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Hi all,
I have been having a problem with the speedometer in my 1992 745T for some time. The problem started when I took the working speedometer out of the cluster once, reinstalled it, and I came to find an 8 mph offset that started after driving. I tried several used clusters to realize that 1993 and up clusters do not work in 1991-1992 cars only because the fuel sending unit and hence gauge is different. I have also found that many of the other Yasaki clusters had black capacitor electrolyte goo that leaked all over the chips and the circuit board.
The fix for the original speedometer was simply to remove the unit from the cluster and replace all of the capacitors on the circuit board and resolder all of the joints. The speedometer can be disassembled by pulling the needle straight off and then by removing the four screws holding the meter motor mechanism as well as the two screws holding the odometer motor. I then replaced almost all of the capacitors that I saw on the circuit board (electrolytic, metal film, and ceramic disk) using parts from Digi Key. Performing the replacements was relatively easy, but the double sided circuit board presented a few issues since a normal solder sucker does not work very well on double sided boards. I found that a cheap desoldering iron worked wonders at getting the old solder out as did desoldering braid. After replacing the capacitors and touching up all of the old solder joints re-assembly was the reverse of removal and my speedometer now works without any offset.
I am not sure whether replacing the capacitors or resoldering the joints nailed the problem, but after going through many dead clusters from the 1991-1992 year it seems that capacitor replacement and resoldering the circuit board certainly cannot hurt.
Mike
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