XJ900F Tachometer/Electrical

Hi All,

Long time contributor and lurker been out of action for awhile but now back with Spring in the southern hemisphere approaching.

Started up the might XJ900F beast and all is well (it had a rebuild from the ground up 18 months ago).

Before shutting it down for a couple of months over winter everything worked fine, including the tachometer. However, on startup about a week ago the tach budged and is moving but won't get over around 500rpm. Blip the throttle and it just wiggles at around 500rpm.

Seen posts on here about a grey wire but mine doesn't have a grey coming from the tach. I'm presuming it's a brown wire but can be corrected. I think it's just a loose connection but have checked the connector and all seems solid with all 4 wires (ground and instrument lights included). Could the fault be in the loom back to the TCI? There seems to be something happening because the needle moves but won't go beyond an initial point. Haven't tried the multimeter yet for continuity but will do so.

All other electrical functions working fine...sidelight, headlight, indicators, horn.

Any suggestions...?

Thanks!

 

the electrical tach connects to the coils can hook to the coil gray or orange connection FSM for 900G says orange and gray wire

 

Thanks. I'll check and see the wires/colours/connections.

First nice weekend in a while and I'm delving in the headlight bucket...

Cheers.

 

could be one of those giant killer spiders you guys have down there made a home in the tach

 

Oh yes...the aptly named HUNTSMAN spider. Honestly they freak me out. Not poisonous but not nice up close. Had one apparently hiding on the bike and it decided to go for a walk across the instrument panel and over the handlebars while I was doing 60mph (100kmh) one day!

At least it wasn't a black widow spider. They really are scary.

 

Back to the tach issue...needle wiggles around 500rpm but goes no higher when engine throttle blipped etc.

I checked wiring connectors from the tach to the 4 pin connector (both male and female sides) and there was continuity on brown/power and black/earth wires.

There was also continuity from the grey wire in the TCI connector up to the brown (I think from memory) to the 4 pin connector up front.

I haven't check the earth connection properly yet.

Is there a way to test the tach...that is, run a ground wire direct from tach to the frame or exposed metal part? Would this then indicate that a bad earth connection existed if the tach started working?

Wiring issues are always a process of elimination unless you strike it lucky first time...

 

It might just be dirt or corrosion in the tach itself. I had that issue with the electronic tach on my XJ650RJ.
I tried to disassemble and F'd it up beyond my ability to reassemble. Had to replace the tach with another.
I've heard you can spray a contact cleaner into the mechanism to free it up.

 

I am pretty sure the black wire is isolated from the case of the tachometer. There is not much else to check other than the 3 wires that go to the tach. The brown and black supply power to an internal frequency to voltage CCA. The grey wire supplies the frequency to be converted.

They are quite delicate inside and as Simmy noted things can go quickly downhill trying to repair them. That said, if you are convinced the gauge is defective it might be able to be saved.

Here is an example of a 750 Seca tachometer that utilizes the Atari setup. These are really easy to get apart (to a point) and also easy to isolate whether there is an issue on the CCA or the meter movement.



Yours would likely look much different inside, but the principle would be the same. Frequency is converted to a voltage and applied to the meter through an electromagnet to move the meter. On the above model on the opposite side of the CCA are two small spade connectors; the output of the CCA and input to the meter. Yours would have the same thing but I believe they are soldered in place.

This is a good place to electrically test the meter movement and several methods can be employed. Note there could be a mechanical issue causing binding in the meter movement. Note if you do any cleaning in there protect the faceplate - chemicals such as isopropyl alcohol will remove the paint on the faceplate.

1. If you have an old VOM with the analogue meter movement set it to the R x 1 scale. Typically this will be a low impedance setting and will have a voltage potential of 1.5V between the two probes with enough current available to deflect the tach needle. Touch the positive probe to the red wire and the negative probe to the black wire that exit the internal CCA, the tach needle should deflect to 6 to 7 K. Note some VOM's reverse polarity, so reverse the probes if the tach needle does not move.

2. Use a DMM to check by connecting the meter to the red and black wires exiting the CCA. You should read the resistance of the electromagnet coil, which is around 75 ohms. The tach needle can then be gently moved to see if an open appears because of a poor solder joint on one of the springs that provide the current path to the electromagnet. Note the DMM should change resistance slightly as the needle is moved as the permanent magnet will induce a voltage into the coil of the electromagnet. The real point here is just to apply some very gentle upward movement on the needle to see if an open occurs.

3. You could disconnect the red and black wire and apply a voltage across them. The best way is with a variable power supply, but you can just connect a 1.5 volt AAA battery to those two wires and the gauge should read close to 7000 rpm. If the gauge meter movement checks out then there is an issue on the CCA, and although fairly simple circuitry, it would require some electronic skills to troubleshoot and repair.

If you wanted to check the gauge externally to the bike you would need a voltage source (battery) and a signal generator.

 

Thanks for this.

Very detailed and helpful.

Back to the tach and headlight bucket for me now...

 

A follow up on where we're at with this issue at the moment.

I took the tachometer to a well regarded auto instrument repair business nearby and after putting it through some tests they have advised that the tach is working perfectly.

Sooo...having tested the wiring as per Haynes and making sure all connections/continuity are clean and working with my multimeter I'm left with two possibilities:

1. A bad earth somewhere but highly unlikely as I've tested all connections with the multimeter.

or...

2. The TCI on the pulse wire to the tach (emanating from the 2/3 coil) is not putting any signal out beyond around 500-600rpm which is where the needle wiggles around when the engine is running. (Note: The engine runs fine and is firing nicely on all four cylinders). The TCI's on these things are now 30 years old.

Anyone care to venture an opinion on either of the above?

 

You did a continuity check, but I would suggest measuring the voltage at the back of the tach where the harness attaches just to be sure you have 12V there when measuring from Br to B. Not sure how easy that is on the 900, but on the 750 Seca you can temporarily leave the instrument cover off to expose the wiring.

Not sure exactly where this is and if there are variances in the wiring, but the only schematic I have of the 900 shows power and signal for the tach going through a 9 pin connector.

 

So I did a quick check on the 750 tachometer, which I suspect the two are electrically very similar.

The 750 tachometer utilizes a Toshiba T2295 frequency to voltage converter, which is very forgiving with both amplitude of the signal and DC offset. The tachometer would continue to work with DC offsets as high as 3.2V and amplitudes as low as 3.4V.

So, if there was an issue with the signal and continuity is certain on the wire to the tachometer from the coil, then it would most likely be an issue with DC offset that might be caused by the TCI output transistor or a poor connection on the ground side of the TCI. Unfortunately, other than checking for solid connections diagnosing that problem could only be accomplished by scoping the signal or by swapping in a known good TCI.

 

Thanks for the information.

I have a spare old TCI which worked well but cut out occasionally. I might try that to see if at least the tach works. If it does I've seen aftermarket ones for around AUD $200 or less.

 

Good morning XJ faithful. I Hope all are well.....

I recently took my 83 XJ900 out for a short ride and noticed my tachometer is acting exactly the same as CafeBlack described. It worked fine on the previous ride (approx. mo ago) and the bike is kept covered inside and I have not performed any work on it during the down time.

Before I dig into it, I wanted to resurrect this thread to see if CafeBlack found a solution to the issue. Selfishly I am hoping to focus my time and efforts.

Thanks for any updates, resolutions, recommendations, etc.

Jack

 

Hi,

Testing my memory here but as stated I took the tach to an auto instrument repairer locally for testing. They tested it and the report was that it was working perfectly.

So...back to the headlight shell. I think I disconnected, cleaned and reconnected ALL the little plug in connectors (might as well while I was in there) as well as the ones inside the underside of the tach itself and afterward it was working fine again.

I think from memory when I did the rebuild I put some dialectic grease on each plug-in connector and what may have happened is the some or a little too much got on he metal of the connector and had an effect on the connection. Also because the original wiring was just long enough for the original setup of the bike, when I put a fairing on the front of the bike some wires were a little tight which could also have had an impact on the connection.

I would suggest that if the tach was working fine try cleaning and reconnecting all tach wires up front as well as all connections into the TCI. Check fuse connections as well and that the earth connection is OK. Sounds like a lot but it's probably only an hour's work if you go straight to the direct connections for the tach. If it was working before and only partially working now I would suggest that the tach is fine and it's the connections are the problem.

See how you go. Damned electrical problems like this have you thinking the worst at times and in the end it's probably a rogue connection that just needs to be cleaned and secured.

 

Thanks CafeBlack! Really appreciate your reply and helpful information. I will likely not get a chance to dig into the wiring until later this fall but knowing it is likely a non-secure connection in one wiring connectors or a ground helps me with my strategy.

Thanks again!

 

Just to complete this thread on a fix from 1965soda that he noted in another thread:

"When you get back to the XJ....I had a similar but maybe different problem on my 900. The tach just quit working completely. Disassembly, cleaning, and reassembly of the wiring harness connections in the headlight housing got my tach working again. Not certain which connector may have been the culprit, but I cleaned them all since I was in there."

 

Excellent thread.

The electric tach on my 1987 yx600 isn’t working so I’ll be referencing this information as I troubleshoot the problem.

 

Quick tach related question:
Can anyone confirm the Tachometer ratio for a YX600? I believe it's 5:1 like every other Yamaha of this vintage, but I wanted to confirm.


I spent some time trying to figure out why the electronic tach on my '87 yx600 isn't working. I checked and greased all plugged connections. I pulled the DMM out and found that I have power on both plugs going to my tach and the lightning comes on. The signal wire has voltage on the three wire plug (pic below) but I didn't see the amp variance when I revved the engine. As I sit here and think though, I may not have had any DMM configured to read mA's - I may have had it on the voltage setting. I'm no pro with multimeters.

I tried to open up the tach, but it didn’t come apart after taking all four screws out and doesn’t appear to be the same type rooster53 referenced above.

I'm thinking about just buying a new or used tach to see if that fixes the problem. Generally buying new parts to fix an issue of unknown origin isn't a great idea, but I need a tach for my 1986 yx600 anyway so I figure I can't lose

 

To evaluate a tachometer active signal wire you really need a scope to see the pulses. The best you can do with a DMM is if it has a frequency counter built in you can see if it reads a reasonable frequency, and if it does then the tach should also work

Some gauges don't come apart without some persuasion as noted in the below repair. You would want to be darn sure the gauge is bad before attempting this repair

https://www.xj4ever.com/repairing your 700 gauges.pdf