MEP 003A Unstable Voltage

[cuad4u]

I have a MEP 003A that the output voltage is not stable. Most times when started the voltage is 120/240 as it should be. Occasionally when started the voltage goes to 150/300 and stays there. When I shut the generator down and restart it sometimes the voltage goes right back to 300+ and sometimes is goes to 120/240. When output is 120/240 the voltage is stable regardless of load and the voltage adjust "pot" adjusts from around 210-260 as it should. When the voltage is 150/300 the voltage adjust "pot" will adjust voltage from around 280-320. I have cleaned and tested all grounds. I loosened and retightened all connections on the voltage regulator board. I have replaced T2. The voltage adjust "pot" reads from 0-1000 ohms as it should. The voltage regulator board "looks" OK. There is no goo coming out of the caps and nothing looks burned. I do not have a spare voltage regulator board. If I did I would swap it out. Intermittent problems are (for me) the hardest to find and fix. Does anybody have any suggestions? Thanks............

 

[DieselAddict]

One thing I would suggest is to exercise the pots on the VR board. Be sure to mark the position of the pots before you start. Move them back and forth a bit to clean their contacts. At least one other user here has indicated that solved instability issues.

My VR is a bit unstable when its cold outside. I'm going to swing the pots around a bit to clean them when I get down to it on my ToDo list.

 

[Isaac-1]

I had a similar intermittent problem on my MEP-002a, ended up swapping out the AVR board since then it has been rock solid.

 

[Triple Jim]

When output is 120/240 the voltage is stable regardless of load and the voltage adjust "pot" adjusts from around 210-260 as it should. When the voltage is 150/300 the voltage adjust "pot" will adjust voltage from around 280-320.

Good clue here. Since the range of the front panel pot changes during the problem, it would seem the pot itself is not causing it. The suggestion of cleaning the voltage adjust pot on the regulator board is a good one. Maybe just replace it. Have you tried tapping on various components of the regulator board with something like a screwdriver handle while the generator is running, to see if you can make the problem come and go?

 

[Ray70]

Exactly what everyone else said.... Mine was doing the same thing and I found the 1K pot on the VR to be intermittent. Some times a few turns in either direction will clear it up, otherwise I found a replacement on ebay, just verify the length before you buy. Almost all are .75" long. The one you need is 1.25"

 

[Triple Jim]

...just verify the length before you buy. Almost all are .75" long. The one you need is 1.25"

No doubt that if you want an exact replacement you need to check the dimensions. But if you're a little handy, you can drill new holes in the board and solder in a pot of different dimensions. That's what I did to repair one original regulator I worked on. If you do it right, the now holes will still be on the traces, so soldering is easy. If you goof and miss the traces, you can point-to-point wire the pins anyway.

Also, at least some original regulator boards have holes for two different pot shapes, so that gives you some flexibility too.

 

[glcaines]

I had exactly the same problem - verbatim. I replaced the transistor on the VR board and it fixed my problem. I suspected the pot as well, but it turned out to be the transistor. I can't take credit since Speddmon is the one that pointed me in the right direction. The key is never idle the genset. Start and stop it when it is reading 60 Hz. I've since bought a second VR board as a spare, but tested it first before putting it aside.

 

[cuad4u]

Thanks for all the replies and suggestions. I "exercised" the two multi-turn pots on the VR board. That did not help. Earlier today I ordered a couple of VR output transistors Q3 from Mouser. When they arrive I will replace Q3. Hopefully that solves the problem. If not I will replace the VR board with one offered by one of the regulars on this site.

 

[cuad4u]

It was the VR board. I removed a working VR board from my personal 002A and installed it in the 003A I bought at a GSA auction that I am refurbishing to sell. I hope the VR boards in the 002A and the 003A are the same. Voila! The voltage comes right up to 120/240 each time the generator is started and it stays there. I load tested the 003A at 10KW for over an hour this afternoon with no problems. Since the defective VR board does not show any burned components or any goo coming out of the caps and the diodes check OK in the circuit, I assume the problem must be Q3. I ordered a couple of Q3 transistors from Mouser earlier today. When they arrive I will replace Q3 and hope that gets the original VR board working again.

 

[Isaac-1]

The boards are not the same, or may not be, the original MEP-002a board will burn out if used in a MEP-003a, but a MEP-003a board can be used in MEP-002a. It also appear that the 10KW 400 hz version of the board may be able to be used in a MEP-002a

 

[cuad4u]

Thanks Isaac-1. As soon as the Q3 transistors arrive from Mouser, I will swap out Q3 with a new one and see if the old VR board works. Of course to test it I will have to reinstall it in the 003A I took it out of. This is one of the generators I am refurbishing. Of course if the repaired VR board works I will leave it in the 003A. Since I have several 002A and 003A generators I am refurbishing for sale, I plan to check a 002A VR board against a 003A VR board side by side on my "bench" to see if I can detect any difference in components or in component values or ratings between the two. I will report my findings between the two VR boards. Thanks again.

 

[Triple Jim]

The boards are not the same, or may not be, the original MEP-002a board will burn out if used in a MEP-003a, but a MEP-003a board can be used in MEP-002a. It also appear that the 10KW 400 hz version of the board may be able to be used in a MEP-002a

Ike, the parts manual that I have for the 002A lists 72-5020 and 72-5338 as the two AC regulators that were used. Both are configurable with jumpers for 60 Hz and 400 Hz. These are the same as the ones used in the 003A. Were there others?

 

[cuad4u]

I just checked a VR that came out of a 002A and a VR that came out of a 003A. There is no difference in the number of components. All resistors are the same value and the same wattage. Ditto for the capacitor values and voltage ratings. The 3 transistors are the same. There may be a difference but I cannot tell from a close examination. Earlier today I picked up two "almost new" 003A generators from a GSA depot. While checking them over the next few days before I offer them for sale, I will examine the VR's in them to see if I can find any difference between them and those in the 002A's I have. Thanks for all the help.

 

[jamawieb]

Yes, they are both the same. I've swapped around 002a to 003a VR boards and vis versa several times. They have nothing to do with the KW rating, they only control voltage via hertz.

 

[Triple Jim]

There are some small differences between the 72-5020 board and the 72-5338 board, but it's things like resistor power ratings which don't really change anything operationally. Those numbers are silk screened onto the boards.