wow, thanks for the quick replies.
John Sorensen:
"...about that much"
That was one of the funniest things I've read in a while. Although quite true. It is not my money, I do know how much it costs and although down time is an issue, albeit not major, we try to save money where we can. If it were necessary to change all three modules than so be it and everyone would be happy. I guess it's probably just me who really wants to know if it is necessary or not. I just hate throwing money away mine or not. My boss would probably say screw it and replace them all. I have them on order and will probably just change them all.
Styx:
I had measured the diode drop of the three modules before replacing the first module, I had not measured the gate-emitter capacitance. I found the upper IGBT in the one module to be bad, the lower IGBT tested fine. This is the module I replaced.
After reading your message I checked the Cge for the originally failed module and found that the upper IGBT had 0 capacitance and the lower had the same capacitance as the new module (10nF). Unfortunately I did not check Cge for the second failed module before I powered it up.
I have now checked the second failed module Cge and found to be the same as the first, the upper IGBT appears to be bad and the lower appears to be fine.
I have also checked the remaining module Vdiode and Cge and is almost identical to the brand new module.
Oh, I should also point out that the modules did not fragment, and appear fine cosmetically. The reason the drive was replaced was because of a short circuit fault even with the motor disconnected. This is when I traced the short to the failed module.
I guess my question now would be since the remaining module tested fine should I bother replacing if money is an object? Could it be bad although it appears to be fine. Time is no issue here and I have ordered two more modules just in case. We are fairly small shop and are trying to save money were we can. I was just wondering if it was common practice for a drive repair shop to replace all three modules.
The reason I asked the question in the first place was because we normally send these drives out to be repaired, and this particular drive cost about $2000 to get repaired. The individual modules cost 400 a piece and replacing all 3 would still only run 1200. The problem is were not really satisfied with the repair shops we have been using. To give an example why, this is the first drive I have tried to repair and after taking the drive apart I found the braking transistor emitter wire was not even connected. It was left uninsulated dangling behind one of the control boards. I tested the braking transistor and it is shorted collector to emitter. It seems this would surely have blown the dc-bus fuse had it been connected. This is probably the reason the drive was sent out for repair in the first place. We have the happen fairly frequenty(dc-bus fuse blowing). So did we pay 2000 to have someone disconnect the emitter wire and send it back as fixed?
I didn't mean for this post to be quite so long, but I do appreciate all the help.
James