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Old 20 September 2017, 02:49   #1
motosega
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a500 jumper settings for 1mb chip on MB?

i just soldered an extra 4 ram chips onto a rev6a a500 (8372A agnus)

playing with the jumper settings i can only get the extra ram to be recognised as slow ram.

with default settings the ram is not recognised, but if change jp7a to top jumper i can get it to recognise an extra 512kb slow ram.

i tried reversing jp3 too, but it makes no diference. and if it just cut jp3 without reversing it, no boot.

systest show that it works fine, but what i want is 1mb chip ram. any ideas?

there are loads of other threads on this subject but they all seem have dead links to images that suposedly show the right way to set the jumpers....
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Old 20 September 2017, 04:18   #2
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I always refer back to this post over at AmiBay... clear examples.
Some of the pics are gone but you'll get the idea.
Your config may be different as you've added the 4 mem chips.

http://www.amibay.com/showthread.php...ssive-H-W-pr0n!
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Old 20 September 2017, 06:21   #3
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Perhaps this might be helpful despite the different revision ?
http://www.nightfallcrew.com/31/08/2...-1mb-chip-ram/
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Old 20 September 2017, 11:24   #4
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thanks guys, i'll try jp2 next, according to the rev6 schematics, it should change the memory location of the installed ram.

when i work it out i'll make a tutorial, this is something that should be well documented since its such a cheap and useful upgrade for the a500. I have another identical a500 that needs exactly the same mod. So i can take nice photos.
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Old 20 September 2017, 12:05   #5
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yay! success! i now have 1mb chip ram soldered onto my rev6a motherboard.

what i had to do was this:

solder in 20 pin sockets for the 451256 chips (mine were oki 451256-10 100ns, the ones on the board were 120ns)

add the 4 missing 0.33uf bypass caps.

now the jumpers:

leave jp3 in the default position.

cut the trace in jp7a and leave all pads disconnected.

cut the trace in jp2 and re-solder it into the alternate position.(top)

tested with systest. everything is ok!

thanks to everybody who posted info about this in the past!
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Old 20 September 2017, 13:02   #6
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If you can get hold of the right agnus and memory chips you can also upgrade to 2MB chip

There's a guide around here somewhere and I can confirm that it works fine
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Old 20 September 2017, 18:16   #7
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2mb chip would be great, too bad those 2mb agnus chips are rare.

theres a way of getting 1 mb chip plus 512k trapdoor ram too, maybe that one is less dependant on hard to get parts.

1mb chip ram will keep me busy for a while, mustn't be greedy!
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Old 20 September 2017, 19:16   #8
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Quote:
Originally Posted by motosega View Post
theres a way of getting 1 mb chip plus 512k trapdoor ram too, maybe that one is less dependant on hard to get parts.
I thought you needed a Gary in-between board to be able to do that.
My AdRAM has this and my machine has 1MB Chip + 1MB Fast
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Old 21 September 2017, 00:55   #9
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Quote:
Originally Posted by Akira View Post
I thought you needed a Gary in-between board to be able to do that.
My AdRAM has this and my machine has 1MB Chip + 1MB Fast
yep, theres some messing with the gary chip involved, luckily some guys on this board have made a pcb design:
http://eab.abime.net/showthread.php?t=85395

if it turns out i really can't live with only 1mb chip, i'll make that board. its pretty cheap.

there are a few other older designs out there but it looks like the new one is better.
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Old 06 September 2018, 20:29   #10
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Angry

Sorry for resurrecting an old post, but I attempted this mod:

My A500 is showing 1MB chip RAM and 8MB fast RAM via HC533 accelerator w/8MB, 512 on Rev 6a Motherboard, and 512k on trapdoor A512 board.

JP2 has proper continuity (top/middle pads)

I cut JP7A trace bottom to middle. The bottom solder pad actually separated from the board . I'm still getting continuity with a multimeter between all three pads. Shouldn't there be no connection between these pads?

Workbench 3.1 boots off the CF card on the HC533, Sysinfo shows the Fast/chip RAM OK, but now a ton of games begin to load and go through the cracktro or initial load screens but then hang. Is this because of the extra 512k Chip RAM or is there a memory error of some type caused by my mod (that I probably screwed up)?

Any help would be much appreciated. I've searched a lot but couldn't find anything about the continuity between the three pads on JP7A other than the trace between middle and bottom pad must be cut.
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Old 19 September 2018, 12:17   #11
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Quote:
Originally Posted by Neil View Post
Sorry for resurrecting an old post, but I attempted this mod:

My A500 is showing 1MB chip RAM and 8MB fast RAM via HC533 accelerator w/8MB, 512 on Rev 6a Motherboard, and 512k on trapdoor A512 board.

JP2 has proper continuity (top/middle pads)

I cut JP7A trace bottom to middle. The bottom solder pad actually separated from the board . I'm still getting continuity with a multimeter between all three pads. Shouldn't there be no connection between these pads?

Workbench 3.1 boots off the CF card on the HC533, Sysinfo shows the Fast/chip RAM OK, but now a ton of games begin to load and go through the cracktro or initial load screens but then hang. Is this because of the extra 512k Chip RAM or is there a memory error of some type caused by my mod (that I probably screwed up)?

Any help would be much appreciated. I've searched a lot but couldn't find anything about the continuity between the three pads on JP7A other than the trace between middle and bottom pad must be cut.
Having exactly the same setup (except trapdoor memory - some 0,5 MB noname A502/16 with 16 150ns RAM chips), same accel. card and similar problems. Random freezes after Workbench load, WHDLoad crashes, KS1.3 much much more stable than WB3.1 ... I have tested memory, done re-capping of A500 and power supply, contact cleaning of socketed chips ... Everything looks ok (except CIA precision timers, see below) but problem stays same. Still waiting for PLCC chip extractor to check'n'clean Agnus (8372). If that don't help, remains only either check which other trap memory (which I don't have nearby ) or undo mod and test stability. But, 512KB chip mem is unusable today

BTW, I suggest you do testing of Amiga with SysDiag (look at bottom for binaries) https://github.com/keirf/Amiga-Stuff ... It found problems with my CIA precision timers on both CIA chips which are related to my WB3.1 mouse click freezes.

Last edited by technomancer; 19 September 2018 at 12:27.
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Old 20 September 2018, 05:38   #12
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Hey technomancer, thanks for the reply. I will have to hook up my A500 (been working on an A1200 project) and give the SysDiag you linked a try just to be sure there aren't any hardware problems.

I think my issues are a more an issue of the 3.1 "upgrade" as I switched ROMS from 1.3 pretty much simultaneously to the install of the CF card and A512 board. My workbench is stable and so are normal programs I run (non game programs work perfectly).

Since my post, I installed WHDLoad and have had pretty much 100% success with games after working out all the kinks with getting it set up. A lot of the older games needed a kickstart 1.3 rom installed into devs/kickstarts.

Prior to the HC533, A512, KS3.1 and CF upgrades, I was rocking a stock A500 with 512k Chip RAM and KS1.3 and a Gotek. Almost every game I tried (.adf) ran perfectly. I probably should have expected things not to go well with 3.1 and old non-patched games.
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Old 21 September 2018, 02:01   #13
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Systest has been running for about 20 hours on — Direct Memory Scan —. It’s on round 670something... I think my memory is all OK. It recognizes Chip 1mb and Fast 8mb as it should after the modification.

My main concern was the continuity between all the
solder pads on JP7A even after cutting the trace on the motherboard - coupled with the fact several games stopped working immediately after the mod. I’m assuming it’s probably the KS3.1 that is the culprit and/or now having 1mb Chip RAM which may or may not play well with some games.
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