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A-T-A-R-I

A repair question

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I was playing Circus Atari tonight and notice now that there is shadowing on my blue screen. From the left to almost the middle of the screen, the coloring is a deeper blue and when I turn my paddles left to right, you can see the shading change as well as movement of the shading up and down. Anyone know a fix?

 

I reflowed the whole board and changed the 3 chips to see if it would make a difference, but the problem is still there.

 

Thanks

Edited by A-T-A-R-I
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I was playing Circus Atari tonight and notice now that there is shadowing on my blue screen. From the left to almost the middle of the screen, the coloring is a deeper blue and when I turn my paddles left to right, you can see the shading change as well as movement of the shading up and down. Anyone know a fix?

 

I reflowed the whole board and changed the 3 chips to see if it would make a difference, but the problem is still there.

It may be a problem with your TV. Can you try another TV, or a different console? If neither, can you at least post a screen photo?

Edited by A.J. Franzman
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Does it on all tvs in the house, but only using this console, so I am sure it is something with this console. Here are some pics, not that great.

 

Really strange. When you turn the paddles, you can see movement within the darker area going up and down.

post-25071-126863470807_thumb.jpg

post-25071-126863470875_thumb.jpg

post-25071-12686347099_thumb.jpg

Edited by A-T-A-R-I
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Try changing the channel up one and then down again on the tv while a game is on. Could be interference or slightly off tuning.

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Tried that, still no change. I notice it seems to be only affecting the blue and green background screens.

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Have you ruled out the RF cable by trying a different one, if you have another one? I don't know if that's helpful, but worth a shot, I guess.

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I forgot to mention this is a six switch model.

 

Can't be the RF box. I tried two other switchboards (which have the rf boxes mounted on them) and no change.

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Then I don't know, mate, get another TV?

Edited by Osbo
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Then I don't know, mate, get another TV?

 

LOL! Already tried 3 different ones in the house.

 

Paging A.J. Franzman, any ideas?

Edited by A-T-A-R-I
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Maybe the TIA chip is dying or damaged somehow?

That's one possibility. Another (I guess) might be a power supply or filter capacitor issue. Really strange though, I haven't seen anything quite like that before.

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being that it's a 6er, does it have the static strips in place? If not you can make them from foil tape. Also could be cracked wire in the MB to SB harness or ribbon cable.

You seem to have terrible luck in picking systems so far

Edited by zylon
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Koopa That's what I thought first was the chip was dying, so I changed all three.

 

Zylon Yep, static strips are on. Also, this 6er does not have the ribbon cable. It is the multi colored wires with the brown connector. And you are right, I have TERRIBLE luck on these systems. I always think I am going to get a good one, but never happens. Now I have 5 that are not fully functioning.

 

A.J Could the CMOS buffer chip (4th chip) be a cause of the problem? Not sure what that controls.

Edited by A-T-A-R-I
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Here is some more interesting info. Been sitting here and pounding my head against the wall and thought hey, what happens in B/W mode. I switched to the B/W mode with the Circus cart in and while the screen works correctly and goes B/W, those lines that showed up in color mode in the pics above as being darker, are still there in B/W, but show up as very faint "rainbow"colors. Really strange.

 

Also decided to change X200 colorburst crystal, nope, problem still there.

Edited by A-T-A-R-I
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Does it on all tvs in the house, but only using this console, so I am sure it is something with this console. Here are some pics, not that great.

 

Really strange. When you turn the paddles, you can see movement within the darker area going up and down.

I have the exact same issue with my 7800, but it's a lot less visible with my console than on the screeshots posted by A-T-A-R-I. It's a PAL-B version and it has composite video out. The effect is the same using the real cart or the rom loaded in the Harmony. I can't say if the issue was there before the A/V mod, because the rf modulator didn't work when I bought the console.

post-10599-126873748756_thumb.jpg

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Do you have the big metal shield box still over the chips? If not, maybe some digital noise is creeping into the RF.

 

-tet

 

Yep, it's on, with the bottom too.

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the channel select switch can cause some on screen problems if it's dirty inside. is this the only game this happens on?

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the channel select switch can cause some on screen problems if it's dirty inside. is this the only game this happens on?

 

Happens on Combat, Home Run, Circus, etc. Seems like anything with a green or blue background.

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I switched to the B/W mode with the Circus cart in and while the screen works correctly and goes B/W, those lines that showed up in color mode in the pics above as being darker, are still there in B/W, but show up as very faint "rainbow"colors. Really strange.

 

Also decided to change X200 colorburst crystal, nope, problem still there.

If you're getting color in B&W mode (on a game that has a true B&W mode), it can only be the TIA or instability in the color circuit. It's possible that you were close with the crystal, but I believe the transistor or capacitors would be more likely. If I had that console here though, I would try swapping the TIA first, just because I have them handy and it's an easy check.

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I switched to the B/W mode with the Circus cart in and while the screen works correctly and goes B/W, those lines that showed up in color mode in the pics above as being darker, are still there in B/W, but show up as very faint "rainbow"colors. Really strange.

 

Also decided to change X200 colorburst crystal, nope, problem still there.

If you're getting color in B&W mode (on a game that has a true B&W mode), it can only be the TIA or instability in the color circuit. It's possible that you were close with the crystal, but I believe the transistor or capacitors would be more likely. If I had that console here though, I would try swapping the TIA first, just because I have them handy and it's an easy check.

 

Already swapped the TIA and the other chips when the issue first started, but no changes.

The colors in B/W mode ARE VERY FAINT, but you can still see them, just where the darker lines are.

Which transistor or caps should I check?

Thanks for the help.

Edited by A-T-A-R-I

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Could the CMOS buffer chip (4th chip) be a cause of the problem? Not sure what that controls.

The CD4050 buffers the joy fire button inputs (2), the TIA luma outputs (3), and I forgot what the sixth channel buffers... probably the video sync. If both your joy port fire buttons work, and you get a nice 8-level shading of the sky in Air-Sea Battle/Target Fun, that chip should be OK.

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Which transistor or caps should I check?

The ones right by the crystal. From one of the schematics in the service manual, I believe Q200, Q201, C202, or possibly C203 or one of R200-R205 could be at fault.

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