Koso TNT-01 Multifunction Meter

TimG

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I purchased the Koso TNT-01 meter and everything is wired up and functioning properly except the tachometer. The attached instructions show that there are multiple ways to cable the tach wire. In talking with Koso tech support they said to attach the tach wire directly to the positive wire coming off of the ignition coil. I have tried both the brown wire and the orange wire shown in the attached picture of the coil but it doesn't seem to work. The attached also shows how I currently have it wired which is to wrap around the plug wire. This method works pretty well and there is only a little bit of tach chatter. the response to the throttle is also pretty good. I feel like this could be rock steady with the proper wiring and would prefer to hard wire it.

Does anyone have any idea of which wire (positive side of coil) I should be using? Or have any other ideas?
Any help would be greatly appreciated.
IMG_7047.JPG IMG_7046.JPG IMG_7045.JPG
 
Is there something you can change on the meter, maybe a dip switch inside, or wire to a different terminal to select between tach sources? To see which coil wire is ground measure from the terminals to ground and the one with the lowest resistance is the ground.
 
With the old-school points ignition, you'll get your tach signal from the coil's negative side, the orange wire in this case. Getting tach info from the coiled wire means that the instrument's tach input is working. The coiled wire signal is quite suppressed compared to the points signal. You may need to put a resistor in series to the orange wire.

Similar challenge.
Posts #81 to the next coupla dozen discuss his tach wiring.
Post #206 is his solution.
http://www.xs650.com/threads/large-spine-frame-xs650-egli-rau-cafe-racer.51029/page-5#post-542812
 
I have a koso gauge -- you need to go into the settings for tach, and switch to "Lo" or "Lo-Act", you also have to set the pulse setting to "1" ( the reason for this is to tell the gauge the signal is negative, "Hi" is for positive coil inputs).

Make sure you splice into the negative coil wire. ORANGE!

The UK Koso representative told me they are not set up from the factory and won't work unless you do this -- after much head scratching.

I also added a 2Mohm resistor inline to the gauge, because it will read high otherwise - well it did on mine, by about 1K.

Cheers
 
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I added 3M ohm resistor (it was the closest I had to 2m) and the tach seems to work well but the bike runs rough. Could it be the gauge wire I used to make the splice cable? Orange wire connects to a 2-way split that has 1 wire with a resistor in line with the meter and the other is a straight connection to the grey wire that the orange was originally connected to. As soon as I put the wiring back to original and take the split cable out of the equation, the bike runs great again.
 
Yeah, I didn't cut my ignition wire, just soldered the gauge wire to it further down the loom and wrapped it back up. It doesn't seem to make any difference to the running.
 
which is why I wonder if I used too small a gauge wire...Not being a jerk, just scratching my head still.
The orange wire to the coil is the negative pulse for your Koso, you are only taking a signal from it. You only need to "tap" the wire to get a signal.
Ideally just solder your orange wire back together, and while you're there, solder on your red/brown (to the Koso). If you chopped and spliced your orange wire the hardware you used (or how it is connected) may not be up to the job.

Grim
 
Koso tech support has been super helpful. I was sent a faulty speed sensor and they took care of it right away. They don't really have any advice as far as the tach issue goes though. I ended up buying a $2 22-turn 220K Ohm trimpot and wiring it inline with another 100K fixed resistor before the meter as a filter. Koso wants $30 for the exact same 500K ohm "Tach Signal Filter". I also took out the homemade Y connector and soldered a splice right off of the orange coil wire. The bike is running perfect and the tach seemed to smooth out at around 230K Ohm of resistance.

Screen Shot 2019-07-02 at 2.54.53 PM.jpg
 
Good news.. as a follow up, I took my 2Mohm resistor off and wired it direct, found that it works just as well. As long as the settings in the tach are correct!
 
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