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No color after composite mod


jacl3
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I have an CX2600A 4 switch wood grain NTSC system, I am in Canada.

 

I decided to go ahead and do the composite mod, following instructions from Instructables

 

I built this circuit

FHWJ09SIE7J59Y3.MEDIUM.jpg

 

And removed the transistor

FAB7S38IE7J5A0X.MEDIUM.jpg

 

And then removed these 2 resistors (R222 R209) and 1 capacitor (C209)

F1HENQ0IE7J5A3R.MEDIUM.jpg

 

I also removed the RF module as seen in the Instructable page.

 

I wired it up using the instructions found here http://www.coolretroprojects.com/Atari_2600_AV_Mod_Installation_Guide.pdf for the NTSC system,

 

Sound works great, and the picture looks good but it only stays in color for a second or so before switching to black and white (no it isn't the Color / B&W switch).

 

Looking back through the instructions from coolretroprojects pdf it seems that the R222 and C209 should only be removed in PAL systems, and not NTSC systems (DAMN! I should have looked at that page before I removed the pieces as instructed by the Instructables page).

 

I found the Field Service Manual for the 2600 here http://www.digitpress.com/library/techdocs/Atari_2600_VCS_Domestic_Field_Service_Manual.pdf

 

Looks like C209 is a 47pf 50v ceramic capacitor and R222 is a 15k resistor (12k for a CX2600 but 15k for the CX2600A which is what I have).

 

I will be replacing both C209 and R222 tomorrow with new ones as I damaged the capacitor when I took it out.

 

Has anyone else had a similar problem with no color after doing the composite mod? Is it because of that cap & resistor do you think or something else?

Edited by jacl3
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Yes, you should instead remove resistor 209, and transitor 202 for the NTSC 4 switch models but not necessary according to instructions.

 

Don't worry about C209 that is on the output of the audio and won't affect your color, and I'm assuming since you have sound you tie into the audio before that point so you are fine. Just put the 15k ohm resistor back in place and recheck it is from the point you connect for your video in on your mod to ground and should probably be there.

Edited by SignGuy81
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I tie in to audio on R206 I believe, it is a few to the left of R209 here is a screenshot of the one I connected to for audio from the instructions

 

bxhGwKw.png

 

I have R209 and transistor 202 removed.

 

I will try adding back R222 first then to see if that works. Are you 100% sure that C209 is audio not video?

Edited by jacl3
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I tie in to audio on R206 I believe, it is a couple to the left of R209 here is a screenshot of the one I connected to for audio from the instructions

 

bxhGwKw.png

 

I have R209 and transistor 202 removed.

 

I will try adding back R222 first then to see if that works. Are you 100% sure that C209 is audio not video?

Positive, I looked at the schematic. As a matter of fact it is in series with the resistor you were supposed to remove anyway and that cap would have no affect on anything with that resistor(R209) removed anyway.

Edited by SignGuy81
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Positive, I looked at the schematic. As a matter of fact it is in series with the resistor you were supposed to remove anyway and that cap would have no affect on anything with that resistor(R209) removed anyway.

 

Ah nice, yeah I just pulled up the schematic too and you are right they appear to come off AU0 and AU1 on the TIA which I assume is for audio, it has been a long time since I read one of these, and Osgeld seems to be echoing saying that he removed C209 always without issue as well.

 

eZIjIhw.png

 

Now hopefully it is R222 that is causing my issue then.

Edited by jacl3
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Still looking at this,

 

If I'm reading it right TIA pins 2 5 8 and 7 are the video circuit and by removing R222 it has removed the connection to ground for audio and video, so the whole circuit now will not ground correctly.

 

I suppose it still grounds in my circuit through the 3k3 resistor, probably.

 

I will update tomorrow.

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Still looking at this,

 

If I'm reading it right TIA pins 2 5 8 and 7 are the video circuit and by removing R222 it has removed the connection to ground for audio and video, so the whole circuit now will not ground correctly.

 

I suppose it still grounds in my circuit through the 3k3 resistor, probably.

 

I will update tomorrow.

Yeah I didn't even think about that, so you may have problem elsewhere. Reason is that when you have resistors in parallel the total resistance is always less than the smallest resistance, so it really doesn't matter the resistance there is going to be around 3.3k anyway but slightly less, so putting the 15k ohm back in won't make much difference so yeah you should probably start looking at something else. You said you already checked your black and white switch correct?

 

EDIT:

I just did the math it works out to be a little more than slightly less than 3.3k it would actually be 2.7k ohms with the 15k and the 3.3k in parallel but sure you get my point and I believe your problem is elsewhere.

Edited by SignGuy81
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That red wire in your pic that you used for ground. It looks to me like it is just sitting on top of the blob of solder on the board as if it may have broken off, or it could just be the way I'm looking at it not sure. Can you send pic of whole board both sides and including your mod board.

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Hey Guys,

 

The pictures I shared were just examples of what I did,

 

Here is a picture of my actual board, what I did was soldered in a wire with a male pin on it to the board leaving a female connector exposed, I did this for VCC, Ground and Video Out, for the audio I just connected to the resistor since I didn't have anything to go through. On my board I made I soldered in a male-male wire, this lets me still remove the main 2600 board by simply disconnecting my connectors, I kept it all color coded so red goes to red (vcc from atari), yellow to yellow (video out from atari), black to black (ground out from atari), white to white (audio out from atari direct to RCA), blue to blue (ground out from my circuit to RCA) and green to green (video out from my circuit to RCA). They are only a couple inches long. The same kind of connectors are soldered to the RCA jacks.

 

GrX089n.jpg

 

Here is my circuit

a5ugCla.jpg

 

Please note I soldered in a 75ohm resistor between the emitter and ground to try to fix the B/W problem, it didn't fix the problem so I will likely remove it.

 

Strangely though, in desperation I put 3 75ohm resistors in parallel and the picture did come in color but the pictures started bounce up and down so I took off the extra 2.

 

Here is another view of my circuit, hard to get a clear picture.

ge81AAg.jpg

Edited by jacl3
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I added back in R222, still no color. I removed the 75 ohm and still no color.

 

I was reading about the "Version 2" of Ben Hecks composite mod where he adds a resistor between VCC and the transistor, I put one in temporarily and at 150ohm I am still black and white, at 225 I am color but it is too dark to see well.

 

Getting somewhere but not where I want it

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Looking at the schematic and the board the 22pF and the 6.8k ohm resistor that are in series are opposite of what they show on the schematic, and I guess that is why they have the "S" shaped line there to show it was a mix up. This cap is now right beside that 15k ohm resistor that you first removed. Did you just clip the the lead of the resistor or apply head with soldering iron and remove. I'm wondering because you already mentioned you damaged one cap and wondering if perhaps the 22pF(C211) may have had heat applied to it too long. This can easily happen since it is right next to it and the trace goes right over too it. You may even notice too when either desoldering or soldering one of those resistors that the solder will melt on one beside it where it is so close to the other. The heat travels right too it. So if left on too long that cap could have some thermal damage. Reason I'm asking is this is right in line from the color output. I would place a jumper across that cap temporarily to see if anything changes. If so change the cap.

Edited by SignGuy81
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color is a combination of LM1,2 and 0, I think if C211 was broken, one would not get a picture at all

 

nevermind looking at a better schematic I see how that could be relevant as its the color-burst reference signal

Edited by Osgeld
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color is a combination of LM1,2 and 0, I think if C211 was broken, one would not get a picture at all

 

nevermind looking at a better schematic I see how that could be relevant as its the color-burst reference signal

Yeah I believe I just said color but you are correct it is color burst.

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Looking at the schematic and the board the 22pF and the 6.8k ohm resistor that are in series are opposite of what they show on the schematic, and I guess that is why they have the "S" shaped line there to show it was a mix up. This cap is now right beside that 15k ohm resistor that you first removed. Did you just clip the the lead of the resistor or apply head with soldering iron and remove. I'm wondering because you already mentioned you damaged one cap and wondering if perhaps the 22pF(C211) may have had heat applied to it too long. This can easily happen since it is right next to it and the trace goes right over too it. You may even notice too when either desoldering or soldering one of those resistors that the solder will melt on one beside it where it is so close to the other. The heat travels right too it. So if left on too long that cap could have some thermal damage. Reason I'm asking is this is right in line from the color output. I would place a jumper across that cap temporarily to see if anything changes. If so change the cap.

 

I applied heat, I didn't clip them. Hopefully I didn't damage it but I will test putting a jumper across C211 tomorrow to see if that helps.

 

I will also get more pictures up tomorrow (front and back of the board).

 

As I mentioned in the original post, color comes in for a second (well not quite a second) but then goes to black and white. Some more stuff I am reading is that it may have to do with the X200 (3.579545) crystal, I may try that later as well.

Edited by jacl3
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well, that's sort of the reason I offered you a video driver, NTSC is pretty forgiving but not nearly as forgiving as RS170 (aka black n white predecessor of NTSC) so if your getting color for a moment, and it craps out, I would more likely assume something off balance in your transistor amp

 

if it were me I would just hook it up to the scope and see whats up, but its not me, so please tinker away and see if it clears up, just dont do anything you cant easily undo with your parts on hand, and if its not cleared up by the time my board snail mails in, least it will give you another sanity point, as I have used the exact same board on dozens of atari's

 

if the problem goes away, it's something in your amp not playing nice with your specific revision of 2600 (cause every durn rev of a vcs uses different resistors) , if it doesn't, its something in your 2600, least you know

 

btw I have yet to see a bad crystal, but I have seen a bad 3906 transistor that buffers the weak and fragile clock signal to the TIA chip, but in that case the system was dead as a doornail until I replaced it ... going back to resistors, the stock resistor in that system was like 56ohms and the schematic on AA says says 390, 56 is fine but kind of explains why it burned out if there was a power "event"

 

1980's, low cost, and taiwan during their early days, what can you do heh

 

btw

https://atariage.com/2600/archives/schematics/Schematic_2600A_Low.html

Edited by Osgeld
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I'm having fun with the project to be honest, if this was something current gen, there would be no easily serviced resistors or capacitors. I will happily put in your driver circuit to see if it fixes the issue.

 

I wasn't planning to play with the 2600 again tonight but curiosity got the best of me, I jumped C211 and this is what happens, color but very weird jaggady picture

 

The last second of the video I pull off the jumper and we go back to black and white.

Edited by jacl3
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Does the jaggady video in color indicate that it may be the C211 cap? Unlike when I was adding resistance to the VCC on my circuit the picture came in very bright when I jumped C211 but as you can see it is, well, jaggedy, not sure what the correct term is haha.

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Does the jaggady video in color indicate that it may be the C211 cap? Unlike when I was adding resistance to the VCC on my circuit the picture came in very bright when I jumped C211 but as you can see it is, well, jaggedy, not sure what the correct term is haha.

That is probably just because it doesn't have a cap in it now to smooth it out. Just take the cap off the RF box, it is a 15pF with one lead tied to one of the transistor leads. Take the jumper out and place that cap in there and check. When you desolder that cap try not to hold heat on it very long. Add a little solder to it first with the iron or flux if you have any. Also you could take an alligator clip and hold on the lead close to the cap to help avoid heat damage but as long as you don't hold heat to long you should be fine.

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