xj900f ignition troubles

[reabo]

Hi i have a 1992 xj900f and have covered 39k miles in 13 months with only the expected minor niggles. But now it has me stumped. I started it yesterday and it would only run on 2 cylinders, the right hand coil which runs the tacho isn’t working. The tacho kicked in once and the ignition fuse blew. I replaced the fuse and now it will only run on cylinders 1 and 4.

I have disconnected the instrument console + tried – no difference

I have isolated the tacho – no difference

I have checked the resistance of the pickup coils – ok

I have checked primary winding + secondary windings resistance on ignition coils –ok

I have swapped the wires to the coils over – no spark on any plugs

Have swapped non-working ignition coil with a known good one – sparks on 1+4 only still

I have checked the wiring and connectors

I have beaten the damn thing to death with a 14lb sledge hammer (not yet but may be the next step)

As i see it the only thing left is the tci unit, which on mine is a pattern one. So has anyone got the Yamaha part number for the tci unit on a 1992 xj900f (4bb model)? Is this unit used on any other bike? Has anyone got any ideas or can see something i have overlooked?

Thanx in advance for your help this has been a fantastic bike, it now has only 71k miles on it + i have done most of them and would hate to scrap it now.