Eyetech Group Ltd
Amiga Technical Notes
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.
In response to these problems, and in conjunction with Amiga International, Eyetech has developed a set of hardware modifications applicable to 1.D.4 and 2.B motherboards. These modifications bring the 1.D.4 and 2.B boards up to 1.D.1 specifications and result in the correct and stable operation of the A1200 with most permutations of performance-enhancing accessories. If you send us your A1200 motherboard (on its own or in its metal shield - but not in the A1200) we can undertake these modifications for a fixed charge of £30 + return carriage. Alternatively we can make the modifications and fit and test your accessories at the same time - please ring for details.
Eyetech-supplied Amiga International Magic Packs
Like several other Amiga dealers Eyetech has been supplying Amiga 1200 Magic packs since the became available from Amiga International in late 1997. Where applicable these packs bought from Eyetech have had the 1.D.4 and 2.B modifications already carried out. There are however two design limitations on these Magic Pack computers which were not present in the earlier Commodore-manufactured A1200's. These are design limitations rather than manufacturing defects and the rectification of them - although usually possible - is specifically excluded from all warranty provisions.
These limitations are as follows:
Some copy protected games software uses floppy disk drive signals which are not present on the Magic Pack floppy disk drives. This software - which is in a minority - will not run on the Magic Pack A1200's without the addition of Eyetechs EZ-DF0 floppy drive interface.
Changes to the A1200's video circuitry to meet new EC interference emission standards means that some monitors exhibit horizontal 'tearing' of the screen image when using the PC-compatible screen modes of DBLPAL, DBLNTSC, Super72, Productivity etc. (Standard 15 kHz screen modes work fine). Eyetech can undertake a (charged) modification to the A1200 main board to replace these suppression components with ones which allow the vast majority of PC-type monitors to function perfectly. However do check first - you may find that your A1200 functions fine with your monitor in these screen modes without further modification.
Please contact Eyetech if you experience these symptoms and would like to arrange for your motherboard to be suitably modified.
