Blown Transistor ? Bridgeport Series 1

[astr]

It seems that blowing stepper motor drive transistors is an ongoing problem with the Series 1 mills. I noticed in the documentation that in later serial numbers of the controllers, Bridgeport add diodes across the Emitter-Base junctions on all of the output transistors. I assume that this was an attempt to address this problem.

Did adding these diodes help?

Should I add these to my older machine?

What diode should I use?

As I have my controller all apart, this would be a good time to add these diodes.

Thanks in advance.

[machintek]

They also added the SMS board. The best way to keep transistors from blowing is to keep the output of T2 less than 63 VAC and do not press Emergency stop while doing a rapid move.

George

[astr]

Thanks again George. I can certainly keep my hands of the e-stop button but I'm not sure what I can do to lower the output of T2. Now, it is around 73VAC. Maybe I can change the input taps. My line voltage coming into the building is 485 VAC, 3-phase. Any suggestions?

[machintek]

Buck/boost transformers.

George