Upgrading chip RAM on Rev 6A Amiga 500

Killseeker

Hi everyone, has been ages since I've posted anything but I've been doing a bit of trawling various forums today and am keen to verify some information.

As mentioned in the post title, I have a 512k Rev 6a A500. The motherboard has additional socket spaces for another 512k of chip ram and the Agnus chip is rev 8372a #318069-02, which I believe supports up to 1mb chip ram?

To upgrade the memory to 1mb chip ram do I only have to populate the empty ram sockets and add in the necessary capacitors and Agnus will recognise the additional memory? Or will I have to also make changes to jumpers ie. JP2 or JP7?

I have 2 A501 512k trapdoor expansions so was thinking of using one as donor components as the chip versions match, then using the other as regular slow/fast ram in the trapdoor for a total of 1.5MB. Will that work?

I have also read an article on how to convert the A501 expansion into chip ram. Keen to know if anybody has done this hack and whether it's been successful and worthwhile.

Cheers for any info you guys can provide Very Happy

motrucker · Posted: Mon Mar 19, 2012 11:44 pm Post subject:

Yep, the jumpers need to be changed. One jumper depends on what you are using for the extra chip RAM, the 501 or the motherboard.
I'll dig up a link for you asap.

Killseeker · Posted: Thu Mar 22, 2012 6:21 am Post subject:

Hi Motrucker, thankyou Smile

I've bought ram sockets and capacitors today for the princely sum of $4AUD.

Just thinking though, if the 8372 Agnus can only support up to 1mb ram total, whether it be chip or fast, I'm guessing that an extra 512k in the trapdoor is not going to be recognised....

motrucker · Posted: Sat Mar 24, 2012 3:51 pm Post subject:

Here's one link. Not the one I was thinking of, but it seems to have the needed info:

http://vmpalvelin.dyndns.info/Computers/A500/A500.html

You should still be able to use the trapdoor expander as fast ram, IIRC.
Hope this helps

Killseeker · Posted: Mon Mar 26, 2012 5:50 am Post subject:

Thankyou motrucker. I'll have a look through the links and see what I can find.
Cheers Very Happy

Jurbo · Posted: Wed Apr 18, 2012 10:20 am Post subject:

It's not really useful to populate the motherboard sockets, imho. Just do the jumper trick (of course you need the 8732A Agnus), and the trapdoor 0,5 MB Fast RAM will be recognized as extra Chip RAM, totaling 1 MB Chip RAM. If you populate all the motherboard sockets, the trapdoor 0,5 mb won't be recognized at all.

Can't remember exactly what will happen if you have a larger trapdoor expansion with a Gary socket. You'll probably get 1 MB Chip RAM with the rest as Fast RAM.

Killseeker · Posted: Sat Apr 21, 2012 8:15 am Post subject:

Hi Jurbo,

I went ahead and soldered sockets and chips on to the motherboard along with the required capacitors. I had a spare A501 512k ramboard lying around which became the donor for the additional onboard memory. The battery for the clock had well and truly leaked everywhere so I didn't feel too bad about butchering it. Was only AU$10 on eBay too!

After modifying the jumpers the 500 started straight away and showed the additional memory in WB. However, when I plugged in another working A501 the system wouldn't start at all. Upon removing it, everything was okay again.

Am guessing the 8372 can only ever address a maximum of 1mb ram. At least without any other mods or a cpu fast ram socket board addition, that is. Unfortunately those are a still a bit too pricey.

Happy to say though that the 500 boots properly and works fine, even though I need a new floppy drive. Was a fun little project Smile

Jurbo · Posted: Sun Dec 16, 2012 5:20 pm Post subject:

I know this is a really old thread by now, but anyway (haven't been around here for some time)...

Additional fast ram at the side expansion port does not depend on the Agnus (correct me if I'm wrong). Thus 8 mb (maximum) side expansion ram will be recognized by the system, even if there is 1 mb on the mobo or 512 mobo / 512 trapdoor. Additional expansions may hamper compatibility here.