Alfa Romeo Forum banner
1 - 1 of 1 Posts

·
Regional Support, For Lincolnshire - AOL
Joined
·
16,494 Posts
I don't know if the set up on the Spider is anything like it is on the Alfetta but here is how I solved my problem on that.

Step 1 of today was to check the wiring from Sensor to Head for continuity and shorts, all OK except for one bizarre thing which I will get to in a tic.

Step 2 was to check the ignition switched 12 Volt feed which joins in the game at connector S2, all OK.

Step 3. Looking at the Speedo Head I found that the 12 volt into the Head had been disconnected on the Head itself. Why ? Was it blowing fuses or was this a " Clocking " attempt ? I suspected the latter.

Step 4. Reconnected this and checked all fuses and services, all OK.

Step 5, the crafty bit !!!! Disconnected the plug from the Sensor and connected two pigtails to the plug that goes to the Speedo. One pigtail was connected to a an ordinary metalworkers file tang, the other pigtail is then scraped along the face of the file. ( Ignition has to be 'ON ' for this of course. ) Wow, the Speedo starts flicking about, result !

Full of hope as I thought a previous owner was trying to stop the miles from clocking up I went for a drive, sadly still no Speedo.

Step 6. Removed the Sensor from the Gearbox, easy job, undo one bolt and the unit pulls out. No oil is lost at this point. The way this unit works is a mag pulse generator driven by a square ended Speedo sort of drive. Across the two terminals you should be able to measure the coil resistance, mine showed to be so high I considered it to be open circuit. Then twist the drive cable with your fingers, you should feel a bit of " jerkiness " as the magnets interact with the coil, mine did.

Step 7. Can't vouch for this bit of the testing. Connected a drill to the drive to spin it and tried to measure the output with a DMM, got no readings at all either DC or AC Volts which is what I would expect if anything on this method. A 'scope would have been handy at this point but sadly I no longer have one.

Conclusion. The coil in the sender is open circuit, I need a new one, or at least one that works. It is made by Veglia and the markings on the case read :-
68 - 1027 - 2D
12v - 4 - P/G

Finally solved it In the end by replacing the two Transistors and the Zener Diode in mine ( BC 327 & 33 Volt Zener ) and that got it going, I suspect that it was one of the Transistors. If you are, or know someone who is, happy working on Printed Circuit Boards, then it’s a fairly simple job, the hardest part is Splitting the Unit itself, the rest is easy.

First thing though is to make sure that it is the Sender. Check the connections are clean and tight. Check that the 12 Volt supply from the car is present. To test the Sender disconnect the connections from it and attach flying leads to the wires that go to the car. Connect one of these firmly to the tang of a normal metal work file, switch on Ignition, scrape the other wire along the File, the Speedo should flick around at random. If this doesn’t happen remove the Speedo Head and check all connections and the 12 Volts there.

It could be that you have dry joints on the PCB, this is the next thing I would try, remove all the old solder, clean up very carefully and resolder.
 
1 - 1 of 1 Posts
Top