Circuit Board, Filter, or Tach Itself?
Thread Starter
Drifting
Joined: Aug 2004
Posts: 1,763
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From: Fayetteville NC
Circuit Board, Filter, or Tach Itself?
My tach does not work. I have a '75 coupe (electric tach). Is there a procedure or sequence I can go thru to determine where my defect is located? Don't want to buy a new circuit board if that's not the problem. I've read on the Forum before about new tach boards being defective, which REALLY throws off the whole troubleshooting process. I can see that happening to me. Maybe we could all get together and purchase a "Forum Tach Circuit Board" and pass it around for everyone's tach repair work. I'll be the holder of the board since I'm so trustworthy. Thanks.
Team Owner
Joined: May 2001
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From: Exiled to Richmond, VA - Finally sold my house in Murfreesboro, TN ?? Corner of "Bumf*&k and 'You've got a purdy mouth'."
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St. Jude Donor '06-'10, '13
You can get a cheap aftermarket tach from any parts store. I use on so I can see the RPM's while working in the engine compartment. Just attach some alligator clips to the 12V+ and 12V- leads. Then unhook the factory wire and slip in the signal wire for the new tach. That will show you the tach output of the distributor works. Then reconnect the factory wire and disconnect the wire coming out of the filter, and then test it there. If it still works after the filter, then usually the circuit board is to blame.
Race Director
Joined: Sep 2002
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From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by BSeery
You can get a cheap aftermarket tach from any parts store. I use on so I can see the RPM's while working in the engine compartment. Just attach some alligator clips to the 12V+ and 12V- leads. Then unhook the factory wire and slip in the signal wire for the new tach. That will show you the tach output of the distributor works. Then reconnect the factory wire and disconnect the wire coming out of the filter, and then test it there. If it still works after the filter, then usually the circuit board is to blame.
Heck it makes sense to me!
Instructor
Joined: Aug 2000
Posts: 107
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From: Houston Texas
BSeery is correct that checking at the distributor is a good first step. If that checks out OK try removing the tachometer and checking the tach wiring up to the connections to the factory tach. If it works OK up to that point it is likely the board. You can buy a tach/dwell meter for about $10 at an auto parts store to do these tests.
My Corvette has a cable drive tach, but I have used the replacement board in my '76 Suburban factory tach, no problems.
Also, the tach filter is a noise filter for the radio, it should not cause your tach not to work. You can bypass it as a test, if need be.
Good luck
Jeff
My Corvette has a cable drive tach, but I have used the replacement board in my '76 Suburban factory tach, no problems.
Also, the tach filter is a noise filter for the radio, it should not cause your tach not to work. You can bypass it as a test, if need be.
Good luck
Jeff
Melting Slicks
Joined: Apr 1999
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From: Moon Twp. PA USA
I, too, am having tach trouble. Little hand tuneup tach works when connected to the line in front of the tach filter. Does not work when connected after the tach filter. Using a volt meter, the voltage is the same on each side of the tach filter - it pulses. Vehicle tach does not work when hooked direct - bypassing the filter.
I did try another tach filter with the same results. Circuit board is out for testing, but I bet that will be the problem.
While driving, tach dropped to zero than needle continued counterclockwise to finally stop at about 7000 rpm.
Who sells tach boards without the rheostat, as I read there are problems with that type of board.
Thanks,
I did try another tach filter with the same results. Circuit board is out for testing, but I bet that will be the problem.
While driving, tach dropped to zero than needle continued counterclockwise to finally stop at about 7000 rpm.
Who sells tach boards without the rheostat, as I read there are problems with that type of board.
Thanks,
