Speedometer intermittent

[suzuki12]

I have an 1986 K75. The speedometer on initial riding goes up to 60 kph and when ridden faster drops to 0. If I slow down a bit speedometer works again up to 65 or so. With increased riding it eventually will increase to 100 kph but never higher. It will always just drop to 0 if I go faster.
I’ve disassembled the gauge to ensure good connections and also checked and cleaned the sensor at the rear wheel. I’ve not found any other similar issues discussed on this forum.
Any thoughts?

[Laitch]

Trace the wire from the sensor to its plug located beneath the right side battery cover, clean the plug's connections, reconnect it and maybe that will help.

[suzuki12]

I did clean and reconnect the plug on the right side with no improvement.
Thx

[Laitch]

 

[The Mighty Gryphon]

Do the odometer and tripmeter measure distance accurately?

The instruments work by taking the pulses from the rear wheel and splitting them two ways.  One path goes to a step motor that drives the odometer, while the other path goes to some circuitry that takes the pulses and turn them into a voltage that swings the needle on the speedometer. 

If the odometer works properly, the problem is in the circuitry for the speedometer located in the cluster.  If such is the case, I would probably look for a speedometer module or complete cluster.  As far as I know, there is no information available to allow repair of the speed conditioning circuit.

[Chaos]

Did you use a good contact cleaner like Deoxit when you had the cluster apart?  Your symptoms are classic for intermittent conductivity.  I bent some of the pins to get better contact. 

[suzuki12]

The odometer only works when the speedometer is working. Nothing when the speedometer is at 0. I have had the unit apart at least 3 times to rebend the pins to improve contact. I used sandpaper on them as well. I didn't use Deoxit but the contacts certainly look to be clean with no corrosion.

[suzuki12]

The odometer only works when the speedometer is working. Nothing when the speedometer is at 0. I have had the unit apart at least 3 times to rebend the pins to improve contact. I used sandpaper on them as well. I didn't use Deoxit but the contacts certainly look to be clean with no corrosion.
It's quite puzzling that it is initially only going to 60 and slowly increases to 100 but not higher

[Laitch]

If all else fails, this outfit does good work.

[daveson]

I've had that problem and fixed it with cleaning and a slight twist to the pins, as you have. Before I did the twist, I pushed the pins in and out multiple times to clean the pins sockets as well. If I ever open it again I'll definitely be using contact cleaner as well.

[Chaos]

Probably not the issue buy something to check, the speedo sensor ring (#20) in the final drive has been know to come loose, causing intermittent readings. 

[daveson]

Those symptoms sound just like what I had, dunno if the odo was a go tho.

[rbm]

Did you use a good contact cleaner like Deoxit when you had the cluster apart?  Your symptoms are classic for intermittent conductivity.  I bent some of the pins to get better contact.

+1

The symptoms point to bad connectivity.  Any corrosion on the connections between the rear wheel sensor and the speed conditioning board inside the OEM gauge cluster will cause signal degradation.  The signal coming from the rear wheel is only 1 Vp-p, very small indeed.  It will manifest itself as intermittent speedo behaviour because the corrosion will cause various levels of signal loss depending on frequency.

I'd suggest an overhaul of the speedo, concentrating on cleaning the connections between the interface cards and the flexible wiring circuitry.  Use a good contact cleaner like Deoxit on both the pins and the receptacles on the flexible wiring.

[suzuki12]

Thanks for the input. I will try the Deoxit.

[suzuki12]

Another update. I dismantled the speedometer again and used Deoxit on all connections. Twisted all probes to ensure a good connection. I took the sensor from the final drive and cleaned again and also the connection by the battery on the right side. Everything sprayed with Deoxit.
Speedometer initially goes to 60 kph and if power is very slowly increased speedometer will increase to about 70. If power is quickly increased speedometer immediately drops to 0.
I'm stumped on this one.

[rbm]

Might be a defective conditioning card or speedometer driver card then. The Mighty Gryphon outlined the problem in an earlier post.

[The Mighty Gryphon]

You don't make it clear as to what happens if you accelerate very slowly.  If you do, will the needle move above 60-70kmh?  How far does it go in that situation?  Does it always stop at 60-70kph and drop to 0 or does it sometimes go higher?

[daveson]

Also, did you allow the deoxit to dry before plugging it back together? If not, it might come good in a few days when it dries out. And maybe see that the black/blue wire in on the coil Properly, and give it a clean. (Edit: doh, that wires for revs not speed,  I keep mixing that up)

[suzuki12]

Deoxit was allowed to dry prior to reassembly.
Speedometer initially works correctly to 60 kph. Very slow increase it works correctly to 70. Quick increase it immediately drops to 0. A slight reduction in speed and it starts working again. I’m able to very slowly increase max speed to 100 but it takes about 30 minutes of riding. It won’t go above that speed.
The sender unit in the final drive appears to be securely fastened.
Thanks for all your input.

[The Mighty Gryphon]

As I mentioned earlier, the speedometer works by converting pulses into current to magnetize the coils in the meter movement, deflecting the needle.  These same pulses control the motor that turns the numbered wheels in the odometer and tripmeter.

Your description of the problem makes it sound pretty consistent.  That is not the way loose connections work, if that was the problem, the speedometer would be going to zero at more random speeds, and would actually work properly from time to time.

I asked if the odometer and tripmeter worked when the speedometer went to 0kph.  I think you said they stopped working at the same time as the speedometer.  If that is the case, the problem can be in one of two places; either the sensor at the final drive or the signal amplifier in the instrument cluster.  It's easier to imagine a failure in these parts creating a more consistent problem.

I would consider trying a different speed sensor first since it is the source of the pulses necessary to make things work.  It's also the least expensive and easiest part to replace.

If that doesn't get things working, the problem is probably in the signal conditioning electronics in the cluster.  Unfortunately, I don't think there is any information available on these circuits that would make it possible to troubleshoot them.  The only option would be to replace either the cluster of just the speedometer mechanism.  Fortunately, there are a fair number of used units available in places like eBay.

[rbm]

The circuit diagram for the speedometer/odometer circuitry is here: https://www.motobrick.com/index.php?topic=10566.0
Look for the section entitled Speedometer/odometer and click on the link provided.

The boards use standard off the shelf electronic parts so looking through the manufacturer's datasheets, will tell you how the circuit works.

[bocutter Ed]

Any thoughts?

I think you could be a tad more more specific with your location ...

I have a spare motometer on the shelf.

[The Mighty Gryphon]

If you can read Italian this link takes you to what looks like an explanation of how the K100 instrument cluster operates.

http://www.k100.biz/NT/NT_tachimetro.pdf

Here's info on the main IC that runs everything:

http://www.k100.biz/Electr/Strumenti/uaf2115_1ds.pdf

[suzuki12]

Another update. My friend is an electrical engineer who is now helping me. He put his oscilloscope on the sender unit and the connection by the battery and found normal signals. He then hooked it up on the speedometer where the 3 probes are and found the intermittent signal above 60 kph. He then started probing the motometer with a multimeter. I didn’t even know anything about the motometer prior to this.
He is now almost certain a capacitor is the problem. He’s taken the unit home to solder in a new one.

[Laitch]

Thanks for the update.