8375 AGNUS for A500 rev6a mod

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unbrain

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Ongoing attempts to revive some of my amigas, I am looking for a 8375 AGNUS chip (318069-16).
 
Thanks for your reply, I was under the impression that the 318069-16 model number of the 8375 should be pin compatible with the 8372A that was in there from the factory?
 
Thanks for your reply, I was under the impression that the 318069-16 model number of the 8375 should be pin compatible with the 8372A that was in there from the factory?

According this page:
http://www.pmsoft.nl/amiga/amiga-parts-chips.html

Agnus (2MB) 8375 (390544-xx) is not pin compatible with 8375/8372AB/8372B (318069-xx) !!

But I just read here:
http://theamigamuseum.com/the-hardware/the-ocs-chipset/agnus/

++ 318069-16 (PAL) or -17 (NTSC). Vbb replacement to the 8372A. 1 MB support, pin compatible to the 8370/71/72A family.
Typically found on very late Amiga 2000-B systems (some require a small fix for stable operation with these chips – same when using them as a replacement to an existing 8370/71/72A).

Them, depends of your A500 revision. :)
 
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@Minter
Yep, I wrote that entry for theamigamuseum.
The rework necessary is documented in the amigawiki webpage.

What puzzles me is the OP mentions a "mod", I suppose he means the 1 MB chip RAM mod, in which case the usual request is for the quite common 8372A (318069-29) and not for the 8375 substitute (318069-16 or -17), let alone that applies to the very few rev6A's which shipped with the earlier 8371 Agnus. The rest already have the 8372A.

Maybe it's the 2 MB chip RAM mod for the rev6A (which uses either the quite rare 318069-03 Agnus (8372B) or the Vbb substitutes 318069-18 or -19 from the 8375 series) and the OP got the -16 (1 MB version) and -18 (2 MB version) mixed up.

(*) -16 PAL, -17 NTSC
(**) -18 PAL, -19 NTSC
 
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Maybe it's the 2 MB chip RAM mod for the rev6A (which uses either the quite rare 318069-03 Agnus (8372B) or the Vbb substitutes 318069-18 or -19 from the 8375 series) and the OP got the -16 (1 MB version) and -18 (2 MB version) mixed up.

(*) -16 PAL, -17 NTSC
(**) -18 PAL, -19 NTSC
if i got You right: 318069-18 and also 8372B/AB can be placed instread of standard a 8372 giving 2Mb of chipRAM? If so - i am looking for one of these too :)
 
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@Minter
Yep, I wrote that entry for theamigamuseum.
The rework necessary is documented in the amigawiki webpage.

What puzzles me is the OP mentions a "mod", I suppose he means the 1 MB chip RAM mod, in which case the usual request is for the quite common 8372A (318069-29) and not for the 8375 substitute (318069-16 or -17), let alone that applies to the very few rev6A's which shipped with the earlier 8371 Agnus. The rest already have the 8372A.

Maybe it's the 2 MB chip RAM mod for the rev6A (which uses either the quite rare 318069-03 Agnus (8372B) or the Vbb substitutes 318069-18 or -19 from the 8375 series) and the OP got the -16 (1 MB version) and -18 (2 MB version) mixed up.

(*) -16 PAL, -17 NTSC
(**) -18 PAL, -19 NTSC

Ah, my bad, yes, I'm after doing the 2MB chip conversion for my A500, got the wrong part number, sorry!
 
if i got You right: 318069-18 and also 8372B/AB can be placed instread of standard a 8372 giving 2Mb of chipRAM? If so - i am looking for one of these too


8372AB is probably no different from the 8372B silicon - all AB chips seem to have the B printed as an afterthought, which implies it was a batch of "B" versions fitted in "A" packaging and later the designation was "corrected" with the additional "B".


As to the question, the 8372(A)B and its Vbb 8375 equivalent actually are not drop-in replacements for the 8372A.


If you only have a single bank of RAM (that is, the default 512KB) then it'll still work, but if you have 1 MB of RAM (onboard + trapdoor) then the extra 512KB will disappear. This new Agnus only has a single RAS line, so it doesn't support two RAM banks.


So if you wish to install this Agnus on a rev6A A500, it should best be done at the same time with upgrading the RAM to 2 MB. The process is 4-step:


1. replace Agnus
2. change jumper blocks
3. remove the four 256Kx4 chips from existing RAM bank
4. install four 1Mx4 chips in the other (previously empty) RAM bank


It must be pointed out again that the whole 2 MB forms a single RAM bank now, so the trapdoor is rendered useless for RAM purposes. You can remove the RAM chips from a standard 512 KB trapdoor expansion however and have it work as an RTC-only card.




Finally, while technically the requirement is a rev6A board, as it has the necessary provisions (suitable jumper blocks and trace support for 1Mx4 chips), there's a way out with using a rev5 board, but you must get an A501 rev6C trapdoor card, replace the chips with 1Mx4 chips there, change some jumpers on the A501 and a couple on the rev5. That way the onboard 512 KB will be bypassed and the Amiga will use the (now) 2 MB on the A501, naturally as chip RAM.
 
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if i got You right: 318069-18 and also 8372B/AB can be placed instread of standard a 8372 giving 2Mb of chipRAM? If so - i am looking for one of these too


8372AB is probably no different from the 8372B silicon - all AB chips seem to have the B printed as an afterthought, which implies it was a batch of "B" versions fitted in "A" packaging and later the designation was "corrected" with the additional "B".


As to the question, the 8372(A)B and its Vbb 8375 equivalent actually are not drop-in replacements for the 8372A.


If you only have a single bank of RAM (that is, the default 512KB) then it'll still work, but if you have 1 MB of RAM (onboard + trapdoor) then the extra 512KB will disappear. This new Agnus only has a single RAS line, so it doesn't support two RAM banks.


So if you wish to install this Agnus on a rev6A A500, it should best be done at the same time with upgrading the RAM to 2 MB. The process is 4-step:


1. replace Agnus
2. change jumper blocks
3. remove the four 256x4 chips from existing RAM bank
4. install four 1Mx4 chips in the other (previously empty) RAM bank


It must be pointed out again that the whole 2 MB forms a single RAM bank now, so the trapdoor is rendered useless for RAM purposes. You can remove the RAM chips from a standard 512 KB trapdoor expansion however and have it work as an RTC-only card.




Finally, while technically the requirement is a rev6A board, as it has the necessary provisions (suitable jumper blocks and trace support for 1Mx4 chips), there's a way out with using a rev5 board, but you must get an A501 rev6C trapdoor card, replace the chips with 1Mx4 chips there, change some jumpers on the A501 and a couple on the rev5. That way the onboard 512 KB will be bypassed and the Amiga will use the (now) 2 MB on the A501, naturally as chip RAM.
seems You have a lot experience in it.. Respect!
i have two amigas here, first is a standard A500 rev.6A and other is A500 with rev.8A board, 8375 Agnus, and (initially) 512kb of RAM. I have added TTL logic and 512kb onBoard, modded the jumpers JP2 & JP7A to add expansion to chipRAM, and now i have 1.5Mb, hope will get 1Mb expansion soon and then it will be 2Mb. My question is same as the topicstarter has:
how can i reach 1.5 - 2Mb on a standard rev.6A board without purchasing expensive MiniMega? propably, the best way is just to lookin for rev.8A board, and do same upgrades i've done on my machine, cause the price for 8375 Agnus (or miniMega) is pretty high, and You'll end up with same price You A500 rev.8 can get!
 
i have modded an a2000 rev 6 with 8372ab and new ram, same mod for a500 rev6
 
seems You have a lot experience in it.. Respect!
i have two amigas here, first is a standard A500 rev.6A and other is A500 with rev.8A board, 8375 Agnus, and (initially) 512kb of RAM. I have added TTL logic and 512kb onBoard, modded the jumpers JP2 & JP7A to add expansion to chipRAM, and now i have 1.5Mb, hope will get 1Mb expansion soon and then it will be 2Mb.
I think Individual Computers now makes a 512 KB expansion with a passthrough connector so you can plug your existing 512 KB card too and have 1 MB on the trapdoor. Might want to consider that option too.


My question is same as the topicstarter has:
how can i reach 1.5 - 2Mb on a standard rev.6A board without purchasing expensive MiniMega? propably, the best way is just to lookin for rev.8A board, and do same upgrades i've done on my machine, cause the price for 8375 Agnus (or miniMega) is pretty high, and You'll end up with same price You A500 rev.8 can get!


With the 8372B etc Agnus (and suitable RAM chips) you can't get 1.5 MBytes, it goes straight to 2 MBytes.
I will agree, the most practical solution is to get a rev8A board.
 
Search Metalguy66 here on Amibay for the thread and image.

I have also done the above A500 Rev 6a mod to 2MB Chip RAM. You need the A3000's 8372AB or B (the B is what counts), or the applicable (and rare) A3000-replacement 8375 Agnus (318069-18PAL/-19NTSC) 2MB Agnus - note that there is a signal that needs to be addressed (just like the A2000 Rev 6.4/6.5 mod for the -16/-17 chips) on the latter 8375 variant (hence the VBB marking). They both have the classic pin out for the A3000. The A500's existing 4 256x4 RAM chips are removed. You need the VERY low profile machine pins sockets if you are going to use sockets, and put them in the RAM places next to the chips you removed. The 1MbitX4 (4 pieces) memory is very hard to find in DIP - it took me a few tries - but they go in the sockets. The J2 (3-pin, switch positions)/JP7A (all 3 spots open) changes for typical 1MB Chip RAM are done, plus JP3 goes from 2x horizontal traces (=) to 2x vertical(||) solder blobs, and the JP5 setting, which at the top has a reverse L - that L gets cut completely (2 cuts), and what was the top of the L, solder that to the pad to the left. Leave the lower 2=2 pads intact.

I tracked down someone with made-to-order A500/500+ trapdoor Ram/clock modules, and got just the clock, no RAM, with a SuperCap, though a battery was an option.
 
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