MEP-002a Starter trouble shoot question S1 to K-3

[dependable]

I decided to get an 002 out of storage and run, since it has been a while. This is a low hour unit(89) that has been stored in shipping container so no weather or rodents. Cleaned up fuel system, checked IP plunger etc. Hooked up good batteries, primer and heater work, but would not crank.

I went though steps and tested S1 switch per TM, and continuities on start circuit tested good.

Also tested continuity to ground on K-3 ground circuit. And tested and found there is no voltage to positive K-3 circuit (actuating terminal) when in crank position.

If I jump solenoid w screwdriver it cranks over, when I jump K-3 stater relay it cranks over, and it will start and run fine if I holding start switch over to actuate fuel solenoid.

I have spent some time re familiarizing w TMs and looking at wire diagram, but may be missing something, since I tested S1 and there is also no reason for it to go bad stored dry & safe.

Are there any circuits or switches between S1 and K3 that I am missing?

I did check starter lockout switch and it looks fine, points clean & closed. Also tried bypassing it, just in case.

 

[Guyfang]

Did you check CR1?

 

[dependable]

Thanks for the reply, CR-1 seems good, .698 in one direction, OL in other.

 

[Guyfang]

With the S1 in the start position, and held up for all tests:
Do you have 24 VDC at TB4-10?
If so, do you have 24 VDC at A1-5?
If so, do you have 24 VDC at A1-6?
If so, do you have 24 VDC at K3-X1?

 

[dependable]

Yes (24V) at TB4-10, yes A1-5, no (0 volts) A1-6 and of course no at K3-X1. If there is nothing between A1-6 and CR1, maybe should check for cold solder joint on CR-1.

I'll have to admit I'm one of the many who is more of a mechanic, with limited electrical knowledge apart form basic trouble shooting, not well versed in reading schematics. I really appreciate your help.

Edit: I took off the circuit board and confirmed CR1 is soldered in. Not sure how relevant , but voltage on both ends CR-1 is around 13.5 when S-1 in crank position. I see it is involved w other components on board, but at this point beyond my knowledge level.

I could just run a jumper from #28 on S-1 to K3-X1 and run generator, but this is a nice unit & I don't want to screw anything up, and wonder what function/protection I'd be bypassing.

 

[Guyfang]

Yes (24V) at TB4-10, yes A1-5, no (0 volts) A1-6 and of course no at K3-X1. If there is nothing between A1-6 and CR1, (No there is not. Look at the wire diagram.) maybe should check for cold solder joint on CR-1.

I'll have to admit I'm one of the many who is more of a mechanic, with limited electrical knowledge apart form basic trouble shooting, not well versed in reading schematics. I really appreciate your help.

Edit: I took off the circuit board and confirmed CR1 is soldered in. Not sure how relevant , but voltage on both ends CR-1 is around 13.5 when S-1 in crank position. (Above, you said you had no 24 VDC at A1-6. And you said you had 24 VDC at A1.5 CR-1 is between these two points, Now you say you have 13.5 VDC on both sides of CR1, so what do you have? ) I see it is involved w other components on board, but at this point beyond my knowledge level.

(According to the first test, CR1 is bad. If you have 24 VDC at A1-5 and no 24 VDC at C1-6, then CR1 is bad. Try, with someone helping, to jump around C1. While you hold a wire between A1-5 and A1-6. Then have someone turn the S1 to start. Will the starter turn over? If so, replace CR-1)

I could just run a jumper from #28 on S-1 to K3-X1 and run generator, but this is a nice unit & I don't want to screw anything up, and wonder what function/protection I'd be bypassing.

Open to see comments

 

[dependable]

Open to see comments

CR-1 tests good w static diode test on circuit board w Fluke. I might not have been clear, CR-1 tests around 13V to actual diode on circuit board when S-1 is in crank position (when A1-5 has 24 V) That is probably not a test in TM, just checking things out, trying to learn. The numbers I reported at terminals are correct.

I took the circuit board out just to see somehow there was a cold solder joint that would cause problems even if diode tested good. I see the back of board is well soldered and sealed. Not like some old amps and automotive components. I did notice circuit is not just to CR-1 on the board, the circuit is connected to some capacitors and resistors w solder path on back of board.

It will start and run by jumping to K3-X1. Knowing what that circuit is for might help trace the problem, or like some circuits added to military stuff, knowing not needed in current use would be good.( For example; all the capacitors if your not running radio nearby.)

Edit: The CR-1 diode and attached circuit, could this be similar the diode above horn relay on CUCVs ? That's there to suppress radio signal form horn relay, a fail point causing horn to stay on.

 

[Guyfang]

Follow the green line. When S1 is held up, you should have 24 VDC to K3-X1. If not, then the problem is between K3-X1 and the last place you had 24 VDC in that circuit. That is and can only be CR1. Replace it. It cost less then a box of matches.

 

[dependable]

I'll swap out the board w a spare and check that while I order the CR-1 diode.

My lack of knowledge of basic circuitry adds to my confusion, 'cause like I stated, that diode is not isolated on board, made me wonder if any of the other components it is connected to could be a problem, since the diode itself tested good. But I take your word for it, as you know more about it than I ever will.

Thanks again.

Edit, I'm still wondering if diode is just for radio noise suppression, like the diodes on some circuits in military trucks.

 

[Guyfang]

No. Its there to stop voltage going in the wrong direction.

 

[INFChief]

I decided to get an 002 out of storage and run, since it has been a while. This is a low hour unit(89) that has been stored in shipping container so no weather or rodents. Cleaned up fuel system, checked IP plunger etc. Hooked up good batteries, primer and heater work, but would not crank.

I went though steps and tested S1 switch per TM, and continuities on start circuit tested good.

Also tested continuity to ground on K-3 ground circuit. And tested and found there is no voltage to positive K-3 circuit (actuating terminal) when in crank position.

If I jump solenoid w screwdriver it cranks over, when I jump K-3 stater relay it cranks over, and it will start and run fine if I holding start switch over to actuate fuel solenoid.

I have spent some time re familiarizing w TMs and looking at wire diagram, but may be missing something, since I tested S1 and there is also no reason for it to go bad stored dry & safe.

Are there any circuits or switches between S1 and K3 that I am missing?

I did check starter lockout switch and it looks fine, points clean & closed. Also tried bypassing it, just in case.

This tells me there is a fault in that circuit. I cannot see the schematic very well - but can you trace that circuit back to each component in that circuit?

Are there any circuit breakers? Low oil sensors that prevent starting?

 

[Guyfang]

View attachment 846191
This tells me there is a fault in that circuit. I cannot see the schematic very well - but can you trace that circuit back to each component in that circuit?

Are there any circuit breakers? Low oil sensors that prevent starting?

Open the #8 post above. The schematic is better quality.

 

[dependable]

View attachment 846191
This tells me there is a fault in that circuit. I cannot see the schematic very well - but can you trace that circuit back to each component in that circuit?

Are there any circuit breakers? Low oil sensors that prevent starting?

Generator starts and runs with this circuit bypassed.

Low oil sensor runs fuel shut off on these, I believe, and I did check. Also checked starter cut out circuit and overheat circuit before I posted this thread. Am only aware of the DC breaker on panel and the main current breaker. There is a component that plugs into block A-1 that might be a circuit breaker, I did test swapping out that with two other of same part from other units, w no change.

The only purpose for this circuit that I can think of is either radio suppression or some sort of field flash aid, but may be overlooking something. I do see one diode in same set in civy configuration (Onan DJB), but do not know what it is for. Attached is that diagram.

I did order diode, and will install on this board. This weekend will check unit with another newer "A-2" board I have, one in unit is original I think.

I do understand the utility in keeping set original, especially if I need Guy's help in future {; .

One of my problems besides no electrical training is I have a bit of experience bypassing radio noise suppression diodes in multiple CUCVs, which in those cases fixes a problem.

 

[dependable]

Tried to start with another board today, still no crank. I tested the CR-1 diode before installing it and it tested good.

I also seem to have made a mistake in post #5 . I stated I had 24V at A1-5 w S-1 in crank and zero at A1-6. I mixed that up, I have 24V at A1-6, and zero volts to A1-5 in crank. Confirm 24V to TB4-10. That does not make sense to me, as is out of order on schematic, but that is how it just tested.

I have to admit I'm pretty confused now. Been studying schematic and tracing wires w test light and Ohm meter for about an hour. Maybe it is a good thing it started raining, so back away form this project for a bit.

Any other circuits or switches I could be overlooking?

 

[Guyfang]

OK, two more questions. Are the A1 card wires hooked up like this:
1. P66E
2. P55P
3. P61B
4. P64A
5. P57B
6. P58B
7. P60A
8. P57C

And the A1 card is supposed to have nuts on the mounting screws that go through the card, to keep the back of the card from touching the control cube and shorting out. This is a long shot, but have seen it happen.

 

[dependable]

A-1 hook ups are as you listed except for #6 which is P58A, not P58B. I'll add that I never messed w the wiring in this, and I used it a few times to run house before I got my 802, so I know it worked then. No P58B nearby that I could see either.

In taking the A1 terminal out to check if it was not grounded, I see the component pictured in back. If I bridge the one that is pointed to, which is connected between A1-5 and A1-6, it will crank. Looks like it might be a diode from the arrow painted in back ground.

I have been testing the only diode I could see labeled CR-1 that I could see, which is on the A-2 board VR board. If this component in picture is also designated diode CR-1, than that would clear up a lot of confusion.

Another case of less than helpful TM schematic, or my basic electrical incompetence?

Maybe I'll pull same component off spare control box & see if that does the trick.

 

[dependable]

Well, I'm an idiot, but that is not news to me. I was wondering why they would have put CR-1 diode for crank on VR board, but there it is, a diode also marked CR-1 and the only one visible. Probably I missed something in TM that would have told me correct location.

I see the diodes mounted behind A-1 are also designated CR-1 & 2. I replaced that CR-1 diode and problem solved, we have crank & run without jumping any circuits.

Thanks for the help Guy, I never would have found the correct CR-1 if you had not asked me to check that the terminal was not grounded to board.

At least I learned a few things that may help in future. Now to take the other 002 and the 701 out of mothballs too.

 

[Chainbreaker]

REALLY glad you found the problem! I was following this thread and couldn't for the life of me figure out how you were able to jump the circuit and get it to start/run if the CR1 diode wasn't faulty. Now thank goodness the mystery has been solved.

Don't be too hard on yourself...we all have made the "assume mistake" before. Its a good lesson in retracing troubleshooting steps and verifying results with others to get back on track to accurately diagnose the problem at hand.

 

[dependable]

While I was dealing w this, I got out my spare control box I bought cheep back when everyone was parting these out. I noticed the VR board is newer, dated 1996. The rest of box shows a lot of age and wear, with almost 4K hours on meter.

I see this board has a bunch of jump wires on it that are not on the VRs from my other 002s. Wondering if this is stock, don't want to mess up a running machine just to test a VR board, but would be good to know if it was viable spare.

Any advice on this?

 

[Chainbreaker]

Yes those jumper wires are in the right locations for the A2 card according to my schematic. If you download the schematic that Guy provided in post #8 and look at PDF pg 2 of schematic you will see just the connector part of the A2 schematic section with Terminal Block at bottom left with those jumpers on those terminals (incidentally the rest of A2 schematic follows on pg 3)

Not sure if new replacement boards normally come with those jumpers pre-installed. Perhaps that is a "take out" board since one would typical just remove the Control Box internal wiring harness from the board to remove board thus leaving the jumpers in place since you wouldn't normally take off jumpers and leave them loose in control box I guess. I would think if one received a "new board" w/o jumpers as a replacement you would transfer jumpers from board being replaced.