Leeroy_25

So my 1994 FD3 rev Counter (Tach) when all crazy town on me but I have actually managed to get it fixed by the look of it. At least partly. After replacing the Capacitors and re-soldering everything. Mainly the chip legs I think. The Tach now reads nice and steady. only issue is it appears to read about 500rpm high if the readout from my microtech ECU is good. Which I assume it is? So maybe the variable resistor or what ever it is on the back got knocked during soldering and refitting and so on.
Does anyone know if there is an easy way to calibrate this out of the car as there is no way to get at it when it is fitted other than that it will be guess work adjustment and I don't know which way or how much to move the screw top to start with? Any help on this would be great please.
Thank you
Lee

Leeroy_25

Anyone please help on this?

OG BBF

when you took everything apart on the board you done the repairs where the tacho attaches to, remember seeing a blue round plastic adjuster in the top right corner? That's the potentiometer, it's where the factory calibrates it from. youll need access to this but also an accurate rpm signal which I doubt is possible at home. You may be better off sending it off to be calibrated by a shop.....they are better equipped to do this. The speedo is easy to do yourself but the tacho from what I can remember would be very hard.

but for the screw it requires small adjustments.

clockwise will decrease rpm reading
anticlockwise increases it.

so if your reading 500rpm higher. Try turning it a touch clockwise and see what it reads then when plugged up

Leeroy_25

Perfect.. If there is a tried and tested way to do it on a bench someone let me know otherwise I will go with the trial and error using the adjustments above. Thank you for that info.
I did start reading a post somewhere about doing one on an early RX7 Gen1 tach with a battery and battery charger but I didn't quite get it and not sure if it would work for the FD tach. Not the sort of thing I want to try on the off chance in case I totally fry it having just got it working again!
Have not got a clue where I would take it to get it calibrated? Who does that sort of thing usually? i.e what trade would they fall under? so I can try a local search.

Cheers
Lee

OG BBF

There's a machine they use which basically connects to the rear of the cluster board to the appropriate terminals, one ground and one 12v power to make the board work but it has a 3rd attachment which connects to where the tacho receives its rpm speed signal. Then on the machine you have a **** that you turn to send a certain rpm signal for example 200rpm then you just adjust the potentiometer on the cluster so the needle reads the same. They do this for all the ranges to ensure accuracy. Such a machine would cost thousands :/

Companies like hypertech or US speedo would be your best bet for this, just goog the up

all the best.

Leeroy_25

Thanks for he info.. I will give it one go as a guess and mark the potentiometer before I move it. Then if it is no good maybe I will send it off somewhere or see if there is someone anywhere near me. I can't bloody believe this.. Just thought I would google those companies you came up with and then off the back of finding what they do I googled speedo calibration. A place came up in the industrial estate not 2 mins up the road from me!! Walking! I will wait to see if they have the gear though. Speedo and dash cluster specialists though. Fingers crossed!

Cheers
Lee

DaleClark

iTrader: (55)

I've calibrated mine, it's SUPER easy.

If you have a good external tach reference (like a PowerFC commander, boost controller, or an aftermarket ECU) you can use that. Just adjust the pot until it matches. If you want to be SUPER careful you can adjust it with the car off, start the car and check, but you should be able to do it live.

I've done it on my car in the past. This isn't some crazy fancy exotic circuit, it doesn't require some special tools or anything. If you can get it close enough so the tach is useful, you win.

Dale

Leeroy_25

Thanks Dale.. How did you go about that? I assume you must have stripped the tach out of the cluster and wired it in straight to the screws in the back that hold it into the cluster? If so what wires do I need to go for.. I might give that a go. sounds a bit dicy to make sure nothing gets shorted but other than that I can see it should be okay!? Should have thought of that sooner really! I presume nothing else gets messed up not having the rest of the cluster connected?
Cheers
Lee

DaleClark

iTrader: (55)

I did it so long ago I can't remember. If you can't get to the screw with the tach assembled you may need to do it in stages (turn pot, install, start car and check, remove tach, repeat) or you could get 3 jumper wires with alligator clips and have it out in your hand. Just be careful not to touch anything electrical when the system is live, but that shouldn't be hard.

Dale

Leeroy_25

Had a stab at his today and ended up getting it within about 50rpm or so after about 4 goes. Thought that was pretty reasonable. Took me a little longer as an earlier post suggested turning the potentiometer clockwise to reduce the over reading. However it turned out to be counterclockwise! I reckon to correct around 500rpm over reading I moved it about 30degrees. Sound 12oclock back to 11oclock should anyone need to do the same.

Thanks for the help guys after a year of having a completely useless tach I now have one that works.. For the time being at least!