PAL 1200XL mod - goes B&W after a few mins

[oracle_jedi]

I installed Dropcheck's 1200XL PAL GTIA board in a 1200XL with an Ultimate 1MB.

 

The machine had a Clearpic 2002 upgrade, and the ANTIC and timing crystal (Y1) was replaced as part of the mod.

 

With the U1MB in place, the machine already had a 600XL/800XL ROM set as default.

 

After the mod the system was generating a PAL colour display, but the image switched to monochrome after a few hours.

 

I checked the install and could not determine any problems, but did also notice that the 1200XL would emit keyboard clicks, with no characters displayed, after a few mins of sitting at the READY prompt.

 

So I pulled the mod, and set the 1200XL back to NTSC. The key click went away and that machine is ok again.

 

I then installed the mod into a second 1200XL, again with an 800XL ROM, PAL ANTIC and the replacement timing crystal.

 

Again I have a color display for a few mins, then it goes to monochrome. No keyboard click this time.

 

What could be the cause of the color signal going away after a few minutes? The GTIA was pulled from a PAL 800XL that worked fine. The symptoms occur on both a Sony PVM 1344Q monitor and a Sony KV-AR25 multi-standard TV.

 

Thanks

 

Graham

 

 

 

 

 

[flashjazzcat]

Has all the hallmarks of a thermal problem, perhaps resulting in a dry solder joint opening up somewhere on the PAL adapter board.

[Dropcheck]

Could be a thermal problem. At least for the colour change. Something else was going on for the keyboard clicking. Otherwise I would think it would happen on the second 1200XL too.

 

Were you using Candle's U1meg upgrade on the second machine or the more involved 800XL ROM upgrade? Also were there any mods to the second 1200XL's video circuit?

 

Just trying to eliminate possibilities.

[flashjazzcat]

The keyboard click is generated by GTIA as well, so this also points the finger. Could be a bridge to blame for that, with open circuit causing the colourburst to spontaneously drop out.

[oracle_jedi]

I switched to a second PAL GTIA adapter on the second 1200XL (512K RAM/800XL OS/stock video) and it appears to generate a stable PAL colour image.

 

Any suggestions on video mods that are compatible with a PAL 1200XL? The colours are over saturated with a good deal of noise in the display.

 

Thanks for the help on this!

Edited September 17, 2014 by oracle_jedi