#Fatter Agnus and A500
5 messages in this thread
I have just received a Fatter Agnus chip for my Amiga 500, but I don't know
what needs to be done to the logic board to let the computer access 1meg of
chip RAM. If someone could tell me what modifications need to be made, I
would appreciate it. The chip has already been installed, so I just need
to know the logic board modifications to make.
Move the jumper at J101 from pins 1-2 to pins 2-3. Cut the trace
between the two pads at J500. NOTE: the trace is VERY small and VERY close
to other traces…if you slip, you may end up with a DOA A500. CBM
reccomends a small sharp knife like an Xacto for the cut…I cheated…I
used a small drill bit (#65) in a hand chuck (like a jeweler's screwdriver)
and simply turned it a couple of times and the trace was cut. Obviously,
if you use my method, you only turn the drill far enough to cut the
trace…not put a hole in the motherboard! One or two twists by hand is
plenty.
Another method that works well is to use an Exacto knife, but not in the
'normal' way you would think. Using a 'slicing' motion is the main cause of
a slip, so another technique is required.
Using the very tip of the knife, 'find' the trace, using no pressure on
the blade (or at least not enough to cut it. Then, turn the knife so that
the blade is at about a 45 dgreee angle, and press down, cutting through
the trace without 'sawing' or 'slicing'. Turn the blade so that it is at
the opposite angle, move the blade a little to the other side, and do the
same. It's rather like cutting a notch in a stick. A little twisting motion
on the second cut will lift the trace out. Neat, and safe.
Larry,
Right…that method, or the hand drill is quick, easy and safe. In
fact, the worst method is the slicing with a blade. It's too easy to slip and
cut some of the other traces also.
Don
Don,
thanks for the information. However, my logic board doesn't have any jumpers
on it that I can see. It is a Rev. 5 logic board. I didn't even see any pads
marked J101. Where are the pads for J101 and J500 located?