Dear Fellow Brickboarders,

Hope you're well. If a 1991-92 speedo shows changes in miles-driven - but the speedometer's needle does not move at all when the car is moving - is this proof that the entire speedo has failed? I'm aware that 1991-2 speedometers are vulnerable to capacitor failure.

Or, is there another problem, i.e., with the circuit card?

Thanks for your help!

Yours faithfully,

Spook

Dear Spook,

On my 94 940 speedo there are two motors (thus 2 separate circuits on same board) - one to drive the needle and another to drive the mileage counter. I have yet dismantled any 1991-92 speedo to confirm any similarity with 94 but if the mileage counter is still running but the needle does not, this might suggest same circuit scheme.

On my 94 speedo the capacitor was leaking and its electrolytes have started to corrode the circuit traces but speedo hasn't failed yet. I've managed to replace the capacitor by using tweezers (tight spaces to insert finger in) and cleaned the board with acetone swabs.

Amarin.

Dear Amarin,

Hope you're well. What's the location of the problematic capacitor? Thus, if one faces the back of the speedometer - with the instrument oriented as if it were installed in a cluster (75 mph / 120 kph at the 12 o'clock position) - is the problematic capacitor at the 12 o'clock edge of the board, or, say, at the 6 o'clock edge of the board?

What color is the capacitor in question?

I didn't see any discoloration resulting from leakage. But some capacitors can fail because they "dry out", or so I'm told.

Thanks for your help.

Yours faithfully,

Spook

IIRC its the top electrolytic capacitor, about 12 o'clock position. Dark brown in colour. For the lower 6 o'clock capacitor there's ample space to insert finger in to replace. No problem with that.

Just a side note:
The installed electrolytic capacitors are of industrial/professional grade rated for 105C temperature able to withstand high cabin temp if car parked in sunlight. I just had normal/domestic grade 85C capacitors in my parts bin so I used those for time being. Looks like another soldering job waiting.

Industrial grade variety could be ordered from online electronic webstore such as Mouser, Farnell, RS and so on. This takes time to order but then I wasn't expecting any leak to happen.

Amarin.