Speedometer troubles.

[captainphiliptaffski]

My P reg Bongo has developed a fault on the speedometer assembly, the speed gauge still works fine and registeres the correct speed, as varified by GPS. However the tripometer and also the milometer have both stopped logging any distance.
Is this a cable drive problem or is it electrical as i believe the speedometer is electrically driven?
Any help would be greatly appreciated. I am fairely good mechanically and electrically but dont want to start ripping the dash apart until I know what to look for. Thanks.

[fatcatlawyer]

Thats a fault? think of the resale value!!! Repair it just before you sell it!

Ian G

[scanner]

and that's advice from a lawyer - now you see how he became a fat cat one.

[captainphiliptaffski]

Thanks for the advice, I did think it was a fault, perhaps someone could tell me how the fault became a fault and thereby disclose the remedial action required ipso factum.

Thats a fault? think of the resale value!!! Repair it just before you sell it!

Ian G

[westonwarrior]

Its electrical you can romove the speedo and carefully rock the dials as I have heard of them being stuck

try the trip reset first though just in case

ps Im moving this to tech section as its more suited to there and may get a better response

[steviebongo]

hi there mine does the same was going to change the speedo head eventually,but if theres a fix for the original one that would be great .

cheers stevie

[captainphiliptaffski]

Thanks muchly, now I know it is electrical I will remove the unit and bench test it to see if its circuit related a dry joint or corrosion maybe even a tired component which needs replacing.
If I find the cause/fault I will share.

[patnben]

The speedo and odometers are driven from a square wave frequency
generator on the final drive of the gearbox. If you remove the complete
instrument panel, you can use an audio square wave generator to test
and calibrate the speedo precisely.

On the rear PCB are 3 termiinals marked IG, SP-, and SP+. Connect a
12 volt positive supply to IG and a negative (ground) supply to SP-.
The square wave frequency is connected to SP+.

The speedo and odometers are driven by a bunch of electronics behind
these terminals. Start with a low amplitude on the signal generator and
gradually increase it until the speedo starts to register, set the output
frequency to around 100 Hz and the speedo should show about 70 KPH.

If you have a converter fitted to convert to MPH then you have to do
the maths to set the frequency to the correct ratio as we are working
with the original KPH signal. When the speedo is working, the odometers
should also be recording and if they are not the you will have to remove
the speedo head and dig around the electronics.

The speedo is linear with respect to the output signal so you only need
to calibrate it in one position. Full deflection of the speedo is around 250
Hz. PM me if you need any further information.