1986 xj700s maxim tachometer issues...help!

Hello. I have a 1986 xj700s Maxim and the tachometer decided to stop working. When I got the bike a month ago it was fine. Now, the lights work but the RPM has zero response. I checked, cleaned and reconnected all the wire plug connections then took out the tach and cleaned it with air since it's a sealed unit....no luck. Aftermarket tachometer for this bike are non-existent so I gotta figure out how to fix the original system. Anybody got any ideas or run into the same issue and have a solution? Thanks in advance!

 

How did you clean contacts?
Mine failed after reassembling from fixing speedo. I cleaned with vinegar soak (not easy to just soak the connections) for couple hours, then sprayed with contact cleaner, then sat overnight.
Worked in the morning.
I wonder if there is a way to troubleshoot with volt meter to see if its the tach or the bike.

 

I don't have that diagram for the 700S but the 700X the gauge lights get power from a different circuit than the tach, so noting that the lights work may not be relevant

Are the flashers and horn working OK?

Checking that the tach is getting 12V would be a good place to start. After that a lot of meters these days are equipped with frequency counters that should be able to measure the signal at the tach signal wire, which should measure around 20 Hz at idle for 1200 RPM. It may be difficult to probe the back of the tach, but should be fairly easy to back probe the connector with the tach signal - and just a bit of caution even thought it's the primary side ignition coil signal I would suggest keeping any bare skin from contacting