lsintampa

I didn't want to hijack the thread here:

https://www.corvetteforum.com/forums...post1594558920

So, I'm starting a new thread.

In testing the tach board, it appears to be OK... that is when I apply +12 and ground the needle does seem to "settle" at some point.

Following the video, I reset my needle and the needle now sets to ZERO when I apply power with no input - just power.

I'm going to test continuity next, but I have run into a question.

I can't seem to find this "filter" in the engine bay. Seems like the tach wire runs right into the harness - no filter can be found.

What is the function of the filter and do I need one?

May be worth noting that the engine is a 1980 Z28. Doubt that matters much, but worth noting.

Thanks,

Len

lsintampa

Well I did the zero-set thing and the tach works just fine.

I still don't see any "filter" and I'm questioning it's function?????

Thanks,

Len

BKarol

Usually it is located here. It offers some protection to damage that may occur if high voltage is running amok. Mine was removed in 2001 and so far no problem. If there was a problem it is easier to replace a burnt filter then going behind the dash for the circuit board. :

0Willcox Corvette

Even if the zero set worked this doesn't mean the tach board is good...

If you test continuity you don't test through the filter... you test from the filter connection to the clip inside the speedo/tach housing.



The tach filter on a 1980 should be located in the position shown below... if you don't have one this will not stop the tach from working.



The purpose of the tach filter is to knock the edge off the square signal and help prevent spikes to the tach board. But the factory tach board and all reproduction boards can read either a square signal or a rounded one.

The only way for you to test the tach at this point is if you can input a square signal on the input wire or send it to me.

Since the board can read both signals, it's common for people to remove the filter and plug the tachometer wire directly into the distributor... So not having a filter doesn't seem unusual.

What is the tach doing when it's installed in the car? With power and ground the tach should go to zero... but if there is an issue on the board with either side (sine or co-sine) the board may not function properly.. so again, what is the tach doing when it's installed.


Willcox

lsintampa

Well, when I said it's working fine, I mean that it is installed in the car ... albeit sans the filter and sans in it's final resting place in the lower dash pad. Meaning the tach is hooked up to it's connector... zero set.... when I start the car the tach is behaving properly as I throttle the motor, the tach responds as it should.

0Willcox Corvette

Sorry, I missed your "works fine" in this post...