[DML] Tach PC board

["ironranger7012" <kvlauhala@xxxxxxxxx>]

This has to do with that wacky tach of mine.  As I stated earlier the 
tach reads high and wavers. I checked with a service tach off of the 
back of the tach studs under the dash and the readings on the service 
tach were correct (by the sound of the engine) and rock solid. Not the 
tach in the dash. I purchased a new tach a couple years ago which 
produced similar results.  The reason I haven't done anything about it 
until now is a long story.
 
I took my original tach that I kept and removed the PC board from the 
tach gage and made a schematic of the circuit.  I ohmed out the 
resistors and checked the diodes and capacitors.  All appear to be 
functioning properly. By looking at the schematic, there are three 
terminals on the gage. All of the terminals on the gage come from the 
14 pin IC on the board (pins 1, 2 and 12) It makes me wonder if the IC 
is cause for my erradic readings. The IC has a number on the back 
(159777 and CSC 8111). Does anyone know if a common??? IC would 
replace this and what is a replacement number and where can I get one?
 
I would like to try replacing this and check it out by just connecting 
up to +12v, coil and ground. Then I will change it out with the one in 
the car.

Thanks 
Vic 






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