MEP-831A High Temp Alarm.

[captain]

I have a mep-831a that was a reset unit and I have done a lot of work on it to get it running. Eventually, it ran fine. I ran it at 3kw for about 4 hours and it ran did ok. All of a sudden now it shuts off instantly with a high temp alarm. What is odd is that before you start the unit the high temp alarm is in and there is no low oil pressure alarm. The test button lights up all fault lights. I understand that the high temp alarm is a NO switch. I unplugged the high temp switch and the fault is still there. I did my best to trace the circuit from the J7 amphenol pin 24 on the plug side out to the plug for the switch and back to TB4 #6. I see good continuity and no short-to-ground. Can the A2 malfunction group have failed internally and caused this? At this point, I am even second-guessing my self as to if it was the high temp or low oil pressure fault that was on at start-up when the unit was working. If anyone has any suggestions for me to try I will be going back out to the unit tomorrow. Maybe you guys can save me from having to cart it all the way home and back out again. I'm not sure where to go from here other than throw parts at it.

Thanks.

Update. It has been more than 3 minutes so now I'm forgetting what I tried to get the generator to run. With battle short on it will not even crank. At least I think I tried that!

 

[kloppk]

Normally the LOP light is on before you engage the starter.
The Fault Indicator will only display 1 Fault, not multiple ones. Electronically the first fault is senses is what it displays.
The fault indicators can go bad. I've repaired a few of them out of 831's and 802, 803's, 804's. Every time it was an SCR that was shorted.

It will not crank with Battle Short on.

Try this.
Unplug the Fault Monitor.
Start the engine.
Switch ON Battle Short.
Plug the Fault Monitor back in.
Measure the DC Voltage with respect to chassis ground on pin 8 on the back side of the plug to the Fault Monitor with it connected to the fault monitor.
If the DC Voltage there is 0 or close to zero then the problem is a bad Fault Monitor.
If the DC Voltage there is around 24 volts then there is something else wrong.

 

[captain]

Thank you. I will try all of that in the morning and report back.

 

[captain]

I have 26v on pin 8. K15 has a red light. The engine also seems to hunt slightly with the updated governor controller. With the s1 off and the e stop pushed in (or out) i still get battery voltage to ground on pin 8.

 

[kloppk]

K15 is the starter cutout relay. That LED should be on when the generator is running indicating the starter is disabled.

26 volts at pin 8...
Try this.
Unplug the Fault Monitor.
Start the engine.
Leave the fault monitor plug disconnected.
Measure the DC Voltage with respect to chassis ground on pin 8 of the plug.

 

[captain]

Still 26v. 26v also on pin 8 at the harness with it unplugged and s1 off

 

[kloppk]

Ugh.. Going to require digging into the wiring to check the path from pin 8 all the way to the high temp switch plug to find where power is getting to that path.

 

[captain]

With J7 unplugged. On the engine side both the plug and bulkhead pin 24 give me 12v. I also have 12v now on s1 and 10.5v on pin 8 of the fault indicator

Ok let me revise that. There must be a cap in there. The panel side voltage everywhere is now 0.8. I still habe 12v on the j7 plug pin 24. Ill keep going that way.

 

[captain]

J7 pin 24 and the red wire side of the high temp switch plug are 12v. Black wire side of plug is 2v. This is with the high temp switch unplugged

 

[captain]

Pin 17 in the j7 amphenol plug is a little messed up looking. It has 24v. Maybe its shorting to pin 24 below it. Now i just need to figureout how to take apart the amphenol

 

[captain]

$315 in tools later and I am still not sure how to remove the wire and socket from the plug. I guess they are the wrong tools. Can anyone shed any light on how to remove the socket and wires from the p7 plug?

 

[kloppk]

What tools did you buy? Part numbers.

 

[captain]

Jonard kr-260 and ka-260. I spent a number of hours on the internet trying to find out exactly what tools i needed. I thought I needed the front side removal tools vs the more common rear side extractors.

 

[kloppk]

I believe the extraction tool you need to get the pins out of P7 is:

 

[captain]

I had looked at a universal one like that at first. Its for sizes 20 to 16. I thought the individual ones would function better. The small red size 20 one does not fit into the socket as the video shows to do before pressing the plunger to release the wire. I can try the one you listed as well.

 

[kloppk]

I had looked at a universal one like that at first. Its for sizes 20 to 16. I thought the individual ones would function better. The small red size 20 one does not fit into the socket as the video shows to do before pressing the plunger to release the wire. I can try the one you listed as well.

P7 is PN 206150-1
All the gold plated 18 AWG sockets Contact size 16 female sockets that could go in it can be removed with that tool per the DigiKey website

 

[Guyfang]

This was a tool only the CECOM LAR's had. They did not trust the unwashed masses with it.

 

[captain]

That tool did not work either. The plunger does not even come out past the barrell. The OD of the barrell of the new tool is closer to the #16 size tool. The red #20 tool is to big to fit into the socket of the plug. It appears to require an even smaller size such as a 24. However I can not find anyone anywhere that makes a tool in anything but 12 16 and 20 size. I hate to cut wires just to test if the plug is the problem but I appear to be out of options.

 

[Guyfang]

Let me try and write a CECOM guy and see if he will give me me the tool name and number.

 

[captain]

Last week I put the generator in the back of my truck and drove it 12 miles. P7 pin24 only has 2v on it now and I ran the generator for 45min. I would still like to investigate the plug/pin issue. It appears all the pins around the 24v power pin have some low voltage. I'm not sure what else it could be. Moving the harness around in the engine bay does not make the voltage on pin24 change. From what I can tell pin24 in p7 goes directly to the high temp switch plug.