Ray70
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I'm sure many of you have read lots of threads about machines with the output voltage going high
, but this one might have a little different spin to it.
When I first got this machine I noticed an intermittent high voltage problem. After inspecting the VR board visually I noticed that at some point during it's career, someone had apparently drilled out the rivets and changed the ID plate onto the side of the control cube and proceeded to drill right through the VR board and severed the left leg of C2. I removed the board, fixed the Cap and everything seemed good.... for a while. After a recent periodic test, the voltage started pegging the gage high yet again, a few seconds to 1 minute after startup. I narrowed the problem down to the VR board by swapping control cubes, then swapping just the vR board. So... after reading lots of threads about high output voltage, I found a pair of NOS mil-spec Q3 transistors on ebay for cheap. Replace Q3, fired it up and dang... voltage goes high again
. I checked for bad connections and everything but voltage still goes high after a short time. So I pulled the board out and brought it to work today. I tested the old Q3 and it appears to be good. New Q3 also appears good. I start checking for cold solder joints and bad components. Eventually I get to the R15 trimmer pot.... supposed to be a 2K 1w pot. Tested it and its reading 2K from pin 1 to 3, (ok)... reads 2K from pins 1 to 2, and 1 ohm from pin 2 to 3, both odd unless the pot was maxed out. So I gave it a few turns in and out and it bounced around a bit than jumped down to 1700 x 300. After some more measuring and turning the screw in and out it now appears to be working smoothly. Hopefully in a few days I'll have time to put it back in and test / recalibrate it. Hopefully it works correctly.
If all goes well we can add "defective R15" to the list of potential causes of high output voltage on MEP-002A, 003A machines. For the sake of <$10 I'll probably order up a new potentiometer just in case this one flakes out again. To those that I haven't put to sleep yet, thanks for reading!
![Beat the dead horse :deadhorse: :deadhorse:](https://www.steelsoldiers.com/images/smilies/beatdeadhorse.gif)
When I first got this machine I noticed an intermittent high voltage problem. After inspecting the VR board visually I noticed that at some point during it's career, someone had apparently drilled out the rivets and changed the ID plate onto the side of the control cube and proceeded to drill right through the VR board and severed the left leg of C2. I removed the board, fixed the Cap and everything seemed good.... for a while. After a recent periodic test, the voltage started pegging the gage high yet again, a few seconds to 1 minute after startup. I narrowed the problem down to the VR board by swapping control cubes, then swapping just the vR board. So... after reading lots of threads about high output voltage, I found a pair of NOS mil-spec Q3 transistors on ebay for cheap. Replace Q3, fired it up and dang... voltage goes high again
![Banging Head aua aua](https://www.steelsoldiers.com/images/smilies/icon_smile_banghead_125.gif)
If all goes well we can add "defective R15" to the list of potential causes of high output voltage on MEP-002A, 003A machines. For the sake of <$10 I'll probably order up a new potentiometer just in case this one flakes out again. To those that I haven't put to sleep yet, thanks for reading!