The particular webster wqesd4 I have looks like about an '86 or so board, from chip dates, and the main chip that is socketed is marked with "ENGR-SAMPLE"...doh.... Maybe I do have a very early board that won't run with a faster cpu. The rom is a part no. 080469-01 REV 01, if that means anything to anyone, as marked on its paper label. The later sigma board does not have the problem. Oh, well, if I have to run it with a KA630 at slo-poke gait, so be it....(:+\\... There are two diodes, one looks like an ordinary silicon rectifier and one looks like a zener of some sort, possibly, off pin 19 of the 74ls240 at position V2 on the board. Those come off the J6 pin 10 of 10, and are in parallel. Thanks Bob