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Audio/Video composite mod - colors switched to shades of gray


Scyzor

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I have installed composite out mod following steps from https://vintagegamingandmore.com/installation-guide-6-switch/ but I can't get colors to stay on the screen. Green will go to blue and the all will become shades of gray except yellow color.
Color potentiometer adjustment will not change much except it will make video out gone or display.
Any thoughts on that?

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13 hours ago, ChildOfCv said:

Check the voltages at the color potentiometer.  When the color fades, keep the black probe on a ground point somewhere and report on the voltages at each connection of the pot.

I have measured voltage on all 4 points from the attached picture and on three of them I had a voltage drop when colors were gone:

 

#1: 6.2V -> 5.56V

#2: 4.2V -> 3.20V

#3: 3.56V -> 3.18V

#4: constant 0V

 

Initial voltages make sense for each measure point but voltage drop is unknown for me.

 

Should I replace power transistor or that big capacitor?

 

Thanks and Happy New Year!

2020-12-31 14.54.24.jpg

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33 minutes ago, ChildOfCv said:

Check the voltage at the regulator (probably what you referred to as the power transistor) on the switch board, all 3 pins.  Should be around 9V in, around 5V out.

Is 10.25-10.27V on IN and 5.10-5.12V on OUT.

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16 hours ago, ChildOfCv said:

Those look good.  This is even when you get B/W out?

 

What are the voltage readings on both sides of CR201?

Yeah - that is with B/W, no changes there.

 

C201 is stable 5.05-5.06V 

CR201 is 6.75V and 5.68V

 

Also found that diagram for repairing 2600 so will try to follow it.

atari2600repair.JPG

Edited by Scyzor
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So based on above diagram I'm getting below 5V on pin #10 of A201 and 6.75V on cathode of CR201 so it comes that it may be defective:

- C208

- C209

- R211

 

I think I can rule out defective R211 as there is valid voltage on CR210. At that case I think one of capacitors may be defective: C208 and/or C209.

 

 

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When I max out R211 (counterclockwise it to #1) I have between 7-5V (when will change to B/W) the same on CR201 cathode. Even I have pulled out A201 and clean up the socket. Did not help much but now when I will leave console up and running it will fade out to B/W and then is getting darker. 

 

When I was adjusting R211 from #1 towards #4 I was getting those readings on

C209: 5.75V (with drop when goes B/W), 5.10, 7.07 (R211 in the middle), 7.22 and 7.40v (when turned on #4)

C208: 4.56v (with drop when goes B/W), 3.87, 1.92 (R211 in the middle), 0.56 and 0.20v (when turned on #4)

 

No clue from where those drops are coming from

 

PS.

I have left multimeter attached to CR201 and voltage started to fluctuate between 7.2 and 4.64 after like 2-3 minutes. To have it back to 7V I need to turn off console and unplug power supply. 

Edited by Scyzor
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Based on schematics below it looks like that C208 and C209 are behind the CR200 and CR201 but C209 is before R211 so voltage fluctuation source can be C203, and looking at CR200 I should to have stable 5V on anode side of it no matter how I will adjust R211. Also I have have no clue if Q201 will have anything to do with that or it is just there for as signal from a crystal. 

2600video.JPG

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If I understand your voltage readings, the voltage at CR201/#1 of R211, when it goes to B/W are:  5.1 when turned towards #1, and 7.4 when turned towards #4.

 

If that is correct, it indicates that the TIA is your problem.  After it warms up enough, the delay line shorts to ground, so the voltage multiplier C203/CR200/CR201 just can't keep up.  When you turn the pot towards ground, it is no longer loading down the voltage multiplier and it can reach its best output (but the delay voltage is also too low, so no color either).  At least, assuming I understood your readings above.

 

If you have canned air, blow on the TIA after it goes B/W and see if the color returns.

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And I think this is the problem. I have put 60mm PC fan above it and it was working stable for more than 5 minutes. Only one thing which I have noticed are strange shapes on the screen where is green color on the picture below (left side and bottom - top right is fine). It looks like a scan of a memory bank or so. Doesn't look like typical "jail bars".

 

So back to the TIA - should I replace it or put some radiators on it or do some small 5V/9V fan mod?

 

 

2021-01-02 18.37.19.jpg

Edited by Scyzor
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