M925A1 charging and PCB problems

[SFCPappy]

Got back last month from a road trip of 1200 miles in my M925A1. All was good until I was 120 miles from home, coming back. It was late night and noticed my headlights getting dimmer. I pulled into first available truck stop and wait for daylight. No luck finding a place to park a 5 ton pulling a M989A1 HEMAT. Just as I was pulling out to park on exit Ramo shoulder lights lit up pretty bright. So I decided to continue on to Knoxville. About a mile from the truck stop I started smelling electrical smoke. I pulled over at the exit I was coming up on and checked for fire. Parked for the night. Next morning I bypassed the PCB and started it up. Went on into Knoxville and stopped at truck stop. After assessment I found the PCB had crashed and the alternator was what was smoking when I turned battery power back on and started engine.

Question 1. Would a bad PCB cause the alternator to fry?
2. If not what caused the alternator to go into super charge? Bad rectifier? Bad regulator? I've found a way to build a cheaper yet more efficient pcb but without the circuit board. A new PCB is @ $350.00. I'm poor. But I don't want to toast my 5 ton. I still use it by bypassing the PCB but with the alternator disconnected I have to charge each battery by battery charger. So I'm asking for the best advice.

 

[Suprman]

If you ran the batteries down because the pcb had a worn out relay, when you bypassed it if the batteries were really low then the alternator may gave been overworked trying to recharge them.

 

[SFCPappy]

If you ran the batteries down because the pcb had a worn out relay, when you bypassed it if the batteries were really low then the alternator may gave been overworked trying to recharge them.

That's my thinking but with that circuit board in the PCB and one lead goes to the alternator from that board, I wasn't sure if it might have been that circuit or a stuck protection relay. I've opened the PCB up for inspection. Looks like the battery relay is fried and the starter lock out relay is corroded. Looks as if they never opened the drain plug to check for moisture, fairly rusty.

 

[SFCPappy]

With my electronics knowledge and after studying all the circuit and wiring diagrams I can build a modified unit that would be similar in working as a M35. Only no neutral safety circuit , reverse polarity protection .

 

[Suprman]

I opened an old one of mine it was welded sealed with no drain though. The relay contacts had just gone bad over time from use. They are rebuildable there is 2 relays and a diode if I remember correctly.

 

[juanprado]

check epay seller [h=1]cage-1y875[/h]
or their website : southern automotive wholesalers

They are oe on the pcb and sell for average of $150 or less directly on epay.

 

[SFCPappy]

Thanks for the information. I follow him over there and found that one a few weeks ago. Sounded great until I read it's an 800 series PCB.

 

[SFCPappy]

Here is two pictures of the PCB out of my M925, internal view (note the rust and contamination). The other image is one I made showing the PCB pins and the circuit wires that are in the plug that connects to the PCB.

Pin 81. Is the large black wire that goes to the main terminal on the black relay then jumpers to the main lug on the silver relay.

Pin 5 Is the other large black wire from plug to silver relay. Then it jumpers to the circuit board.

Pin 74 Is the orange wire from plug to circuit board.

Pin 499 Is the smaller black wire to opposite main terminal on black relay.

Pin 566 Is the red wire to the circuit board.

Pin 459 Is the off white wire to the circuit board.

By referring to TM 9-2320-272-24-1 Section 1-22 ELECTRICAL SYSTEM OPERATION starting on page 1-45 you can easily trace each circuit and what it controls. Either inside the PCB or other vehicle components.

 

[juanprado]

Thanks for the information. I follow him over there and found that one a few weeks ago. Sounded great until I read it's an 800 series PCB.

They list and sell the m939 one all the time for the same price. I would send him a ebay message or call/contact them directly via the website. It strikes me crazy when I see folks sell them used for 2x the new and new for 3x-4x for what you can get it directly.

Good luck with your issue!

Happy Turkey!

 

[tractors0130]

When I contacted Southern Automotive about a M939 PCB a week or so ago, they said they were currently sold out due to filling a large order; however they would be making more.

 

[SFCPappy]

They list and sell the m939 one all the time for the same price. I would send him a ebay message or call/contact them directly via the website. It strikes me crazy when I see folks sell them used for 2x the new and new for 3x-4x for what you can get it directly.

Good luck with your issue!

Happy Turkey!

I'll do that and happy Thanksgiving to you and everyone at Steel Soldiers.

 

[SFCPappy]

When I contacted Southern Automotive about a M939 PCB a week or so ago, they said they were currently sold out due to filling a large order; however they would be making more.

I want to thank you for this great information. I just got off the phone with Southern Automotive and he said they are building them now. Just waiting on delivery of one component. Estimated date for sale is mid January and the price per PCB for the M939 family will be around $150-$165. He also told me that unscrupulous surplus vendors buy direct from them and then turn around and sell them at double the price.

I know there is a way on here to say Thank You better and give feedback scores but I don't know how. This information saved me close to $200.00 and those of us with M939 family vehicles need to know about this. They also sale other PCB's , generators and other mil-spec electronics.

 

[Scarecrow1]

I think you should keep looking on SS I found a guy parting out one and picked up shipped for $81.00. You have to be quick and look everyday to find one ........

 

[jcappeljr]

I have 1 for sale,$100 plus shipping.

 

[73m819]

The PCB is military thing, I have run many a crane over the years that were Cummins powered, they had a master on/off switch that controlled a master solenoid and a start button, this was it, the master turned everything on and off. I guess it was figured that if you were smart enough to run a crane, you could tell if the engine was running. When the PCB dies in the 819, this WILL be the way I will go as a fix, it will be one less thing that can die when I do not need things dying. this is how the 39 series 5ts and the deuces were/are setup.
BASICLY K.I.S.S. -- Keep It Simple Stupid

In fact, does anyone have a pcb plug that is on a dead box bottom that could come this way so I can make a plug and play when my pcb decides to take a crap.