davem@hp-lsd.COS.HP.COM (Dave K. Martin) (01/06/91)
I believe that the A-500 does not have the jumpers on the motherboard that
the A-2000's have. There are some jumpers to be moved and traces to be
cut to allow the new Agnus to access the additional memory. If this is
not done, then the chip will stilll only access 512k.
When I upgraded my A-2000, rev 4.2, my dealer gave me an instructiion sheet
showing what to cut and jumpers to move. The following is quoted from that
sheet. Any typos, etc are mine :-).
The new "fatter" Agnus 8372 IC, which can address 1 megabyte of chip ram
will require the:w following modifwing modifications to the A2000 pcg
operation. Without these modifications the IC will adress only 512k of
chip ram and operate only in NTSC mode.
1. Locate jumper pad J500 (to the lower left of the 8520 at U301).
This is a 2 pad jumper with a trace connecting the two pads. With a
Exacto knife cut the trace which connects the pads. Be careful not
to allow the blade to slip and cut another trace. Note: see page 9
of A2000 system schematics, cutting this trace keeps the _EXRAM from
being tied to ground.
2. Locate jumper J101 (to the lower right of power connector CN400).
Move shorting block to the left, shorting pins 2 and 3. Note: see
page 13 of A2000 system schematics, this wil enable address line 19
from the 68000, which controls the 1 meg adress range.
Note: Use correct IC extractor tool when removing F. AGNUS from the
socket. (Available from the parts dept. PN #314874-01, cost is
$20.00.)
The sheet also has some pictures to aid in locating the jumpers but they are
pretty easy to find. Use care when extracting the IC, It seats *VERY*
tightly in its socket. I used a couple of small jewlers screwdrivers and
a couple of paper clips with small hooks bent on the end to extract the
IC. Make sure that you observe the static precautions. Usually if you zap
a chip on a do it yourself installation, there is no refund. If you don't
work with this sort of stuff or know someone who does and can help, it is
better to spend the extra $15-20 to have the dealer install it.
Hope this helps....