Tach finall works

[BDHender]

I learned a few things that might come in handy to others in my backdating of a 3.2 Carrera to become a Euro SC for Club Racing purposes. I learned a lot through partial help, a little thought and some good guesses. One of the areas I could fine the least help in was the tachometer.

The Carrera tach does not appear to be compatible with a Bosch CDI from an SC. I could not get any signal at all to show up in the wiring when connected correctly between the Carrera tach and the CDI box. I even bought a fancy multimeter to determine this. I figured my old one just could not pick up the signal. My first thought was this was because the CDI was not generating a signal and was bad. I read an old email from Lauren who indicated the CDI only provides a ground that opens and closes. He said you could even use a grounded file to make the tach work by rubbing the “signal” wire on it. This made sense although several folks seemed to disagree with him. I bought a new SC tach and instantly had a working tach and a measurable tach signal. Like many gages the tach apparently is powered by a 12 volt wire and uses a variable ground to make the gage read. My guess is the Carrera tach is looking for a positive signal from the Motec.

Bryan

[Early_S_Man]

Bryan,

It sounds like you need to ad a pullup resistor to +12 Volts ... a 1000 Ohm, 1/2 Watt resistor between the TD signal wire and the +12 Volt lead on the back of the tach should do it ... then see if your 'fancy' meter can read a signal! Meters of the plain or fancy variety aren't the preferred choice for looking at puls trains ... as previously mentioned, a logic probe [set to CMOS levels] or oscilloscpe are the tools of choice!

Otherwise, you might try to find a friend with electronics experience ... NOT of the board-sapping kind. It takes soldering iron use, and component-level troubleshooting ... to know what to do next!