ALFAGTV6.COM

[MD]

The wife has a 1990 automatic 75/Milano with an irratic speedo display.

On the test bench both sender and speedo head work perfect.
In the car with an independent B+ and ground, it works fine.

When the tachometer is introduced to the circuit board, it causes the irratic speedo display again.

When connected, the tacho works well all the time and is otherwise normal.

Anyone experienced this tacho induced speedo display issue?

Please note. This is not related in anyway to the usual speedo issues that arise when doing 75 to GTV transaxle swaps. I know all about those problems and how to solve them.

[sh0rtlife]

you might try running a direct feed off the battery to the sender and see if the signal cleans up....it sounds EXACTLY like the transaxle swap issue and the only fix was to either A go into the wireing and seperate the tach wireing from the speedo wireing as the signal is bleeding...

or to eliminate the power coming from the speedo to the amplifier and run a new power wire from the battery to the amp...

imo its worth a shot to try running fresh clean power to the amp and see if it cleans up..quick simple and painless...if it fixes it use a relay on the new feed line and use the old speedo power line as a trigger for the relay

[MD]

Shortlife, I know you are trying to help and it's appreciated. HOWEVER,
like lots of owners, you need to understand a few quirks about the transaxle speedo configurations, namely:-

The 75 Auto doesn't have an amplifier.
The manual 75 can do if it uses a two wire sender. If it uses a three wire sender, it doesn't.
The "amplifier" is not an amplifier although for convenience everybody calls it that.
The three wire sender makes the same signal as the two wire sender +"amplifier" together.
This is because the speedo head requires the same type of signal.
The signal from the Jaeger senders 2 or 3 wire is completely different to the original GTV6 or GTV2 ,Alfetta senders.
That is why it will never work on its own when you do a transaxle change over. It requires a signal converter.

So we come to the Automatic speedo head and sender. This is the same as the early GTV2/6 Alfetta combos that had electronic Veglia speedos. It is not the same as the manual version of the same car.

I hope that helps you and anyone else working on this issue.

None of this however has anything to do with the tacho interference problem which is why I didnt want the subject raised.

[sh0rtlife]

ok sorry

im just going from a signal referance point of veiw...

this may sound VERY weird but what about pulling the speedo out ..and wireing it to the sender ...EG wired with its own wires not the stock harness setup...i know you bench tested it but a road test is in order.......it sounds to me like you need some clean power to the speedo

either way you look at it you have the coil sending spiked voltage into the wireing harness..much the same way alot of old american iron will do with points and a HOT coil...useualy causeing ALOT of noise in radio equipment ..due to not haveing an electric speedo we ignore it....a noise filter is the normal fix but i think a noise filter on the coil would kill the tach

have you tried removeing the tach wire on the coil just to see if the speedo works correctly?...just a thought

[ar4me]

Does the instrument cluster in the automatic 75 have the same flimsy "flexible print board" on the back of the gauges? Perhaps worthwhile checking if it has somehow cracked or otherwise become compromised causing signal problems.
Jes

[MD]

Shortlife,

All of your suggestions (and then some)have been tried without success over a 3 day period and let me say, there is nothing wrong with your line of thinking so all is cool.

ar4me,

Yes the circuit board is the plyable plastic sheeted printed circuit board. It is however in exceptionally pristene condition and has not been affected by either corrosion or fatigue.

Alas, being an automatic, the tacho is more of a galmour item than an epecially useful one so it had to go. The speedo must take preference for keeping the speed tickets at bay.

I will close by saying, I now have the speedo working smooth and accurate at the expense of losing the tacho as I am not wasting any more time on sorting this out for a very marginal gain.

I have written this up in case others come across the problem in the future.

Thanks for your input guys.

[sh0rtlife]

loseing the tach...hmm that sucks....what about running a single new fresh signale wire wire to the tach from the coil...this should give you the tach back without effecting the speedo

with the projects i take on ..or should i say throw myself into i have to think so far outside the box that i cant see the box

[Barry]

Remove the darning needle you melted into the back of the bent indicator due to the harsh heat of the sun...It will work again...

Can you believe I did that once ? wouldnt even move off the stop..

[Greg Gordon]

Problem solved....