63 lines
3.3 KiB
Plaintext
63 lines
3.3 KiB
Plaintext
From luth!sunic!mcsun!hp4nl!telmail!neabbs!johans Wed Nov 1 12:30:45 MET 1989
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Article 36064 of comp.sys.amiga:
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Path: luth!sunic!mcsun!hp4nl!telmail!neabbs!johans
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>From: johans@neabbs.UUCP (HANS VAN DER WERF)
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Newsgroups: comp.sys.amiga
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Subject: Fatter Agnus
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Message-ID: <237122@neabbs.UUCP>
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Date: 30 Oct 89 18:28:14 GMT
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Organization: NEABBS multi-line BBS +31-20-717666 (13x), Amsterdam, Holland
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Lines: 49
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Hi there superfat Agus fans,
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here is the story of upgrading my A500 to 1MB Agnus.
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After buying the Fat Lady (dfl 150,-) i opened up my A500 (for the
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first time). I assumed that i had a REV 5 board, so the transition
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should be fairly easy. What i found after removing all screws and
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and shielding defies description. First of all there was no JP2
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between the ROM and the CPU (oink), second there was no REV number on
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the board (what ???), thirdly the _ROMEN pin on the Kickstart ROM was
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torn out of its socket. Soldered to it was a blue wire wich on the
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other end connected to a 3D mounted transistor (shiver). After uttering
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some strong words i also removed the bottom shielding. This revealed
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some more manual modifications, and last but not least the REV number.
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The REV number said 3. After sitting down and taking a deep breath i
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tried to think of a sunny side of all this. All i could come up with
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was that this board might be a collectors item by now (anybody
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interested???).
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Now how to put Mrs. Obese in there? Since there was no JP2 i made my
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own. What JP2 does on REV 5 boards is connecting A19 on Agnus to A23
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or A19 on the CPU address bus. My Agnus A19 was hardwired to A23 on
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the CPU address bus. So i carefully cut this connection on the bottom
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side of the board between the CPU pins. Then i soldered in a new
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connection from the CPU A19 (pin 47) to where the previously cut
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connection runs through the board from bottom side to top side, thus
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effectuating a connection between CPU A19 and Agnus A19. The rest is
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fairly straight forward. The _EXRAM signal on GARY must be kept high
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thus preventing it to detect the RAM expansion. I did this by cutting
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the connection near the GARY socket (pin 32) on the top side of the
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board. The connection to a pullup which keeps pin 32 at VCC is still
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intact since it runs under the socket in the opposite direction.
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Now the only thing left to do was replacing HER. Ahh, wait a minute
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wasn't there something about Agnus pin 41 and PAL/NTSC. Yes, Agnus
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pin 41 should be kept at a high level to force a PAL display. Because
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i live in Europe i'm kinda attached to PAL. So i bent the pin 41
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inside the Agnus socket outward (careful now), preventing it from
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forcing the PAL/NTSC input to GND level. After putting Humpty Dumpty
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back together again, i crossed my fingers and turned on the power ....
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It worked. Avail reported somewhat over 1040K chipmem, hmm nice.
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I'am still in the process of trying out what software works, and what
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doesn't anymore. Up till now only ACT OUT refused work altogether,
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actually it GURUed. Furthermore, it is a pity that you must have fast
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ram to use DPAINT-III's animation features. By the way, is there somebody
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out there who has a list of programms that freak out when a 8272(A) is
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installed ???
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