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Tach Failure


samdroid
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Another round with this dead horse then....grab your beatin' sticks.

 

My (Veglia) tach quit on me coming back from a recent camping trip ( 00' Greenie)

With the bike shut off the tach reads ~300rpm, not 0. With the bike running the needle will limply flap around below ~1500 rpm but I assume this is only vibration moving the needle. This leads me to believe it is a mechanical failure inside the instrument housing.

A cursory check of my charging system doesn't indicate anything untoward. The bike has siemens relays, but i've not experienced any issue with lighting, horn etc that one might expect from a faulty relay. (Tach, indicators, lights all controlled by 2nd relay from front no?). I've swapped a few relays around and verified no funny business or change in brightness of the lighting, response of the indicators etc.

I've got the tach out of the dash and on the bench, is there anything I'm missing or should consider before I start opening the tach?

 

My profuse thanks in advance.

 

Sam 

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If this were my tach, I'd give Joel Levine a call.

 

But then, he's only a 45 minute ride from me.

 

<edit> Oh, and my Greenie tach shows ~400 rpm with the engine not running.  It seems to be accurate, otherwise.

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So,

I've got the tach apart, electing to do things the hard way as is my custom. Rather than hack the case I painstakingly uncrimped the chrome bezel, cracking the glass in the process (typical). No matter, I'm in the local glass shop a few times a month anyway.

What I discovered was that one of the ultra-fine copper wires has broken at the solder joint. Assuming this is the culprit, as I suspect it is, I should be up and running again shortly. 

31 minutes ago, nc43bsa said:

 

<edit> Oh, and my Greenie tach shows ~400 rpm with the engine not running.  It seems to be accurate, otherwise.

I hadn't noticed prior to the failure if the tach ever read 0, but in my disassembly, decided that it couldn't conceivably have done so, a simple case of the needle being stuck in the shaft a few degrees too high, I'll fix that too since I'm in here. Thanks for the peace of mind.

 

Assuming all goes swimmingly I'll post a write up with pics and add it to the pile. The numerous threads on the issue already have been most useful. 

 

Cheers

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For sure these tachs commonly read 300-500 rpm too high. Must be easier to stick the needle on there on the assembly line. Definitely matters when setting the idle and it is actually 300-500 rpm low (1050-500=650!) :o

I'm glad you found some tach threads. From memory, I was thinking there are magnets that can come loose? A spring can break? Maybe a diode that can go bad?

Thanks for getting back with what you find!

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On 8/31/2022 at 3:48 PM, samdroid said:

Another round with this dead horse then....grab your beatin' sticks.

 

My (Veglia) tach quit on me coming back from a recent camping trip ( 00' Greenie)

With the bike shut off the tach reads ~300rpm, not 0. With the bike running the needle will limply flap around below ~1500 rpm but I assume this is only vibration moving the needle. This leads me to believe it is a mechanical failure inside the instrument housing.

A cursory check of my charging system doesn't indicate anything untoward. The bike has siemens relays, but i've not experienced any issue with lighting, horn etc that one might expect from a faulty relay. (Tach, indicators, lights all controlled by 2nd relay from front no?). I've swapped a few relays around and verified no funny business or change in brightness of the lighting, response of the indicators etc.

I've got the tach out of the dash and on the bench, is there anything I'm missing or should consider before I start opening the tach?

 

My profuse thanks in advance.

 

Sam 

You might note if you hear something rattling around in it.  If so, it's likely the counterweight.  If you can get the bezel off, then you can glue it back on.  Getting the bezel off is the hard part.  I used a big hose clamp to squeeze the metal case and then I used a paint can opener to pry the bezel off off.  I might've filed the opener to fit and be careful not to break the glass.  If you do, a glass shop can cut you a new one (don't ask how I know).   Glue the weight on with a light application of epoxy.  Use soap or silicone on the rubber gasket to reinstall the bezel.  

If it doesn't rattle, don't even start.  Call Joel Levine.

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As far as taking the bezel off:

I machined a piece of engineering plastic that the bezel just fit in with a light press. That keeps it from deforming and breaking the glass as you slowly uncrimp the bezel with a tack puller or something similar.

If you don't have that tech.. maybe rout an oversize area the right depth, put some Bondo in it, and fit the (heavily waxed) tach face in it and let it cure. Then uncrimp it.

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I broke the glass trying to reinstall the bezel.  A harder job for me than taking it off.   

A press and prying fixture makes a lot of sense.  I'd bet Levine has something like that.

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Joel has a lathe with a plastic "face" in the chuck that holds the lens/bezel while he uses a ball bearing in the tool holder to "roll" the bezel tight.  The tailstock holds the speedo or tach against the face.

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  • 1 month later...

So. My cursory inspection of the charging system seems to have been a little too cursory. A melted 15a fuse led me to check again. Voltage surging beyond 15 volts with revs. Id been intermittently burning out dash lights. Should have known better. Yup time for a voltage regulator.

 

Fuse and regulator replaced. Stator leads good. All accessible connections cleaned and checked.

 

I've reassembled the tach but still no signs of life. 

On the tach wiring I have 12+v on the red/black wire (power)

On the yellow/black (signal). I get ~34hz at idle, and the frequency increases with revs. However I am only reading ~10.9v with key on/engine off. ~5.5v DC with engine running. 

I know there is a method of testing the wire for AC voltage from which similar inferences can be drawn as checking the frequency. 

Is it normal to be reporting such voltages on the tach signal wire or have I got a bad sensor or short to ground that I need to be chasing down?

Probably going to go the speedhut route and dispense with the troublesome veglias.

My thanks for your collective wisdom.

Sam

 

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Just about any Fluke meter has a Hz function . I'm sure any meter has it now .  I'm partial to Fluke .

 If you're looking for AC on a wire , turn your meter to AC and check . If it is generating a square wave , you won't get a (I think)  good  reading. 

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13 hours ago, samdroid said:

So. My cursory inspection of the charging system seems to have been a little too cursory. A melted 15a fuse led me to check again. Voltage surging beyond 15 volts with revs. Id been intermittently burning out dash lights. Should have known better. Yup time for a voltage regulator.

 

Fuse and regulator replaced. Stator leads good. All accessible connections cleaned and checked.

 

I've reassembled the tach but still no signs of life. 

On the tach wiring I have 12+v on the red/black wire (power)

On the yellow/black (signal). I get ~34hz at idle, and the frequency increases with revs. However I am only reading ~10.9v with key on/engine off. ~5.5v DC with engine running. 

I know there is a method of testing the wire for AC voltage from which similar inferences can be drawn as checking the frequency. 

Is it normal to be reporting such voltages on the tach signal wire or have I got a bad sensor or short to ground that I need to be chasing down?

Probably going to go the speedhut route and dispense with the troublesome veglias.

My thanks for your collective wisdom.

Sam

 

There are 3 wires for you to be concerned with . The power wire , 12v , the ground wire and the tach signal wire . Check for a good 12v and ground with a test light . very important . You are checking the 12v to ground integrity. If these are good , The "way over" 12v has destroyed the tach .

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Gentlemen,

Thank you for your responses.  I have good power on the red/black and well grounded.

What specific values should I be looking for on the yellow/black.

DC v:

Hz:

 

I'm trying to verify if I have harness/sensor/ecu damage after the voltage spike. 

Yellow/black signal wire returns 34hz, climbs with revs (good)

But I'm only getting ~5.5v DC on the signal wire with the motor running.

 

Normal?

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Hmmmm , the pin 3 or pin 5 depending on which model bike you have is the tach signal wire . I will try to poke around my bike tomorrow to see what the output is at idle and 1500 RPM .

 I will hook up some contraption and see what I get .

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I checked my Greenie just while ago .  At pin 3 (yellow/black stripe) I got 50hz at idle . At 3k I measured around 150hz.  

 HTH . Sorry for the delay .

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