Path: utzoo!utgpu!cunews!dgbt!netfs.dnd.ca!rutgers!sun-barr!olivea!uunet!comp.vuw.ac.nz!canterbury!chem194
From: chem194@csc.canterbury.ac.nz (John Davis)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: 32bit DMA lockups (Was: More info on A2091 woes)
Message-ID: <1991Feb7.105352.30@csc.canterbury.ac.nz>
Date: 6 Feb 91 22:08:23 GMT
References: <555376@neabbs.UUCP> <1991Feb4.134725.10@csc.canterbury.ac.nz>
Lines: 31

> I had exactly the same problem on fitting a 2630 to my rev4.3 b2000 using a 
> 2090a. A call to CBM revealed it was a known problem, and could be fixed by 
> adding a pullup resistor across one IC on the motherboard. It cured the 
> problem totally for me (I left it copying a 1.5mb file around the hd for
> a few hours to test - no problem whatsoever). As far as I know the
> fix _ISN'T_ needed on rev6 boards, but it could well be worth 
> checking with CBM anyway (and definitely worth checking on your friends
> rev4.x machine)

Sorry about not posting the actual details of the fix initially, I couldn't
find my notes on it. Anyway, here's the info ....
 
fix for DMA probs with rev 4.x m/boards and accelerator cards
-------------------------------------------------------------

fit a 3k3 ohm resistor across pins 11 and 20 (top right to bottom right
pins of chip, when looking at motherboard from front of machine) on
chip U605 (it's one of a group of 6 to the left of the 68000, again
looking from the front of the machine).  
 
Worked like a charm for me - before putting the resistor in any write
of >100k crashed the machine, now I can write 5mb files (with a single
write() call) 'til I'm blue in the face, without a hiccup.

-----------------------------------------------------------
| o  John Davis - CHEM194@canterbury.ac.nz               o |
| o  (Depart)mental Programmer,Chemistry Department      o |
| o  University of Canterbury, Christchurch, New Zealand o | 
| o                                                      o |
| o  co-sysop AmigaINFO BBS,1200/2400 baud CCITT,        o |
| o           24 hours a day, ph NZ +3-3371-531          o |