Tacho / Rev Counter

[ajstars]

My 3rd Gen Tacho has died. A search on the forum only suggests check for loose connections which I have done at both the dash end and at the fuel pump end (although I am not too sure which of the 5 connectors it is) or to look at the circuit board on the back of the tacho.
Well, having removed it the board looks ok to the naked eye - it seems a simple affair containing a couple of resistors and capacitors.
Any ideas how I can test the tacho or the signal coming to it?

Update - discovered from the last owner that the tacho has been intermittent for a while. Not sure if that helps or not!

[ajstars]

Fixed

Thanks to some guys on the electronics point forum, this has now been fixed.
Initially it was thought likely to be a capacitor, which I replaced, but to no avail, but then just as I was about to give up I briefly touched each soldered joint with a hot iron and component marked 153 (top of the photo) flew off the board as soon as I touched one side of it. It was very clearly a dry joint which was invisible to the naked eye or under a magnifying glass (but strangely quite obvious on the photo!).
A simple dab of superglue on the end of a paperclip allowed me to hold the component back in place whilst I re-soldered it.
Result, one working tacho :-)

So if anyone else is having intermittent faults with components, before spending time and money chucking stuff away and searching for replacement parts, try the quick method of a hot iron on each joint, held very briefly (less than 10 seconds and do one side at a time allowing the component time to cool). I used a gas soldering iron with a pointed tip, so that I could vary the temperature so as to not be too hot, but just enough to melt the solder within a couple of seconds.

It literally took me five minutes to fix and re-solder every joint, just to be on the safe side!

I would imagine this is the same fault that people are experiencing with their speedos too. I am no expert in electronics, (although do have some relevant experience) so I am sure most technically minded people could fix it, however if you feel you can't, I would be happy to have a go for you and save you the expense of getting new components.

[PaulUganda]

Thanks for this good info! I am having exactly the same problem with my 3rd gen.
Is it easy enough to dismantle the dash to get access to this board?

[Karma Supra]

I love fixes like that, really satisfying!

My rev counter doesn't work properly, but that's because I fitted a V8 and the pulses input is wrong

[BUSHWHACKER]

I love fixes like that, really satisfying!

My rev counter doesn't work properly, but that's because I fitted a V8 and the pulses input is wrong

It should still work, the 1UZ gives out a four cylinder pulse the same as the 1KZ.
Did you take the tacho signal from the ECU or the diagnostics box?

[ajstars]

Thanks for this good info! I am having exactly the same problem with my 3rd gen.
Is it easy enough to dismantle the dash to get access to this board?

Really easy, less than 5 minutes. Two screws above the dials, two on the top of the panel below the steering wheel, ease out the bit around the key cylinder and then four screws holding the dial unit in. Just make sure you know which screws are which as a couple are slightly different.
Remove the electrical connections and clear plastic screen from the dials then there are three small brass screws holding the tachometer in. The needle can be eased off with a small screwdriver. Try to mark where it goes on the shaft if not mine was on 0 at normal resting point.

[Karma Supra]

It should still work, the 1UZ gives out a four cylinder pulse the same as the 1KZ.
Did you take the tacho signal from the ECU or the diagnostics box?

Yup, but the I think the VVTi is different to the earlier 1UZ. The rev counter does work, but reads 1/4 of what it should.

I took the Tacho signal from the ECU.

I don't recall the diagnostics port having a tacho point?

Largely most of the wiring worked first time..

Things that don't seem to:

-ODBII Port
-The Aircon idle up ( I took ages getting the aircon gassed and haven't looked at it)


I think I can get the cruise control working too

[PaulUganda]

Really easy, less than 5 minutes. Two screws above the dials, two on the top of the panel below the steering wheel, ease out the bit around the key cylinder and then four screws holding the dial unit in. Just make sure you know which screws are which as a couple are slightly different.
Remove the electrical connections and clear plastic screen from the dials then there are three small brass screws holding the tachometer in. The needle can be eased off with a small screwdriver. Try to mark where it goes on the shaft if not mine was on 0 at normal resting point.

I have followed your instructions and the Tacho is working! It was an intermittent fault but before I started the counter was dead. I took it apart, resoldered all the joints on that board, and it's now working. Time will tell but I am hopeful. Thank you for sharing this information!

[toyjeep]

Big thanks for this info. Had a rev gauge issue where the the needle had become totally erratic jumping all over the place.
Took the rev gauge out and remelted all the solder on the board and it fixed the problem. The photo above no longer seems live. For anyone else with a rev gauge problem this is the likely cure. The joints all looked fine to the eye but clearly were not. Thanks again