#1Meg Agnus + 2.0
16 messages in this thread
Could anybody detail the steps needed to install a 1MB Agnus on a A500? I need
to know if there are any other steps nescessary other than just swapping the
chips. Also, If I upgrade my ROM's and sytem to 2.04 do I need to reformat my
Hard Disk? Any info will be appreciated.
Thanks, Joe Costa.
Joe,
To install the 1 meg Agnus in a 500, you need to cut 2 traces on the
motherboard and add one jumper. Not that hard, but you need a steady hand
with an x-acto knife and a soldering iron. You also need to have the right
kind of belly slot memory board. The generic 512k boards should be OK,
it's the larger ones that may be problematic. Some aren't designed
properly…
Upgrading the ROM should not require you to reformat the HD. The installer
program on the 2.x disk will update the system automagically.
I should have the 500 upgrade info around here somewhere… just have to
find it….
-Jim
MOS via Autopilot & Amiga
Jim, thanks for the reply! I had my 500 apart today to fix my Disk drive's
eject button and got to wondering about the Agnus swap. If you (Or anyone
reading this) could tell me right tweakings to bbe done I would assume full
responsability for any damage that may occur by my clumsyness.
Thanks a lot.
Joe Costa
Joe,
The first thing to do is find jumper pads JP2. They should be near or
between the CPU and ROM chip. Pins 1 and 2 will be connected with a trace.
You need to cut that trace and jumper pins 2 and 3 instead. The other cut
is a trace comming from pin 32 of the RAM expansion slot. The exact
routing of that trace varys between revisions. I always trace it out from
the connector to be sure… But I don't have a 500 handy to check it out.
-Jim
MOS via Autopilot & Amiga
Thanks Jim, I'll have a look and try to locate everything before the butchery
starts.
Joe Costa
Good luck…. The pin 32 trace (EXRAM\) is the tricky one. BTW, what
revision is your 500? I've seen some Rev 5's fail with this mod.
-Jim
MOS via Autopilot & Amiga
Im not sure what revision my 500 is, with my luck it will be rev. 5…
Joe Costa
Don't worry if its a rev 5, Joe. I performed the operation on my A500
with rev 5 motherboard in 1989, and it still works without a hitch.
–IBM compatable technician by day, Amiga madman by night–
Rick Green, Mobile, Al
Thanks Rick, all that's left now is for me to locate said 1 meg Agnus chip…
My local dealer (Local as in a 50 mile radius…) wants 60 bucks for the
thing… So I'll try my luck with mail order.
Joe Costa
I paid $100 for mine in 1989 and $150 for the A501 (sniff, sniff 🙁 ).
There is an ad in AC for DeVine computer sales. Their ad says they sell
the 1MB Agnus for $37.95. I used DeVine recently to purchase my CSA
12 Guage accelerator. I had no problems with their business. Give them a
call at (800)578-7617 for sales or (302)836-4139 for tech support and
product info.
–IBM compatable technician by day, Amiga madman by night–
Rick Green, Mobile, Al
I paid $120 for my A501 and $600 + tax for my 52mb (49mb really) GVP HD+ with
2meg Ram…A month later they released the HD+ Turbo with the 40 mhz '030, saw
it listed for the same price I paid for my plain controller…talk about
frustration.
Thanks for the info, I'll give DeVine a call.
Joe Costa
(Btw, I originally traded a broken 1982 Honda XR200 for my A500: 512k RAM,
green Monitor and 8 pin printer, no books, no extras disk. Best deal I ever
made.)
It should be stamped or silkscreened on the board somewhere… But a quick
way to tell is by the number of RAM chips. Rev 6's only have 4 where the
5's have 16. A good percentage of the 5's will work with the mod, it's
just that everytime I've heard or seen one fail, it's been a 5.
-Jim
MOS via Autopilot & Amiga
Well, my 500 has proved to be fairly reliable so far (Hardware-wise anyway.)
And (Knock on wood…(C= exec's heads would do.)) the patient will survive the
operation. Now, for 2.0 are there any extra steps required past plucking the
old ROM's and putting in the new ones?
Thanks.
Joe Costa
Yeah, I've seen alot of rev 5 500's work with this mod, so you could be
fortunate…. but I figured a warning was prudent. Usually the symptoms
are general flakiness & crashes, especially in hi-res screens. Sometimes
the moving screen objects leave droppings behind as well.
As for the ROM that's pretty much a pull & drop operation. Just be sure to
follow the instructions that should come with it. There's a jumper wire
on two pins. That should be cut for 2000's but I forget if it's left on
for all 500's or just older ones. If you have a rom switcher, it's cut
regardless.
Good luck with the surgery…
-Jim
MOS via Autopilot & Amiga
This is to you and Jim.
The 2.0 ROM on my rev 5 motherboard has the jumper wire installed. I
believe it is necessary for all A500's. I believe that is the difference
between 2.04 ROM and 2.05 ROM. I think the 2.04 is the one with the wire.
–IBM compatable technician by day, Amiga madman by night–
Rick Green, Mobile, Al