I have tried everything you stated in your reply.
LPT is set to Normal in BIOS and Addr 378H & IRQ 7.
I have tried all printer ports in PicoScope program(LPT's 1,2 & 3).
There are no conflicts with IRQ 7 or Addr 378.
Rechecked same PicoScope program using ADC10 with prog set to ADC10 & LPT1 - This works fine.
Tried running DOS PicoScope set to ADC12 in Command prompt Window under Win XP - ADC12 works fine.
The Trace still saturates and sites at the top of the scale, irrespective of what scale is used in PicoScope under XP, again if I swop the ADC for the ADC 10 and change convertor in program to ADC 10 and LPT1 this works OK.
Both the ADC10 & the ADC12 are quite old( 8 to 10 years approx), but if it works ok under DOS window then I have to assume that there is no problem with the ADC IC(LTC1292) or any of the other components on the PCB. All connections & joints are good.
As I stated in previous post this is the same on both Laptop AMD XP1800+ and Desktop AMD XP1500, so I don't think that there is any problem with the ports.
Any other suggestions would be welcome :