I've got a 1985 740 turbo which uses a Bosch ignition ECU p/n 0 261 201 012 as part of the EZ-117K Jetronic ignition system. After dying several times only to start up again the car finally died completely and I had it towed home. So I've finally been able to troubleshoot this problem. This ECU is the second one I've had; it was last replaced in December 2013. Opening it up I found no obviously fried components but on a hunch removed the largest transistor, the only one that was attached to a heat sink and found that it has failed. It is an NPN transistor with a p/ n of ON 946. It is a TO-220 style transistor which I believe was manufactured by Philips.

I'd appreciate any suggestions on finding a suitable replacement transistor. Preferably the most robust transistor possible for this application. DigiKey didn't have the data sheet on the transistor and I can't find it online. I'd also like confirmation that this is the correct ECU. Online some sources seem to indicate that the p/n should end with a 011 rather than 012.