3 Blown Transistor Packs in 8 months!!

[TSIsean]

A friend of mine is having a problem with blowing transistor packs on his 90 Tsi. This is the third time in 8 months that this has happened. Two were old and 1 was brand new! We can not figure out why this keeps happening, it's very irritating, time consuming and costly to have this keep happening. Everything else electrical on the car is fine, ECU and Coil.

I'm pretty experianced with DSMs but my friends and I are stumped as to why ONLY the transistor keeps blowing. This time was the longest time it lasted. We have the origional one and a used replacement blow within 2 months of each other. Then we got this one and it blew 6 months later.

Has anyone ever seen or experianced anything like this? Or atleast have an idea WHY this is happening?

 

[TSIsean]

Any electrical experts on here?

 

[steve]

Just off my head, I'd look closely at the coil and make sure that the PTM mounting is clean since it's used as a heatsink.

Steve

 

[TSIsean]

I'll try sanding it down and making sure the mounting points are clean.

 

[TSIsean]

This problem is persisting. It's happened two more times. We even tried to wire in a new pigtail for the transistor and it still does nothing. Any ideas??

 

[ginsu417]

Have you checked to see that it's always the same coil that's not firing? The transistor pack is a relatively simple device. There's 2 power transistors in it (one for each coil) with each transistor having an emitter, collector, and base. When the base pin gets a positive voltage from the ECM, the transistor grounds the collector (in effect, grounding the primary in the coil), which in turn, charges the coil. When the ECU is ready to punch a cylinder, it cuts the voltage to the base, disconnecting the primary coil's ground, which by magnentic phenomenon sends a pulse through the secondary, and fires the spark plugs on that coil.

The transistor is rated for very high voltage on the collector and emitter to deal with the return voltage spike that comes from firing the coils. So the only voltage-sensitive area is the base on the transistor. I'd suspect that to be the most likely failure point. Check your base voltage (marked B1 and B2 on the transistor pack or pin 54 and 55 on the ECU) to see that it's not more than 3V. If it is, then try another ECU. If it isn't, then replace the coil pack.