bigkev wrote:hi all
my friggin speedo is drivin me mad i see quite a few other membersw have the same problem.i have a new sensor in the diff i hav continuity between the speedo and sensor and i have resoldered all speedo points but still no speedo does anyone have resistances for the speedo/sender unit
PLEASE HELP
Kev,
The speedo sensor is just a magnetic switch that opens and closes when the toothed wheel inside the diff passes through it. It will either be zero ohms (short circuit), or infinity ohms (open circuit).
I once had a problem where my Speedo started to get intermittent. Sometimes it would work, other times it was totally dead. I also noticed that it seemed to come back to life when I had the heater on and the car was nice and toasty inside.
I traced the signal all the way from the diff sensor to the back of the instruments, and this proved to be working fine. I pulled the instruments and stripped them down, and had a good signal path all the way to the speedo head itself.
After thoroughly checking it over, I found what appeared to be a dry solder joint on the circuit board on the speedo head. After re-soldering the joint, everything worked fine. I also checked the same joint on another speedo, and it also showed signs of a bad joint.
If you look at the circuit board on the back of the speedo (talking about VDO here, not sure if Motometer is the same), you will see several components soldered to the board. One of these is a silicon chip of some sort. This is under the big coil of wire on the side of the speedo.
In the centre of the chip, are two very wide pins. The wide pin nearest to the edge of the circuit board is quite close to another component (capacitor) that is a small rectangular shape. If you look at the solder joint for this capacitor, you will hopefully see that it looks slightly cracked around the join. You may need a magnifying glass to see it clearly. Even if you can't see a faulty joint, it is always worth heating all the joints with a bit of fresh solder as dry joints are not always visible to the eye.
Mine has been fine ever since.
Cheers,
Ian.
If it aint broke - Modify it...
