Changes made to Service manual schematics:

+12V & -12 V referenced to VIN, should be to 0V.

Trimmer capacitor TC1 540pF replaced by fixed capacitor C53 22pF on issue 6.

Video circuit - issue 5 C31 is 16pF, issue 6 C31 is 22pF.

VSYNCH line decoupled to OV via C48 10nF (not shown on issue 5 or 6).

Issue 5 and 6, IC17 74LS00 (ROM decode) doesn't exist on QL PCB (ROM's self-decode).

Issue 6 IC27 74LS03 doesn't exist, function replaced by IC38.

Issue 6 IC38 (HAL) wiring incomplete/errors. New wiring shown.

IC24 IPC pin 37 (P26) not connected (not shown, but can be used for CAPS led).

Issue 6 R102/103 shown twice, were 33K now 0 ohm. Function replaced by R107/108 33K (mod on top of IC23).

Issue 6 IC23 (ZX8302) is connected to the CPU data bus, not the RAM bus


Other notes:

ROM port connecor J2 pin A1 has no connection (sometimes shown as 0V).

Expansion connector J1 pin A25 has no connection (QL concepts guide shows as DBGL).