anyway)

Watch the video first...
YouTube

Anyone else got some great examples? IMG_20200222_132648_100.jpg IMG_20200222_121415.jpg
 

ubergeeknz

Member
2018-08-31 12:32 pm
So... As you might expect, both drivers were gone along with the thermal compensation transistor. Also 2 biasing resistors. With all that replaced, it lives again. I did replace the PNP driver as well, just so they "match", but it was okay.

I used TIP41C/42C for the outputs, a 2n3904 for the thermal comp. (with crossed B and C legs) and a pair of recovered TO127 transistors, which seemed closest to the specs required, for the drivers.

The amp is a Pioneer SA-420, if anyone's interested. Pretty basic, with loose biasing requirements of 2-100mV across the output emitter resistors according to the manual, and no adjustment pots. Both channels sit at about 25-30mV, I had to change R54 to 680 from 560 to achieve this. Then I gave the PCB and heatsink a good clean. IMG_20200223_090516.jpg IMG_20200223_171236_994.jpg