Ever see inside the Protective Control Box?

[5tonbrian]

Yes. I bypassed the pcb and it fired up great.

 

[cwc]

5tonbrian, see the diagram in post #21 (top of page 3). If you have gages then there is power on wire 5. Beside the PCB, other problems could be the starter switch on the dash or the Neutral Safety switch. Can you probe wire 499 (Term E) at the PCB and see if you are getting 24V there when you activate the starter switch?

 

[Andyrv6av8r]

I knew when I picked up my 932A2 I had a PCB issue. It wouldn't start, batteries didn't charge any after 5 hours of running although the amp meter was showing charge, ABS light was on. It had to be slaved every time. So I removed the PCB, popped the top off with a thin scraper and I knew immediately it was toast. There was signs of corrosion everywhere from water getting in.I replaced both relays and sealed everything back up. Now after slow charging all 4 batteries, it stars and runs like a champ. No ABS light either.

 

[ryanaubra]

Thanks for all the great help guys. I have a 923 having the same starting issues. Took off the PCB and looks corroded on the inside. Just ordered my solenoids and doide. Was wondering if anyone knew what the diode was on the top left going to ground?

 

[Valor]

Thanks all for the great info. I just got my 923A2 the other day and it was missing the PCB so I am learning a lot. I will see if I can jumper the wires and get it running. If anyone has a core PCB that they don't need/want, I could use one!

 

[Tinstar]

After reading this thread again, I bought the parts to rebuild my failing spare.
Had to get new one.

I hope it's as easy as it seems.
Will find out next week when I tackle the job.

 

[Ghost1986]

Help! I'm new to the forum, don't usually like asking for help, but I'm stuck. My m923a2 (just bought) is having issues starting. Sometimes you turn the batt switch on and all that happens is a click. No gauges or anything else. I took my pcb apart and it looks just like plode's picture on here. Only one solenoid is clicking when I turn on the batt switch. I tried tapping in the other one but to no avail. I'm at my whits end here. Any help should be much appreciated

 

[juanprado]

Help! I'm new to the forum, don't usually like asking for help, but I'm stuck. My m923a2 (just bought) is having issues starting. Sometimes you turn the batt switch on and all that happens is a click. No gauges or anything else. I took my pcb apart and it looks just like plode's picture on here. Only one solenoid is clicking when I turn on the batt switch. I tried tapping in the other one but to no avail. I'm at my whits end here. Any help should be much appreciated 

ghost,
step 1 is to check each of the batteries individually and make sure they are 100 charged 12.6v and load test to rule out bad battery(s)

 

[Ghost1986]

I'm sorry I didn't say anything in my last post, I just replaced the batteries thinking that was the problem. So update. I can connect the pcb and jump the two larger wires and it fires and everything works.( I remove the jumper after it starts) Sometimes I can turn it off and it will start right back up with no problem.

 

[av8or]

The PCB's pictured appear to have a varying amount of complexity. The M809 series PCB boxes were simple with 2 solenoids ( ONLY ) no diodes or boards. They ( simple 809 series boxes) seem to work the same in M939 trucks for my experience, but there must be a reason for all the complexity. Does any know the reasons for the model changes and what can and can't be interchanged.

 

[jaws4518]

Hey I apologize. I read your reply again and realized that I needed to find post #20 and read up from there. I had so much going on in my head that I did not pay attention to your instructions. I'm still having issues, but I will figure them out. Your instructions and electrical schematics are a huge source. They fill another gap in learning how the ignition control system works. It explains why I'm not getting any "good smoke", a term we used for getting the "green" light. I've got more reading to do anyhow. Thanks again!

 

[DrOfData]

I know this is an old post, but I was wondering if this ever went anywhere? I would definitely pay to have mine rebuilt versus buying a NOS.

 

[ryanaubra]

DrOfData - they are very easy to rebuild. Ive done multiple 5 ton boxes for about $35 and an hours worth of my time. If you dig, someone on here has the part numbers already laid out. All you have to do is put wire "A" back on post "A", so forth and so on, and it is done. This is all they are on the inside.

 

[ryanaubra]

DrOfData - they are very easy to rebuild. Ive done multiple 5 ton boxes for about $35 and an hours worth of my time. If you dig, someone on here has the part numbers already laid out. All you have to do is put wire "A" back on post "A", so forth and so on, and it is done. This is all they are on the inside. The most technologically advanced piece was the capacitors on the solenoids. I think i bought 20 of them on ebay for $5. View attachment 735741

 

[jaws4518]

I know this is an old post, but I was wondering if this ever went anywhere? I would definitely pay to have mine rebuilt versus buying a NOS.

I say rebuild! My rebuild went just fine. Now that I know how to do it, I can get myself out of a (dead start) situation. From now on, I will always keep a set of rescue jumper wires in the tool box. Knowing how to jump-start from the harness, or right on the starter is a must! It could save you hundreds (if not) thousands of dollars on a tow charge. My advice to anyone with a big truck is to learn it, and practice with confidence. I was very lucky because there were several instances of failure before the battery solenoid went out. I didn't know what was going on? Luckily I was back home.

The contacts in the battery solenoid went bad due to weak (old) batteries. I could have avoided this problem if I had replaced my truck batteries sooner. The main (battery power ON) solenoid still actuated, but no power across the main lug. This fooled me at first until I got a little further into tracing power through each point in the control circuit. I was prematurely focused on the PCB board because it had one. If the PCB board were bad, I would have copied the M809 model of the control box with Zener diode grounded to the solenoid. I just glanced at it so someone correct me if I'm wrong. I only opened up the 809 box ends to see inside it. Like earlier posts explain, the M809 series control box won't work unless you bypass the neutral start switch. Seems like there was something with alternator voltage presence that kills the circuit on M809 too. Don't quote me on that though. The original author(s) of this thread mention it. So do the TM(s) for troubleshooting starting problems. The M900 series does not have wiring harness lead.

So, my conclusion is... don't spring for $300 replacement unless you have no desire to learn how. It would be embarrassing to stall-out and not know what to do.

I will post some pictures.

 

[74M35A2]

PCB’s with a circuit board have starter re-engagement protection, they prohibit the starter to be engaged if the engine is already running. This is typically monitored via an AC output from the alternator or oil pressure signal.

Best PCB jumper is a dead PCB box. Cut the connector out, and place a shorting wire link between the battery terminals. Then can just plug into harness.

 

[jaws4518]

Now that I think about the labor involved, I would buy a control box if your not interested in the repair project. Actually, it is a lot of work! I did it to learn something though. The first one is always the hardest to do. Honestly, I have many hours of diagnosing, take down, fabrication, put back etc... I have a lot more than $300+ in this one. The next one won't be so bad. The bright side of this now is that I won't get caught in a bad down situation. Hopefully!


Finished & ends sealed


weep holes on bottom


tack weld top & bottom


bench testing new battery solenoid


tack weld solenoid & starter relay/solenoid


so much for hermetically sealed...


got to improve my skills with the VTM

 

[jaws4518]

PCB’s with a circuit board have starter re-engagement protection, they prohibit the starter to be engaged if the engine is already running. This is typically monitored via an AC output from the alternator or oil pressure signal.

Best PCB jumper is a dead PCB box. Cut the connector out, and place a shorting wire link between the battery terminals. Then can just plug into harness.

Yeah, 10/4 on that.

 

[jaws4518]

Sergent Major, that's nice clean reconfigure. Are those caps are diodes? Look like diodes...

 

[74M35A2]

How do you have > $300 into it? Did you stop by the strip club on the way to get the solenoids?