Speedo problems

[Strutty]

There are numerous entries on web sites / forums about XJS / Jaguar speedos failing that point to the same areas to check. However, my problem was something else - hence this entry - so that someone who has my problem may find it sooner than I did. The items you are advised to check are 1; the sensor that bolts into the final drive unit, 2; the transducer (tucked up in the rear left hand wing) and 3; the clock itself.
Fortunately my neighbour is a computer / electonics whiz so he had an oscilliscope which he wired up to the car to test for a 'pulse' from the back end. We tested the sensor, wires in and out of the connection blocks, the transducer and related wires and found that there was a pulse in each (he tells me it's a square wave if that means anything to anyone). The conclusion was that the clock must be knackered so I bought a new one from JDHT - everything else on the instrument panel was working - or so I thought. With new clock fitted, I fired her up and ... no speedo. Dead! I then trundled along to a local auto engineer / electrician who tested everything we had tested and found the pulse as we had. However, when he connected a wire from the transducer directly to the back of the clock the speedo worked. Closer inspection of the instrument panel revealed that the ABS warning and radiator level warning lights were not working when the ignition was switched on - not something I had noticed. The power supply to these bulbs AND the speedo is part of the PCB on the back of the panel and a small crack in the PCB meant that power was not getting through. Simples - as they say. Quick solder join and Hey presto - I have a speedo .... and a spare one if anyone wants one. So if anyone experiences a dead speedo - check the PCB very carefully!!!! I now consider myself a self taught expert in this matter so if anyone has this problem please feel free to get in touch.

[PaulE]

Well done! A detection saga worthy of Poirot himself. Paul.