Tiger Tach Rebuild: Getting one for your car
Dec 3, 2002
Updated: May 3, 2011
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Price and Ordering Information:

Assembled and tested board: $100 US, shipping included.
Rebuild service for your tach: $180 US, plus shipping by your preferred carrier.
Prices may change without notice.

You can buy the boards, modules, or get your tach repaired by the following people:

Theo Smit
107 North Valley Bay
Calgary, Alberta T3R 1H9

Tom Hall
5712 San Luis Ct
Pleasanton, CA 94566
Tom's email: modtiger@comcast.net

I accept cash (sent at your risk), money orders, personal cheques (10 day hold), or PayPal.

This circuit is not a cure-all for your tach or your car. If the function of your tach is impaired by a mechanical problem with the meter movement, or if the movement coil or the transformer coil are broken, this circuit can't compensate for that. The calibration procedure described in this document sets the meter display to be correct at a single engine speed, within the tolerances of the meter movement's mechanical friction and inertia. The testing and verification of the tach accuracy at other RPM values are up to you. This tachometer circuit has no function as an engine RPM limiter. If you think that you might be exercising the upper end of the rev band with your engine, invest in a quality rev limiter.

Schematic Diagram and Circuit Board information

Installation in Your Tach and Calibrating Your Circuit

The picture below shows the required connections on the board. The wire colours follow the scheme used by Smiths. The intent is that you'll be able to hook up the circuit without permanently altering anything inside the tach, just in case you'd ever want to restore the thing to it's original condition.

Installation begins by disassembling your tach.

Assembling the circuit board into the tach requires some soldering skill, and a pencil-tip electronics soldering iron of 25 to 35 Watts. Do NOT use a transformer-type solder "gun" like the 100/140W Weller, because the magnetic field set up by these things will affect the tach's field magnet, and because it's way too big for the job.
The best solder for the job is 60/40 rosin core electronics solder. Don't use acid core solder under any circumstances, and "lead free" solder is meant for plumbing, not your tach.

First remove the OEM connections to the meter movement and the current transformer wires.

The circuit board is installed by ziptieing (?) it to the meter movement's magnet bridge.

The power connections are made next.

Finish up with the current transformer wiring.

Calibration is required to correct for tolerances in the electronic components, in the magnetization of the meter movement, and the mechanical condition of the meter movement. Like the OEM circuit, the new tach circuit has a single calibration adjustment, which allows you to set the scale reading to a reference at one RPM. I recommend that you do the calibration at 2500 to 4000 RPM. Lower than this, and any errors made in the calibration will multiply by two or more at the top of the scale; Higher than this, and you run the risk that the lower and middle range accuracy is seriously compromised due to mechanical or magnetic errors in the meter movement. Besides, if you've built a high-revving killer motor for your car I'd hope that you'd protect it with an electronic rev limiter, as opposed to just the connection between your eyes and your foot. A Smiths tach is NOT a racing instrument of the 21st century. To install the tach in the dash, refer to the appropriate diagram on the wiring page. If you're not using the voltage trigger mode, insulate the end of the white trigger wire, and tape it up out of the way; if you're not using the current trigger connection, don't run any wires through the current sensor transformer loop.

Tach Rebuild Service
The tach rebuild consists of If you decide to ship your tach to me, please observe the following precautions:
1. Tape off any holes on the back of the tach case (the light hole)
2. Enclose the tach in a ziplock baggie or similar air-tight bag.
3. Use foam, packing peanuts, or bubble wrap to COMPLETELY fill the box you're shipping it in. If the tach can't rattle around in there it stands a much better chance of survival.
4. I live in Canada. Customs regards anything that comes across the border as something that I've bought, and therefore they reason that I ought to pay GST (7%) of whatever the value of that thing is before I get it in my hands, unless there is clear evidence that I didn't buy it. So by all means, insure your tach for whatever you think it's worth, but label the contents as being "used antique car tachometer", and that the value is "for customs only, no commercial value". The Harmonized Tariff Code is 9029.20.40.80, near as I can figure, or you can try to find a better match in the official doc at: ftp://ftp.usitc.gov/pub/reports/studies/0205htsa.pdf
5. You can figure out what the return shipment cost will be by choosing your method (Canada Post, UPS, or another courier service), hitting up their website, and finding their rate calculator.

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Images and text copyright 2002-2005 Theo Smit. All rights reserved. Information presented on this webpage is presented for educational purposes only and I make no claim about its suitability for your particular situation.