Thanks Boots.

The boards were both tested yesterday MPU and solenoid driver. All worked fine on Ken Skybeu's tester. Many thanks for the diagram. Is there any point in going further with the chips if both boards were tested and functioned fine?

J.D.

Hmmm definately something hiding there.
The connectors must be ok of the coil fires when you earth the driver transistor.
Are the IC's I mentioned socketed?
If so you could do a quick swap out to 100% eliminate them.
Perhaps something got zapped when you were testing before you changed the coil diode.
It wont hurt to check the chips with a multimeter, that will only take 5-10 minutes.
If the switch signals getting to the boards, I would definately change the chips, like I said cheap and easy and if its not necessary at least the new chips will be socketed for any future problems.