Veglia tacho replacement electronic board

Very interesting, and useful link. Thank you for the post.

 

Hi Adrian,

I have been very interested to read your post regarding old Veglia tachometers and also had a good look at your replacement circuit board on the dinoplex site. Impressive !

The reason for my interest is based on the now inoperative state of the tachometer in my 1977 USA spec 308GTB. Before I bought the car some 5 years ago, it was fitted with a single Marelli distributor using a magnetic trigger. An MSD 6A ignition with an 8920 Tach adapter was also fitted. The whole setup was fine if a little roughly installed. There was also the ballast resistor wired in as shown in the MSD insructions but this seemed ugly and redundant, so I removed it with no apparent consequences. So far so good and everything was working.

A few hundred kilometers ago ( years at my low usage ), the tachometer started to jump to life only after the car had been driven for half an hour or so. I just put this down to an intermittent contact somewhere up near the tachometer itself and decided to ignore it. I have 'fixed' numerous other electrical faults by just cleaning contacts previously.

But as of my last decent drive, the tachometer is permanently static.

I spent the day pulling the car apart and reading up on the net. I have tested the circuits between the MSD, the Tach adapter and the tachometer and it all appears to be doing what it should......except the old Veglia wont move....
I also tried connecting the square wave 12v output from the MSD 6A directly to no avail.

The car starts and runs perfectly by the way.

I have ordered a new Tach adapter just in case it is faulty.

My question after that lengthy explanation is this:
How likely is it that the tachometer is at fault?
Should I hook up a square wave generator directly to check it ? (I have never used one before )

PS, there is a tiny typo on your dinoplex page regarding the RPM / Hz conversion for an 8 cylinder engine. I think the 10 was meant to be a 15 ?

Thanks, and any guidance will be appreciated

John

 

John- Those are also the symptoms of a tachometer sending unit failure. Had to replace one on my 78 GTS in the good old days.

 

Adrian did this for my tach, it is brilliant. Thanks again Adrian

 

Adrian- Right you are. I was thinking of the speedometer. Brain fart.

 

Many thanks to all and Adrian in particular.
After installing a new MSD 8920 Tach adapter, my Tachometer is now working.
Given that the Tach adapter feels like a solid lump, it makes me wonder what failed in there?

Thanks again.

John

 

Hello Adrian,
Qo you still answer questions about this subject?
I started manufacturing some Veglia board and I would have some help!
Thanks

 

Great!
Firstly many thanks for your help.
I tried a lot of differents ways to keep my tacho in working condition.
The last one was to change all internal electronic by a SpeedHut mechanism. Without success!
Now I am trying your solution. During the soldering step I noticed that the D4 diode was only present on the PCB. Not on the part list nor on the schem.
As I don't know a lot in electronic, could tou pls explain that difference?
Sorry but I am only able to follow existing instructions.

 

As I already sold it, can I let it in place?

 

Thanks a lot. Now I only have to make some tests to determine The value of R1 resistor. I have only one cylinder (In fact two with one coil per cylinder).
I'll come back to give you the results.

 

Sorry but I have an other question!
For the 220nF C6 Radial ceramic capacitor, you said that it is only required for a Coil (-) connection setup.
Could it be kept in place for an electronic ignition signal?

 

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I have a Veglia speedometer from a 91 Testarossa that is dead. Is there a fix for it?

 

I am not the best guy to answer but as nobody answer, I will try. If you are sure that the fix is in the tacho you have to check the condensers first. They have a limited life and that is often the failure cause.