MEP-803A: wiring issue... please HELP

[SQF]

Hi all, new member here from SE Michigan. Building contractor by trade, but military generator fan. I purchased a 2008 803 a couple years ago and it has served us very well on job sites ever since. Today we started it up and it fired up as usual but the AC interrupter won't activate. Here are my symptoms:

1. Hour meter not working (just started not working)
2. K1 relay not engaging
3. No power to x-terminal when activating AC interrupter switch.
4. When 24V is applied to x-terminal, K1 engages and power is sent to lugs.
5. Engine runs great, no other known problems

I am lost on where to start tracing why I don't have power to the x-terminal. Please excuse my relative lack of knowledge on these units. This is our go to piece of power equipment so it's killing us having it down. Is there something to do with the oil pressure sender that energizes that circuit?

Thanks!

 

[jamawieb]

1st question, after the unit is up and going, if you hit the start switch back to start do you hear the starter grinding?
It could be K20 relay which is the oil pressure relay or the mag pickup or the ac interrupter switch.

 

[SQF]

I can't tell you because it never occurred to me to try that. I will try it first thing in the morning and let you know. I can say I went through the TM testing of the ac interrupter switch and the diode - everything tested out correctly. The other thing that leads me to believe it is not the switch is that by forcing 24V to the x terminal, and then activating the ac interrupter, K1 engages. Without me forcing voltage to the x-terminal, no dice...

What is the mag pickup, what does it do, and how do I test for that other than what you already asked?

Thanks AGAIN!

 

[jamawieb]

The mag pickup is located on the bellhousing right below the starter. It tells the starter to disengage and energizes the field. According to the DC wiring diagram it plays a roll in the 24volts to the hour meter and x connector on k1. I believe if you try the start switch after its started and it grinds we will see if it needs adjustments. The TM tells you how to adjust it, it's real easy. If you have time to read the TM tonight you can see how to test it and adjust it properly. I'll try to find it too.

 

[jamawieb]

Here you go I found it.

Screw magnetic pickup (7, Figure 2-25) into flywheel housing until pickup bottoms out on flywheel.
Back magnetic pickup out 1-1/2 turns and finger tighten nut (6).
Connect electrical connectors and remove tags.
Adjust magnetic pickup (7) in accordance with paragraph 2-94-4.
2-130
2-94. MAGNETIC PICKUP.
Removal.
Installation.
ARMY TM 9-6115-641-24 AIR FORCE TO 35C2-3-456-12
2-94-4. Adjustment. a. Set multimeter for AC volts and connect to terminals 3 and 6 on crank disconnect switch (35, Figure 2-11).
b. Connect negative battey cable and dead crank engine with DEAD CRANK switch.
Do not adjust magnetic pickup more than 1/8 of a turn at a time. Failure to observe this caution could result in damage to magnetic pickup.
c. Multimeter should read 2 to 3 VAC. Adjust magnetic pickup in or out, no more than 1/8 of a turn at a time, to obtain proper reading.
d. Tighten nut (6) and close access doors

 

[SQF]

I was reading it in the TM just as your post came through. Thanks for sending it. So it sounds like I could simply test for the 2-3VAC at the crank disconnect switch right out the gate tomorrow and see if that's my issue. Next question: what switch is that and where is it located?

 

[jamawieb]

The crank disconnect is located behind the gauges. If you let down the door to the gauges, you will see all the relays lined up on the bottom. The one on the far left that looks different (has a circuit board inside)is the crank disconnect. If you have a helper you can just take the magnetic pickup connectors off and test while turning the dead crank on to read the voltage.

 

[Guyfang]

I don't know why the troubleshooting diagram includes the testing of S5, the AC interrupter switch. I have never in my life seen a bad switch, other then the plastic crap, S1, S6, and S8. The mag pickup works best at 3 volts AC output. Do pull it out first, and see if there is trash, oil and or metal filings on the end of it. It's called magnetic pickup for a reason. Anything on the end of it can make it not work right. If the end is ground off, you need a new one.

 

[SQF]

Thanks again for the posts guys. So this morning I went first thing and checked the mag pick up. Sure enough .55VAC! I thought I had it solved. With the help of one of my guys we brought it up to 2.75VAC. Unfortunately no fix...

So two more questions: 1. On the x-terminal I am getting 1.11v DC for some reason but not 24-26v dc like I assume I need. Where do I go now to find what’s feeding the x-terminal? I am not the best when it comes to reading wiring diagrams. I also have about 1v dc to the hour meter which isn’t working either. According to my tracing of the diagram that is in the same circuit that feeds the x-terminal? 2. Could my problem be the little diode on the ac interrupter? Which way/direction is it suppose to go? One way I install it the indicator light glows lightly and then brighter when I go to close. The other way nothing happens at all. Could the diode be bad causing all my headaches?

thanks again

 

[Bmxenbrett]

Did you look at the wire diagram yet?

 

[Guyfang]

		S5 Switch
From	Wire #	Wire #	From
		1	4
		2	5	152B	TB5-16
K8-7	147A	3	6	100AU	TB5-7
		CR3 diode is mounted between terminals 2 and 5. The Positive side is attached to terminal 5.

 

[USAMilRet]

Thanks again for the posts guys. So this morning I went first thing and checked the mag pick up. Sure enough .55VAC! I thought I had it solved. With the help of one of my guys we brought it up to 2.75VAC. Unfortunately no fix...

So two more questions: 1. On the x-terminal I am getting 1.11v DC for some reason but not 24-26v dc like I assume I need. Where do I go now to find what’s feeding the x-terminal? I am not the best when it comes to reading wiring diagrams. I also have about 1v dc to the hour meter which isn’t working either. According to my tracing of the diagram that is in the same circuit that feeds the x-terminal? 2. Could my problem be the little diode on the ac interrupter? Which way/direction is it suppose to go? One way I install it the indicator light glows lightly and then brighter when I go to close. The other way nothing happens at all. Could the diode be bad causing all my headaches?

thanks again

The diode is dong its job which is to let electricity (voltage and current) flow through it in one direction only.

 

[SQF]

Did you look at the wire diagram yet?

Yes, and I can't determine what feeds the x-terminal.

 

[SQF]

This is very helpful. I will make sure the diode is in properly. Why am I having such a hard time tracing what feeds the x-terminal? And why do I have such low voltage there?

 

[jamawieb]

This is very helpful. I will make sure the diode is in properly. Why am I having such a hard time tracing what feeds the x-terminal? And why do I have such low voltage there?

Look at the wiring schematics in the TMs (its an individual attachment) and find K1 then trace your wires.

X on K1 is wire 150B goes to P6-29 connector
Connects into J6-29 then it goes to TB5-19 (TB mean terminal board) this one is located behind the relays in the control panel.
Then at TB5-19 it jumps to K20-6 (crank relay),M3 (hour meter), J3-V diagnosis port.
That would mean power flows through K20-6 (oil pressure relay), the far relay on the right hand side

 

[jamawieb]

Are you getting 24volts on K1 terminal Y??? Looks like you complete the connection with the AC interrupter switch and it flows from Y to X

 

[Guyfang]

When you push S5 up, it provides a path to ground for the K1. BUT!!!! the hour meter should work when ever S1 is turned on.

 

[SQF]

Are you getting 24volts on K1 terminal Y??? Looks like you complete the connection with the AC interrupter switch and it flows from Y to X

Well, I can't remember honestly. I know I checked Y, but I don't remember what it had. I haven't been back to the job site with it on it, but will tomorrow and will let you know. Thanks

 

[SQF]

When you push S5 up, it provides a path to ground for the K1. BUT!!!! the hour meter should work when ever S1 is turned on.

So, just to confirm, if the fuel pump is running then the hour meter ought to be ticking right?

 

[SQF]

		S5 Switch
From	Wire #	Wire #	From
		1	4
		2	5	152B	TB5-16
K8-7	147A	3	6	100AU	TB5-7
		CR3 diode is mounted between terminals 2 and 5. The Positive side is attached to terminal 5.

Stupid question #27... How does one tell what side of the diode is positive???