Dodge Ram compass module fix

[TheGeneral]

The compass & outside air temp display in my '94 Ram 2500 had been erratic for some time. First the display lost a couple of segments, then there was no display until you'd been driving a few miles & finally it just quit. I could have tried sourcing a new overhead console on Ebay or wherever - apparently all the 90's Chryslers use the same compass module - but I had nothing to lose by trying to fix it.
The overhead console comes out easily, the compass module is in a plastic housing inside. Open this up & there's the printed circuit board.
First job is to get it on the bench under a strong light & look for anything naughty. Well the centre one of the group of three capacitors in photo #2 has split underneath & leaked pus over the board & damaged a couple of tracks - probably responsible for the missing display segments. I bridged them out on the back of the board (photo #3), cleaned the board & replaced the caps, unfortunately still no go.
Both the regulator chips were outputting the right voltages (12V & 5V) so it was time to get the scope out & check for any activity on the processor. That's the big chip at top right with the Motorola logo. Well, no activity at all, deader than Jacob Marley on Christmas day. So I checked the timing crystal, the yellow thing in photo #2. Bingo. No activity. One new 4 megahertz crystal later, we have a working board with a nice bright display & no missing segments. Back in the truck she goes, ignition on, all working. Great. Until the next (cold) day. No display. Damn.
Continued below...

[TheGeneral]

Out she comes again, on the bench, works OK. Hmm. So into the freezer for about half an hour & then run it up again on the bench. No display. Turns out the 5V regulator has a reset output for the processor to make sure it starts up OK, But! the reset output is staying stuck at low temperatures. So, new regulator time. Then back in the freezer for another half hour & then run it up on the bench again. Now we have a display even with a cold board. (photo #5). 'OC' means open circuit as the temperature sensor isn't connected. Photo #6 shows it back in the truck & working. Time for a shot of Jim Beam.
Total cost around £20 as I already had some of the parts.

[ClareSharp]

Fantastic post thank you

Hopefully it will help someone in the future should they have the same issue.