MEP-804A Troubleshooting output voltage

[Landshark_3]

Background
This is a MEP-804A that I don't know much history about. We recently purchased it as a running machine with the AC interrupter bypassed. It started and ran fine and the output frequency and voltage were correct and adjustable. It was connected for low voltage. I replaced the AC interrupter and wired everything back up like it should be. Everything seemed fine the new AC interrupter worked and the output voltage and Hz were correct at the terminal board. I ran it for a couple hours with no load just to make sure everything seemed to work. We started it and watched it run where we bought it, but never saw a load applied to it just did basic voltage and Hz testing on site.

Changes Made
After replacing the output interrupter and feeling confident that it was gonna run ok, I switched to high voltage. Nothing was changed other than the plate was moved to the HV output location. I fired it up checked the voltage and Hz all seemed well. I ran it for a little while and felt confident all was good. It was started and shut down multiple times at both the high and low voltage setting.

Current
I went to load test the unit a couple days later. I fired the generator up it starts and runs fine, but I get no output voltage. I noticed that when you hold the Master Switch in the Start position the volt meter and Hz meter come up and show the correct values. As soon as you let off the switch in the run position you lose the output voltage. You can rotate the switch back to the start position and the voltage comes back. The convenience outlet follows the same, it only shows voltage only when in the start position not the run position. I am getting the under voltage alarm, with the Master Switch in the start position you are able to clear it.


I don't have any service manuals or documentation on the machine. Can someone point me to where to find troubleshooting material. And even better yet does anyone have any suggestions on what it might be? I am very experienced in electrical troubleshooting, but this is my first generator of this type to work on.


Thank You

Kevin

 

[kloppk]

The Technical Manuals for the 804A are available for downloading from here---> 804A TMs
Sounds like the VR or some other part of the VR syatem may have died.
Do the AC VR tests called out in the -24 TM and post up the results of your measurements of each test step.
The 804s used two different AC Voltage Regulator systems. Libby vs TRC. Be sure to use the correct test in the -24 TM

 

[Landshark_3]

Ok this is the first time since I posted that I have been able to get back to the post. I found all the manuals the night I made the post thanks for the link. I am having trouble finding the -24TM ACVR test procedure that you called out. I have looked thru all of the manuals I downloaded but dont see it.
It is a TRC regulator and I have a spare in a parts machine. Thank you for you help.

 

[kloppk]

See TM 9-6115-643-24 see section 4.1
The AC Voltage Regulation system is comprised of:
- AC Voltage Regulator
- Transformer T1
- Resistor R16
- Front Panel Voltage Adjust potentiometer

Those 4 parts are unique and different for a TRC vs Libby system.

Since you have TRC VR you would use 4-1.2 for testing the 01-21501-2 (TRC) Regulator.

Post up the reading for each of the test steps so we can hopefully determine the issue.

 

[Landshark_3]

Ok thank you. I had found that procedure 4.1.2 and 4.1.3 for the 2 different regulators. For the 4.1.2 it calls out Regulator PIN 19870 and for 4.1.3 it calls out Regulator 19890-001. I know you told me to use the 4.1.2 and gave me a part number for the regulator. How would I have determined which was which on my own? Thats what I was working on when you replied which procedure applied to the TRC regulator. I am trying to find my way thru the manuals on my own, I an finding info but having a hard time confirming its the correct info. I will do the tests and reply it probably wont be today wind chill here is 15 and the generator is outside.

I also printed out he 30 pages of the schematics. The page that shows the A1 VR connections does not specify one VR or the other. Does that mean they both have the same terminal connections and wire numbers? I was thinking that I would find 2 different schematics for the 2 different part numbers. I know they are not interchangable, but this leads me to believe they wire in the same.

Thank you for all your help

 

[kloppk]

I was looking at a different revision of the TM. Sorry for the confusion.

122-3054 is the Libby VR
19870 is the TRC VR

To determine it on your own you'd need to open the -24P TM and find the VR part numbers and the corresponding NSN number.


Then go to the website Parttarget.com and put the NSN in the websites search bar
Scroll down the page to see this.


Yes, the wiring in the generator is the same regardless of which VR system is used.

 

[Landshark_3]

I performed the tests in 4.1.2 for the TRC VR. I did find one very rookie mistake. I had failed to check the fuse next to the regulator, it was blown, it is a KLK 3A fuse. I assume that it is F1 since that is the only one I saw in a quick glance of the schematics. After replacing the fuse I started the generator it was already at operating temperature. I now have little to no control over HZ before with the blown fuse when the Master Switch was in the Start position I had normal HZ and very little adjustment. With a good fuse in there the HZ is at the upper end of the scale and I get an overspeed alarm. I also have no adjustment of the HZ.

Per 4.1.2
Step H Basically 0 Vdc it reads 0.004 I consider that 0.

Step J 144.2 Vac

Step L on a 400ohm scale it reads 5.5 ohm on the low end and full scale is 28.48K ohm on a 40K ohm scale.

All readings were taken with a FLuke 87 True RMS meter with a lead resistance of 0.2 Ohm.

Thank You

Kevin

 

[Guyfang]

In the NEW schematics, the Fuse is F2.

 

[Landshark_3]

In the NEW schematics, the Fuse is F2.

Where would I find the new schematics? The ones I have are downloaded from here. File names 15KW TQG Schematics and 15KW TQG Colored Schematics. Both only reference 1 fuse.