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support.Hardware>8375 upgrade for A500 rev5
Hoopz 06:19 01 April 2013
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
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TjLaZer 06:36 01 April 2013
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.
Hoopz 06:58 01 April 2013
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
GadgetUK 16:41 01 April 2013
Originally Posted by Hoopz:
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
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.
Hoopz 19:50 01 April 2013
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?
GadgetUK 20:17 01 April 2013
Originally Posted by Hoopz:
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?
If you just plug it in you will get sound playing faster, and crashes with PAL games as it will default to NTSC when 'just plugging in'. Took me a while to work out but in rev 5 boards it puts a high to pin 41 which puts the 8372a in NTSC mode - hence why I covered that one pin with PVC tape before re-inserting the chip. If you want to put an NTSC / PAL toggle switch you will need to isolate pin 41 from the socket and put a wire connected to pin 41 of the agnus, then take the other wire from a point on the PCB that connects to pin 41 of the socket. When the two wires are shorted via switch it will be NTSC, open = PAL. From what I understand the track we would like to cut (to avoid PVC tape) is under the Agnus socket on the top side of the board, so you end up having to remove the Agnus socket if you want a cleaner install of the mod.

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.
Hoopz 20:37 01 April 2013
Great info! Thanks very much!
TjLaZer 21:40 01 April 2013
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.
GadgetUK 21:46 01 April 2013
Originally Posted by TjLaZer:
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!
Well spotted! Yes, if mobo is NTSC, just plug the 8372a in and it should be OK.
Hoopz 22:52 01 April 2013
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.
Hoopz 23:53 01 April 2013
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
Attached: 8375Agnus.jpg (95.3 KB) 
zipper 01:32 02 April 2013
AFAIK it's a 1 MB NTSC chip.
Hoopz 02:12 02 April 2013
Hmmm. I'm seeing conflicting info online, but I think you're right. It's most likely 1MB.
source 02:30 02 April 2013
Isn't there a solder jump that you have to cut through so that the trap door ram will be used as chip?
Hoopz 02:34 02 April 2013
I have no idea. My A500 has the 501 expansion. Is there a way to tell if its being used correctly?
TjLaZer 05:13 02 April 2013
type "avail chip" in a shell and see if your chip ram is more than 524000 bytes
GadgetUK 13:01 02 April 2013
Originally Posted by source:
Isn't there a solder jump that you have to cut through so that the trap door ram will be used as chip?

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.
alexh 13:03 02 April 2013
Originally Posted by Hoopz:
It's part number is 318069-17 which, I believe, is the 2MB NTSC version.
Originally Posted by Hoopz:
I'm seeing conflicting info online, but I think you're right. It's most likely 1MB.
I did write a "definitive agnus" resource for Big Book of Amiga hardware. But because that resource has been forked to numerous places some versions have the correct information and others still have the old information.

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:

Originally Posted by Hoopz:
How is it possible that my A500 Rev5 already had the 8375 in it? I can't see any specific mods made...
As you already know you have a 1Mbyte Agnus which is compatible with the motherboard as is.

Originally Posted by Hoopz:
It has an 8362r8 Denise chip in it. Since it already has the 8375, I should be able to just plug in a Super Denise chip, right?
I don't think that having an 8375 Agnus is a requirement for a Super Denise. Yes you should be able to just plug and go.

Originally Posted by Hoopz:
Can I still install a hardware NTSC/PAL switch with this version of the 8375? or should I stick with software options instead?
No. This Agnus has no hardware select.
hooverphonique 22:34 02 April 2013
Originally Posted by source:
Isn't there a solder jump that you have to cut through so that the trap door ram will be used as chip?
yes, there is.. think it's labelled jp7a or something like that..
GadgetUK 23:44 02 April 2013
Originally Posted by hooverphonique:
yes, there is.. think it's labelled jp7a or something like that..
Not on the rev 5 motherboard.

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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