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Atari XEGS - Corrupted OS
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20-08-2023 2:07pm#1
Some of you will remember me posting a few months back about picking up a very minty Atari XEGS....and mint it was, except for one thing. It had a weird issue whereby when using the BASIC function, the entire system locked up once you hit enter/return on the keyboard. A cursory glance around the etherwebs, suggested that indeed, the XEGS is a little prone to corruption in the OS rom as the years catch up with the rom chip.
I suppose then there was no better time to get acquainted with the process of ROM programming/burning etc. @Steve X2 kindly nudged me towards the XGecu T48, and indeed it seems a fine little device. I also grabbed some blank chips, some sockets, and found the Atari XEGS OS rom image on said etherweb. So all the tools were in place, time to crack on with the repair!
^^ The system itself. It's quite immaculate, and complete with Light gun and matching joystick.
^^ Inside the machine, there's a seriously impressive shield. Reminds me of the Jaguar with the twist lock tabs all around it.
^^ The OS rom chip in question. That's not corrosion on the pins I don't think, looks more like crusted flux, so that wasn't the issue (would have been far too easy!).
^^ I added fresh solder to the underside of the chip in question. However, desoldering it shows that the top side solder doesn't really receive the heat. Much of what I read online suggests the via/eyelets on this board are VERY prone to lifting as a result of cost cutting (cost cutting Trameasures.) I therefore decided not to continue applying too much heat on these pads, and instead took gently snip the legs of the IC. This will allow me to remove the leg remnants with a tweezers while heating the pad. This worked perfectly.
^^ IC leg remnants in place. All I needed to do was add some fresh solder to these, and grip them with a tweezers while flowing the solder. This seemed much easier on the board, as much less contact time with the soldering iron was needed to clean everything up.
^^ Quick clean of the underside of the board with IPA and a toothbrush. Old IC can be seen on the left of the board.
^^ While cleaning, I noticed a weird corroded pin. No other signs of any moisture/liquid anywhere near the location. Odd...
^^ Reflowed with some fresh solder, and another cleaning. Continuity checked on the trace beside it, it seems all good.
^^ Back topside, time to fit the IC socket. This means I can simply just pop the new chip into place, and won't be putting a soldering iron anywhere near it. It makes changing out the chip a breeze, if ever needed again in the future.
^^ Fits like a glove
^^ Soldered in from the underside.
^^ New EPROM, time to erase it and flash the correct OS image to it....
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Comments
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^^ EPROM eraser, basically a small UV chamber. Pop the chip in for ~15 mins, and let it cook....
^^ That's all there is to erasing, the light does all the work.
^^ The XGecu T48, nice quality feel to it. The new EPROM chip is installed here, and ready for reading/writing.
^^ Search for the correct IC so that the software knows what to do in terms of reading/writing...
^^ I had to turn this setting OFF, otherwise I was getting errors reading/writing/
^^ EEPROM read perfectly, and as can be seen in the background, all FF's confirms it's empty and ready for writing.
^^ Rom image loaded into software...
^^ Done, that should be a new OS rom image ready to be popped into the machine.
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^^ New IC now placed into the socket, and we're ready for testing...
^^ The big question...
^^ I can tell already it's fixed. Once I hit enter, the cursor went to the next line down as its supposed to do. No more locking up!
^^ Done. Perfecto! So that's BASIC back working properly, I then went on to test the built in Missile Command game (pure Atari magic, hard to put that one down), and then external carts....everything perfect, happy days!
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