Thanks for your reply. I have the service manual but it doesn't contain schematics as earlier models did.
We don't have a Welch Allyn office in NZ only a representing company thay sells their products but they use a private service company who are more interested in promoting their own businesss than helping with technical advice for hospitals that wish to do their own serviceing.
The probe has been changed. It does contain an EEPROM which is interrogated when the probe plug is put in and it reads the EEPROM at which point it decides there is an error and does't allow it to work after that. The data is streaming out of the EEPROM before this point.
Keith
