Doom86

Sorry if this is long winded I've been trying to fix this thing for 6 hours and I may be going cross eyed from staring at the circuit board for so long.



Having 2 camaros and both having well off tachs I fixed the 91' tach no problem using the sticky; https://www.thirdgen.org/forums/elec...meter-fix.html

Now the same exact method works for my 86 tach the only difference being that instead of having some handy little board to work on you have to remove the tach and it's on a board on the back of it.

I used the direct method first (no cutting) and like my 91 it needed to have the pins for 4 and 10 cut because it was making the 196k turn to 125k once connected and it was reading low when running. I was checking it against a engine analyzer.

To cut the pins I had to take it apart, easy stuff no problem. This time though when I put it in the car I could smell burned electronics and when I started it the damn thing smoked bad, I yanked it right out of the dash when it started smoking.

The only thing that changed from the first time was the board was removed from the tach and the pins cut and removed. No solder, that's it. The resistors were soldered on the bottom of the board so they didn't need messed with.

Now the REAL problem is the resistors are grounding out now. I checked continuity against them and the ground and its there. The same is now true for the cap, where it was reading 125ohms before, it's now grounded out.

I went over this thing for hours looking at the ground circuit and it doesn't touch anything it shouldn't. I took caps off the board, cut grounds off teh board, took the resistors on/off and I'm lost now. All while probing.

My concern is that I may have assembled it wrong and shorted something and/or fried something, I don't know, it was very straight forward. The only questionable part of the assembly was this white rectangular piece that either went on the back of the oil gauge or tach. Since the only change was this I'm thinking it's fried something. I put the white piece on the oil gauge but I think it could go on the tach. It seems simple to remember but the kids were being kids while I was trying to do this so I was side tracked.

Could a popped capacitor cause a short like this? It's the only thing I can think of because some of them have grounds going to them, the other grounds are all accounted for.

Jim85IROC

iTrader: (2)

My general experience with electronics is that once you let all the smoke out of something, it's usually toast.

That said, if you burned up some capacitors, you'd know it. Your whole car would smell like somebody crapped in some dirty differential fluid and then set it on fire, captured the smoke and mixed it with ammonia.

In other words, burned capacitors stink like hell.

For what 85-89 tachs cost, I'd probably just start fresh with a new one and avoid the headaches.

Doom86

Jim Thanks for the help and advice.

There's not a decent JY around here that I know of. I went and checked one out the day after the OP and it was basically a guys house with a bunch of crap in his yard. But Radio Shack isn't far and I'm good with solder.

What besides crossing solder could cause the tach board to ground out?

Remember the tach was reading off, solder down 196k to bottom, tested in car showed it needed pins cut, cut pins put it back in car to test it smoked and pegged tach needle. Now it's grounded out just sitting on my desk.

I double, triple and quadruple checked that I cut the right pins.