RE:

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

> >I have used the search engine but DID NOT find an
> >succinct answer for this problem.  My '89 200TQ has started doing
> >the speedo dance with the odometer failing as well.
> >Sometimes things work perfectly, other times it is hosed.
> >What is the prognosis and fix?  Is it a DIY'er?
> 
> As Bob Myers pointed out, the most likely place is cold
> solder joints where the four prongs on the speedo unit
> meet the main circuit board ( the green flex thing...)
> 
> If your speedo can be made to temporarily fix itself
> with a (well practiced) whack on the side of the 
> gauge cluster, its probably a bad connection.
> 
> I disagree with Bob about replacing the connector though.
> Just resolder, it will probably be good for another 100k miles.
> 
... which would be great if the original was soldered in!  This problem is
that the speedo head is plugged into the IC's flexprint interconnect board,
not soldered.  This makes it easy to disassemble the unit, but is not
without risk.  The problem is endemic with the cars of this vintage.  Bob's
solution replaced the old tin/lead contact points with gold, which is a very
good thing.  There is a body of experience that shows that simply providing
a separate grounding connection will solve the problem.  Solder a wire to
the ground point on the speedo, connect a ring lug to the other end of the
wire and attach it to one of the grounded screws that attach the flexprint
to the back of the IC.  

HTH!
Steve Buchholz
San Jose, CA (USA)