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Stella TIA Glitches

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#26 save2600 ONLINE  

save2600

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Posted Mon Jan 21, 2019 1:35 PM

 

I've seen this on some composite mods with certain televisions. Is this a composite modded unit?

 

Nope, I mentioned that it's an unmodded console with RF out.   :)

 

I too have seen this, but usually with S-video mods. 



#27 Thomas Jentzsch OFFLINE  

Thomas Jentzsch

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Posted Mon Jan 21, 2019 1:46 PM

The pixel at the left border seem to correspond with HMOVE blanks. If you check the game in Stella and enable Debug Colors (Alt+,) you will find a HMOVE blank in each line where your console displays the right pixels. And the left pixels seem to be in the other lines. The color of the pixel seems to be the playfield/ball color.

 

The playfield itself is also affect as you can see in Crystal Castles. The last but one pixel of each PF block is always disabled.

 

I am not sure what's the cause here, but since this is a general issue, this would have caught easily during production. Therefore I suppose your TIA is going bad.



#28 save2600 ONLINE  

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Posted Mon Jan 21, 2019 2:42 PM

Was hoping it was something as simple as that, but just swapped the TIA out with what I thought is a known good one, and no change.  

 

Both from a 1980 4-switch Rev 14 motherboard. Wonder if that's just a trait of this particular board? After all these years, never really noticed it before until digging in. Doesn't interfere with the gameplay at all. Games look great otherwise. 



#29 Thomas Jentzsch OFFLINE  

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Posted Mon Jan 21, 2019 2:58 PM

So it is definitely not your TIA then. Besides that, no idea what's the cause.



#30 save2600 ONLINE  

save2600

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Posted Mon Jan 21, 2019 3:03 PM

So it is definitely not your TIA then. Besides that, no idea what's the cause.

 

Okay, thanks. Wasn't sure if this qualified as an odd TIA test or not. Be interesting to see if others have noticed this on their revision 14 boards or if something else truly is wrong component wise on my board. I'll start a thread or search around some more to see. 
 

-edit-

 

I scrounged up another Rev.14 board and sure enough, there are the dots. Hmm... might be inclined to think it's an attribute of this particular revision?   



#31 splendidnut OFFLINE  

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Posted Mon Jan 21, 2019 4:50 PM

I've definitely seen that blue line issue come up several times on this forum with people blaming everything from the Harmony Cart, the power supply, composite mods... etc. 

 

I've personally noticed this blue line with my Vader while it's non-existent on my old light-six switch sears model.   The Vader has very saturated color, while the 6 switch is somewhat washed out.  Both Atari's are using just the original unmodded RF signal output.

 

So, I believe the vertical blue line is partially caused by the overly saturated color on the Rev. 14 and up boards.  The other factor being a display enable signal in the TIA causing a slight surge in the video signal.  The surge is unnoticed unless the saturation level is high.

 

With that said... I believe my TIAs are normal, so I can't contribute any more to this topic :)

 

 

For reference, I've played around with NTSC video generation and have had a similar timing/display issue crop up in my own circuit.







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