MEP-804A No AC power when start switch is released.

[Guyfang]

Open the control panel door.
Look for a panel inside where you see the Battery Charging fuse and Frequency select switch, among other things. Unscrew the bracket.
Behind the bracket, is the R16.

 

[defenba]

I never personally saw it work, but my neighbour said that they were using it and it worked fine when they parked it. 1/2 a year later when they went to use it again, it didn't work.

I have the Libby regulator
model #122-3054
PN- 30554SOCN88-22560

I'm trying to determine if I have the correct parts. Having a little trouble with it.
Volt adjust rheostat- Don't see a PN that matches, but based on my testing, appears to be 10k ohms
R16 resistor- Was not able to determine where this is?
Transformer- Is correct

Curious to hear if replacing the A1 fixed the problem for you or not. I has a similar issue as the set was runining and outputing fine then when removing some of the load ( turned off some lights ) the set stopped outputting volatage and shut down. I can get it to start and output voltage as long as i hold S1 in the crank position. It dies( engine shuts down) as soon as the S1 is released into the run position. My am-vm switch knob is broken and i cannot test all positions on it. I will start with repacing it with a spare i have but still curious that it just died and will noy stay running anymore.

 

[kloppk]

When shuts down are any of the Fault lamps illuminated?

 

[defenba]

When shuts down are any of the Fault lamps illuminated?

Not that i saw. I will double check today when i change the am-vm switch.

 

[defenba]

Not that i saw. I will double check today when i change the am-vm switch.

Swapped out the am/vm switch and fires up and outputs great until the start switch is released to run and then sets undervolt light and quits outputing a/c voltage. When looking at the diagram the #7 pole on the S1 for crank circuit gives power to the #1 pole during crank for k22-1 (only have k22 listed on schematic for glow plugs) not sure was the -1 is. However if i jumper the #3 &#7 post on the S1 it will crank as soon as put into any run position and output voltage normally.

Just trying to get this old girl working for a jobsite my company has.

Thanks for the help.

 

[loosegravel]

I recently had a similar problem with an 804A unit. I had some expert help from a member on this forum. It may be a good idea to follow the TM below and properly check your A5 a/c voltage regulator. Write down your results from each step so you can post them here. A big shout out to this fantastic forum for helping me through that process! FYI…there are two different A5 a/c voltage regulators on these units. You will need to identify which system you have. It would be a good idea to take a picture of your voltage regulator and post it here. Others will chime in to help you along. Good luck! Jeff


TM Test Procedure for Libby VR..


4-1.1 Testing (AC Voltage Regulator, P/N 01-21501-1, for MEP-804A/MEP-804B).
a. Shut down generator set.
b. Open output box access door.
c. Note position of voltage reconnection terminal board and set FREQUENCY SELECT switch to 60
Hz position.
d. Start generator set and turn VOLTAGE adjust potentiometer to ensure adjustment ranges on
Table 4-1 are met, depending on position of voltage reconnection terminal board.
e. Shut down generator set.
f. If no voltage or low voltage was indicated or voltage adjustment range could not be achieved,
perform the following steps. Otherwise, AC voltage regulator (2, Figure 4-1) is serviceable.
g. Disconnect wire 141A from terminal 1 of AC voltage regulator.
h. Set multimeter for DC volts and connect positive lead to wire 141A. Connect negative lead of
multimeter to terminal 3 of AC voltage regulator. Start generator set and operate at rated
frequency. Move and hold MASTER SWITCH in START position. Multimeter should indicate
between 4 and 12 VDC.
i. Shut down generator set. Isolate wire 141A.
j. Set multimeter for AC volts and connect to terminals 10 and 11 of AC voltage regulator. Start
generator set and operate at rated frequency. Move and hold MASTER SWITCH in START
position. Multimeter should indicate 210 to 280 VAC.
k. Shut down generator set.
l. Disconnect wire 137A from terminal 5 of AC voltage regulator. Set multimeter for ohms and
connect positive lead to wire 137A and negative lead to terminal 4 of AC voltage regulator. Move
VOLTAGE adjust potentiometer to full counterclockwise (CCW) position. Multimeter should
indicate approximately 3,000 ohms with FREQUENCY SELECT switch in 60 Hz position, and
approximately 0 ohms with FREQUENCY SELECT switch in 50 Hz position. Move VOLTAGE
adjust potentiometer slowly clockwise (CW) while observing multimeter. Multimeter should
increase smoothly to approximately 10,000 ohms.
m. If steps h, j, and l are as indicated above, AC voltage regulator is defective and must be replaced.
n. Connect all wires previously disconnected. Close output box access door.

 

[defenba]

I recently had a similar problem with an 804A unit. I had some expert help from a member on this forum. It may be a good idea to follow the TM below and properly check your A5 a/c voltage regulator. Write down your results from each step so you can post them here. A big shout out to this fantastic forum for helping me through that process! FYI…there are two different A5 a/c voltage regulators on these units. You will need to identify which system you have. It would be a good idea to take a picture of your voltage regulator and post it here. Others will chime in to help you along. Good luck! Jeff


TM Test Procedure for Libby VR..


4-1.1 Testing (AC Voltage Regulator, P/N 01-21501-1, for MEP-804A/MEP-804B).
a. Shut down generator set.
b. Open output box access door.
c. Note position of voltage reconnection terminal board and set FREQUENCY SELECT switch to 60
Hz position.
d. Start generator set and turn VOLTAGE adjust potentiometer to ensure adjustment ranges on
Table 4-1 are met, depending on position of voltage reconnection terminal board.
e. Shut down generator set.
f. If no voltage or low voltage was indicated or voltage adjustment range could not be achieved,
perform the following steps. Otherwise, AC voltage regulator (2, Figure 4-1) is serviceable.
g. Disconnect wire 141A from terminal 1 of AC voltage regulator.
h. Set multimeter for DC volts and connect positive lead to wire 141A. Connect negative lead of
multimeter to terminal 3 of AC voltage regulator. Start generator set and operate at rated
frequency. Move and hold MASTER SWITCH in START position. Multimeter should indicate
between 4 and 12 VDC.
i. Shut down generator set. Isolate wire 141A.
j. Set multimeter for AC volts and connect to terminals 10 and 11 of AC voltage regulator. Start
generator set and operate at rated frequency. Move and hold MASTER SWITCH in START
position. Multimeter should indicate 210 to 280 VAC.
k. Shut down generator set.
l. Disconnect wire 137A from terminal 5 of AC voltage regulator. Set multimeter for ohms and
connect positive lead to wire 137A and negative lead to terminal 4 of AC voltage regulator. Move
VOLTAGE adjust potentiometer to full counterclockwise (CCW) position. Multimeter should
indicate approximately 3,000 ohms with FREQUENCY SELECT switch in 60 Hz position, and
approximately 0 ohms with FREQUENCY SELECT switch in 50 Hz position. Move VOLTAGE
adjust potentiometer slowly clockwise (CW) while observing multimeter. Multimeter should
increase smoothly to approximately 10,000 ohms.
m. If steps h, j, and l are as indicated above, AC voltage regulator is defective and must be replaced.
n. Connect all wires previously disconnected. Close output box access door.

Thanks. I will do those tests tomorrow. I have 2 sets which has let me swap switches back and forth for testing. Unfortunattly the have different VR systems and the older of the 2 ( the running one that is at the job site) is the one giving me trouble.

I appreciate the help!

 

[loosegravel]

Thanks. I will do those tests tomorrow. I have 2 sets which has let me swap switches back and forth for testing. Unfortunattly the have different VR systems and the older of the 2 ( the running one that is at the job site) is the one giving me trouble.

I appreciate the help!

Glad to give you what I’ve learned. I miss-labeled the a/c voltage regulator though. It’s actually component A1, not A5 as I referred to above. Sorry!

 

[loosegravel]

Glad to give you what I’ve learned. I miss-labeled the a/c voltage regulator though. It’s actually component A1, not A5 as I referred to above. Sorry!

One other thing that’s worth mentioning here. If you’re dealing with a Libby VR, then the tests above will apply to your unit. If you’re dealing with a Technology Research VR then I believe there’s a different test procedure in the TM.

 

[kloppk]

Jumpering those two terminals is connecting the RUN circuit to the START circuit. So, when S1 is in any run position the START circuit is continually energized. When this happens the field Flashing function is also continually on supplying flashing voltage to the exciter causing the generator to "make power". During this the AC Voltage Regulator is not actively regulating the AC output.
Do not continue to run the generator with the jumper.
Most likely the VR is bad. Perform the appropriate VR test per the TM and post up the results of each measurement.