English Amiga Board - View Single Post - A500 plus 2MB mod, what am I doing wrong?

Jope · 15 June 2016, 21:04

You're almost there. The crucial problem here is, that now both sets of RAM chips are still connected to the same memory bank.

There are CAS and RAS signals going to the DRAM chips.

In the original setup, the RAS signals are all shared among the chips and the two separate blocks of RAM have individual CAS signals.

In an A501+, we have two RAS signals and two CAS signals.

The A500's trapdoor connector has the RAS signals on pins 37 and 38. Check RAM chip's pin 4 on the expansion, and see whether they're connected to pin 37 or 38 on the trapdoor connector. Seems by the schematics that it should be pin 38 (XRAS1)

What you need to do is bend up pin 4 of the top chips and connect them all together, then connect that RAS bank to the unused RAS pin on the RAM expansion connector Should be pin 37 (XRAS0).

Double check the schematics for the A500 rev 6, A501 rev 6 and the A500+ rev 8 and A501+ to be sure.

Good luck!

Haha, this actually makes me want to make some ghetto A501+s too. :-)

15 June 2016, 21:04	#3
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,861	You're almost there. The crucial problem here is, that now both sets of RAM chips are still connected to the same memory bank. There are CAS and RAS signals going to the DRAM chips. In the original setup, the RAS signals are all shared among the chips and the two separate blocks of RAM have individual CAS signals. In an A501+, we have two RAS signals and two CAS signals. The A500's trapdoor connector has the RAS signals on pins 37 and 38. Check RAM chip's pin 4 on the expansion, and see whether they're connected to pin 37 or 38 on the trapdoor connector. Seems by the schematics that it should be pin 38 (XRAS1) What you need to do is bend up pin 4 of the top chips and connect them all together, then connect that RAS bank to the unused RAS pin on the RAM expansion connector Should be pin 37 (XRAS0). Double check the schematics for the A500 rev 6, A501 rev 6 and the A500+ rev 8 and A501+ to be sure. Good luck! Haha, this actually makes me want to make some ghetto A501+s too. :-) Last edited by Jope; 15 June 2016 at 21:13.