GTIA faulty or not

[zylar]

Hello all,

 

I recently got an Atari 800xl rev D, now the computer booted fine after a few reseats of the RAM and etc, but with cold reboot it boots in the diag menu and a warm reboot it gets to the "ready" stage. so i went in the schematics and saw the 3 button outputs does not go to the porkey but to the GTIA pin 12 13 and 14 and sound comes from pin 15 witch are labeled S0 to S3. When i measure on those pins i get just a few millivolt, 124 mV as maximum.

 

My questions are:

 

*Does these pins get to be pulled up by the GTIA itself or do i miss some other pullup?

*can i order a new GTIA or is there hope for this one?

[Rybags]

If you get the Basic READY prompt then you should be able to enter and run this simple program:

 

10 ? PEEK(53279) : GOTO 10

 

That'll give a readout of what's coming into the GTIA CONSOL register which reflects the keys. Bit 0=Start, 1=Select, 2=Option. Normally read 1, will go to 0 when a key is held.

Valid values returned should be anything 0 to 7 as each key is independant. 7 should be normal state of no key pressed.

If OPTION key is stuck or GTIA somehow thinks it's held then it'll likely read 3.

 

Next thing to try if the key behaviour is suspect would be to remove the keyboard and see if the powerup behaviour changes.

 

The actual keys... I think they're internal pullup in GTIA. The schematics have resistors but they're just inline.

Not entirely sure how the chip functions vs something like PIA - the 5200 actually uses all of the bits as outputs - extra functions being to enable analog pots and to choose which joystick's keypad is being scanned.

Edited October 11, 2017 by Rybags

[Marius]

Any chance to test the Atari with a diskdrive or something like that?

 

With other words: does it boot into selftest too then, or does it boot a disk properly?

[zylar]

well i tryed the peek command, but it was inconsistent, got all the same numbers first time 0 and 2nd time 13, the whole screen full. i did already try it without keyboard, i measured the resistance to ground with keyboard and without, it was ol without the gtia installed and went to 3 ohm when i pushed a button(after the resistor). I even tried installing an pull-up externally on the line but it went to 300mV instead of 5v. So ill order an new GTIA and see if that solves my problem.

[zylar]

Well guy's, good news. I fitted a "new" GTIA from E-bay, and almost all works. buttons work. Sound work. But video, wel just 2 colors now, black and white, no color to be found. after ajusting the pot no lines in sight, but no color too. the auction said they where from an 5200, but the ic numbers where the same, only difference was that the old one had -01 on the end and this one -22, i thought it was just a revision number of the dye. Can anyone tell me if it should work or not, its costing me a lot of money this way.

 

Best regards

Edited October 25, 2017 by zylar

[+DrVenkman]

The GTIA chips are identical. The dash numbers at the end don't matter. The lack of color means another issue with the machine - either the new chip is bad also bad or there's another issue with the machine. Try an experiment: put the first chip back into the machine and see if you have color or not. If you don't, it's possible there's something going on besides the chip.

[zylar]

no, the old ic had color, only the pullup of the option, select and start key was not working. ill go and try to talk to the guy who sold me the ic, else ill file a chargeback.

[+DrVenkman]

no, the old ic had color, only the pullup of the option, select and start key was not working. ill go and try to talk to the guy who sold me the ic, else ill file a chargeback.

 

I think you're missing my point. I know the old chip had color and you've swapped it for the new one and now don't have color.

​I'm suggesting you try reinserting the old chip to verify you get color back. The reason I suggest trying that is to help eliminate the possibility that you have a bad or damaged GTIA socket. I repaired a 1200XL this past spring/summer that had no less than *THREE* bad sockets. So if you install the old chip and color returns, then you can help rule out bad connections at the socket as part of the problem.

[AtariLeaf]

A little off topic but I can't help but notice a lot 800XL problems being posted. Seems almost weekly there's a new post about an 800XL crapping out in some way or another. I'm almost afraid to turn one of mine on only to find a dead machine.

[gozar]

A little off topic but I can't help but notice a lot 800XL problems being posted. Seems almost weekly there's a new post about an 800XL crapping out in some way or another. I'm almost afraid to turn one of mine on only to find a dead machine.

 

I wouldn't worry about it, the 800XL is the most popular 8-bit, I believe, so it would have the most questions. Plus there is a good chance it shipped with the ingot power supply, which doesn't help.

[AtariLeaf]

Yea those ingots are bad news. I cut the din off mine and chucked it. Never used it. It did come with one of the dead units I have which explains it.

[zylar]

Here is a picture of the old IC, color comes back so the socket is fine.

 

This is a picture of my scope with the old IC on pin 21

 

This is with the ic i got

[flashjazzcat]

Does the new GTIA have the same part number as the old one? Which is to say, you didn't replace PAL with GTIA or vice versa, did you?

[zylar]

yes the numbers are the same, ike i said a few posts above

[Level42]

A little off topic but I can't help but notice a lot 800XL problems being posted. Seems almost weekly there's a new post about an 800XL crapping out in some way or another. I'm almost afraid to turn one of mine on only to find a dead machine.

If you never turn them on, they are already dead anyway.....