I have just acquired a series 1 Interact, in a little worse shape than I had hoped. The TNC 151 power supply is dead. Heidenhain says they will fix it, estimate is $100 - $2800 depending on what they find. Before I commit to that, I would like to test the servo drives which I obviously can't do from the control. If the drives are bad, I understand they are unrepairable, so then I move on to the complete control retrofit.

It looks like I can test the drives by energizing the axis release relay, then applying +/- 10 V on the drive inputs from a lab supply. Of course I would need to be careful since I have disabled about 100 safety devices this way. Is there anything else wrong with this test?