Ever see inside the Protective Control Box?

[Iggy913]

Well, you have now! Check out the bottom right corner!


I'm sure there are more informed guys here that can elaborate on it's function, but the way I read it the Protective Control Box (PCB) is basically a massive set of fuses for lack of a better term. If it's electronic and controlled from inside the cab it runs though this box before getting to whatever it controls. It's supposed to "protect" the electrical circuits from high and/or low voltage to prevent any damage. Trouble is when it goes bad these boxes cost anywhere from $200-$400 depending on where you shop.

As I mentioned above don't hold me to that exact definition but I think I'm correct in very basic function.

Mine was no good anymore so rather than just throw it out I decided to cut it open and see what it looked like inside. By the way this is on a 923A2. I'm not an electronics wizard by any means, but as you all can see in the photos something in the bottom right corner burned out. I can also tell you it smells terrible, much worse than other burning electrical connections I've been around before.

One other thing I found interesting to note is there are no exotic looking circuit boards with fancy micro-circuitry present. I'm betting all the parts inside these boxes can be replaced if you know electronics. Again as I said above, I'm certainly not an electronics wizard, but I do know of several and I'll be showing it around to see if this box can be serviced. At worst I figure I can use it as a spare. I'll be sure to update if I can find anything out.

 

[zout]

I bet you could lay a penny across that and shove it back in - use to work for ole fuse boxes in the house

 

[juanprado]

Wow, There have been other threads and pics on these but your pics are nice. Sure looks they are made simpler and cheaper now.

It looks like the solenoids have changed design. The older ones looked like your typical industrial solenoids or golf cart pieces. These look more like marine or small equipment solenoids. I recall the old one having a small board.

Did the box just pry apart? The other ones I recalled had to be physically cut open with a dremel or saw tool.

I think cranetruck is the one who had extensive pcb knowledge from what I recall. Hopefully he will chime in here.

thanks for sharing.

 

[steelandcanvas]

Bjorn (Cranetruck) provided a thread with pix and what to replace when the magic smoke comes out. I believe there was a schematic also.

 

[Suprman]

Heres the old one from my 923a2 its different than yours

 

[Iggy913]

I thought the box might have been soldered or braised together and started along a seam around the box with an oscillating tool and a carbide blade. I cut into the seam all the way around and eventually used a hammer and chisel to get the lid to come off. Once I had it off it looked like it had some kind of crazy sealant holding the lid on the box. I guess that makes sense though, you wouldn't want to weld/solder/introduce excessive heat into a metal box full of electrical contacts. The lid was also held in place by the serious coat of paint over the whole box. I don't think you could just pry it off without at least cutting an edge around the whole box to get the point of a chisel into.

I'm fairly confident it can be repaired seeing the inner workings now.

 

[Iggy913]

Suprman, that's what yours looked like inside? That looks nothing like mine, your looks like a much newer design and probably even easier to repair. Those contacts inside there look like two starter solenoids almost.

 

[Suprman]

I was going to find 2 high current dc solid state relays to rebuild it with.
Will

 

[Tinwoodsman]

I bet you could lay a penny across that and shove it back in - use to work for ole fuse boxes in the house

Yes. And I used to clean my points with a dollar bill. That was in the days when a dollar bill was worth something.

 

[juanprado]

I was going to find 2 high current dc solid state relays to rebuild it with.
Will

Those are common solenoids available at NAPA or a real parts store.

 

[Suprman]

I use the big solid state relays for other things I can get ones good for 80a continuous. I think they would be more reliable.
Will

 

[doghead]

I use the big solid state relays for other things I can get ones good for 80a continuous. I think they would be more reliable.
Will

http://electronicdesign.com/compone...-relays-versus-solid-state-each-has-its-place

 

[cranetruck]

Not much to add, except perhaps that the designers paid more attention to suppression of electrical noise (toroidal cores) than usual.

 

[bchauvette]

My guess is that are a bunch of go/no go switches in the vehicle, like trans neutral and parking brake on possibly in series. if the circuit is complete you can start the engine. The other solenoid might be to maintain the "GO" condition when you put it in gear or release the parking brake. What do you think?

 

[Iggy913]

That theory sounds plausible. I'm not sure what the parts and pieces are inside the box, as I said electrical work is certainly not my area of expertise. I have left the box with a few guys who can repair it so I'll be sure to question them on what exactly each component is inside. Hopefully I'll know something soon.

 

[TexAndy]

Heres the old one from my 923a2 its different than yours

View attachment 453572

My 1990 manufacture 923a2 PCB looks like that.

 

[glassk]

Protective Control Box (PCB). The PCB used on the HMMWV is similar
to the control boxes used on other military vehicles, with an added
provision for the glow plugs. The functions of the PCB are to energize the
glow plugs, prevent battery polarity reversals, energize the starter
solenoid, and prevent reengagement while the engine is running. The PCB is
mounted behind the instrument panel in the driver's compartment and is
serviced only as an assembly.

http://armyordnance.tpub.com/Od16157/Od161570051.htm

Sounds like prevent battery polarity reversals, energize the starter
solenoid, and prevent reengagement while the engine is running are what the box prvents,...???

 

[1 Patriot-of-many]

When someone figures out the parts numbers/items involved please post. It would be great to just repair these rather than buy a new one.

 

[racing4funn]

I bought an extra one because I wanted extra electronic parts for an EMP day. I opened one up and saw to old school type starter solenoids. I thought well those cant be hurt by an EMP (not sure what part of.the truck can.). I didn't pay much attentionto how it's wired but I bet they are parallel so that they share the load and if one goes out then the other still runs the truck. Redundancy that the military usually wants.

 

[TexAndy]

Any EMP close enough/powerful enough to kill the electronics on your truck will be eclipsed by the heat/blast melting the frame and tossing the wreckage 1,000 yards.

It's not an issue.