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Old 20 September 2021, 13:30   #1
RowanHall
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A500 agnus advice

Hi,

I'm just looking come current advice on increasing my chipram on my a500. I've spent some time researching this and i'm finding a lot of conflicting info, so I figured I should come out of lurker mode and post the question!

I have an a500 rev5 with Fat Agnus 8371. There is a 512kb expansion but obv this is showing not as chip ram.

This was always just my goto stock machine of the period and used my upgraded 1200 as the workhorse for most things and tinkering. But now the pistorm is here, I have started modding my a500 more as a project.

I just wondered what the best route to go was these days? Do I pop a 8372A in with the associated mods and use the current 512kb expansion as chipram, or is there a better route to possibly 2mb? Should I remove the old ram expansion and buy a modern one, I don't know? is 1024kb even going to be enough?

The machine will be used for whdload purposes mostly, so obv I'm already running into the lack of chipram errors for some progs.

Hoping you guys can steer me right.

Cheers,
Rowan

Last edited by RowanHall; 21 September 2021 at 11:49.
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Old 20 September 2021, 15:38   #2
Jope
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For chip expansion: install a 8372 with its ntsc switch pin taped off + jp2 toggle + exrom trace cut or trapdoor ram expansion switch off.

After you have 1MB of chip RAM, The Pistorm should handle all other bits of memory you. You shouldn't expand any other RAM than chip RAM with legacy expansions, if you will be using a Pistorm.
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Old 20 September 2021, 22:51   #3
source
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If you are looking for more conventional hardware try Icomp.de they have a 2 meg chip expander that should work.
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Old 21 September 2021, 11:51   #4
RowanHall
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Quote:
Originally Posted by Jope View Post
For chip expansion: install a 8372 with its ntsc switch pin taped off + jp2 toggle + exrom trace cut or trapdoor ram expansion switch off.

After you have 1MB of chip RAM, The Pistorm should handle all other bits of memory you. You shouldn't expand any other RAM than chip RAM with legacy expansions, if you will be using a Pistorm.
Happy days, so just doing the usual mod to 1mb should be enough? No point taking it any further than 1mb?
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Old 21 September 2021, 11:53   #5
RowanHall
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Quote:
Originally Posted by source View Post
If you are looking for more conventional hardware try Icomp.de they have a 2 meg chip expander that should work.
I have looked at these and are a great solution, plug and play, ready to go, but they are currently out of my price range at the moment. Love IC products, have bought a fair bit over the years.
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Old 21 September 2021, 14:03   #6
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Happy days, so just doing the usual mod to 1mb should be enough? No point taking it any further than 1mb?
2MB is the maximum amount of chip on any production Amiga. It is worth getting 2MB if you intend to use the OS, but 1MB will get you started and will be enough if you intend to mainly play games.
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Old 30 September 2021, 23:35   #7
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Quote:
Originally Posted by RowanHall View Post
Hi,

I'm just looking come current advice on increasing my chipram on my a500. I've spent some time researching this and i'm finding a lot of conflicting info, so I figured I should come out of lurker mode and post the question!

I have an a500 rev5 with Fat Agnus 8371. There is a 512kb expansion but obv this is showing not as chip ram.

This was always just my goto stock machine of the period and used my upgraded 1200 as the workhorse for most things and tinkering. But now the pistorm is here, I have started modding my a500 more as a project.

I just wondered what the best route to go was these days? Do I pop a 8372A in with the associated mods and use the current 512kb expansion as chipram, or is there a better route to possibly 2mb? Should I remove the old ram expansion and buy a modern one, I don't know? is 1024kb even going to be enough?

The machine will be used for whdload purposes mostly, so obv I'm already running into the lack of chipram errors for some progs.

Hoping you guys can steer me right.

Cheers,
Rowan
So going from 512k to 1MB chip ram will "solve" a lot of problems, after all there are quite a few games that require 1MB.
I did the common "Fat agnus + cut a trace and use 512k trapdoor RAM" -upgrade some years ago on one of my A500s.
Pic of replaced Agnus:
https://www.exretro.com/galleries/co...gnusMod_01.jpg
trapdoor ram upgrades are cheap and you ned a new agnus, no way aroud that part.

Cheers
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Old 03 October 2021, 18:43   #8
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Hi,

Got some time today to do this mod, was handy enough, all seems good.

I decided to lift pin 32 on Gary instead of cutting the exrom trace? Is this alright to do, any drawbacks? Just might be afraid of catching the leg?

The ram expansion I have is pretty unremarkable, is it worth getting something modern or any particular one? I had to repair it years ago due to the usual leaky RTC battery.

I also have a cap kit here, was going to install it. Do a500's suffer much with failing caps? any in particular?

Thanks again folks for all your advice. I think the 1M chip ram should be enough for now. I've attached pics as it might help others.
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Old 04 October 2021, 08:25   #9
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You need a pull up for the extick signal, so in addition to the leg lift, you need to add a 4.7k resistor between VCC and the leg you turned up.

Maybe a better idea is to disable your ram expansion. It seems it had a switch, which has been bypassed. You can remove the bypass jumper on the ram expansion and this is basically the same thing.

Caps.. A cheap insurance. Some a500s have had explosive caps in these modern times. Me personally, I only bother pre-emptively recapping the surface mount machines.
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Old 04 October 2021, 09:18   #10
RowanHall
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I didn’t realise that. I’ll replace the pin on Gary and move the jumper as suggested. I just didn’t want to cut the trace just yet. So don’t move the jumper to the off position, just remove the jumper altogether?

There was a switch, but the battery leakage damaged it, so I replaced it with the jumper.

Thanks again!
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Old 04 October 2021, 09:56   #11
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Originally Posted by RowanHall View Post
I didn’t realise that. I’ll replace the pin on Gary and move the jumper as suggested. I just didn’t want to cut the trace just yet. So don’t move the jumper to the off position, just remove the jumper altogether?
Take a closer look - my bet is, there's only two traces connected to that switch/jumper (the signal is pulled up on the A500 mobo so it also works when no ram board is installed).
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Old 04 October 2021, 11:25   #12
RowanHall
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There’s three traces on the switch.

After replacing the pin, the machine only shows 0.5mb chip with both the jumper in the off position and the jumper removed completely.

Should I just wire the jumper to on, cut the exram trace and be done with it?

I was also looking at this more modern board from amiga kit, it appears to have a 1M jumper onboard to disable and enable it. I presume this is so the trace doesn’t need cut?
http://amigakit.amiga.store/a500-512...l?currency=GBP

Rowan
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Old 04 October 2021, 11:54   #13
RowanHall
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Hi,

Never mind, I cut the exram trace on the old memory expansion board at the connector. With the jumper in the on position we’re back at 1M again.

Thanks for all the advice folks!

Rowan
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Old 05 October 2021, 08:00   #14
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Ah, hadn't encountered "proper" on off switches like that before on RAM expansions. Good to know, and good that you got it sorted. :-)
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