My most humble apologies for the length of this: EyeTech is source for the first part. The second part's source is a saved file off the net (2002).
**** I am not the author, nor liable for the content****
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
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Second part of my "saved files":
Okay, due to popular demand I have decided to do a full post on fixes for A1200 problems with some expansion slot hardware. This takes moderate technical knowledge. I AM NOT RESPONSIBLE FOR ANY HARM THAT MAY COME TO YOUR COMPUTER FROM PERFORMING THIS MODIFICATION. This modification comes direct from Commodore Engineering on Jan 21, 1994.
Text follows:
BOARD REV. 1D.4
-Budgie Rev -01
Remove E123C and E125C from the A1200 motherboard
-Budgie Rev -02
Remove E123C and E125C from the A1200 motherboard
Remove XR358 470 ohm pull-up resistor
Add 470 ohm pull-up resistor at pin 43 of U2 (ie Alice)
BOARD REV. 2B
-Budgie Rev -01 and -02
Remove E123C and E125C from the A1200 motherboard
Add 470 ohm pull-up resistor at pin 43 of U2 (ie Alice)
Change R118 from 470 ohm to 220 ohm
To find your Budgie Rev, look at the end of the C= part number. It should be something like 365xxx -01 or -02. That's the revision.
