Tach Problem Resurrected
Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 15
Likes: 0
From: Saint James NY
Tach Problem Resurrected
I hope no one is tired of troubleshooting tachs. I read through the old threads first but I couldn't find my problem posted.
Is anyone familiar with what could possibly cause the 12v supply terminal (pink) and the ground terminal (black) to short? After troubleshooting the blown fuse that feeds the gauges (and tearing the dash apart) I found the short in the tach. I didn't pull it yet but now that everything is exposed I very easily can.
The car is a 76. I had it apart while restoring the interior last year and I know that the PCB was intact then. Any help?
Is anyone familiar with what could possibly cause the 12v supply terminal (pink) and the ground terminal (black) to short? After troubleshooting the blown fuse that feeds the gauges (and tearing the dash apart) I found the short in the tach. I didn't pull it yet but now that everything is exposed I very easily can.
The car is a 76. I had it apart while restoring the interior last year and I know that the PCB was intact then. Any help?
Melting Slicks
Joined: May 2006
Posts: 2,590
Likes: 403
From: Nashville TN
St. Jude Donor '09
I don't know what causes the short, but I think it is pretty common. I plan to finally get around to repairing mine this year. I'm just replacing the circuit board. Willcox is now offering replacement tach boards that are calibrated for each year car. Here is a "how-to" from their website that may help.
http://willcoxcorvette.com/instructi...l_11-12=09.pdf
You may want to give them a call as well . . . maybe they can shed some additional light on the subject.
http://willcoxcorvette.com/instructi...l_11-12=09.pdf
You may want to give them a call as well . . . maybe they can shed some additional light on the subject.
Le Mans Master
Joined: Sep 2002
Posts: 5,236
Likes: 898
From: Myrtle Beach SC
Frank
Wilcox has done a really nice job with tach instructions, troubleshooting and installation guidance. I'm attaching link to an article recently published and I think you'll find Wilcox guidance complys with this Corvette Enthusiast article.
Tach Boards
Wilcox has done a really nice job with tach instructions, troubleshooting and installation guidance. I'm attaching link to an article recently published and I think you'll find Wilcox guidance complys with this Corvette Enthusiast article.
Tach Boards
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Frank-
I'm not sure what is causing your short, the tach only requires power, ground and signal to operate. You can test the tach by hardwiring it with power and ground. Once the tach has power and ground it should instantly go to zero. Then run a signal wire from the tach connection to the tach and see if it reads.
If you direct wire the tach and it fails to go to zero, then you have a problem with the tach. The highest terminal on the picture show is the 12 volt terminal, the middle one is the ground and the lowest one is the signal.
I'm not sure what is causing your short, the tach only requires power, ground and signal to operate. You can test the tach by hardwiring it with power and ground. Once the tach has power and ground it should instantly go to zero. Then run a signal wire from the tach connection to the tach and see if it reads.
If you direct wire the tach and it fails to go to zero, then you have a problem with the tach. The highest terminal on the picture show is the 12 volt terminal, the middle one is the ground and the lowest one is the signal.
Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 15
Likes: 0
From: Saint James NY
Thanks for the replies. I'm hesitant to hard wire the board without a fuse. Closer inspection of the board shows a direct connection between 12v and ground with a diode positioned to protect a short circuit. My guess is that that diode is no longer functioning in only one direction. I'm not sure how to test a diode in place so I'm planning to remove it and test it in a test circuit. If its good I'll solder it back in and start over. If it's bad I'll have to figure out exactly what it is and replace it. A wiring diagram of the circuit board would be invaluable if anyone knows where I could find one.
Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 15
Likes: 0
From: Saint James NY
Frank
Wilcox has done a really nice job with tach instructions, troubleshooting and installation guidance. I'm attaching link to an article recently published and I think you'll find Wilcox guidance complys with this Corvette Enthusiast article.
Tach Boards
Wilcox has done a really nice job with tach instructions, troubleshooting and installation guidance. I'm attaching link to an article recently published and I think you'll find Wilcox guidance complys with this Corvette Enthusiast article.
Tach Boards
Le Mans Master
Joined: Sep 2002
Posts: 5,236
Likes: 898
From: Myrtle Beach SC
I think when considering a 76, you're better off replacing the board than messing with an original. New materials, new components and a fresh board. Besides, you don't want to have to tear into that dash again if it goes bad a few months down the road. Today's boards (Wilcox's included) are much better quality than the original's installed.
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Thread Starter
Heel & Toe
Joined: Jan 2008
Posts: 15
Likes: 0
From: Saint James NY
I think when considering a 76, you're better off replacing the board than messing with an original. New materials, new components and a fresh board. Besides, you don't want to have to tear into that dash again if it goes bad a few months down the road. Today's boards (Wilcox's included) are much better quality than the original's installed.
Thanks again - much appreciated...
Le Mans Master
Joined: Sep 2002
Posts: 5,236
Likes: 898
From: Myrtle Beach SC
[QUOTE=Franky Pentangeli;1572706724]I think you're right. I'm getting tired of dumping money into this thing but I'd rather not be penny wise and dollar foolish. I think Wilcox sells Gardner boards. Seeing that John is a CF member maybe he should get the business.QUOTE]
I've corresponded/talked with both. Wilcox now makes his own board and I would rate them at the quality of Gardner...can't go wrong either way. At the time I wrote the article...Wilcox wasn't there. Now he is.
I've corresponded/talked with both. Wilcox now makes his own board and I would rate them at the quality of Gardner...can't go wrong either way. At the time I wrote the article...Wilcox wasn't there. Now he is.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Tom you are exactly right! I like others got tired of the problems and inaccuracies of boards available. So I made them! Each board is pre-calibrated and tested before it leaves the building.
We also have an online video for the 78-82 installation which will walk you through installing the board on the tach as well as how to do the zero set for the needle. (pretty much the same for 1975-1977).
The boards do not have the cheap and cheesy 1 turn pot, they have a 15 turn pot. This creates a more accurate adjustment and also limits the chances of bumping the pot when you install the tach. You can take your finger and tap on a 1 turn put and it will change your reading.
To me and from what I've seen in the past the boards are by far superior to anything on the market. '
Willcox
We also have an online video for the 78-82 installation which will walk you through installing the board on the tach as well as how to do the zero set for the needle. (pretty much the same for 1975-1977).
The boards do not have the cheap and cheesy 1 turn pot, they have a 15 turn pot. This creates a more accurate adjustment and also limits the chances of bumping the pot when you install the tach. You can take your finger and tap on a 1 turn put and it will change your reading.
To me and from what I've seen in the past the boards are by far superior to anything on the market. '
Willcox
Racer
Joined: Dec 2009
Posts: 380
Likes: 0
From: Glendale AZ
I'd consider a new tach board almost a must for every 78-82 owner.
I started with a factory tach that was actually fully functional. One day when doing some adjustment on my timing I hooked up a SUN tach and to my amazement my "perfectly working" tachometer was off by almost 500 rpm. It was correct at around 1000 rpm but as the RPM's went up the tachometer became less and less accurate.
A switch to a new circuit board my factory tach is now within ~100rpm of the Sun tach.
I started with a factory tach that was actually fully functional. One day when doing some adjustment on my timing I hooked up a SUN tach and to my amazement my "perfectly working" tachometer was off by almost 500 rpm. It was correct at around 1000 rpm but as the RPM's went up the tachometer became less and less accurate.
A switch to a new circuit board my factory tach is now within ~100rpm of the Sun tach.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Volition:
You are correct! Factory tach's will do this! If you go to our video on U-tube you'll see that the reproduction board out performed the factory board.
Our factory board was not that far off, but the reproduction board is adjustable where the factory board is not.
18243
Willcox
You are correct! Factory tach's will do this! If you go to our video on U-tube you'll see that the reproduction board out performed the factory board.
Our factory board was not that far off, but the reproduction board is adjustable where the factory board is not.
18243
Willcox
Last edited by Willcox Corvette; Aug 14, 2010 at 09:57 AM.
