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View Full Version : Very tough Atari 7800 problem



omnedon
04-22-2003, 03:07 PM
I knew I shuld not have bragged about my "working" 7800 find. It works in the loosest sense of the term.

Controller port one has issues. It acts like a ColecoVision with a blown controller port. Auto level select, and then game character veers right, and keeps going no matter what. It's not the controller (tried known workings), and whats worse, it's not the port either. I continuity tested all port pins, solder points, and even followed the traces to their PCB destinations. Solid connectivity all the way, with NO bridging. I fear it's at the IC level, or some diode or transistor or something. I've successfully repaired CV auto level select by replacing the offending blown IC. Anyone know if this is possible for the 7800? Which IC I could try to replace?

Or alternatively, anyone have a bare 7800 deck they want to trade away?

sigh. I hate it when a system beats me!

FABombjoy
04-24-2003, 04:22 PM
After looking at the 7800 schematic at AtariAge (http://www.atariage.com/7800/archives/schematics_ntsc/Schematic_7800_NTSC_LL_Low.html) I would check if the filter cap or the diode has developed a short.

You said it auto level selects? That's weird. Maybe the U9 6532 got toasted, since it's reads both the controller inputs / console switches.

You could always desolder the affected pins and see if it still screws up. Then you'd know for sure. The 6532 was used in some flavor of Commodore computer, but I don't know which offhand. Jameco sells them new for $7, but that's a little steep.

Don't let the system beat you! I had a Vectrex that I thought was toast, but a weeks worth of digital electronics reading & $2 worth of RAM later, I had it back. Helps to have a 'scope, tho.

Good luck, and post your progress.

omnedon
04-24-2003, 06:03 PM
Thanks FABombjoy.

I'm all self taught, and I'm at the point where I need to learn more. I want to learn how to use a scope, and I want to learn how to read schematics.

I am sooo close, I might as well take the next step, and learn some of the hardcore stuff.

omnedon
05-17-2003, 03:01 PM
FIXED!!!

Thanks to the tip from FABombjoy! I ordered a new IC from Jameco as suggested. BINGO!! full and proper controller response. Thank goodness it was the socketed IC version, making the labour far less.

Thanks for the help!!
:D

FABombjoy
05-17-2003, 09:49 PM
Sweet! Another console back on the road... er... TV... It's such a rewarding feeling, isn't it?

omnedon
05-17-2003, 10:37 PM
Very much so. 8-) It's like a great find in the wild, except with a sense of personal accomplishment.

Now to get more games.

Out of curiosity, is that chip the same controller chip that the 2600 uses? I've done a controller chip replacement on a 2600 from one to another. I could open one of mine up to check too.

Jameco lists that IC as "close out". Makes me wonder if I should get a few. If it is the same as the 2600, I likely should. If push comes to shove, a guy could cannibalize a dead Commodore I suppose...