Composite Mod Help

[+-^CrossBow^-]

No the resistor is usually installed either on the composite mod board along the video out and ground out connections, or I've also seen other modders install it on the actual video rca jack itself across the center and ground there. If you look at the fist pick in the thread you can see the 75Ω across the Vid-O (Video out) and GND connection on the right of the board.

 

 

 

[NISMOPC]

23 minutes ago, -^CrossBow^- said:

No the resistor is usually installed either on the composite mod board along the video out and ground out connections, or I've also seen other modders install it on the actual video rca jack itself across the center and ground there. If you look at the fist pick in the thread you can see the 75Ω across the Vid-O (Video out) and GND connection on the right of the board.

 

 

 

AH! Yea I do not have that on my 2600 mod. Bare boards that I populate myself. I do recall this was a poster child vader that had a bad TIA and horrible soldering skills from prev owner(s). So, I added a socket and new TIA. Traces are pretty fubar'd and some of the solder points are missing. I'll trace it out when I am bored and see fi I can figure it out.

Edited February 9, 2021 by NISMOPC

[ChildOfCv]

A 75 ohm to ground is flat wrong anyway.  All it does is overwork the transistor.  If it's there, remove it.  It's supposed to be 75 ohms in series.

[SpotAnime]

2 hours ago, -^CrossBow^- said:

Corrosion/time...etc. The trimmer is just a variable resistor so over time corrosion can build up on them and cause the values to go out of whack. In some cases you only need to turn the wheel back and forth a few times to get that initial layer back in shape again. I tend to spritz with a little contact cleaner and then move the wheels fully back and forth a few times to be sure. I use the colorbar generator to get the color lined back up again using a CRT, but in a pinch Pitfall! is good to use as well since you know how that should look and can get a good gauge of color adjustment from that game alone.

 

But the thing is, the composite mod is only amplifying the composite signal that is being sent to the RF modulator. So if you are getting black and white, it is either the color wheel is out of whack or something else along the line of the color signal from Pin#9 off the TIA not making its way to the rest of the circuit.

 

Thanks! Will give this a try! Also love your videos and your service keeping these old consoles alive!

[SpotAnime]

Hmmm... so I found the color wheel and sprayed it with some contact cleaner, then moved it around. Admittedly it was a bit stiff, probably due to age, but I got it moving nice and smooth after that. I also sprayed the switches just in case the B/W switch was stuck. Hooked it back up and...still the same prob. I took some pictures of the mod board, the AV connections and even the color wheel.

 

Then I took a look at the underside of where the mod board is wired up to. I also took off the shield to see if I could find the trace from TIA pin 9 to the resistor, and I took some pictures of all of this. I don't know what I need to do with a multimeter to test that trace though.

[ChildOfCv]

On that pot, the two legs where it says R213, what's the voltage between them? (meter on DC V)

 

Next, to measure pin 9, put the black probe on one of the large silver masses where the RF shielding was, and put the red probe on pin 9 of TIA (the chip that has the 2 resistors and wires soldered to its underside).  Count counterclockwise from the divot side of the chip, starting at pin 1.  For reference, the resistors are connected to pins 12 and 13.

 

Also, with the black probe on one of those large silver areas, read TIA pin 20 (far right side of row with the two resistors and wires).

Edited February 10, 2021 by ChildOfCv

[SpotAnime]

On 2/9/2021 at 7:28 PM, ChildOfCv said:

On that pot, the two legs where it says R213, what's the voltage between them? (meter on DC V)

 

Next, to measure pin 9, put the black probe on one of the large silver masses where the RF shielding was, and put the red probe on pin 9 of TIA (the chip that has the 2 resistors and wires soldered to its underside).  Count counterclockwise from the divot side of the chip, starting at pin 1.  For reference, the resistors are connected to pins 12 and 13.

 

Also, with the black probe on one of those large silver areas, read TIA pin 20 (far right side of row with the two resistors and wires).

Okay, hope I did this right. 

 

So for the pot, it measured .52 as in the first picture.

 

For pin 9, initially it measured 1.3 but as I was rechecking the voltage to make sure I had the right reading, it would steadily decline. That last pic was of .8 was the last measurement I took of that pin.

 

For pin 20, it read the same as pin 9.

 

Thoughts? Or did I measure it wrong? EDIT: keep in mind I changed the knob setting on the multimeter between the pot and the TIA measurements. In further research it almost seems like the TIA is dying. That pot is 5V if I read that correctly?
 

Edited February 20, 2021 by SpotAnime

[ChildOfCv]

.5 is way too low, and it does appear that you are measuring correctly.

 

Keep the black probe on ground, and give measurements of both sides of R212.  One side ought to be close to 9V.  R212 is just below that huge capacitor.

Edited February 20, 2021 by ChildOfCv

[SpotAnime]

Both sides consistent, although I don't think this is 9V...

 

I didn't bother to remove the shield again, so I just placed the ground on the exposed silver part of the circuit board. I don't think that makes difference, does it?

[+fdr4prez]

Is your meter set to 2?

 

Wbat happens if you set it 20 and remeasure everything? 

[ChildOfCv]

8 minutes ago, fdr4prez said:

Is your meter set to 2?

 

Wbat happens if you set it 20 and remeasure everything? 

Yeah the number on each setting is the maximum value it can measure, so the 2V runs over when you measure more than 1.99V.  Definitely set it to 20 for those readings.

[SpotAnime]

Set at 20, I'm getting 0.03 for both R212 and R213, 0.00 on the TIA pins 9 and 20.

Edited February 20, 2021 by SpotAnime

[ChildOfCv]

Wait... in those pictures above, it's not plugged in.  It has to be plugged in and turned on in order to read voltages.

[SpotAnime]

Well, that would make a difference wouldn't it...

 

R213 - 6.22

R212 left side - 9.52

R212 right side - 6.23

TIA pins 9 and 20 - 5.02

 

[ChildOfCv]

Okay, those voltages make more sense.  What is the voltage at pin 10 of TIA show?  It probably needs to be more than 4V, and R213 adjusts its output.


Does the voltage at pin 9 change when it's running a game?  Does adjusting R213 affect it?

Edited February 21, 2021 by ChildOfCv

[SpotAnime]

Pin 10 is 4.66

 

I put in Asteroids, and yes voltage on pin 9 changed to 2.75. Turning the pot clockwise about a quarter turn increases voltage slightly to 2.82. Counter clockwise a half turn and it goes down to 1.81.

 

For Pin 10, turning the pot clockwise about a quarter turn increases to 5.95. Counter clockwise a half turn and it goes down to 0.35. 

 

So it looks as if the pot on R213 does have an affect on the voltage of those pins. I also plugged it into the TV while it was open and it does look like there's some convergence going on when turning it, so it appears to be doing its job. And before anyone asks, switching the BW/Color switch does appear to change the grayscale so that's working as well. 

 

I even tried it on the input on my VCR, same thing. No color. But picture and sound come through fine. Weird that it had been working when I last used it about a year ago. 

Edited February 21, 2021 by SpotAnime

[ChildOfCv]

So the TIA seems to be outputting color signals.  The output goes through C210, C211, and R210.  Those are all near the RF module.  Could you give voltage measurements on those components?

[SpotAnime]

6 hours ago, ChildOfCv said:

So the TIA seems to be outputting color signals.  The output goes through C210, C211, and R210.  Those are all near the RF module.  Could you give voltage measurements on those components?

First, I just wanted to thank everyone for being so helpful (and patient) with me as I triage this issue. As I stated before, I'm a newbie when it comes to EE so all this is new to me, but I'm excited to learn how to maintain my old electronics.

 

Second, apologies to the OP for this thread, as I kinda hijacked it. Hopefully they don't care I made this into a sticky for general composite mod issues.

 

Okay, first the orientation of my circuit board, so when I say "bottom" or "top" for my measurements this is what I'm referring to.

 

^ - Top v - Bottom

 

C210 "bottom" - 4.78
C210 "top" - 5.02
R210 "bottom" - 4.98
R210 "top" - 5.01
C211 "bottom" - 0.19 <- I wonder if this could be the problem?
C211 "top" - 4.98

 

If I look closely, it doesn't look like there's a solid solder joint on the bottom of topside C211 (see above). If I turn the board to the underside, that's exactly where the epoxy is in this picture below:

 

 

I'll be pissed if that's what I have to replace, because that looks like a major pain....

Edited February 21, 2021 by SpotAnime

[+DrVenkman]

3 hours ago, SpotAnime said:

If I look closely, it doesn't look like there's a solid solder joint on the bottom of topside C211 (see above). If I turn the board to the underside, that's exactly where the epoxy is in this picture below:

Isn’t it there under the hot glue? At any rate, it’s not a big deal. You can remove the hot glue with simple isopropyl alcohol - it’ll come right off with no trouble at all. Then you can move the wires aside and have complete and free access to anything you need to check or replace. 

[SpotAnime]

16 minutes ago, DrVenkman said:

Isn’t it there under the hot glue? At any rate, it’s not a big deal. You can remove the hot glue with simple isopropyl alcohol - it’ll come right off with no trouble at all. Then you can move the wires aside and have complete and free access to anything you need to check or replace. 

Yeah, I'd have to remove the glue to check, but I'll let you folks make the informed guess on whether this is a potential problem point or not, based on the voltage measurement above. 

 

And here's a closeup of the joint in question from the topside of the board. 

[+DrVenkman]

That could be a cold solder joint but I don’t know if that would explain the issues. That said, you can re-flow that solder joint from the top if you don’t want to remove the hot glue. Just add a tiny bit of fresh solder to the tip of your soldering iron and melt that joint until it flows again.  

[ChildOfCv]

3 hours ago, SpotAnime said:

 

^ - Top v - Bottom

 

C210 "bottom" - 4.78
C210 "top" - 5.02
R210 "bottom" - 4.98
R210 "top" - 5.01
C211 "bottom" - 0.19 <- I wonder if this could be the problem?
C211 "top" - 4.98

 

C211 "bottom" definitely ought to be joining the b/w signal at that point, so that voltage is too low.  It ought to be connected to R222 and C215 (and R214-217).  So either the capacitor is dead, or as you say, the solder joint may be suspect.  What is the reading for the rest of the solder points between C211 and R222?  (And keep in mind, this is with a game running)

[SpotAnime]

R222 "bottom" - 0.19

R222 "top" - 0.00

I measured the next one over as well, I don't know if that has anything to do with it. 

C215 "bottom" - 0.19

C215 "top" - 0.00

[ChildOfCv]

7 minutes ago, SpotAnime said:

R222 "bottom" - 0.19

R222 "top" - 0.00

I measured the next one over as well, I don't know if that has anything to do with it. 

C215 "bottom" - 0.19

C215 "top" - 0.00

Those are both parallel connections to ground, so 0V is correct for the top sides.  This shows that they are all connected together.  The bottoms of R214-R217 should also measure 0.19.  Again, this is with the game running?

 

That composite mod is interesting.  Might need someone to identify it.  It doesn't use the simple amplifier that we typically see, but instead it uses a specialized 3-channel TV amplifier chip (but only one channel of it).  The simple amp mods will also inject some DC voltage into the system, so you'd see a voltage greater than 1V.  The chip used here does not, so maybe that's an expected voltage.  One thing:  Try to find a game that fills the screen with white or at least a very bright color, and see if the 0.19 voltage increases.

 

Other than replacing the mod board, I'm not sure there's much else that can be done without better test equipment (oscilloscopes and such).  One thing to make sure of though:  Make sure the +5V and the GND are connected to the main board.  You can unplug the system and then check those connections in continuity mode.

[SpotAnime]

Okay, thanks for your help nonetheless. I know I bought it from @Osgeld, I checked it was back in April 2017. I tagged Osgeld here - not looking for any warranty lol, but rather if he has any info on the mod performed which he might be able to shed light on what I'm experiencing with the color loss.

 

I don't know if I have enough skill to replace the mod board with another, especially if the two mods are not compatible. But hopefully it's just an easy fix once I can figure out what's going on with it.