Oh, I am quite happy to accept that all the people he assoiciated with back then who had M1s had doublers. But that was not the original statement. AFAIK it's not the PSU that changed, not even between the European and US models. THey all rand off the same type of 'brick' as the M1 keyboard/CPU unit. You could fit the 2 bricks inside the EI to save space, the European ones were larger (and in metal cases) so you had to dismantle the case and remvoe a redundant plastic tray to do this. Who cares about the warranty anyway :-) This all relates to the DRAM timiog. The DRAM system needs 3 accurately timed signals, RAS/, cAS/ and Mux (this being the control input to the address multiplexer). They are all produced and used on the M1 processor board for the intenral DRAM. ANd they were brought out to the expansion connector. The original intention was to feed those along a ribbon cable to the EI. This AFAIK never worked propperly. The next idea was to fit a buffer PCB in the calbe ot clean up those signals. Then to use a screned DIN cable to carry them. And findally to only use the RAS/ signal from the M1 CPU board and to geenrate the other 2 signals inside the EI using a delay line. My EI is one of the last design. I have just dug out the scheamtics that came with it, and from waht I can see there were no changes to the disk cotnroller section. Thre is no external data separator, the XTDS/ pin of the 1771 is pulled high (this pin is low if you have an external data separator and high to use the one built into the 1771 I think). -tony