Another tachometer thread!

[Lowcountry]

Obviously a common issue and I've read through some older threads but still have questions.

First question: Will a V7 850GT tach fit into my '73 Eldorado civilian dash? I don't have the measurements but they look to be very similar if not identical.

Second Question: Has anyone tried fitting a new movement into their tach. I found this as a possible option: https://urevco.com/   It seems do-able, based on the instructional videos.

[Antietam Classic Cycle]

Obviously a common issue and I've read through some older threads but still have questions.

First question: Will a V7 850GT tach fit into my '73 Eldorado civilian dash? I don't have the measurements but they look to be very similar if not identical.

Second Question: Has anyone tried fitting a new movement into their tach. I found this as a possible option: https://urevco.com/   It seems do-able, based on the instructional videos.

A "V7 850GT" is an Eldorado in slightly different trim, so if both are "civilian" then it will fit and work the same as the original. Both should be electronic and 80 mm in diameter.

I'm sure there's a company out there somewhere doing just that, but I don't know for sure if any are.
https://www.thisoldtractor.com/moto_guzzi_loopframe_gauge_repair.html

[Lowcountry]

Thankyou, Charlie. Much appreciated. 

[Kiwi_Roy]

The Veglia Tach on my 72 Eldorado quit so I pulled it apart to see what I could do.
Here is the circuit I sketched out, I just replaced the transistors with generic types and it works again.

And a few waveforms that might be useful https://ibb.co/album/z6sQr9
I see by my notes I injected the meter with a 16 Volt square waveform from my signal injector.
This is equipment that any electronic repair shop will have, I just replaced both transistors with a modern NPN small signal variety.
If its just the electronics that failed repair your old tach.
I find it interesting that such an old bike has an electronic Tach when much later models were mechanical
Ariel spotted a mistake in my sketch, R1 is between +12 and the Zenner diode.

[ttietjen]

I replaced the tach on my 73 eldorado with a 2.75in dia. drag specialties unit from Dennis kirk  for $65. Used a piece of 3in exhaust pipe as a shroud to fit the gauge holder a little better and painted flat black to match the original gauge. I think it was a replacement gauge mid 70s HD FX. Didn't have much luck trying to find someone to repair electronic tach's.

[Lowcountry]

I found a shop that can replace the internals with better "guts" - dandmrestoration.co m in Greenville, SC. I contacted and and they responded the same day. Seems to be a decent, although not cheap option..

For us to repair the cost will be around $275. For us to replace the board and movement to make all the internals new the cost will be $350. The turnaround will be 3 to 4 weeks.

Thank you,

Nikki Davis
Office Manager
D&M Restoration

57 Creekside Park Court Suite B
Greenville, SC 29615

OFFICE: 864-254-9989
TOLLFREE: 800-722-0854

[ttietjen]

I think I called D & M when my tach quit working and they turned me down ( I know it was a Greenville shop because I thought it was too good to be true being only 35 mi away ) Maybe I'll just take a ride down there and see what they say when I have the tach in hand. The only other price I got was from Bob's speedometer in Mich. they wanted $500 to replace the board.

[Kiwi_Roy]

I think I called D & M when my tach quit working and they turned me down ( I know it was a Greenville shop because I thought it was too good to be true being only 35 mi away ) Maybe I'll just take a ride down there and see what they say when I have the tach in hand. The only other price I got was from Bob's speedometer in Mich. they wanted $500 to replace the board.

I suggest you print out my previous post, it will make a difference to an electronic tech if he isn't faced with a black box to figure out, It may not be 100% accurate. I must have spent the better part of a day drawing out the circuit. Print out the waveforms as well. Perhaps open up the case as well, a normal tech won't have the tools to do that.

[Ariel]

R1 has to be between +12 and ZD1, otherwise ZD1 will burn 

Ariel

[Kiwi_Roy]

R1 has to be between +12 and ZD1, otherwise ZD1 will burn 

Ariel

Good spotting 
You were paying attention then lol

[Ariel]

Good spotting 
You were paying attention then lol

I can't help it, I love electronics.....

Ariel