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-   -   A500 - 6A, 1MB chip + some fast (http://eab.abime.net/showthread.php?t=31816)

Chain 29 August 2007 09:37

A500 - 6A, 1MB chip + some fast
ive filled four free positions on 6A board wit 4256 chips, now - how i can set it as standard ram, not an extension ram? i want additional fast (slow) ram (hooked on expansion connector) at c00000 so exram jumper jp2 must be at A23. Is there any way to tell agnus there is 1MB chip as standard? Do i need some demuxes for cas/ras?

Any help will be appreciated guys, im trustin you. someone here KNOW how to do it :great

Toni Wilen 29 August 2007 10:29

Can't do without extra logic. (I have seen one with 3 TTL chips)

Chain 29 August 2007 11:29

Is there any schematic somewhere?? i can build it, no prob

Zetr0 29 August 2007 12:48


I recently read something like this on hardware heaven or aminet i think... hmmm i may of d/l it...... brb

I cannot seem to find it atm... :( sorry about that.

Chain 29 August 2007 13:05

im searching for that hack almost 14 days, but found NOTHING :(

Toni Wilen 29 August 2007 13:37

Finnish magazine "C=lehti" published the schematics, but the problem is finding it, my "storage system" is not very good :D

Zetr0 29 August 2007 13:42

hmmm i am having trouble finding it too.... just checked my local haunts...

aminet / programmers heaven..... i will keep looking on your behalf :)

Chain 29 August 2007 13:54


Originally Posted by Toni Wilen (Post 353970)
my "storage system" is not very good :D

same here, i have piles of magazines, but finding something particular is almost impossible. still im in half of that, but im now almost sure it was not published in our czech magazines :(

Zetr0 29 August 2007 13:57

@Chain this is the mod that you solder 4 256k chips to the a500 mobo isn`t it?... damn i am sure I read it... now where was it... grrrrr

Chain 29 August 2007 14:02

its not only about 4 dram chips, it also needs some logic chips, othwerwise it works in same adress space as expansion connector (read=useless)

Zetr0 29 August 2007 14:46

I think this is what i was reading up on


hope its what you are looking for

Chain 29 August 2007 14:59

nope :/ its not working that way

(also 6A board does not have 7A 7B jumpers, just "7" which enable exram tick)

Chain 30 August 2007 13:51

:bowdown Bump

Zetr0 30 August 2007 16:27

it seems that I have all the jumpers the document / Mod requires on my a500 so i figure i should take some nice picies... any reason for hardware pr0n baby! it would interesting to note there are differneces within revisions.... you know it wouldn`t suprise me with CBM

some pictures of my a500 (click thumbs to enlarge)

heres the overview of the A500 6A mobo


heres some board info (sorry about the glare)


heres the memory array


heres Jumper 2 (just by the KS ROM )


heres jumper 7A (just by the exansion port)


so all one needs to do is populate the memory chips and then cut a track then join a track, I am a little concerned about the fact there are some caps also missing with the empty memory chips but the mod doesn`t require them.... hmmm

caps [ 23,22,21 and 20 ] would these be needed ?

food for thought me thinks. I was wondering if i could use/rob the memory chips from the A501 (since i have a spare one) and use these (part id: TMS44C256-10N / EDP 044K9 ) either way imma gonna solder some IC sockets in place :D

Toni Wilen 30 August 2007 16:44

1 Attachment(s)
Found it :)


- A500 schematics really needed
- rev6a pin out
- chips must be fast, ALS, F or AS.
- may not work with original A501 because it has extra buffers that can delay signals too much. (most/all 3rd party expansions don't have buffers)
- cut all connections in JP3, RAC0 = topleft, RAF0 = bottomright
- don't forget +5v and GND connections
- J7A = original position
- JP2 = 1MB chip position, A23 = original position

(I built this ages ago and it did work, but also sold the Amiga with expansion ages ago..)

Chain 31 August 2007 10:51

Holy cow! Thanks Toni! :bowdown

I will post some photos to prb.hardware/pics when it will be done (and working)

Chain 31 August 2007 11:10


Originally Posted by Zetr0 (Post 354257)
food for thought me thinks. I was wondering if i could use/rob the memory chips from the A501 (since i have a spare one) and use these (part id: TMS44C256-10N / EDP 044K9 ) either way imma gonna solder some IC sockets in place :D

-it still uses same memory space as a501 (will NOT work with otner expansion)
-you can rob them
-caps are not needed
-dont use sockets, or you will not fit keyboard back ;)

Chain 31 August 2007 11:29

1 Attachment(s)
still a little bit confused about jp3 pin assigments

Toni Wilen 31 August 2007 11:36


Originally Posted by Chain (Post 354480)
still a little bit confused about jp3 pin assigments

Get schematics and double check connections :)

Original (finnish) instructions are also very confusing.. (and have partially incorrect labels, like RAF0 was named RAC2..)

Zetr0 31 August 2007 13:17


so is you rev 6a a500 the same as mine or subtly different ? to be honnest Its being used as a test bed at the moment for some of the upgrade i have been developing / toying with. I tihnk i may of confused you earlier, i wanted to know if i could use the CHIPs from the a501 upgrade module and put these on the motherboard. fear not for the sockets the board wont be going back into its orginal case ;) :) besides... i get days where i need to solder something.... it felt good....


I am a little confused over the differences between the Finnish how-to and the austrailian how-to... acording to the Austrailian version its cut two lines then close one of them (both of these positions i have labled on my 500 mobo) chain however does not... is it possible that my board already has this logic due to its revision of version ?

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