MEP-804b no voltage/hz issue

$775 direct from TRC for the kit which includes the VR, potentiometer, and transformer.

Billy,

Thanks that is better then what I found. I found just the voltage regulator. Did it fix your issue?

I have t even had a chance to work on that specific machine yet. I've sold over 60 machines this year and I only do it as a side gig (I'm active duty Army). Hopefully with this long weekend I'll get a chance to work on it

Cool, I’m hoping it will cure my problem.

If no one has any objections, I'd like to jump in with a similar problem. 2009 MEP-804B. Upon start up, Under Voltage alarm indicated on Malfunction Indicator Panel. I am able to reset the alarm and it does not reoccur. At this point, the generator runs fine and all outputs check good. I am able to adjust output voltages up or down and can verify the change with the DMM. Also, adjusting frequency up/down corresponds to an increase or decrease in engine RPM. Output waveforms look good on the O-scope. Generator runs fine while under load test alarm free. This alarm occurs on every start up. Any flow chart or schematic guidance would be greatly appreciated. Merci'.

Are you holding the S1 in the start position long enough? This is a very common fault.

When you try and start it, and get the fault, what readings do you have on the meter?

After starting, and you get the fault, have you simply tried pushing S1 back up into the start position, WITHOUT resetting the fault? If so, what happened?

Guyfang said:

Are you holding the S1 in the start position long enough? This is a very common fault.

When you try and start it, and get the fault, what readings do you have on the meter?

After starting, and you get the fault, have you simply tried pushing S1 back up into the start position, WITHOUT resetting the fault? If so, what happened?

Click to expand...

Thank you. I will take note of these two items on the next start up.

MEP 8904b

Guyfang said:

Concentrate on getting Excitation. If your S-1 is bad, the exciter will not send voltage to the Main Alternator. Are you guys able to use the schematics? Or, better asked, do you have the schematics? If so, follow the path from the S-1 to the exciter.

Click to expand...

Guy,

Did run your test and looks like I need a new Rotary switch. Haven't been able to find one anywhere online. Do you have any ideas where I might fine one ?

Jack

Moreso on the older sets like 002s and 003s, not as much on the 80x series but worth checking. It seems like the rotary switches need to be exercised and cleaned sometimes. Get a can of DeOxit from ebay (tuner cleaner may work if it is still made), douch it real good into every crevice/hole while working it (like 50 times) without forcing it if it resists and sometimes it cleans and lubricates the contacts. Don’t take it apart unless you really like puzzles and have a photographic memory (or took lots of pictures) and have 4 tiny hands and can locate things when it shoots across the room. I took a similar switch apart from a militay American Kleaner hotsy type washer and actually got it back together. I took another one apart and it is still in a can in a million parts. WD40 also seemed to lubricate the action. Do the other two rotary switches on the panel while you are at it but don’t be a gorilla. Yes, sometimes the switches do break but try this first, you may get lucky. The 80x (at least 804a,b have that door that swings down providing protection as long as the previous idiot left it down and not up.

Robert

Jack,

Take a picture of the S1. There are 3 different types. MK 1&2 switches were not very reliable. They were made from plastic and were open to dust intrusion. The MK 3 was sealed, and I have NEVER seen or heard of one failing.

Try looking these numbers up in a auction web site.
Part number: 75902LV, NSN: 5930-01-531-2976

MEP 8904b

Guyfang said:

Jack,

Take a picture of the S1. There are 3 different types. MK 1&2 switches were not very reliable. They were made from plastic and were open to dust intrusion. The MK 3 was sealed, and I have NEVER seen or heard of one failing.

Try looking these numbers up in a auction web site.
Part number: 75902LV, NSN: 5930-01-531-2976

Click to expand...

Mine has the blue outer cover

Talk with the friendly folks at Electroswitch for a 75902LV: https://www.steelsoldiers.com/showt...2A-803A-S1-Master-Switch-Source-Electroswitch

Jackcdubose said:

Mine has the blue outer cover

Click to expand...

Then you have a MK 1 or 2. The switches were not as reliable as expected, and the Army went to the MK3, 75902LV switch.

Guyfang said:

Concentrate on getting Excitation. If your S-1 is bad, the exciter will not send voltage to the Main Alternator. Are you guys able to use the schematics? Or, better asked, do you have the schematics? If so, follow the path from the S-1 to the exciter.

Click to expand...

Hello, what is S-1?

Guyfang said:

Concentrate on getting Excitation. If your S-1 is bad, the exciter will not send voltage to the Main Alternator. Are you guys able to use the schematics? Or, better asked, do you have the schematics? If so, follow the path from the S-1 to the exciter.

Click to expand...

S1 is the engine control switch 1?

Check the TM for your machine. Operator's manual will describe all the nomenclature. Also, S1 may be labeled on the back of your control panel cover....mine is on my 803

Zed254 said:

Check the TM for your machine. Operator's manual will describe all the nomenclature. Also, S1 may be labeled on the back of your control panel cover....mine is on my 803

Click to expand...

Yes it's the start switch.
You also have schematics on the gen set door, for quick referance.
Yes S1 is labeled on the back of every control panel, on every gen set I have ever seen.

Might be a good idea to start your thread, if you want max help in the forum. That way we do not have to tell 2-3 different folks on the same thread what to check.

Would also suggest reading the TM's. They can be downloaded here in SS TM section.