Fatter Agnes (1 Meg)
6 messages in this thread
I recently tried to install the Fatter Agnes (1 meg) chip in my Amiga 500.
I cut the trace on J2 and bridged the solder pads as directed. Then bent up
pin 32 on the Gary chip… also as directed. Got everything back together
and powered up. Ran a diagnostic and was told I now had 1 meg of chip ram
and no fast ram… that's the fact since my Amiga only had a meg of memory
to begin with. However, when I tried to run various programs with graphic
screens, I got a mess. It looked like the images were streaking and
bleeding all over the screen…. persistance of images one on top of
another. I checked and rechecked everything and can't find my mistake. I
pulled out the Fatter Agnes and put the old Fat Agnes back. Then
re-soldered the jumper and replaced pin 32 on the Gary chip. Everything is
running again as it did before; so I caused no major damage.
However, my diagnostic program says the _Blit failed its test (both with
the Fat Agnes and the Fatter Agnes installed.) I received an error code of
726 and 730 on various runs of the diagnostic program. This may or may not
be involved. I just don't know.
Mike Hanson
Mike,
Your first mistake was to pull the GARY pin. That is not a
reccomended practice…although I know some folks suggest it as the
"proper" way to make the modification.
The Blitter is part of AGNUS so if it's not working with either
chip..it's a good possibility you damaged the AGNUS socket when you pulled
the chip. What kind of chip puller did you use to remove the AGNUS? If
the "tweezer" kind of remover…that's more than likely your problem.
Don
Thanks for your response, Don. I used the tweezer type puller to get the
Agnes chip out. I don't think I damaged the socket. The machine works just
like it always did with the old Agnes installed. If there's something wrong
with the blitter… it doesn't seem to cause any problems in the original
configuration.
If I go back in to install the Fatter Agnes, do I just change the jumper at
J2 and forget about disconnecting pin 32 of the Gary chip? The instructions
I was following seem to indicate that this is necessary to prevent the
Exram signal from being tied to ground.
If installing Fatter Agnes in a 1 meg machine, results in 1 meg of chip ram
and no fast ram, does that present a problem?
Do I really gain anything significant by making this work?
Thanks, Mike
Mike,
Pulling the pin itself is a bad idea. What you need to do is cut
the trace leading to pin 32 on the motherboard. But yes, that connection
needs to be cut.
There have been some very strange things occur if you pull that pin
and leave it just hanging in the air. One user reported everything worked
fine until he put the shield back on, then it went downhill from there.
Not having any FAST RAM shouldn't cause a problem with a properly
designed program.
Don
Don,
Thanks again! I cut the trace originally when I first installed the
Fatter Agnes. I had the image smearing problem when I powered up. I figured
I may have cut the wrong trace since the instructions weren't very clear on
that point. I soldered the trace back together and pulled pin 32 (leaving
it out in the air.) I had the same problem with the screen smearing.
After that, I put pin 32 back in the socket and replaced the jumper
on J2 and put the original Fat Agnes in its socket. In other words, I'm
back to where I started. My machine works fine with the old Agnes… no
smearing on the screen. Maybe I got a defective Fatter Agnes? Maybe I
should just learn to live with 500K of chip ram!
If I solve this quandry, I'll let you know.
Thanks for your help!
Mike
Mike,
It's also possible that you've got one of those 500's that simply
won't take the 1 Meg Agnus upgrade. I don't know which motherboard version
is involved, but do know there are some out there that simply can't be
upgraded. That's one reason that Commodore never authorized the 1 Meg
upgrade for A500s. In fact, not only do they not authorize it…they
specifically have said that upgrading an A500 WILL void any remaining
warranty.