Engine Does Anyone have the Schematic for the Prestolite Ignition Control Module Board ('76 CJ-7)?

[iChuck12]

Hi Jeep People-
Long time reader, first time posting.

I've been reading previous posts about how the factory Prestolite modules get hot and quit working. I bought a '76 CJ7 for parts and sure enough, the module had melted pretty good.

I'd like to take a crack at rebuilding it. I know I can get a new one for cheap, or replace the whole system, but as an electrical engineer I thought it might be a fun challenge. I was able to heat up the goo in the module enough that it released the board. Although not in the pictures (attached), there's an obvious burned component. Before I create a schematic from scratch to figure out what the component was (it's burned beyond recognition) I thought I'd see if there was a schematic for the unit floating around.

Thanks in advance for any information.

Chuck

 

[CJ]

I have searched high and low but no information...

Interesting project though...

 

[iChuck12]

I have searched high and low but no information...

Interesting project though...

Thanks for looking, CJ. I'm having trouble with a few of the components (the tar stuff dissolved the numbers), but I'm hoping to map it to a schematic and just leave the unknown components as question marks. Still might be able to do it.

 

[CJ]

Thanks for looking, CJ. I'm having trouble with a few of the components (the tar stuff dissolved the numbers), but I'm hoping to map it to a schematic and just leave the unknown components as question marks. Still might be able to do it.

This is an interesting project. As an ex engineer who used to repair computer boards for 1st gen CNC machines in the late 70's / 80's I also like to fix things.
Nothing beats a cold shot for finding thermo problems!

 

[iChuck12]

Well, I went ahead and made a schematic of the ignition control module. The big remaining questions: what is the IC-1 chip, and what is the power resistor value (in purple). The power resistor is the part that burned; its a wirewound low Ohm resistor, but I can't tell the value.

If anyone has an old module that you are not using and are willing to part with, I could take it apart to see if I can get the transistor markings and the power resistor markings. That would then just leave the IC to figure out.

And if anyone wants to add any wisdom or information, that would also be helpful.

 

[Belizean]

Well I looked. I thought I had an old 84. I must have tossed it thinking I would never go back to it again.

 

[iChuck12]

I posted this on an electronics forum a few weeks ago, and the helpful people there pointed out that I mislabeled the two zener diodes (they're voltage control diodes) and that T-2 is nor a TO-3 package but a TO-66 package. Man, can they be picky about details.

I think all of the components except the burned resistor are still good, so I'm going to replace that with a higher wattage low ohm resistor, and add some beefy heat sinks to the transistors. Then I'm going to hook it up and see what happens. Wish me luck.

 

[Patrick]

You might just get lucky and get it working. It would be ideal to put it through conformance testing on the bench, but you would need a power supply, signal generator, oscilloscope, output terminations, multimeter and maybe a rheostat. It is just a trigger circuit for an ignition coil with maybe timing and temperature parameters.