Tachometer Electronic-Circuit Boards
Today, we see Corvettes with dramatic horsepower gains, still keeping with emission standards. But to match HEI in the mid 1970s, Chevrolet had to mate a circuit board that could handle those "high-tech" electronics and keep rpms reading normally. Today's late-model C3 owners enjoy Corvette's foray into electronic ignitions but also deal with its circuitry limitations. Vendors are now producing new boards with modern components that are better built than those boards of the 1970s.
Image to the right shows tach boards from 1975-82.
Your Tach Says a Lot. Make sure its right.
High-energy ignition (HEI) was introduced in 1975 and “sparked” 35 percent higher voltage than the conventional ignition coil. To match HEI in the mid 70’s, Corvette had to mate a circuit board that could handle those “high-tech” electronics and keep RPMs reading normally. Today’s late-model C3 owners enjoy Corvette’s foray into electronic ignition but also deal with its circuitry limitations. This article details how to troubleshoot, select the appropriate tach board and install in your late model C3 Corvette.
PS: A new board will fix 95% of all tach problems
This image compares the components of a new board (above) with an old board (below) that calibrates the tach board for each model year. On the left, the blue component that fits a Phillips screwdriver calibrates this board. Below it and to the right is a chip (black and white) from 1970s that was used to calibrate the board. It had to be laser etched. The article referenced above includes a "buyer's beware" section. It outlines what you should look for when buying a new board.