2MB Chip RAM directly on A500 rev. 6 motherboard?

[czarek]

Hi, I know it is possible as I saw few people did it. My question is - how?
I have already soldered whole megabyte onto motherboard and re-soldered jumpers so it's visible as 1MB Chip RAM. The possible problem may be that it's pre A500+ motherboard. It had space for 1MB ram and 8372 Agnus, but doesn't have space for RTC circuit and when I put 8375 Agnus it just gives me black screen. Was no problem with replacing Denise to full ECS though.
So all of you A500 experts - please share your secrets :-)
Thanks in advance!

[czarek]

Ok I just found out that my Agnus 8372A is full ECS Agnus that supports 1MB Chip RAM, only ones that support 2MB are 8372AB and 8375. I have two 8375 Agnus chips, both tested working in real A500+ but when I put them in my motherboard it just doesn't start up. Very strange. I'm wondering if it has anything to do with jumpers? When soldering my actual memory I had to cut JP4, and switch JP2 and JP7A. I just spotted there are 3 jumpers labeled JP5 just next to Agnus. I can't find any information about them - does anybody know what is this one for?

[czarek]

I've got couple of A500 plus, all dead due to battery leakage :-( but their Agnuses (8375) are working in rev 8a A500...

[czarek]

WOOOW - you're the man! Thanks a lot - though that sounds pretty hardcore, especially demuxer chip and all lines to connect it. So one more stupid question (Sorry). If I replace my Agnus with 8372B, add A20 address line, will it allow me to use memory from expansion slot or is it basically the same thing?

[czarek]

Hey I just found those two schematics:
http://falba.net/upload/a500.gif
http://falba.net/upload/a500plus.gif
They look very similar, so maybe there would be the way to make some rewiring between motherboard and Agnus socket or make some adapter so I could use 8375 Agnus? I already have couple of them so it would be no problem with getting one, and 8372B is pretty rare as it was only used in A3000s...
Or is it too much hassle?