Links for testing tach? Failed after dash swap...

[JiXer]

So yeah... My customer brought his car to me after he swapped his dash and the tach is now dead.
I know it could be the SI battery, but I don't have another one handy for testing. May just order one anyway.
But in the mean time, I am looking for tach trouble shooting links and How-to's and havent found a way to use a multi-meter to see if the cluster is getting a proper signal. I figured that the best way to determine if it is chassis side or cluster side.
Anyone got anything?

[e30orDie]

Funny... I pulled my dash last night... put it back in.... and had no tach today....

all fuses checked out.... I also have no MPG gauge (not that it worked) but its no longer powered)

I've been googling around..... I found something about frying the SI boards.... :( and I'd have to almost agree (with my case) its the SI board / Batteries.... because the MPG is no longer powered on (stays a zero typically, Far right side) now its far left....

I send signal via 5v square wave (IIRC) I'm standalone though, but its tied directly into the blue plug on the cluster....


I have yet to tear back into mine to see what happened..... but theres no way my batteries just died, and all fuses check good, and I seriously doubt my solder connection gave loose....




The best thing to do is figure out what else isn't working.... mpg gauge? OBC? cab and trunk lights? There's probably something else that gave, and this will help locate the possible problem.

[Semblance]

From what I understand, the econometer needs both tach and speedo to function, so no surprise if it dies at the same time as the tach.

My tach/econometer also quit after I went to tighten the grounding screws in the cluster. I replaced the SI batteries but that didn't fix it. Finally swapped in another cluster, working fine, so I must have had something bad on the old SI board or main board, I guess my man-handling of the cluster must have broken a weak solder or something. And the mpg gauge on my obc was working fine the whole time the tach/econometer was dead.

From digging around I gather that the tach gets it's signal from the DME so if you swap in a known working cluster and that doesn't fix it, you either have a bad connection or a bad signal coming from the DME. Saw something about a three-pin connector under the dash but was unable to locate it. But if this suddenly happened after swapping the dash, maybe it's just a bad connection?

Edit - here's the link was looking at:

http://www.e30zone.net/e30zonewiki/index.php/Instruments

[Gregs///M]

Try my thread on SI board damage.

http://www.r3vlimited.com/board/showthread.php?t=274422

If your SI board batteries have never been changed, assume they are dead.

[JiXer]

Are motometer and vdo the same battery?

[Gregs///M]

Yes, there are lithium 3V types and Nicd 1.25V types. Both interchangeable between the two brands.

[JiXer]

What about the SI board itself? I'm guessing they are not interchangable?

[Poorboyz]

What about the SI board itself? I'm guessing they are not interchangable?

Yes, they are.

[JiXer]

Really? Wow! Thats surprising to me. OK, so I have a good VDO si board that has been sitting around for years. What are the odds the batteries are still good? :)

[jlevie]

Really? Wow! Thats surprising to me. OK, so I have a good VDO si board that has been sitting around for years. What are the odds the batteries are still good? :)

Slim to none.

Early cars, up to 9/87, have a three pin connector off the engine harness near the DME. The tach & ecoometer signals go though that connector.

[JiXer]

So I'm assuming the batteries are constantly charged while the car is running. Could I simply jumper a 3v (or whatever it is) supply in there for testing?

[Gregs///M]

So I'm assuming the batteries are constantly charged while the car is running. Could I simply jumper a 3v (or whatever it is) supply in there for testing?

Only if the batteries are capable of holding a charge. 20+ year old batteries, most likely not. You can however replace the batteries with an exterior power supply using a DC to DC converter. So you would need a 12V DC converter to a 3V DC converter.

[JiXer]

Favorite place to buy the batteries?