75 Tach Circuit Board (pics)
Thread Starter
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
75 Tach Circuit Board (pics)
Does anyone have a diagrahm of the tach circuit board, or can tell me what the bad compontnts are in the pictures and where to get them ? I installed an aftermarket board and it is junk. Only accurate at idle, and completely drops out after 4000 rpm. So I'm going to try fixing the original. The two components that I'm indicating have the ends discolored as if they have been hot, so I'm guessing they are the reason it doesn't work. Any help you can give me would be great.
I know there is someone on the forum that repairs them, and I guess I would send it out as a last resort, but I'd like to try it myself.
I know there is someone on the forum that repairs them, and I guess I would send it out as a last resort, but I'd like to try it myself.
Last edited by '75; Sep 13, 2008 at 03:22 PM.
Team Owner
Joined: Jul 2006
Posts: 22,192
Likes: 4,180
From: Kannapolis NC
From the pictures, it looks like the solder connections are loose at both ends of the two diodes you point out. I would try getting a good solder connection on those ends. You can measure the diodes out of the circuit and you should get open (infinity) in one direction and not in the other. It looks like the solder connections are broken and that will cause heat. The components may be ok.
Thread Starter
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
OK, I was able to check the diode in the top middle with it in place and it is open one direction and shows abut 3 ohms the other way. The diode on the bottom right, I removed one end from the board and checked it, it's good too. The pic's were decieving about the solder joints, they were all good. Any more Ideas or things to check ?
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Send Aceco a PM. I believe he is an ace with the tach boards.
http://forums.corvetteforum.com/priv...=newpm&u=55004
http://forums.corvetteforum.com/priv...=newpm&u=55004
Team Owner
Joined: Jul 2006
Posts: 22,192
Likes: 4,180
From: Kannapolis NC
Send Aceco a PM. I believe he is an ace with the tach boards.
http://forums.corvetteforum.com/priv...=newpm&u=55004
http://forums.corvetteforum.com/priv...=newpm&u=55004
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
There's no doubt that those diodes have been hot. Either they are undersized by design [and all circuit boards show that kind of heat on those diodes], or too much current was passing through them for some other reason. It wouldn't cost but a few dollars to replace them and see if the board starts working OK. [Keep the band on the same end as the ones you will remove.] You might find that the 'replacement' diodes just get hot like the originals...because something else is the problem.
Race Director
Joined: Aug 2008
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