Ever see inside the Protective Control Box?

[jaws4518]

Well, **** yes!

I think the NAPA solenoid was $40.
Shop supplies = $30.00
Four evenings of Bud Light = $60.00
Research & development = $100.00
Taking off & putting back 5+ times $100.00
Not knowing what the **** I'm doing = $100.00
Not paying attention to forum post instructions (lost time) =$100.00
Some Flex Seal = $10.00
Rust treatment w/Ospho = $10.00
Fabrication = $100.00
Up and down off the front tire ass rash = $50.00
Up and down again for dropping sockets = $50.00
Putting back for the last time & turning the switch = $50.00
Putting up the STE/ICE-R VTM, which I did use after the first hour of diagnosis = $50.00

I figure my time is worth $50.00 an hour.

I guess that's about it... $850.00 ...not including redo of battery cables and tie down brackets. Shoot that was another 8 hours of fabrication to make the old brackets except the new (2) large commercial batteries.

Batteries $160 each
8 hours fab & cable work over @$50.00 =$400.00
Bud Light = $20.00

Total $680.00 + $850.00 = $1620.00

Ah ****! I still beat the cost of that tow truck. Drank beer and got some new batteries too! Forgot about stopping by the landing strip.

 

[juanprado]

Ah, It is clear. We have a certified DOD contractor to gov't spec!

 

[74M35A2]

On/off 5 times and front tire a$$ rash are awesome posts! Plus, not being able to add, means you just made the friend list.

 

[jaws4518]

Was I off on the numbers too? Shoot, that's normal I guess. FUBAR!

 

[jaws4518]

I always try to put 110% into everything I touch. Or say...

 

[tobyS]

This must be my M929A2's problem. I have to jumper across the starter about 1 in 20 starts.

Did anyone ever determine if the 7 pin connector is available? Other than the box, that seems to be the only part that might be hard to supply. Maybe in a Hoffman box.

 

[74M35A2]

Yours may be neutral safety switch. Try going in and out of neutral next time it does it?

 

[tobyS]

Yours may be neutral safety switch. Try going in and out of neutral next time it does it?

Yea, could be. Will try moving it next time.

Still, I'd like to have a replacement control ready to go and would feel more confident about adding auxiliary stuff, knowing my electric supply is in good shape. It might be worth having some additional relays, switched circuits and maybe a few circuit breakers too that could be added to a control. I have some nice din rail 24vdc ice cubes that might work with hydraulics. Alas....it's down on the list, since jumping at the starter does get me going and it's reliable most of the time.

I'm fighting loosing prime over a period of about 3-5 days. I have a new line from the filter to the pump, but haven't done the real work of finding the problem, I expect, in the spaghetti to and from the tank selector (M929A2). So I take the line off at the pump and pour about 8 cups of fuel into the line, back-filling the filter and line. When full, it starts right off.

A friend gave me these, which I might add to the mechanical solenoid, probably not replace.

 

[jaws4518]

Yea, could be. Will try moving it next time.



I'm fighting loosing prime over a period of about 3-5 days. I have a new line from the filter to the pump, but haven't done the real work of finding the problem, .

I have fuel pressure leak at the first inlet into the pump governor. I can see it (slow) drip fuel where that head end piece mounts to the governor body, I believe. Sorry, I don't have the part names committed to memory. Anyway, I loose fuel pressure in a few hours. There is no gasket between the to parts. I torqued the two Allen hex screws down awhile back and my fuel pressure stayed constant for a long time until it started leaking again. Like me, sounds like you have a slow leak in your fuel system somewhere.

 

[74M35A2]

tobyS, I have several compact external 24V solenoids that are issued with our gear reduction starters (mounted directly to them). If you wanted to simply eliminate the starter solenoid in the PCB, you would mount this relay on your starter or elsewhere, and then go direct from dash switch to this. Would recommend to keep the neutral safety switch in place of course. Can send it to you for free, just PM an address. I would advise against the SSR's (Solid State Relays).

 

[TOBASH]

Amazing post. Is this a sticky yet?

 

[Dan Neubert]

Thank you for the troubleshooting guide. I have a 936A2 and I have a no start condition. I have replaced the batteries. When I turn on the master switch the gauges move just a bit and then back to nothing and the engine does not crank. I can turn on the master switch and bumper the starter solenoid and it will fire up. But I would like to fix my problem. Also I can hear 3 clicks from the pcb area when I turn on the master switch and after 1 or 2 seconds another 3 clicks. This sound is not very loud and I have to concentrate to hear it. Anyway your guide will hopefully help me track down this problem.

 

[jaws4518]

Thank you for the troubleshooting guide. I have a 936A2 and I have a no start condition. I have replaced the batteries. When I turn on the master switch the gauges move just a bit and then back to nothing and the engine does not crank. I can turn on the master switch and bumper the starter solenoid and it will fire up. But I would like to fix my problem. Also I can hear 3 clicks from the pcb area when I turn on the master switch and after 1 or 2 seconds another 3 clicks. This sound is not very loud and I have to concentrate to hear it. Anyway your guide will hopefully help me track down this problem.

I think what you are describing the same condition I had. Sounds like you main (battery) solenoid is bad. Your getting power across the coil, but the contacts are done. See, I let my batteries get too weak and the slow cranking put to much load on the battery solenoid. The clicking is the initialization of the PCB relay and other protective switches that make up protective control. Maybe some dash stuff too. You have fix what you have or by a new one. I fixed mine because I wanted to know what was going on so I could help myself recover from a dead situation.

 

[freedom ridge]

Okay so after reading the very informative 12 pages, I have to ask yet another question. I have the PCB off my truck which I came to it being a problem via diagnosing steps in the TM and doing some reading. Anyway, I have been trying to figure out how many diodes there are. I see a diode in between the control side terminals on each relay. This makes sense to me because you can't reverse polarity. But There seems to be another diode that goes to a ground? I will upload some pictures of what I found. I see some PCBs that were rebuilt without something like this and I saw someone rebuild one with something that resembled what I have but could not decipher it from the pictures.
Whatever it is that looks burned. Any ideas? Thanks in advance guys!

 

[Dan Neubert]

Well I received a new(for me but used and checked) PCB and installed it today and that was the problem. I got my PCB from Ken at MV Parts Store in Waukesha. Good deal 100.00 shipped and shipped the next day. So maybe what happened with mine is I turned of the main switch before the engine stopped rotating a couple of times. Or maybe because my batteries were low. Anyway I guess it is kind of a common problem. Anyone know how to bulletproof the PCBs?
[h=1][/h]

 

[74M35A2]

The diodes are likely just to suppress any flyback voltage spike when the solenoid is de-energized. They can act like a mini ignition coil.

Best prevention steps is to switch to a civilian alternator so it does not over-volt, in addition to renew the PCB solenoids every 10 years. Both easy and low cost to do.

You also have an option to remove the PCB starter control solenoid if you go with a newer gear reduction starter that has a self contained external relay on it. This enable direct dash switch control.

 

[Dan Neubert]

I kept my old PCB and want to fix it so I have a spare. Do you know where to get the parts needed...solenoids,diodes etc. Also where might I find a gear reduction starter. Interesting about the alternator. How does that alternator not over volt as opposed to the military alternator. Kind of curious why the military let this problem happen. The military usually over engineers just about everything.

 

[74M35A2]

The military does not over-engineer everything. A lot of this stuff is lowest bidder which meets spec. In this case, they simply carried forward a decades old alternator design. Part of that design uses an external reference for battery voltage to determine alternator voltage output via the regulator. Back then, there was not much forward thinking or controls for fail-safe. Very simplistically, if this battery reference signal is cut (which is what happens in "improper" vehicle switch shut-down order), then the alternator simply sees this as voltage below target, and commands alternator to increase it's output to max possible. This happening while the engine is still running. Voltage then exceeds 28-29V, and the over-voltage is known to damage electrical parts which also have little to no protection (same design concepts). Examples are CTIS and ABS controllers, PCB, alternator itself, etc....

More modern civilian alternators are a later design, where the external voltage reference (if equipped) has limited authority within a certain range. If this external reference signal is lost, the alternator simply switches over to referencing the B+ terminal on the alternator itself, to regulate voltage. Even if that is lost, it will then default to a 13.5V level (on a 12v system, for example), not command a runaway situation.

You don't necessarily need a gear reduction starter, I should not have said it that way. All you would need is the external relay that comes on them, if you wanted to eliminate the starter solenoid in the PCB. You'd really just be replacing it with a smaller, more modern one, located elsewhere.


I don't run a spare PCB, but I did take a burned up PCB, cut the connector out of it, and jumpered the large terminals together so it can restore dash power in an emergency when plugged in as a PCB into the vehicle harness. The starter can simply be jumped at the rear of it if need be. With those two, it will be same as a new, spare PCB, in temporary fashion.

 

[simp5782]

I kept my old PCB and want to fix it so I have a spare. Do you know where to get the parts needed...solenoids,diodes etc. Also where might I find a gear reduction starter. Interesting about the alternator. How does that alternator not over volt as opposed to the military alternator. Kind of curious why the military let this problem happen. The military usually over engineers just about everything.

They are 48v diodes. You do not need them. They only for in case you hook the batteries up backwards.

Cole Harsee 24063 is the solenoid numbers.

 

[Dan Neubert]

The military does not over-engineer everything. A lot of this stuff is lowest bidder which meets spec. In this case, they simply carried forward a decades old alternator design. Part of that design uses an external reference for battery voltage to determine alternator voltage output via the regulator. Back then, there was not much forward thinking or controls for fail-safe. Very simplistically, if this battery reference signal is cut (which is what happens in "improper" vehicle switch shut-down order), then the alternator simply sees this as voltage below target, and commands alternator to increase it's output to max possible. This happening while the engine is still running. Voltage then exceeds 28-29V, and the over-voltage is known to damage electrical parts which also have little to no protection (same design concepts). Examples are CTIS and ABS controllers, PCB, alternator itself, etc....

More modern civilian alternators are a later design, where the external voltage reference (if equipped) has limited authority within a certain range. If this external reference signal is lost, the alternator simply switches over to referencing the B+ terminal on the alternator itself, to regulate voltage. Even if that is lost, it will then default to a 13.5V level (on a 12v system, for example), not command a runaway situation.

You don't necessarily need a gear reduction starter, I should not have said it that way. All you would need is the external relay that comes on them, if you wanted to eliminate the starter solenoid in the PCB. You'd really just be replacing it with a smaller, more modern one, located elsewhere.


I don't run a spare PCB, but I did take a burned up PCB, cut the connector out of it, and jumpered the large terminals together so it can restore dash power in an emergency when plugged in as a PCB into the vehicle harness. The starter can simply be jumped at the rear of it if need be. With those two, it will be same as a new, spare PCB, in temporary fashion.

Thanks for the quick reply. I am starting to understand how this works. I really did not understand why the PCB would fail when it was shut down incorrectly. Sure seems like that would be a problem in the field or actual wartime conditions. I will be looking for a civilian alternator and installing it. Thanks again