exxos's Atari, Amiga & retro forum

Greetings folks,

I picked up a 1200xl 2 weeks ago from a local seller here (facebook marketplace) as working. It "kind of" worked initially. It would output a video signal that seemed to have trouble syncing and would flicker up and down vertically on the screen gradually getting worse and worse and eventually crashing. Given that it was only $75 for aa 1200xl that came with a bunch of cartridges, and a cassette drive, I'm not complaining.

Since I have an 800, 800xl and 65xe, I was to be able to swap out all the various chips and test them. All chips are good. I've recapped all board capacitors and checked the board for dry solder joints reflowing many just in case which fixed the eventual crashing (been running M.U.L.E. now for about an hour straight). However, the vertical flickering still remains albeit pretty minor...still annoying.

I've done the google due diligence and haven't found anything...I thought I'd see if anyone here has seen anything similar and could point me in a direction. I'm considering adding a UAV board (have one on my 800xl and LOVE it) hoping that it might help, but am wanting to try and avoid just throwing $$'s at the problem.

Any thoughts?

Wow $75 is pretty cheap!

It sounds like your Antic and GTIA may be ok.

Have you looked at the video circuit? I know on the 600XL and the 800XL (Probably XE too) there is a C04050B in the video circuit, that feeds the modulator and composite video signals out, might warrant a look.

Thanks I'll take a look at the C04050B!

So prior to all the changes I made, I did test out on my magnavox CRT and it also had the crashing issues. Now it's rock solid on that screen. It just doesn't like the LCD still.

I am now feeling good enough to fix the keyboard and probably add the UAV.

So swapped the 405 chip for my 800xl's that I'd replaced with the UAV mod. No improvement on the LCD but I'm still feeling good enough to try the UAV as well as replace the keyboard mylar now.

Thank a ton!

coonsgm wrote: 09 Apr 2022 15:24 So swapped the 405 chip for my 800xl's that I'd replaced with the UAV mod. No improvement on the LCD but I'm still feeling good enough to try the UAV as well as replace the keyboard mylar now.

Thank a ton!

Sounds to me like the LCD is likely the problem, but UAV is a good solution, personally I like VBXL, but if you're in the US it'd probably be expensive.

The LCD works perfectly with my 800, 800xl, 65xe as well as through VGA (displays 15khz) with my ST's and Amiga.

Such is life with vintage computing....things never quite turn out exactly how you would like them to....

coonsgm wrote: 10 Apr 2022 00:31 The LCD works perfectly with my 800, 800xl, 65xe as well as through VGA (displays 15khz) with my ST's and Amiga.

Such is life with vintage computing....things never quite turn out exactly how you would like them to....

I know what you mean. I recently moved a VBXL from my 800XL to my 600XL, along with an Ultimate 1MB.

VBXL worked perfectly with the 800XL, but in the 600XL is has an annoying shimmer that I just can't figure out. Breaking out the oscilloscope this afternoon I think.