Playing "spot the difference" with two boards shows that MkIII has a few extra components: 2D1+2 are connected in anti-parallel across the telescopic antenna input 2D3 provides reverese polarity protection at the DC input socket Q28 2SK544 N-chan MOSFET is added as a grounded source FM-IF gain stage between T101 and cerafil U2, with R123 now 220r used as the drain resistor (to R124) R125 is no longer fitted and C127 is shorted out A removable test link marked IF_1 on the board underside appears to be in the 455kHz IF line from IC6 to C201 TC3 has been added presumably to tune U6 (the 2nd LO) to 55.3945MHz