01 April 2013, 06:19 | #1 |
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8375 upgrade for A500 rev5
Hey guys,
Just bought an amiga 500 rev5 (NTSC) to tinker around with. The first project I want to do is to upgrade the agnus. I've been reading these 2 resources: http://www.skeptictank.org/files/cowtext/buildit.htm http://www.l8r.net/technical/t-agnus-installation.shtml Before I realized there were different versions, I went and bought a 318069-10 assuming it would be compatible. After a lot of google searches, I've found a variaty of conflicting and vague info on the topic. I would love some clarity from anyone who has experience with this. Can I do the above mods with the chip I have? Thanks! H |
01 April 2013, 06:36 | #2 |
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No that will not work, that is for the A500+/A600 which can handle 2MB Chip ram via a 1MB ram card.
The A500 can only handle 1MB Chip ram with a 512k card. You can get an add on adaptor though that adds 2MB Chip, like MegaChip. |
01 April 2013, 06:58 | #3 |
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Ok. Thanks for the quick reply.
So I should look for an 8372A? The main reason I want to do this upgrade is so I can install the PAL/NTSC switch mod on pin 41. I am assuming I can only do that with the fat agnus chip. Thanks again, H |
01 April 2013, 16:41 | #4 |
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Yes, an 8327A will work and if installing into a PAL machine you need to isolate pin 41 I think, or make it switchable. I isolated mine with an extremely small sliver of PVC tape - just wide enough to mask the pin - extended tape under the agnus so when you push the chip in the mask stays in place.
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01 April 2013, 19:50 | #5 |
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Thanks for the info.
Is the 8372A plug and play with the rev5 a500 mainboard? Or do I need to mod the board for it to work? |
01 April 2013, 20:17 | #6 | |
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Quote:
Best advice I can give is use very fine wire and tape that to pin 41 with a sliver of PVC tape so its thin enough to cover pin 41 only but make the tape finish under agnus, and put a larger piece of PVC tape under agnus to support that thin strip. The carefully refit agnus into socket. The end result should be agnus in socket with a wire sat between agnus 41 and a pvc strip - isolating both the wire and the pin from pin 41 of the socket. Then you can find a point on the top of the board that connects to socket pin 41 for the other switch wire, or just run the second wire from underneath the board at pin 41. |
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01 April 2013, 20:37 | #7 |
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Great info! Thanks very much!
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01 April 2013, 21:40 | #8 |
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He lives in the USA so he is NTSC, no need to do anything but plug it in, unless he wants to build himself a PAL machine. You can software switch to PAL if need be, or build a toggle switch.
There is a program on Aminet called "Switch Install" that puts a small patch on the bootblock of disks to force the disk to boot in PAL! Works great! Even works on some disks with custom bootblocks! There are also other programs, like Degrader, that can force system to reboot into PAL too. Last edited by TjLaZer; 01 April 2013 at 22:03. |
01 April 2013, 21:46 | #9 | |
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Quote:
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01 April 2013, 22:52 | #10 |
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Yeh, I've got an NTSC machine, and I wanted to install the PAL/NTSC switch.
I'll try the software options first tho. Appreciate the info. |
01 April 2013, 23:53 | #11 |
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Hey guys!
I just opened my A500 to make sure the Agnus chip hadn't already been replaced, and I was shocked to see an 8375 chip already in there (see attached picture). It's part number is 318069-17 which, I believe, is the 2MB NTSC version. Couple of questions:
Thanks! H |
02 April 2013, 01:32 | #12 |
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AFAIK it's a 1 MB NTSC chip.
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02 April 2013, 02:12 | #13 |
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Hmmm. I'm seeing conflicting info online, but I think you're right. It's most likely 1MB.
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02 April 2013, 02:30 | #14 |
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Isn't there a solder jump that you have to cut through so that the trap door ram will be used as chip?
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02 April 2013, 02:34 | #15 |
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I have no idea. My A500 has the 501 expansion. Is there a way to tell if its being used correctly?
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02 April 2013, 05:13 | #16 |
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type "avail chip" in a shell and see if your chip ram is more than 524000 bytes
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02 April 2013, 13:01 | #17 | |
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Quote:
Yes, its pin 32 I think on memory exp slot - you will know youve got the right pin because its joined to pin 32 of Gary (check continuity using multimeter). Ive added a fast(slow) / chip 1Mb switch on mine. You also need to toggle the JP3 jumper as well (I think its JP3) - located between CPU and ROM on rev 5 PCB. Looks like 8375 is pin compatible, I guess no one tried it before. |
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02 April 2013, 13:03 | #18 | ||||
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Quote:
Quote:
Out of date : http://www.amiga-hardware.com/showha...gi?HARDID=1448 http://www.bigbookofamigahardware.co...t.aspx?id=1478 Updated : http://www.bboah.com/index.php?actio...cat=51&id=2174 Couple of questions: Quote:
Quote:
No. This Agnus has no hardware select. Last edited by alexh; 04 December 2017 at 17:31. |
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02 April 2013, 22:34 | #19 |
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02 April 2013, 23:44 | #20 | |
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Quote:
It's JP2 (not 3) which sits inbetween the CPU and ROM chip - toggle the position there. Then cut the track that goes to pin 32 of the trapdoor - as already mentioned you can check which is pin 32 because it connects to pin 32 of Gary (just test continuity to make sure you've got the right pin). I soldered a double throw switch between the 3 pins on JP2, and on the second 3 contacts of the double throw switch connect 2 of the pins to either end of the cut track coming from pin 32 of the trapdoor. |
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