Very odd, definitely had me scratching my head. Going to do a little more digging today and see what I can find. I’ll probably order some clocks aswell

 

See if you can borrow standalone tach from garage. These are used to verify tach signal in exact cases like this. Will probably display RPM just fine since waveform looks correct.

Only other thing I can think of is disassemble clocks trace RPM-signal wire from connector to tach and verify it's intact and not shorted to any other circuit.

 

So after further tests and another set of clocks I’ve come to the conclusion it can only be the ecu! Second set of clocks, we’re the same as mine. Disconnected tach wire where clock loom and main loom meet, ran a wire direct from ecu, to clock loom, still nothing, decided to borrow a feed from number one ignition coil (where the gear indicator was wired to,) to the clock loom, and hey presto, tach sprang into life! The rev counter didn’t anywhere near match the engine rpm tho unfortunately so can’t use it as a temp/permanent repair. At least it proved the clocks though. All very odd when the reading on the oscilloscope looked good!

 

So strange....
did tach on 2nd set of clocks work on whatever bike it came from?

 

I’m in need of ecu