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I just uninstalled a QuarterMeg XL upgrade that I originally installed 35 years ago


spicyjack

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When the "QuarterMeg XL" article by @ClausB came out in the September 1985 issue of BYTE, I had to try it on my K-Mart special Atari 800XL.

 

For reference, here's the original BYTE magazine article: Quarter_MEG_ATARI_800XL_256kB_RAM.pdf

 

I bought the chips mail order from a place in San Jose, bought the perf board and chip sockets from my local Radio Shack, and threw it together.  After the upgrade, I explained to one of my friends what I had done, and he asked me to do the same upgrade to his 800XL.  Years later, he got out of 8-bit Ataris, and he gave me all of the old hardware that he hadn't sold on Ebay.
 

This is his 800XL which I had upgraded about 35 years ago.  I remembered that I had did this upgrade to my 800XL, but I had forgotten that I did the same upgrade to his 800XL.

 

I recently took this machine apart to document things (was the board socketed or not, how much corrosion was there on the RFI shields, etc.), and I "found" this upgrade attached to it.

 

SURPRISE!

 

The thing was, I used telephone hookup wire for most of my electronic projects at the time, since I had a bunch of it sitting around (my dad worked for the phone company), so I had a sneaking feeling that I had done this upgrade, but I wasn't sure.

 

For about an hour or two, I was pretty convinced that this was my original 800XL that I somehow ended up with again as a craigslist/Ebay purchase.  It was pretty spooky.  But, I thought about it some more, and realized what the deal was; this was my friend's machine, and I did this mod on his 800XL after I did the mod on my 800XL.

 

Thanks to @ClausB, his instructions were solid, and the trick about using half of an IC socket to so you don't have to solder directly onto the PIA was great, it was a clean install which uninstalled very quickly, I just had to cut one wire that I had soldered on to the board, "above" the row of RAM chips.

 

So here you go, I'm going to remove this QuarterMeg XL upgrade from ~35 years ago.

 

I pulled off the keyboard, and the RFI shield was still in place.  The discoloration of the RFI shield most likely comes from the part of San Diego where this machine was used and stored, it's a few miles from the Pacific Ocean.

img_2379.atari_800xl_with_rfi_shield.thumb.jpg.10fbe926b095c4183ebb42ad893589fb.jpg

 

I pulled the RFI shield off, and WHOA! what's that there?

 

img_2383.atari_800xl_with_quarter_meg.thumb.jpg.8cea1d2c6e6f70151b4d525c4ac1efe0.jpg

 

Close up of the perf board with the RAM refresh chips, and the ribbon cable where it plugs in to the board

 

img_2384.atari_800xl_quarter_meg.thumb.jpg.a3d46b414fd313bb38f93d11349396be.jpg

 

The pins on the PIA bent up, and the wires soldered to half of an IC socket, in order to make it easy to attach/unattach as needed.  You can see the piece of electrical tape that covered the tops of the pins to protect from shorting it out against the RFI shield

 

img_2385.quarter_meg_pia_pins.thumb.jpg.3dea530e20093afe8c7382b3c717fa3d.jpg

 

Starting the uninstall

 

img_2386.quarter_meg_pia_pins.thumb.jpg.c153a0c7407a7c379dfb54413177e577.jpg

 

Close-up of the perf board, with the electrical tape attached to the bottom

 

img_2390.quarter_meg_perf_board.thumb.jpg.58169b43943721f45c20e4e14ad40cc5.jpg

 

And here's the board post-uninstall.   The 74LS153N got resocketed from the perf board back into the 800XL board.  I have a chip pin straightener, so I was able to get the PIA pins back to their "normal" angle pretty easily.  The machine boots fine with the 256KB RAM chips still installed, only the first 64KB would be used at this point

 

img_2392.atari_800xl_without_quarter_meg.thumb.jpg.48a96473a71b17d5e6c61c35a21987a9.jpg

 

Thanks for reading, feel free to ask me any questions.

Edited by spicyjack
Mentioned resocketing the 74LS153N
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Sad to see it go. :( Looks like you used the original 32K bank version, not the later 16K bank version I distributed after the article came out.

 

BTW, the LS158 goes back in the motherboard socket, not the LS153.

Edited by ClausB
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1 hour ago, ClausB said:

Sad to see it go. :( Looks like you used the original 32K bank version, not the later 16K bank version I distributed after the article came out.

I did what the article said;  I didn't realize that you had done a 2nd version.  I still have everything in my garage if I wanted to re-install it.

1 hour ago, ClausB said:

BTW, the LS158 goes back in the motherboard socket, not the LS153.

I powered it on it after I put it together and it booted fine, I just didn't get a photo of the right chip in the right socket, and guessed.

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2 hours ago, spicyjack said:

I did what the article said;  I didn't realize that you had done a 2nd version.  I still have everything in my garage if I wanted to re-install it.

Claus updated the design to use the same 16K bank size as the 130XE.

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