The tachometer on my 1980 stopped working so I replaced the circuit
board. Works now but reads low. Used to read approximately
2400 rpms at 60 miles per hour, now reads about 2150.

Is there any adjustment on the circuit board or on the tachometer
to increase the rpms?

Circuit board was one designed for 1980-82.

 

Mine is actually reading too high, so I'll be keeping an eye on this thread for a solution.

Les

 

TTT. Anyone know?

 

On the one I replaced (a 75) there was an adjustment on one of the resistors (I think that's what it is) , it was white, and in the top left corner of the board with an x for using a phillips driver. Very small adjustments made the needle change dramatically, so I went for "close" at WOT.

Michael

 

I don't know how you adjust it but unless you have a tachometer then I wouldn't bother. You might be calibrating it to a wrong value.

 

ttt

 

I ran a second "sun gauge" tach and matched the readings at 5500 rpm. I found a pic in my files. The new board is obviously the lower one. The round white resistor(?) in the top left corner of the new board is the one I adjusted.

 

Any chance you post some better pics of that circuit board?
Looks like a burnt trace on the ground line, probably due to over voltage and blown zener. The Zener is probably under the brown spot on the left hand side.

You might be able to save that board.

 

I'll check in the parts bin when I get home .... I believe I tossed it.

 

I followed the suggestion in this thread of using another tach to
calibrate the one in the car. I hooked up the dwell/tach meter to the
distributor and placed it facing the windshield. Then started the car and compared the two tachs at different rpm's. I removed the tach in
the car and found an adjustable resister. To increase the rpm's I had to turn the control counter clockwise.
I also discovered that you can remove the tach without removing the
entire dash cluster. Just remove the plastic lens, the faceplate over
the dash bezel, then the tach. When adjusting it, this made it easy as I just had to pull the tach, turn the resister, then plugged the tach
back in and compared the tach readings.

Finally got the two tachs to read the same, but when I drove the
car the tach read too high. Not 100 % accurate, but finally adjusted
it by driving the car to 60 mph and noting the tach reading.
Then pulled off the road, turned the car off and adjusted the tach.
Plugged it back in drove some more and readjusted it till it read
as it did with the original circuit board. Car turned about 2400
rpms at 60 mph.