2.3 MB RAM on A500 through Trapdoor - help needed

[bleep]

Hi all,

I wanted to expand the memory of my A500 through the trapdoor,
so I fetched an used expansion card from eBay.
I seems ok, since I've got about 1.8M RAM when booted, but
I can't get the complete 2.3M. The reason is, that there is
a wire from the Gary-adapter which is not connected, because
I dont know where to connect it!
I remember that there used to be such RAM-Expansions where
the wire had to be connected somewhere on BigAgnus, but which
Pin? I can't find any documentation about this :-(
Does somebody have such an expansion (they can't be that
different) and could please look and tell me where this
wire has to be connected to?
Thanks very much in advance !

Dominic

[whiteb]

Hi.

The adapter.. What kind of RAM does it take ?

Does it look anything like this that i submitted to Big book ?

http://www.amiga-hardware.com/showhardware.cgi?HARDID=1697

MY expansion, the Gary adapter connects to the trapdoor expansion via a 3 wire cable.

It did not employ a cable to the Agnus, it employed a single cable from a solder point (JP9) over near the CPU that connected to the Gary adapter.

[bleep]

Hi,

thanks for the reply and sorry for my unexact description.
I didn't know that it is possible to have more than 2.3M
through the trapdoor.
My expansion card uses 16x 421000C (well one I found to
be defective and replaced it with a 511000).
This are 1MBit Chips (1M x 1Bit).
There is only 1 wire going to the Gary-adapter, and 1
wire, as said, is left over :-(
They both connect to the GAL16V8B on the Gary-adapter.

I´ll check what JP9 is and if that made sense.
In my schematics, there is no JP9; I have a PCB Rev 6A
with a Agnus 8372A.

Thank you,

Dominic

[Zac67]

I guess whiteb was refering to JP2, which maps trapdoor RAM to  C00000 ('Ranger' memory) or 080000 (for 1 MB chip RAM). The JP2 setting has to correspond with the Gary adapter your expansion is using; for an older model you'd probably have to limit chip mem to 512 KB (C0 setting) to be able to use all RAM. The same applies if your Agnus can't handle 1 MB chip (but then the jumper would already be set to C0).

[glitch]

Is it an ICD AdRam with dip style chips?

If so, the one wire needs to go to a solder "pad" either near the CPU or near the expansion port connector - can't remember which.  Check futher to find the make and let us know.

[Argus]

Or a Baseboard by Expansion Systems?

[bleep]

@glitch, argus
The expansion board is labeled "MicroniK A500 2MB"
I did a google search, but didn't find anything useful.
It isn't mentioned in the "big hardware book" either.

@Zac67
The Agnus is a 8372A, therefore should handle 1MB Chip RAM.
When I've got more time, I can check if the RAM is mapped
to C0xxxx or 08xxxx (can't remember).
Connecting the wire from the Gary Adapter to JP2 doesn't
make much sense to me, since there are the A23 and A19
lines which can be also found on the Gary socket itself
(therefor the GAL could pick it up just there)

The RAM chips are 18Pin DIL, btw

[glitch]

Post a picture of it fitted in place, and we can all have a look-see...

[whiteb]

Yeah sorry, I did mean JP2.

I only went with the instructions in the manual, to use THAT jumper block as the source to wire to the Gary adapter.

JP2

[ ]

[ ] <---- Solder wire from Gary adapter to this.
 | <---- cut this trace
[ ]

[Zac67]

I was wondering about the JP2 cable, too. But this actually does make sense, as the 'A19' line to the trapdoor board is routed through the gary adapter.
Not necessarily for your board though...