A1200 motherboard revision levels
When the A1200 was designed there were - as is common in designs of that complexity - some 'bugs' in the chip designs. Many of these were corrected by the time the main production runs started, but some were not, and in fact several bugs still remain in the latest revisions of the AA chip sets.
The main production board issued in the UK - Rev 1.D.1 - had onboard provision for hardware workarounds to fix the main bugs, notably bus timing problems in the Gayle and Budgie chips. In general these boards work fine with most combinations of expansion hardware and are the boards which we use to test A1200 expansion products on before shipment.
The later revisions of motherboards - particularly the revision 1.D.4 and 2.B are a different story however. These boards revisions were designed to take corrected versions of the Gayle and Budgie chips - and therefore were designed without provision for the earlier hardware workarounds. However, revised versions of the custom chips were never produced and as a consequence all but a few of the last of the AT/Escom manufactured motherboards were shipped without either bug-free chips or hardware workarounds.
In general these 1.D.4 & 2.B defects only make themselves felt when the A1200 is expanded by the addition of an '040 (or above) accelerator, high performance IDE hard drive/CDROM subsystems, Zorro slots or I/O expanders (PortPlus etc). Often any one such accessory will work, but two or more will not work in combination. Typical symptoms are an accelerator exhibiting instability problems, a graphics card failing to be recognised or a CDROM failing to show disk icons.