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Author Topic: Help getting an unknown Gigatron A500 card running in my Amiga 500 (rev 6a)  (Read 2721 times)

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Offline pSyChO dAdTopic starter

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Help getting an unknown Gigatron A500 card running in my Amiga 500 (rev 6a)
« on: May 02, 2020, 06:04:25 PM »
Hi everyone,

While cleaning up my attic I stumbled across my old Amiga stuff and decided have a look at what still works. This stuff has been in boxes for more then 15 years now. One of the Amiga 500's has a memory expansion card in it. But when I boot Workbench I only see the standard 512KB Chip RAM. On the card it says Gigatron A500. From what I can tell this is a 2MB expansion card. I had a look on Google, but couldn't find any manuals for this specific type of card. I did come across a card that looked very similar called a Gigatron MiniMax here: http://amiga.resource.cx/exp/minimax
That card comes with a Gary adapter, which also seems te be present in my Amiga, but not connected to the card. I tried all the jumper options from the MiniMax manual on my card, but it never adds any extra RAM. Also the switch currently does nothing. Has anyone ever seens this card and/or have any idea how to hook it up so it works? Even if it's only 512KB extra I would be really happy.

Here's a picture of the card.
Here's a picture of the motherboard of my Amiga 500.

Any help would be greatly appreciated.
« Last Edit: May 02, 2020, 07:55:30 PM by pSyChO dAd »
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Offline klx300r

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Re: Help getting an unknown Gigatron A500 card running in my Amiga 500 (rev 6a)
« Reply #1 on: May 03, 2020, 05:30:19 AM »
first off welcome aboard ;D


I've never seen that particular card but had a similar experience with my A500 when I took it out of storage....what got the 512MB ram seen by Workbench for me was just reseating the adapter over the fat agnus..also good idea to press down/reseat all other socketed chips as well while your at it


good luck!
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Offline pSyChO dAdTopic starter

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Re: Help getting an unknown Gigatron A500 card running in my Amiga 500 (rev 6a)
« Reply #2 on: May 03, 2020, 08:57:11 AM »
Hi, and thanks for the reply.

I'll give that a try. Hopefully I will get atleast the 512KB RAM working. What I can't figure out is why there is no cable running from the memory board to the Gary adapter. I seems to me that's what's required to get more memory available. It doesn't seem hard to make a custom one if I just knew which pins to run to where.
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Offline Antti

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Re: Help getting an unknown Gigatron A500 card running in my Amiga 500 (rev 6a)
« Reply #3 on: May 03, 2020, 07:17:24 PM »
Hi pSyChO dAd

First of all, I see that you have a jumper connected to ST2. ST2 is for connecting the memory board to the Gary adapter. Jumpers are used in JX A & B.

Anyway, I have Gigatron MiniMax in one of my A500. I didn't get any memory out of it without the cable connected to the Gary adapter. I took a picture of my setup and marked the pins if you want to make your own cable (I used my own pin numbering). Just connect 1 to 1, etc.

Also you might get 512KB if you remove the Gary adapter and set jumpers to JX A and B as the manual suggests. I have not tried that myself.

Hope this helps :)
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Offline pSyChO dAdTopic starter

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Re: Help getting an unknown Gigatron A500 card running in my Amiga 500 (rev 6a)
« Reply #4 on: May 04, 2020, 11:14:41 AM »
Wow, Thanks so much Antti,

That's really helpfull! I already tried several jumper options (Removing the one from ST2, several memory settings using JX A+B from the manual, using the switch, or disconnecting it), but all without luck. I never took out the Gary adapter though. I've orders some connectors from China to create a custom cable. Might take a while before they arrive though. With your pin-layout I can connect the whole thing and hopelfully have it running with most memory available.

Thanks again! I will post a reply once I have every setup and tested.

Cheers.
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Offline pSyChO dAdTopic starter

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Re: Help getting an unknown Gigatron A500 card running in my Amiga 500 (rev 6a)
« Reply #5 on: May 04, 2020, 06:25:59 PM »
Okay, so I had an extensive look today. The Gary adapter had one broken pin. I managed to fix that. I created a custom cable with the pin-layout of Antti's example. Hooked up the Amiga, and still nothing. I tried changing the jumpers JX A+B to several settings, powering off each time. Also no luck. Eventually I removed the Gary adapter all together and set the card to what 512KB settings. Again nothing.
I then opened up my other Amiga 500 swapped the 512KB card from that one. That worked fine. So it's not the Amiga that's causing the problem. After some closer examination of the Gigatron card I noticed on the back side that the JX A+B connection run over the 'line' that the battery is using. This seems to be a little corroded. See pictures below. Could this be causing the problem? And would I need to replace the battery or can I just resolder? I don't care much for the realtime clock.

« Last Edit: May 04, 2020, 06:27:06 PM by pSyChO dAd »
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Offline Antti

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Re: Help getting an unknown Gigatron A500 card running in my Amiga 500 (rev 6a)
« Reply #6 on: May 16, 2020, 08:53:59 PM »
Ouch, that doesn't look too good :o If you have a multimeter you could check the rail for continuity on that corroded area. Or solder a patch wire and see if that's enough to bring the card back to life. Card's on/off switch ST3 seems to be connect to that rail also. Anyway you should remove or replace the battery or eventually it will kill the card for good. I doubt the battery is required, usually they just keep the clock powered when Amiga is powered off.
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Offline pSyChO dAdTopic starter

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Re: Help getting an unknown Gigatron A500 card running in my Amiga 500 (rev 6a)
« Reply #7 on: May 17, 2020, 10:13:03 AM »
Hi Annti,

Thanks for your reply. I came across an add from someone selling his Amiga 500 with this exact same card. From what I could tell from that the card is only 512KB en not 1,8MB or 2MB. The Gary adapter that comes with it adds the full 512KB as Chip RAM giving you 1MB Chip RAM. This sounds about right since my Amiga used to have a Hardroc drive connected to the side which also had a bunch of memory in it.
Since the card is only 512KB and dead, and the fact I'm not very good at soldering I desides to just buy a new memory expansion. AmigaStore.eu sells them new for a mere €18,95
Once that is up and running I might have a look at fixing this card when I got the time.
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