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TimsterAA

Expanding the 400

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I had posted this in another topic, but I feel it may not get seen there, so I thought I'd start a new one.

 

I cracked open my 800 because the video had gone fuzzy on me, and I wanted to swap out the RF cable, which I did successfully. While I was in there messing around, I found under the top cover (the part behind the cart slots) the place where the RAM expansion 'carts' are. I found my 800 has three 16K carts and one 10K ROM cart. I assume this is the limit the original 800 can be expanded.

 

Regardless, I got thinking that even though I fixed the video quality problem, I know for a fact that my 400 has even crisper video out. I thought maybe I could put the extra RAM from the 800 into the 400, and use that. But when I opened up the 400, it's 'ram-expansion' innards were not there (or at least not like the 800).

 

My questions are: 1) is the 400 expandable like the 800, and 2) if so, where/how do you expand the memory?

 

Thanks for all the help everyone! This Commodore-raised boy truly appreciates it!

 

--Timster--

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There was a kit for expanding the memory of the 400 to 48K, but it required soldering. Beyond that I don't know how much more the 400 could be expanded.

 

Tempest

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In 1982, the MACE Newsletter published my article, a DIY upgrade to 48K for the 400. It was later plagiarized by "The Windhover Project." You might find it on-line somewhere if you look.

 

If you're handy with solder, give it a try. If you can't find it, I can scan the article and post it.

Edited by ClausB

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would 41464 chips be usable?

IIRC, those chips require an 8 bit refresh address, which the earlier ANTICs did not supply. You could add more circuitry to do the CAS before RAS refresh. Also, they are not pin-compatible with the RAM board sockets, so it would need much more work to use them.

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would 41464 chips be usable?

IIRC, those chips require an 8 bit refresh address, which the earlier ANTICs did not supply. You could add more circuitry to do the CAS before RAS refresh. Also, they are not pin-compatible with the RAM board sockets, so it would need much more work to use them.

thanks, I will have a look for some 4164s and make life easier :D

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I've read that Atari used to sell professionally-installed 48K upgrades for the 400. Does anyone have pictures or docs or schematics of this upgrade?

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I've read that Atari used to sell professionally-installed 48K upgrades for the 400. Does anyone have pictures or docs or schematics of this upgrade?

 

Yes they did. I have one NIB but I never opened it. I can take pictures when I get a chance.

 

Tempest

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Good search! The first link is a copy of the original with added comments. The second link is the rip-off.

 

I scanned the article anyway:

 

 

So I just did this and all appears to be well, question though the -5 volt supply looks to be a rather low powered rail, does anything else use -5 besides ram? cause otherwise I have been running this off of a DC power supply since the upgrade

 

Thanks!

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So I just did this and all appears to be well, question though the -5 volt supply looks to be a rather low powered rail, does anything else use -5 besides ram? cause otherwise I have been running this off of a DC power supply since the upgrade

 

Thanks!

The Sobola schematics show the power LED connected to the -5V circuit, it wouldn't be hard to change that.

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The Sobola schematics show the power LED connected to the -5V circuit, it wouldn't be hard to change that.

 

Yea, that is the only other thing I saw in the schematics, just wanted to make sure I was not missing something, thanks

 

Here is the wiring for the

Atari made 64k ram card ( yes, it says it on the card ). The 400 only sees 48k.attachicon.gifimage.jpeg

 

good reference, I did the above method of converting a 16k card into a "48" k card cause I did not want to hunt down the upgrade kit, which generally cost more than the 10$ I paid for chips + extra's but it is more involved, and made me double and tripple check instructions while doing (my first)

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The Atari 400 48K RAM upgrade boards are getting hard to come by. Best ran out of stock sometime in 2016. Sadly, this is becoming a recurring theme. I have a 400 with this upgrade, a B-Key keyboard and the 5200 S-video board that uses an Atari 5 pin DIN monitor jack. Now it's the 800's equal in half the footprint. It's a pure nostalgia thing for me. The 400 was my first computer. Very thankful that my father shelled out $400 (1981 dollars) for it. That's like $1,200 today! If you can find an Atari 48K board, jump on it. There are a couple video upgrades for the 400 now and as far as keyboards, the B-Key seems to be the most available, but they too are hard to find in the wild. I think we're in a surge of retro collecting and prices and availability have reflected this.

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Still waiting for a 400 Incognito board....but actually my 400 is waiting for some desk space to have its video upgraded and then get the Axlon card installed that ClausB provided me with a wiring for to use on the 400...

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Good search! The first link is a copy of the original with added comments. The second link is the rip-off.

 

I scanned the article anyway:

 

 

Ok, I'm trying to do this upgrade and i've screwed up. I did the first part of the ram card modifications and swapped in 4564 ram from a working 800xl. Then tried the 400 and it worked fine as 16k. So I continued on with the rest of the mod and didn't see the skips in the alphabet for the edge pins. Ending up having a wire connected to pin P instead of M. Computer now boots to a black screen. I fixed the screwup and checked the rest of the routing. As far as I see everying looks correct now. Computer will still play star raiders too. Which chips have I fried???

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Was the wiring mistake on the RAM board or on the motherboard? If on the RAM then no damage done. If on the motherboard then two outputs (S3 and A14) were connected which could damage a chip or two.

Edited by ClausB

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Mistake was on the ram board. So now I guess I need to go back through again and see if I can find any reason at all for a black screen. I noticed that your original instructions say to use 4164 ram chips, do the 4564's I used work? They seemed to be fine @ 16k level.

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Mistake was on the ram board. So now I guess I need to go back through again and see if I can find any reason at all for a black screen. I noticed that your original instructions say to use 4164 ram chips, do the 4564's I used work? They seemed to be fine @ 16k level.

Part #s for the 64k x 1bit DRAM chips can change depending on the manufacturer, 4564 is the # Mostek used.

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Allright, I found my mistake and the computer is working again. Doesn't look like I fried anything, so far anyway. I made the exact same mistake on the motherboard, but only on one wire. The one that connects to pin M again I had going to P. I somehow managed to put the other wire correctly. Amazing how you can check and recheck your work and make the same mistake over and over again. Anyway, thanks for your help Claus and for creating this upgrade to begin with! :)

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