A500 8×44256 (1 RAM=256 KB×4 bit) to 2×514400 (1 RAM = 1 MB×4 bit) possible?

[psxphill]

FWIW I think this hack will prevent you from using a genlock as the original fat agnus in the a500/a2000cr had part of the genlock logic incorporated from the a1000 motherboard, but the 2mb fat agnus in the a500+/a3000 had it split back out again because they needed an extra address input for the cpu access to chip ram (pin 35 changed from xclk to a20). This is what removing the resistors and the connection to gary is for. It's probably possible to reimplement that logic by looking at the differences between the a500 & a500+ schematics, but this hack doesn't appear to do that.

The rest of the hack updates the a2000 motherboard for the 2mb agnus dram changes (pin 56 changed from ras1 to dra9, pin 57 is now the only ras). ras1 goes to ras on the 2nd (now unused) bank of ram, so the hack routes that to pin 5 of the 1st bank. Pin 5 on the old ram chips is a "No Connect" but is now a9. I'm guessing the connection from a9 to +5 through a resistor is because the address pins need external pull ups but the ras doesn't, but I haven't bothered investigating further.

I'm surprised this hack wasn't documented earlier, but the lack of genlock (which IIRC the megachip upgrades do handle properly) might have been a reason. Plus the megachip upgrades were an easier sell, popping a couple of chips and one wire is much easier than removing all the ram and doing all that rework to the board.

[psxphill]

I do not want to expand the memory. A500 rev. 6A, 8372A = max. 1 MB chipRAM.
2 MB chipRAM not possible, 2 MB Agnus not possible.
I want to use 2 piece 441000 chips instead of 8×44256 chips.
This possible with A500?
C64 8×4164 = 2×4464 work.

2mb chip ram appears to be possible if you hack the board and use the right 2mb agnus (there are two 2mb agnus variations, one is compatible but the other has a much different pin out that definitely won't work). But if you don't want to replace agnus then your maximum is 1mb.

Using 441000 without a 2mb agnus is going to be hard, but it might be possible. Google doesn't throw up anything, so you're on your own figuring out the logic to calculate the extra address lines from the chip selects. If you are keeping the old agnus then you probably ought to have one chip in each of the banks (the 2mb agnus hack has the second bank completely empty).

I couldn't find a c64 hack for 2x4464, the only result I found was someone saying they killed their c64 trying.