Dead (electronic) speedo and odometer on 1990 RRC

[Richard Savage]

Speedo and odometer on my RR has been dead for some time and I suppose
I ought to find out what's wrong.

Suggestions as to how to test the various bits are sought from the
font of wisdom, please!

It looks as though getting the transducer off the chassis rail would
be a total ordeal so I don't really want to take it off if I can test
it in situ - especially if I find that it is functioning.

Also, does anyone know what the o/p of the transducer is so that I can
try to reproduce the signal as a means of testing the speedo.

Is there likely to be a simpler fault?

TIA

Richard

[DaveB]

In article <871223d6-0cce-4f41-83e9-1ea3998b5f06
@l16g2000vbl.googlegroups.com>, alt...@excite.com says...

The drive to the sensor... Bad/dirty connectors on the electrical
side?

What other errors are showing, or things not working quite right, the
speed signal on some vehicles is used for all sorts of things,
Aircon/heating settings, radio volume/tonal ballance, suspension
firmness ride hight vs speed etc etc. Just showing you how fast your
going is incidenta....

The sensor output is probably digital.

For a good intro to automotive electronic deviousness, look at:-
http://www.picoauto.com/automotive-library.html
(No affiliation.)

Take care, much of that stuff is electricaly delicate too, so it won't
survive an accidental short to 12V...

Dave B.

[Richard Savage]

On Feb 7, 5:29 pm, DaveB <g8...@uko2.co.uk> wrote:
>
>
> The drive to the sensor...   Bad/dirty connectors on the electrical
> side?
>
> What other errors are showing, or things not working quite right, the
> speed signal on some vehicles is used for all sorts of things,
> Aircon/heating settings, radio volume/tonal ballance, suspension
> firmness ride hight vs speed etc etc.   Just showing you how fast your
> going is incidenta....
>
> The sensor output is probably digital.
>

> For a good intro to automotive electronic deviousness, look at:-http://www.picoauto.com/automotive-library.html

> (No affiliation.)
>
> Take care, much of that stuff is electricaly delicate too, so it won't
> survive an accidental short to 12V...
>
> Dave B.

Thanks Dave. Will look at that site.

There are no 'incidentals' in a 1990 RRC! The speed transducer only,
as far as I can work out, feeds a little (stepper?) motor in the
speedo unit which operates the speedo needle, odometer and trip
recorder.

I'm tempted to connect an oscilloscope to the o/p of the transducer
and spin the drive with an electric drill. But I was hoping that some
kind soul was going to tell me of their frustrating lack of success
with that or similar attempts at solving the same problem. I've
tolerated the dead speedo for the last 3 MOT tests and used a spare
TomTom as a speedo but it's not great. I'd take the transducer off
the vehicle for a closer examination only it's fixed by one of the
transmission supports which appears to need more serious spannering
than I can exert while lying under the vehicle in the snow.


Rgds

Richard