1988 420SEL, for sale
Discussion Starter · #1 ·
I've read all the posts I could find on speedometer bench testing, but still not quite sure if I have all the information. I replaced the odometer gears and capacitors a while back to fix that issue, and it worked okay for a while, so now I think there is a bad trace somewhere, as I could tap the dash to revive it each time it quit, but that stopped working. That old PCB was hard to solder without damaging the foil. Is there a schematic for the speedometer section? And does the square wave for testing get applied to the big pin or to the middle pin on the 6-pin connector, between the +12v and GND pins? I have a function generator to drive it on the bench. Thank you for your help!