vfd scrs

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mark480

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I have a vfd that is blowing main input fuses and the driver boards are good , the question I have is how do I check a semi conductor scr. In the old days I would use a ohm meter and check each diode for high or low resistance. This is a cutler hammer 7000 series 18 pulse vsd for a waste water pump.It has two diode internally in one block or unit. Thanks
 
I am not familiar with that drive but I still use the 'ole ohm meter to test pretty modern drives. (AB, ABB, Lenze, other wierd Euro-stuff) You see "other stuff" with your reading but usually when they're gone it's pretty easy to see.

Either that or put bigger fuses in, the problem component will reveal itself then.;)
 
What do you do then?

What do you do then?

I've never heard of testing SCRs. What do you do when you find the problem SCR. Do you replace the board, resolder new scr, replace whole drive?
 
mark480 said:
I have a vfd that is blowing main input fuses and the driver boards are good , the question I have is how do I check a semi conductor scr. In the old days I would use a ohm meter and check each diode for high or low resistance.
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In my experience diodes and SCRs almost always fail in short circuit mode.
A half decent multimeter will detect that.
Less easy is finding out which one. You might need to drop off the power connections on the suspect device to isolate the fault.
 
StephenSDH said:
I've never heard of testing SCRs. What do you do when you find the problem SCR. Do you replace the board, resolder new scr, replace whole drive?
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What you do is up to you. What I do depends on a number of factors, but if a board is relatively easy to get an "iron" on, with out cooking other components, I'll do some component level repair. If it's something that requires a high level of availability, or is a real pain to swap I'll get a new board or a new drive.

As you may guess, I'm not a board level guru. I've found that sometimes the "bad" component I found, and replaced, died for a reason. That reason doesn't become evident (to me) until after some, post "fix", run time. If you aren't out anything trying to fix it yourself it's a good learning experience.

Doug S.
 
76nemo said:
Any of you use a curve tracer and look at lissajous figures????
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I did as an undergraduate many years ago. It was a nice feature that some oscilloscopes had. XY rather than the usual YT, if I recall correctly. I've had fun with some since but I'm not sure that it is a useful tool for diagnosing SCR failures.
 
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