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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: bfilipe on September 11, 2007, 06:08:13 PM

Title: 2mb chip ram in Amiga 500 Rev 6
Post by: bfilipe on September 11, 2007, 06:08:13 PM

Greetings,
My amiga 500 (rev 6 board)is hacked to 1mb chip ram (8372A Agnus),ECS denise and kick1.3/3.1. My ram expansion in the trap door is the KCS Power PC Board rev 4.2 with 1mb.

If I replace the agnus 8372A with a 8375 (2mb version 390544-01) and socket another 0.5meg of ram in the amiga motherboard, will I get 2MB chip ram or do I have to hack the board again?

I'm unable to get the 2MB MegAChip upgrade.

Many thanks.

Title: Re: 2mb chip ram in Amiga 500 Rev 6
Post by: Zac67 on September 11, 2007, 06:37:25 PM

Well, it's possible... But quite a bit of work.
Don't forget that there a various 8375s around, one for 1 MB chip (replacement for older 8370/71), one for 2 MB in A3000 (32 bit chip RAM), one for A600/500+.

Take a look at the table in the German Wikipedia article (http://de.wikipedia.org/wiki/Agnus_%28Amiga%29) where the variants are compared and choose one of them. There are a couple of changes to be done to the PLCC socket (rerouting of traces) - nothing the simple onboard 1 MB expansion compares to - and a MegAchip is a much simpler solution. Or just get an A500+.

Title: Re: 2mb chip ram in Amiga 500 Rev 6
Post by: narmi on September 11, 2007, 06:50:54 PM

The 8372B (2MB Agnus) is pin compatible with the 8372A.  I had one in my Rev 6 A500 with 2MB chip ram on board (sold long ago).  I didn't do the mod myself, but I remember that it was hard to get the required RAM chips.  It is not an easy mod, even if you can get all the parts.

That being said, if I had the parts I would try it on my Rev 6 A500, just to see if I could do it.

Title: Re: 2mb chip ram in Amiga 500 Rev 6
Post by: Zac67 on September 11, 2007, 06:58:45 PM

The 8372B can't be pin compatible w/ 8372A since the latter doesn't have reserved pins for the additionally required address lines. It's largely pin compatible though, but even Alice fits that...

Title: Re: 2mb chip ram in Amiga 500 Rev 6
Post by: bfilipe on September 11, 2007, 07:37:16 PM

The Agnus 8375 I've mentioned is form Amiga 500+/600. I thought it was pin compatible with the 8372 that came on the board.

I've seen in Aminet a hack that implies making a PCB for the Agnus.

I have ram chips to solder in the empty ram sockets in the motherboard (from an old ISA vga card). But without the 8375 it's useless to put them in there.  The system already has 8mb Fast and 1 mb chip ram.

So much for the easy road...  :-(

Thanks anyhow.

Title: Re: 2mb chip ram in Amiga 500 Rev 6
Post by: Tenacious on September 12, 2007, 02:00:38 AM

I did the motherboard mod back in the early 90s on one of my A500s. It is still running strong.  The entire 2 megabytes go on the motherboard (all new chips, IIRC). The half-meg on the A501 is disabled but the rtc is still used.

Title: Re: 2mb chip ram in Amiga 500 Rev 6
Post by: Jeff on September 12, 2007, 03:26:51 AM

I also did that hack to a rev 6 500. The article was in Amazing Computing Amiga magazine in the end of '93 I think. You have to replace all the motherboard ram locations with 1Megx4 Dram DIP's. You use an 8372B 2Meg Agnus (A3000 Style) and modify some traces on the motherboard.

It works great, but finding a used DKB Megachip on ebay would be a lot easier. The 1Mx4 chips were hard to find back then, and the Megachips go for less than $100.00 usually.

Have Fun,
Jeff

BTW This the above also applies to the rev 6.x 2000's as I recall.

Title: Re: 2mb chip ram in Amiga 500 Rev 6
Post by: 57goldtop on September 12, 2007, 10:12:12 AM

Quote

You use an 8372B 2Meg Agnus (A3000 Style) and modify some traces on the motherboard.

An 8375 318069-XX will work too, was found in some A3000 and A3000T machines.