Autohelm 800 power transistors

[winater]

Hi,
Our trusted Autohelm 800 started a mutiny, and after opening her up the problem appeard to be fried power transistors.

Two of the four transistors on the position TR4 and TR8 were fried beond recognition
the others were;
BDW 93B 8923 on position TR7
and
BDW 94B 8917 on position TR 6(?)

My question to the gathered wisdom here is; what were the typenumbers of the unrecognisable transistors?
Bonuspoints question ;-) whith which type of transistors could all four of them best be replaced?

 

[breezetrees]

A little googling shows that the 93B is a NPN while the 94B is a PNP darlington transistor. An H-Bridge circuit would make sense for the motor driver and this circuit takes 2 NPN and 2 PNP very commonly. Using the pinout from the data sheets you could probably trace the power, ground and motor wires to see which goes where: PNP would be connected to the +12V and the NPN would be connected to the (-)


Some references:
http://www.nathandumont.com/blog/h-bridge-tutorial
https://www.fairchildsemi.com/datasheets/BD/BDW93C.pdf
https://www.fairchildsemi.com/datasheets/BD/BDW94C.pdf

Tell us how it goes!
-Mike

 

[Wylieguy]

An underlying question is "why" the transistors failed. A power spike? Before just replacing the transistors, I'd look further back in the system. -- Pat