Whistle Rock ML918 getting VERY hot

[Potato Cakes]

Hello friends,

I have a couple of DOAs that were built some time ago are not working and I thought I would try to fix them before I tossed them out. One of them is an ML918 and Q8 gets insanely hot, to where smoke starts to come off of it. The working one of these I have obviously does not do that. I replaced Q8 with a new transistor and same thing. I've gone over the usual suspects (cold solder, bridges, placement, orientation, etc) and I'm down to a bad diode or possibly another bad transistor. I don't really have a way to test diodes and I can test transistors, but I have to pull them off of the board. So before I start guessing desoldering parts, has anyone else have this happen, or at least maybe someone has a better idea than I about who the culprit is?

Thanks!

Paul

 

[Potato Cakes]

Found it!

After emailing Mike at Whistle Rock, he told me to check to see what kind of DC voltage was on the output pin, which was -15V. That led me to find out that the MJE171 was bad as there was continuity between the emitter and the collector. Swapped it with a BD140 and all seems well.

Thanks!

Paul