MEP-003A Rectifier Board Burn Up

[screejunk]

Starting a new thread for this issue.

Hello, we have a similar issue with rectifier board burning up, including a new one We have installed a new master switch and we have checked the diodes. Our tech, who is amazing, is still scratching his head... Is anyone aware of other points of failure to check to prevent the rectifier board from burning up? Any help is much appreciated. THANKS

We did check this useful information:

There are 2 diodes in the A1 assembly, which is located in the control box, where the gauges are located (upper right corner). These 2 diodes, control the current to the rectifier board. If they fail, current will continue to back feed to the board and burn the resistor. It took me 3 weeks to figure it out. The diodes are between A1-5 and A1-6 ; then A1-7 and A1-8. If you take those wires off and test between them you can check the diodes without taking the panel completely out. The diodes are tucked behind where you can't see them. Also this will cause the starter lockout not to function and your starter will stay engaged without ever letting go, burning the starter up.

We also installed new master switch.

Just wondering if there are other issues that can cause the resister to burn up. We are using the new Klopp version of the board and he has been very helpful.
THANKS

 

[Guyfang]

Kurt and I talked about this, shortly.

1. You changed the old one out because it was also burnt?
2. You are 1000% sure you wired it right?
3. Did you ever see the set work right?
4. Have you, (or someone else) made any other repairs on the set of late.
5. Have you pulled the AC output box off the set and compleatly checked every wire and connection? Looked for mice crap and chewed wires? Worn wires?
6. Inspected every component to make sure that nothing is damaged?
7. The master switch should have nothing to do with it, but to exclude it, you have checked that its correctly wired? If it were me, I would just unscrew all the wires and re-hook them up, being very, very careful to make sure its right.
8.Have you checked the VR? All the wires on it. It can be hooked up wrong. I know all about that! Is it a Military VR? or an aftermarket VR?

 

[tmoody]

Did you get your unit running by changing the 2 Diodes on A1 Assembly? My original rectifier burn up, bought new Klopp Version, it made power a few seconds & burned up the resistor on the new board. Looking for any updates. Thanks

 

[cstumpf750]

I would test the windings in the generator head. Sounds like you have a short in it that is blowing the rectifier diodes.

 

[Guyfang]

Did you get your unit running by changing the 2 Diodes on A1 Assembly? My original rectifier burn up, bought new Klopp Version, it made power a few seconds & burned up the resistor on the new board. Looking for any updates. Thanks

What you should do is start your own thread. This one is two years old and never completed anyway.

 

[tmoody]

So noted cstumpf750, thx

 

[Triple Jim]

Is the start disconnect switch working properly?

 

[tmoody]

I believe it is Jim, in the weeks leading up to the issue all was working well with cranking/shutting down. Physically, the switch feels good like it is supposed to; not to say something could be going on electronically in the switch. I have a good fried that is very experienced in electrical field, I am sure we can test that. Also cstumpf 750 mentioned testing the windings. I have a new resistor coming from Kurt for the new board & I located the 2 diodes mentioned in the A1 assembly. None were not very expensive to change (Will save the original for spares if they test good). If I find the root cause of the issue, I will be sure to post for others. Thx All who replied so far. Terry

 

[Ray70]

I believe Jim was talking about the centrifugal disconnect switch located under the little tin cover ( held on with a small wing nut ) to the right of the oil filter.
This is the mechanism that disconnects power from the starter motor whenever the motor is spinning more than ~600 RPM.
This is what allows you to continue holding the main switch in the crank position after the motor is running ( while waiting for oil pressure to build ) without grinding the starter motor.

 

[tmoody]

Ray70, Thank you for the clarification, I got the repair manual out last night to study it. I looked this morning & see the cover you mentioned (Tiny Pic attached). I have not noticed this before but I’m on it now!! Makes perfect sense that could cause something to burn out. It will take a little time for me to follow this through but I will 100% check & report back.

 

[Ray70]

That's the one! Its very easy to test / verify.
When you start the machine, if you have the old style starter with the external linkage for the bexdix, when the engine first starts, watch the linkage while you continue to hold S1 in the crank position. You should see the starter gear disengage even though you are still "cranking" the engine.
You should also be able to turn S1 to the crank position at any point while the machine is running and the starter should not engage if the S7 starter disconnect switch is functioning properly.
If you find that it does not disengage properly the adjustment procedure is pretty simple.

 

[tmoody]

Ray70, Very good instruction! I have not ran across this in the manual, yet….. I printed your notes, will check it out & add to my tech book.
Awesome info, thx.

 

[Guyfang]

Its in the -34 TM. If you need help, say something.

 

[tmoody]

I do have the old style starter, the linkage disengaged as it was supposed to. After it was running, I turned the switch to start again, the linkage didn’t move. Apparently that part is working as it should. Glad we were able to mark that off the list. Thank you for the Pro tip.

 

[tmoody]

Hello all, last week I took the generator to someone who knows how to work on them and left it. It will be several months to go get it due to the distance but I will let you guys know the result. You tried to help and I appreciate that, this issue is above my abilities but I can pay someone who is capable. Thx

 

[kloppk]

Hello all, last week I took the generator to someone who knows how to work on them and left it...

I assume to J... in Tennessee. Really smart 002/003 gent.

 

[tmoody]

Follow up… I went & picked up the “working generator” this past weekend. A critical point I did not mention was this set was originally a 400Hz converted to 60Hz by Jimmy in TN. I didn’t’t mention this because it was working good (It was a 003 now). Apparently one wire was overlooked, it should have been disconnected from the A4 board that burned out, I believe it was a ground. I‘m guessing since it’s not something done every day, it was missed, I have overlooked things many times so not a big deal, I’m glad to have it fixed and have an understanding of what the problem was.
It took nearly a year because there was no particular rush and I left him alone till he was ready; I hope this helps someone.

 

[jamawieb]

Follow up… I went & picked up the “working generator” this past weekend. A critical point I did not mention was this set was originally a 400Hz converted to 60Hz by Jimmy in TN. I didn’t’t mention this because it was working good (It was a 003 now). Apparently one wire was overlooked, it should have been disconnected from the A4 board that burned out, I believe it was a ground. I‘m guessing since it’s not something done every day, it was missed, I have overlooked things many times so not a big deal, I’m glad to have it fixed and have an understanding of what the problem was.
It took nearly a year because there was no particular rush and I left him alone till he was ready; I hope this helps someone.

So this was a very weird situation we ran across. When I first got the unit it was a 400hz so we swapped out the gen head, output box and several pieces in the control cubicle and worked perfect. Then after a long while it burned the resistor on the excitor board. Tmoody replaced the board with an updated verison of Klopps and burned it again. Thats when I got it back. Replaced the resistor and burned again so I replaced the output box and and it burned up that one too. So I had to wait till I got another 003 in to replace the control cubicle. That fixed it. So I started testing everything in the control cubicle and it tested perfect. Then I was reviewing the wiring schematics and realized the 400hz has a different ground connection for the the negative on the excitor board which connects directly to the negative of the resistor. I swapped the wires in the control cubicle to memoc the 003a and it worked. On the 400hz it contects directly to ground and the 60hz connects to tb connection before the starter disconnect.

 

[Ray70]

Glad to hear you figured out the problem, sorry you ended up smoking a few parts in the process!

 

[BeStihl]

I was looking at some pictures from inside an A1 AVR from a 813 (400hz) and noticed the ground scheme looks different than that on my 803 AVR. Good find.