Dead Tach help

[gnevelesx08]

Tach needle just bounces around and never has worked. What kind of reading should I get when I rev the engine and checking for voltage to the tachometer? Which wires do I test? Do the tach wires come straight from the alternator or do they pass through some kind of relay or rectifier? I'm just a amature when it comes to elctrical. Any help Thanks

[mikej-t]

Hi there,

my tach stoped working when the regulator/rectifier failed, and prior to this is it worked intermitently. The problem was with the reg/rectifier. Fitted a new one and all fine.

Check that the three white wires to the reg/rect show equal readings when the engine is running. One of mine was reading low as the reg/rect had an internal fault.

See how you go...

Mike.

[gnevelesx08]

Thanx, I'll give that a try and see what I get.
Dan

[Shuriken]

I also have a dead tach. I've gone through the testing as per the Yamaha manual. I have good charging and voltage to the tach. The problem I have noticed is that I have more than 5~7v AC apparently going to the tach (15v). I'm not sure about that but that much over voltage couldn't be a good thing on the tach, either. I have 2 voltage regulator/rectifier units and neither makes any difference.

[gnevelesx08]

Question,
Wiring diagram shows a diode in the circuit. Where is this diode located?
Thanks

[Shuriken]

Where are you looking? The diode should be inside the voltage regulator / rectifier unit.

I still have a dead tach after wire harness replacement (long story) but now I see 3-4 volts AC on the wiring to the unit, manual says it should be 5-7. Hmm..... Maybe I can pickup 2 volts by cleaning all the connectors or maybe I have a weak ACG output wire...

Ben

[gnevelesx08]

okay, I know this thread is probably dead, but the tach issue is still there. I checked the voltage to the tach, engine idling I get 7 plus volts. I rev the engine and it goes to 9.25 plus volts. My clymer manual says that the voltge regulator/rec shoul divert voltage above 14 volts. I checked the tach wiring harness and the wires to the gauge where they plug into the back of the tach are solid. I checked for coninuity between the white and black wires on the tach itself and it reads open/dead. I don't know if the circuits inside the tach convert ac power from the alternator to dc power for the tach needle? I should I be reading continuity or not ? the tach is a sealed unit so I can't get inside to check the board. I'm just trying to make sure the tach is the problem before I fight everyone on ebay for another used tach. If I can get one cheap enough I'll take the old one apart to see if it can be fixed.
thanks guys
Dan

[skids]

Voltage to the tach... I just fixed a problem with the Rat (81H) where the battery slowlly drained. I was getting about 13.5 volts charging at 4000 rpms which is a little low. Dead tach but gas gage worked. That volt regulator in the tach housing is for the gas gage. The tach counts pulses from one of the three phases of the alternator. I checked the clip behind the fuse panel (yeah, you have to pull the panel upwards to see it) and the plactic clip showed arcing as it had partially melted. I replaced the connector with individual connectors for the 3 whites and one yellow and the tach began working fine. The bike showed 14.5 volts charging at 4000 rpms. Check it out.

Originally posted by gnevelesx08
okay, I know this thread is probably dead, but the tach issue is still there. I checked the voltage to the tach, engine idling I get 7 plus volts. I rev the engine and it goes to 9.25 plus volts. My clymer manual says that the voltge regulator/rec shoul divert voltage above 14 volts. I checked the tach wiring harness and the wires to the gauge where they plug into the back of the tach are solid. I checked for coninuity between the white and black wires on the tach itself and it reads open/dead. I don't know if the circuits inside the tach convert ac power from the alternator to dc power for the tach needle? I should I be reading continuity or not ? the tach is a sealed unit so I can't get inside to check the board. I'm just trying to make sure the tach is the problem before I fight everyone on ebay for another used tach. If I can get one cheap enough I'll take the old one apart to see if it can be fixed.
thanks guys
Dan

[gnevelesx08]

Okay guys thanks for the info.
I checked rectifier/reg and get 5.0 plus ohms when reading red or black to the three white wires. I reverse the leads on the ohmmeter and it reads infinite. The manual states the readings should be at least 10 units difference, if not replace the rec/reg. I also read somewhere in another thread that it the amount of difference was not as important as showing continuity one way only. The regulator works fine and charges the battery. The wiring diagram shows the alternator White wire to the tach also going into the rectifier. Does the rectifier being in the circuit convert the ac voltage from the alternator to dc voltage to the tach? Oh I checked all connectors behind the fuse panel under the gas tank and at the tach and ignition switch. Only the main red wire to the ignition switch had any sign of arcing or melting, cleaned it up and it did not matter for the tach. If the tach is supposed to get only 3-5 volts and I'm getting 7-9 volts, is the low resistance on the rectifier the problem? Any more help out there about this?
thanks much
Dan

[skids]

Yes, the rectifier does convert three phases of alternating current to DC. The recitifier diodes are like one-way valves.

Make sure that the rectifier/regulator is grounded to the frame. There is no black wire on both side of the clip...it is grounded through good contact to the frame. You say it is charging, so what do you read across the battery terminals at 4000rpms? It should be above 14volts. The tach may be malfunctioning if your connections are good. I have two bad ones in a box of parts. I would try a known good tach, if you are getting proper charging.

Infinite ohms is not low resistance. Maybe I am misunderstanding what you are saying.

Originally posted by gnevelesx08
Does the rectifier being in the circuit convert the ac voltage from the alternator to dc voltage to the tach? Oh I checked all connectors behind the fuse panel under the gas tank and at the tach and ignition switch. Only the main red wire to the ignition switch had any sign of arcing or melting, cleaned it up and it did not matter for the tach. If the tach is supposed to get only 3-5 volts and I'm getting 7-9 volts, is the low resistance on the rectifier the problem? Any more help out there about this?
thanks much
Dan

[gnevelesx08]

Hello skids,
I will check the voltage across the battery. Haven't done that yet. I know the battery reads 12.5 volts. I' have to do the check to see that it is at least 14 volts no more than 14.5 when engine is reved up. The rectifier readings were 5.25 to 5.65 range and when leads were reversed I got zero on the digital meter. Book said a difference of at least 10 units. I also read 7 to 9 volts at the tach when I rev the engine so I know there is voltage there. Maybe time to fight ebay wars for a used tach.
Thanks

[randy]

gnevelesx08,

Dumb question:

Are you testing the regulator OUT of the circuit? ie: unplugged?

Suggestion: there is a multi-pin connector behind the fuse panel that connects the rectumfryer to the alternator. Pull it and clean it. Clean it even if it 'looks good'.

[fxrer]

Randy,

I forgot to mention this yesterday, but my tach is also bouncy, especially when passing thru (upwards and downwards) the 4 k range. Years back, a spider crawled inside and made a web that was visible over the dial face. That’s when I first noticed that, when I revved the motor, the needle seemed like it got caught on the web, then would “break free” around the 4 K mark.

So last winter, I opened the tach, cleaned the web, and put it back together, only to see that the needle still “bounces”.

Could that multi-pin connector you refer to be causing a problem? How is the best way to clean it?

Check for a p.m.

Rick

[gnevelesx08]

Randy,
Yes the rectifier was out of the circuit when tested except for the ground wires to the case. Should I take it off the bike to test it. Should it not be case grounded when tested?
Dan

Skids, I did check that connector behind the fuse box, I will double check and clean it regardless.

Another (same) question again. What voltage am I supposed to read at the tach connector? Is it dc volts or ac volts and what is the proper scale of reading per 1K of revs, any info on that?

I am going to price a tachometer gage for setting idle and test it in the circuit when I can afford one.

thanks for the help on this saga

[xs1100yam]

Hi,

the tach is in fact a "frequency-meter" showing frequency of the AC current coming from the generator. (Frequency of current being linked to generator RPM)
That's why the tach don't work when the charging circuit have a problem.
As your charging system seems to works fine, the problem is with the tach itself (IMHO)