Problem with my 1200XL

[Gunstar]

Murphy's law has been hounding me for months now, as I repair and upgrade my Atari's. As soon as I seem to fix one problem, another pops up.

 

This 1200XL currently has the following upgrades installed that all appear to be working fine as far as I can tell with my current problem detailed below: 800XL OS&BASIC, dual-pokey stereo, Rambo XL 256, SV2.1 video upgrade.

 

Anyway, this time my START, SELECT and OPTION keys are unresponsive. I have carefully look over the keyboard and concluded it is fine, the RESET key is on the same trace there and it works, but I carefully checked it over and all seems fine.

 

I've traced the circuits for the keys from the ribbon cable connector all over the motherboard and can see no problems, and everything else seems fine.

 

I can load many programs that disable basic themselves but if they require those keys above to get the program started I'm stuck at the title/menu screens. As such though, I've successfully loaded extended memory games (reinstalled Rambo upgrade successfully) up to 192K and the games that have demo or attract modes seem to function correctly as far as the POKEY chips go, the music and sound effects all work including stereo (Dual pokey upgrade).

 

When I'm IN BASIC, the rest of the keyboard seems to work perfectly, including the function keys and break/inverse keys next to START, SELECT and OPTION, but I don't think there's any use for those keys in basic anway by default.

 

I've gone over all the POKEY connections between the two and the motherboard and it all seems fine. I just can't use my START, SELECT and OPTION keys which means I can't load a tape or start games that require START, I can't bypass BASIC with the OPTION key or access the self-test mode, unless I type "DOS" in basic then it will take me to self-test, but I can't SELECT or START anything, only RESET back to BASIC.

 

Is this a POKEY problem if the keyboard is fine? Where else could something go wrong that would only disable START. SELECT and OPTION? Could it be an OS problem? Everything else seems to work accept were BASIC being active screws things up for some programs.

Edited January 26, 2012 by Gunstar

[Rybags]

Those 3 keys go to GTIA, Pokey has no involvement at all, and they don't go through the normal multiplexor/matrix either (each has a dedicated trace)

 

To eliminate GTIA as the direct problem, run a cart game with the keyboard off and try grounding the relevant GTIA pins and see if the proper reaction occurs.

[Gunstar]

Thanks! I can swap GTIA first, if that doesn't work I'll do as you say.

[Gunstar]

Those 3 keys go to GTIA, Pokey has no involvement at all, and they don't go through the normal multiplexor/matrix either (each has a dedicated trace)

 

To eliminate GTIA as the direct problem, run a cart game with the keyboard off and try grounding the relevant GTIA pins and see if the proper reaction occurs.

 

Thanks again for the GTIA heads-up with those keys. I swapped out the GTIA and now it works fine, ALTHOUGH, the original GTIA chip is probably fine as it still didn't work at first, but then I noticed one of the socket pins was bent back where it wasn't making contact with a chip pin, so I bent the chip pin a bit to make contact and correct the problem.

 

The really weird thing about this "Murphy's Law" incident is that in all my upgrades, repairs and trouble shooting, I've left the GTIA untouched, and it was working fine upto a point. How the socket pin was bent back like something too big was plugged in when that GTIA had never been removed is a total mystery.

Edited January 26, 2012 by Gunstar

[Gunstar]

Now I can get started trouble shooting my other 1200XL and put this one up for sale.

[sloopy]

The GTIA may have been pushed in far enough the bent pin was touching before, but the movement and twisting of the PCB while working on it, may have worked it loose enough to loose contact...

 

sloopy.

[Gunstar]

That seems a logical explanation I'll accept since I have no other. Although at every point that some problem cropped up, my first reaction was to make sure all socketed chips were fully inserted. Of course I wasn't removing them at while doing this, just lightly pressing down.

Edited January 26, 2012 by Gunstar

[Gunstar]

never mind, wrong topic.

Edited February 10, 2012 by Gunstar