From: dkm@col.hp.com (Dave K. Martin)
Subject: Re: Problems 2 RamCards installed
Date: Tue, 18 Aug 1992 17:36:57 GMT
Organization: HP Colorado Springs Division

I believe the following mods are the ones you are looking for.  I had to do 
them on my 4.3 motherboard to fix some problems with a GVP disk and memory 
board.  They may or may not help your memory problems (they did fix mine 
though).

In my case, GVP thought that the pull-up resistor provided on the GVP card
was not sufficent and that I needed to add a resistor directly to the 
motherboard.  This was to pull the DTAC(?) line on the 68000 (pin 10) to +5v.
Next to the silk screened printing identifying the IC number for the 68000
(U100)there are two feed through pads on the mother board.  A 470 ohm 1/4 watt
resistor should be tack soldered across these pads.
                
		|                                               |
		>                                               |
   < Front of   |		68000 Processor			|
   < Amiga      |_______________________________________________|
			  pad --> @ U100 <-- silk screened number
		             ____/    @  <-- pad
                             |         \
			     |-resistor-| <--resistor soldered across pads

I used a 470 ohm, 5%, 1/4 watt resistor as it was the first I found in my parts 
box.  While I had the system apart, I also added the resistors described in 
steps 5 and 6 below.  

After adding the resistors, my system ran great, no more memory problems and 
no more read/write errors on the hard drive.  

-------------------------------------------------------------------------------
From bryan@cs.utexas.edu Fri Jun 21 11:41:34 1991

In article <1991Jun21.021132.23327@trl.oz.au> aduncan@rhea.trl.OZ.AU (Allan Duncan) writes:
=-
=-Has anyone got the details of what was done between the board revisions?
=-Mine is about 4.2 or 4.3 (I'm not pulling the lid off just to look while
=-on-line:-))
=-

Here's the short version, summarizing the procedure given in Issue #26, section
3-2.1 (Jul-Sep 89) of the Commodore service technician's update, "TechTopics:"

A2000 field upgrade to rev 4.5:

1. Remove if installed:  R901, C917, C902, C910, C911, C905, C908, C230, C240

2. Install 1.3 Kickstart ROM

3. Install RP904, RP905, RP906 only if U205 and U206 are 74HC244 type ICs

4. Add .01uF ceramic cap on solder side from pin 12 of J300 to nearby ground
pads. 

5. Add 3.3K ohm, 1/4W resistor across pins 11 and 20 of U605. [Note: Dave Haynie
recommended 1K ohm resistor in a previous article]

6. Add 470 ohm, 1/4W resistor from cathode of D800 to second pad from the left,
under CN605.  (Already installed as R1000 on rev4.3 and above)

7. If R5719 not present, add 470 ohm resistor between Vcc and CPU side of R106.
Use pad located to the right of U100, and the pad on the ground trace running
under pin 14 of the 68000.

8. Replace Toshiba GARY (U102) with MOS GARY.



DISCLAIMER:  While making these modifications eliminated some problems with my
A2000, I take no responsibility for the results obtained by anyone else
following the above procedure, nor for any inacuracies or errors I may have
introduced.  For a full description of the procedure, obtain a copy of
TechTopics #26 from a Commodore dealer.  In addition, it may be that the
procedure was revised in a later issue.


That said, let me mention that the most important step in *my* case appeared to
be the replacement of the Toshiba GARY with a MOS GARY.
------------------------------------------------------------------------------- 

Hope this info is helpful.

-- Dave Martin - dkm@col.hp.com
Newsgroups: comp.sys.amiga.hardware