MEP 005a diode issue and no output

[bboughey]

This winter I bought a MEP 005a with 2hrs on the runtime meter that had been put in a mothballed condition. Getting it up and running was simple. I put about 10 hours on it, and now it's giving me fits. I had an overvoltage condition (270V) that I couldn't figure out. So I bought a rebuilt voltage regulator. I hooked it up - 0V. Swapped the old one back in to see what was going on - 300V and rising. So I put the rebuilder back in, and it gave me 220V but didn't respond to my rheostat. Eventually it drifted to 240V, but like to shed the load and go back to 0V. I checked the field - F1 to F2 show resistance within norms. And then I went to replace the rotating diodes because the voltage regulator rebuilder certainly thinks it can't be his box. I completely spaced and put in 6 1190 RA diodes and didn't pay attention to polarity. So I need help with two things: 1. Can someone help me figure out which slots should take the forward and reverse stud diodes. 2. Any ideas other than voltage regulator or rotating diodes for my no output issue? I've checked all 6 diodes that I remove and they all show between 0.43 and 0.51 V drop across them.

 

[PeterD]

(Crap! I just deleted my entire reply!)

1. I suspect your original diodes were good if they had the forward drop you state, and were 'open' in the reverse. (That is not shorted.)

2. What regulator did you (re)install? Same one, or an aftermarket substitute? Just because the rebuilder thinks it is OK, doesn't mean it is.

I'd carefully check the voltage adjust rheostat and wiring as a start. That could account for virtually all your problems except the fubar'ed diode installation. Then I'd run any tests in the manual to test the regulator--you do have the manuals right? If not they can be downloaded from the web for free from a number of different locations. Also same manuals will have information on diodes (which ones go where...) to allow you to sort out the mistake you made there.

 

[bboughey]

Thanks Peter. I found the diode layout in the manuals (I have several of them I've fished up online). The rebuilt voltage regulator is the original type (and wasn't cheap either). I troubleshot the old one a little bit with my DMM but there was only so much I could do without a variable power supply. Maybe it's time to get one. Got one you recommend?

 

[PeterD]

For stuff like that I got to an industrial supply surplus seller that I know in Manchester NH. They have all kinds of great stuff, such as three phase variacs, and general purpose power supplies. (The place is called ESS on Candia Road for those of us in New England.)