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

[amigaksi]

I have an Amiga 500 with 2MB chip ram; don't recall which revision of motherboard it is but there's no DKB or any other expansion installed.  

[amigaksi]

>by alexh on 2008/10/18 5:25:55
...
>8375 318069-11 replace it with 8375 318069-10
>8375 390544-02 replace it with 8375 390544-01
>8375 318069-19 replace it with 8375 318069-18

...

>It's an A500+ (rev 8a)

I just opened up the A500 and it does state A500+ on the motherboard and is rev. 8A.  It has 390544-01 8375 and boots as PAL by default unless I go to the startup-menu.  Anyway to make it boot as NTSC by default without cutting traces or soldering? Some applications/games don't seem to care what the startup-menu boots up as.

[amigaksi]

>Yes its very easy to put 2 megs chipram on an A500+ (rev 8a) motherboard.

>The A500+ (8a) motherboard already has the 74LS139. Its marked as U32 on the motherboard. To put 2 megs chipram on the motherboard, just piggyback another 8 chips, bend up all the pin 17s, and hook the left 4 pin 17s to pin 11 of U32, and the right 4 pin 17s to pin 5 of U32. It's that simple.

My a500+ slot has the additional meg without any jumpers/piggybacking so I guess all the signals that are needed must be there in the slot connector.  However, I do have an Atari 520ST that uses a similar method you mentioned to expand it's memory.

>As far as hard-switching PAL/NTSC, I dont believe that the 8375 agnus has that capability. On the 8372 version, grounding pin 41 of the agnus makes it default to NTSC. Leaving it open (or hi) makes it default to PAL. I dont believe this pin is in the same place on the 8375, if it even has it. The 8375s are listed as either PAL or NTSC specific chips.

Is that pin 41 on 8372 an input to Agnus?  If so, which chip is it coming from-- perhaps easier to ground the signal from the source since Agnus is a square chip and it's very hard to ground a pin w/o cutting trace or soldering.

[amigaksi]

>Yes, the PAL/NTSC jumper(JP4) is an input to agnus on the rev 6a A500 board. It goes to pin 41 of the 8372(a or b) AGNUS. If you close the jumper, it grounds the pin, and tells AGNUS to boot in NTSC mode. If the Jumper is left open, the input floats "hi" and AGNUS boots in PAL mode.

Okay, my other A500 w/1MB chipram (rev. 5A) does not have a jumper for NTSC/PAL so I think breaking pin 41 would have the same effect.  I don't need the PAL functionality.  I was asking whether there was a better spot where that disconnect can be done.

>YOU CAN'T DO IT WITH AN 8375 AGNUS... And you can not put an 8372(a or b) in an A500+ agnus socket because they are not pin-compatable. Theres about 20 pins that are "rearranged" between the two.

>So basically, be happy with your PAL machine..

How about putting a PAL->NTSC decoder on the output.  I see some on Ebay.