Flakey 200TQ speedometer revisited

[jp@barclay.net (JP Timmerman)]

Thank-you Igor for faxing the service bulletin. I examined the points noted
very carefully and could not see any problems with the solder joints. I
re-soldered them anyway just in case I couldn't see the problem. I also
re-soldered the mating pins on the speedo head. On the test drive it failed
after driving for nine minutes. The speedometer still stops working in the
same manner I first described. I feel that the decreasing speed cutoff
threshold is an important indicator of what is going wrong, but I have no
idea what could cause such behavior.

Anybody have any thoughts?

JP Timmerman
'89 200TQ
'86 5000CDTQ Avant
'85 5000S
'80 5000S Diesel (sold but hard to forget)