How Does The Tach Work?

2002 VFR800 non-ABS just shy of 40,000 mi.

I dumped the bike back in Dec '05 and in that accident the tach quit working. Lacking funds, I didn't get it fixed.

Well, now I've acquired another instrument cluster. Turns out its from an ABS model and has 31,000 mi on it. I was hoping I could swap the tach from the new cluster to my old one. Thus leaving my mileage correct.

In case you're wondering, the tach is soldered onto the board. Its not hard to remove at all, just a bit tedious.

After removing the new tach and installing it on the old board, it doesn't work.
So, just in case the board was damaged, I tried putting the tach back on the new board. That doesn't work either.

Yes, the tach did work on the new, un-touched, board. So the wiring on the bike can be ruled out.

At this point, I have good connection between the pins from the tach, there's 4 of them, and the board but no motion from the tach.

Does anybody know how the tach works so I can begin figuring out what is wrong with my setup?

TIA

Follow the wires leading out of the tach. Most tachs have a wire connected to the coil, one is a ground, and one to a power source.

How did you wreck your bike? I'm not asking about the accident itself, but what exactly got damaged?

The tach I believe comes from a sensor on the primary drive gear, but I couldn't find it just now. Try hooking up a voltmeter to the tach wires and start your bike and rev it some to see if you can get a reading, that will tell you if the sensor and wiring is ok or if the problem is the gauge. Good luck, I hate electrical gremlins, so hard to find sometimes

[image: View Post]EmeraldVFR, on Aug 24 2009, 09:04 PM, said:

Follow the wires leading out of the tach. Most tachs have a wire connected to the coil, one is a ground, and one to a power source.

How did you wreck your bike? I'm not asking about the accident itself, but what exactly got damaged?
My '02 has 4 wires coming from the circuit board to the windings. I don't know what wires come from the ECU to the dash cluster as they aren't labeled on any diagram I have.
On the circuit board itself, the pin at 11 o'clock says SIN- on it, the 2'oclock pin says SIN+, the 5'oclock pin says COS+, and the 8o'clock pin says COS-.

Here's an image that I took of the old board showing the tack mount w/o the tach face in the way.
http://i60.photobucket.com/albums/h1/1talltxn/tach.jpg

The bike landed on its nose and tail. Damage to the tach itself was the thin metal housing around the winding coil being dented. The windings themselves appeared fine, so I assumed it would work, not the case.

[image: View Post]mrmatt, on Aug 24 2009, 09:07 PM, said:

The tach I believe comes from a sensor on the primary drive gear, but I couldn't find it just now. Try hooking up a voltmeter to the tach wires and start your bike and rev it some to see if you can get a reading, that will tell you if the sensor and wiring is ok or if the problem is the gauge. Good luck, I hate electrical gremlins, so hard to find sometimes
Since I don't have a pin-out diagram of the dash connector, I don't know which of the 20 pins is the tach lead from the ECU. I've stared at the FSM diagram and haven't come up with anything useful. The don't bother to tell you what each wire going from the ECU to the dash do. Rather annoying.

[image: View Post]tx_vfr, on Aug 24 2009, 09:43 PM, said:

2002 VFR800 non-ABS just shy of 40,000 mi.

I dumped the bike back in Dec '05 and in that accident the tach quit working. Lacking funds, I didn't get it fixed.

Well, now I've acquired another instrument cluster. Turns out its from an ABS model and has 31,000 mi on it. I was hoping I could swap the tach from the new cluster to my old one. Thus leaving my mileage correct.

In case you're wondering, the tach is soldered onto the board. Its not hard to remove at all, just a bit tedious.

After removing the new tach and installing it on the old board, it doesn't work.
So, just in case the board was damaged, I tried putting the tach back on the new board. That doesn't work either.

Yes, the tach did work on the new, un-touched, board. So the wiring on the bike can be ruled out.

At this point, I have good connection between the pins from the tach, there's 4 of them, and the board but no motion from the tach.

Does anybody know how the tach works so I can begin figuring out what is wrong with my setup?

TIA
My tach stopped working on my 5th gen 1998 VFR. Turns out the tach is driven my the ECM. Check the wiring diagram in the shop manual. I bought a used tach and ECM from someone parting out a bike. Changing the ECM fixed my tach issue.

The good news is it is easy to change the ECm. The bad new is they are expensive - look for used.

Jack

[image: View Post]joneill, on Aug 25 2009, 09:22 PM, said:

My tach stopped working on my 5th gen 1998 VFR. Turns out the tach is driven my the ECM. Check the wiring diagram in the shop manual. I bought a used tach and ECM from someone parting out a bike. Changing the ECM fixed my tach issue.

The good news is it is easy to change the ECm. The bad new is they are expensive - look for used.

Jack
I am sure that it is not my ECM as the tach did work prior to my attempt to switch it from the new board to the original board.

Talked with an electronics wizard I know and have a couple things to check, but I haven't had time to do those checks yet.