70 challenger tach circuit board

[mdliska]

so here is my problem, one of the resistors in my tachometer is burned up to the point that i cannot figure out what resistance was suppose to be. i would like to fix it and not just replace it with a new board. i was woundering if anyone on here would be able to tell me as i cannot find a picture of an orignial tach board anywhere. it is a 1970 challenger rallye dash tach. i have included a picture, the resistor in the red box is the burned one obviously. thanks for you help

[Pete in NH]

Hi,

I'm a retired electrical engineer and I would be willing to bet that one burned resisitor is very likely not the only problem on that circuit board. Those old carbon composition resisitors are pretty rugged. If it cooked that badly something else, like a transisitor, died and caused the resistor to handle a lot more power than originally intended. Sorry, don't have any information on these tachs, so I really can't comment further on what the original value might have been. You might try tracing the circuit and making up a circuit diagram. That might give a clue as to that resisitor's  position in the circuit and a hint as to a range of original values. That's somewhat of a long shot though and in the end a replacement board might be the only real option. Good luck with the project!

[mdliska]

yeah that was one of my major fears but i have checked everything else on the board with a multimeter that i can and everything looks fine. it just the one stupid resistor that i cannot read. the tach shorted itself out against the block with the signal wire and that was the only thing that died, lucky i guess.

[DC_1]

Just buy a new one. Don't risk another failure

http://www.mrheaterbox.com/premiumdashdecals.com/tachboards.htm

[mdliska]

if i cant get it working i will try one of those boards, thanks for the link to the oem stuff though, that helps