MEP-003A STABLE THEN UNSTABLE VOLTAGE

[Dhmarkley]

I have had this Genny for awhile now and it used to work perfect until about a month ago when all of a sudden it started over volting out of the blue. When you first start it it normally puts out 120/240, then in about 2 to 3 minutes it starts acting up. Now today I had it running with just my VM hooked up and it started wildly ranging voltage as it was running. I have the TMs from the site and have looked through them but honestly I don't know where to start. Also I have field flashed the unit by turning the start switch back to start for a few seconds and it has been hit or miss. Sometime it will work for awhile and the next time is doesn't work at all. Any pointers to a direction to follow would be much appreciated.

Thanks in advance.
Derek

Here is a link to some videos of it running.

Running videos - Google Drive

drive.google.com

 

[DieselAddict]

Start by cleaning all your switches with deoxit. Including the POTs on the VR board.

My 003 would start out flaky and smooth out after warming up. It was the POTs on the VR board causing the problem.

 

[Dhmarkley]

I did use contact cleaner on everything in the control housing and cleaned each terminal one by one on the VR. I'll get some of that deoxit and try it again. Everything looks fairly clean for the age surprisingly.

 

[DieselAddict]

Did you clean the actual adjustment pots on the VR board?

You have to make sure you set them back to where they were when you started.

 

[Dhmarkley]

Did you clean the actual adjustment pots on the VR board?

You have to make sure you set them back to where they were when you started.

The way I cleaned the pots was to spray them with contact cleaner and rotate them back and forth. They should be back close to where they were originally.

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[glcaines]

Also I have field flashed the unit by turning the start switch back to start for a few seconds and it has been hit or miss. Sometime it will work for awhile and the next time is doesn't work at all. Any pointers to a direction to follow would be much appreciated.

Thanks in advance.
Derek

Here is a link to some videos of it running.

Running videos - Google Drive

drive.google.com

When starting the unit, you should leave the start switch in the start position until the oil pressure is up and the field is flashed. I usually hold mine in the start position for about 15-20 seconds. Mine flashes 100% of the time.

 

[Dhmarkley]

When starting the unit, you should leave the start switch in the start position until the oil pressure is up and the field is flashed. I usually hold mine in the start position for about 15-20 seconds. Mine flashes 100% of the time.

I do that Everytime. Here lately(since I started having the issue) I have even been giving her an extra 10 seconds but it doesn't seem to make a difference. Is it possible for it to "loose" flash while it's running?

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[Guyfang]

Field Flash, better known as Excititation, is two separate functions. The initial Excititation is with the S2. When you release the S2, the A1 volt regulator is supposed to take over this funtion. So if the set produces the right voltage durring the start sequence, and continues to do so as long as S2 is in the start position, then you know the Excitor coil, rotor, and diodes are good. If the power falls off after releasing the S2, then the A1 and other componets in the AC portion of the set need to be checked. I would start with the A1.

 

[dependable]

I had one that was behaving simialrly and it turned out to be a loose cannon plug from output to control box.

 

[Dhmarkley]

Field Flash, better known as Excititation, is two separate functions. The initial Excititation is with the S2. When you release the S2, the A1 volt regulator is supposed to take over this funtion. So if the set produces the right voltage durring the start sequence, and continues to do so as long as S2 is in the start position, then you know the Excitor coil, rotor, and diodes are good. If the power falls off after releasing the S2, then the A1 and other componets in the AC portion of the set need to be checked. I would start with the A1.

I think you nailed it, or at least it makes sense to me. I just remembered that when I first got the Genny the fuse was blown on the back side of the front air box. I replaced it and it has been fine (not blown) ever since. Is there a way to test it to see if one of the components are going bad? And if it is the A1 where do you source your parts?

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[Guyfang]

Read the test procedures in the -34 TM. If the A1 is bad, a member here, TRIPPLE JIM sells a volt reg card to replace the old style cards. Its not a bank buster, and I have NEVER heard anyone complain about it.

The fuse you wrote about was for the 24 volt battery charging circuit.

 

[Chainbreaker]

I have had this Genny for awhile now and it used to work perfect until about a month ago when all of a sudden it started over volting out of the blue. When you first start it it normally puts out 120/240, then in about 2 to 3 minutes it starts acting up. Now today I had it running with just my VM hooked up and it started wildly ranging voltage as it was running.

I had a similar experience on my MEP-002a with AC voltage going high and then returning to normal. It turned out to be a broken winding wire in one of the transformers inside the control box. Off the top of my head I can't remember exactly which one it was but it was either the T1 or T2 transformer. The transformer winding wire beneath the craft paper that is soldered to the screw tab for the wiring harness connection had broken near the screw terminal tab (vibration) and became intermittent until it failed completely with voltage high. I only found it by using one of the test procedures as was suggested by Triple Jim using an ohm meter. Since these transformers are part of the voltage regulation circuit they should be checked among other TM tests for the VR circuit.

I found this in my notes out of TM:

HIGH GENERATOR OUTPUT VOLTAGE (NO LOAD).
Step 1. Check for voltage regulator failure. Remove voltage regulator lead (wire 39C16) from terminal 17. If voltage goes even higher, the voltage regulator is good.
Test and repair defective regulator (paragraph 6-6),
Step 2. Check voltage adjust rheostat (R1).
Replace rheostat (R1) if necessary.
Step 3. Check current voltage transformer (CUTI) (paragraph 6-9b(7)).
Replace bad transformer.
Step 4. Check transformer T2 (paragraph 4-38( 15), TM 5-6115-584-12).
Replace bad transformer.

 

[Dhmarkley]

I had a similar experience on my MEP-002a with AC voltage going high and then returning to normal. It turned out to be a broken winding wire in one of the transformers inside the control box. Off the top of my head I can't remember exactly which one it was but it was either the T1 or T2 transformer. The transformer winding wire beneath the craft paper that is soldered to the screw tab for the wiring harness connection had broken near the screw terminal tab (vibration) and became intermittent until it failed completely with voltage high. I only found it by using one of the test procedures as was suggested by Triple Jim using an ohm meter. Since these transformers are part of the voltage regulation circuit they should be checked among other TM tests for the VR circuit.

I found this in my notes out of TM:

HIGH GENERATOR OUTPUT VOLTAGE (NO LOAD).
Step 1. Check for voltage regulator failure. Remove voltage regulator lead (wire 39C16) from terminal 17. If voltage goes even higher, the voltage regulator is good.
Test and repair defective regulator (paragraph 6-6),
Step 2. Check voltage adjust rheostat (R1).
Replace rheostat (R1) if necessary.
Step 3. Check current voltage transformer (CUTI) (paragraph 6-9b(7)).
Replace bad transformer.
Step 4. Check transformer T2 (paragraph 4-38( 15), TM 5-6115-584-12).
Replace bad transformer.

Thanks! I will give that a shot tomorrow.

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