Hello Mick
All the information that I have was obtained from the NOTES ON INSTRUMENTATION by Perry Newman. The information I was quoting can be down loaded as a PDF file on the C5 alive web site in the down load section titled unofficial service guide, its very interesting but does not really go into enough detail as mentioned.
The other modifications are fairly straight forward, I have changed supply on IC2 from 12 to 5 volts and will be fitting the 47K resistor in the pod shortly. Hopefully these mods will help, pity about those catch diodes?
Waran.