[matspar]

Well, I've finally got round to checking those diodes, and I have made some interesting discoveries.
The meter I use has a built-in diode tester, and I also took resistance readings of each one.

The CG12E reads 200ohms (direction of current flow) and o/c when reversed. Resistance readings are 9k and 1k respectively.

The CG6E is o/c in both directions!! (on both settings)

The WX6 is o/c in both directions (on diode test) and reads around 3meg each way on resistance!!

So I have two very likely culprits, I don't have anything suitable to replace them with, all I currently seem to have is high voltage rectifier diodes.

I've found some data online which suggests a 1N4148 can be used to replace the CG12E and the CG6E, and an OA81 in place of the WX6.
Can anyone confirm this or suggest anything else? any thoughts are much appreciated as always!

Matt