composite video mod - what's wrong?

[dphirschler]

Not happy with the picture after composite video mod. See pics here:

 

Before the mod:

 

after the mod:

 

Here is after the mod on my Sharp TV:

 

 

Here is a pic of the mod kit:

 

So the picture seems crisp, but there seems to be some extreme sharpening artifacts. Like doubled and ghosted lines at the edges. And it doesn't even work on the Sharp TV!

 

What could I have done wrong?

 

Darryl

 

Edited May 6, 2017 by dphirschler

[SignGuy81]

Yeah someone else had similar issue and I had one of the exact same mod that wouldn't work on one of my TVs. I swapped out the 2.2k with a 4.7k ohm resistor and the 3.3k with a 6.8k ohm resistor and it solved the issue for me. Try it and see if it helps.

 

The problem is that the video signal is to weak with the mod. Changing those values increases it.

Edited May 6, 2017 by SignGuy81

[SignGuy81]

If you don't have a set of resistor values to choose from replace the 2.2k with the 1.5k from the RF board you removed(heard that tip from Osgeld he is very good at this stuff), that should work too and I'll show you link to post explaining it. Here is link to same problem http://atariage.com/forums/topic/265208-no-color-after-composite-mod/

 

And here is one I did showing problem with video signal being to low after composite mod. http://atariage.com/forums/topic/264563-no-picture-composite-mod/

Edited May 6, 2017 by SignGuy81

[SignGuy81]

PS, Can you tell me what Rev # you have for your board. I believe it is either 14 or 15 just want to know which one for sure for something unrelated.

[+save2600]

You can also snip that tiny resistor (between the video and ground output of your new board) off to brighten up the pic. Might be all you need to do...

[dphirschler]

PS, Can you tell me what Rev # you have for your board. I believe it is either 14 or 15 just want to know which one for sure for something unrelated.

Rev 14.

[dphirschler]

Also, I completely removed the transistor instead of just clipping one of its legs. Don't think that has anything to do with it because some of the tutorials I saw said to remove it completely. You should be able to see that in the picture above.

 

Also, the b/w picture on my Sharp TV bounces up and down a bit at times. Doesn't roll, just a bounce.

 

So, what is the purpose of the 75 Ohm resister between ground and video on the output side of that circuit?

 

 

Darryl

Edited May 6, 2017 by dphirschler

[SignGuy81]

not sure what you meant about clipping the lead or removing completely i don't think anyone was talking about that resistor(the one you removed from the main board). The other guy was talking about just clipping the 75ohm resistor which is added for impedance matching. I don't believe it is going to solve your problem but you can try it. When I was testing the video output on my scope I tried with and without the 75 ohm resistor and it made no difference I only had around 200mV peak to peak signal with the composite mod until I changed the two resistor values. A composite video signal should be 1V peak to peak and some TVs are not going to accept a much lower signal because the TVs are designed to see that 1V peak to peak and aren't even going to recognize it as a signal if it is way too low.

Edited May 6, 2017 by SignGuy81

[SignGuy81]

Have you tried like the other guy said yet though(just heat and lift one leg of the 75 ohm resistor because you may want to put it back in place) to see if it makes a difference? Also have you tried swapping the 2.2k ohm with the 1.5k ohm(it is located on the RF board you removed right beside the diode)? Or the other option I gave if you have the resistors to do so?

 

EDIT:

Another option you may try is to just leave the 2.2k in place and solder the one you removed that I thought you were talking about clipping earlier when you instead meant the transistor(R209 which is a 1.8k ohm) across the 2.2k ohm and will be like having a 1k ohm in its place with the two in parallel, just to see if that makes any difference(or just removing the 2.2k ohm and trying the 1.8k ohm in its place is another option to try).

Edited May 6, 2017 by SignGuy81

[SignGuy81]

I just realized you said you didn't clip the transistor and just removed and not talking about the resistor but yes you are correct that doesn't make any difference as far as whether you clipped or removed it totally and I thought you meant one of us replied that it did which it doesn't.

Edited May 6, 2017 by SignGuy81

[dphirschler]

Yes, you are correct about the transistor. I brought that up on my own. I was concerned that maybe I caused it by removing it rather than clipping the lead.

 

Concerning the 75 ohm resistor. I am inclined to leave it in place for now.

 

But I am curious about the options mentioned above. I was reading the other thread to try and understand the reasoning behind why replacing 2.2k ohm and 3.3k ohm with 4.7k ohm and 6.8k ohm works. Seems to me, if you nearly double the resistance, won't you weaken the signal? But even if that's a good solution, I don't have them on hand yet. I need to get some resistors.

 

I haven't spent time checking into the other two solutions yet either... using the R209 (1.8k ohm) and the 1.5k ohm from the RF modulator.

 

Darryl

[SignGuy81]

 

But I am curious about the options mentioned above. I was reading the other thread to try and understand the reasoning behind why replacing 2.2k ohm and 3.3k ohm with 4.7k ohm and 6.8k ohm works. Seems to me, if you nearly double the resistance, won't you weaken the signal?

 

 

If there were a resistor in series with the video signal before it goes into the base of the transistor that you increase, then yes you would weaken the signal. But that is not the case.

[SignGuy81]

The best way to describe it for you would be that electricity will try to take the easiest path(least resistive) so what you have before increasing the values like I mentioned is part of the video signal can leak and not get into the base. But increasing the values makes the path more resistive so less leaking of video signal before going into base of the transistor.

[SignGuy81]

Here is a link to some resistors. I gotta restock some myself.

 

http://www.ebay.com/itm/1500pcs-Carbon-Film-Resistors-1-4W-75-Values-Assortment-Kit-1-ohm-10M-ohm-5/131867507451?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D40130%26meid%3Dba7a283cfce2439790b124005a2cc8b6%26pid%3D100005%26rk%3D6%26rkt%3D6%26sd%3D322467236930

[SignGuy81]

If you can't wait you might be one of the lucky ones that still has a radio shack near you to go in and get resistors https://www.radioshack.com/apps/store-locator

 

 

Looks like a lot more even closed just a couple months ago I didn't realize that. Sad.

Edited May 7, 2017 by SignGuy81

[dphirschler]

OMG! 1500 pieces! Thanks for the link.

 

Darryl

[dphirschler]

OK, please be patient. I won't be able to report back until I get some more resistors. I ordered them from the link above. Since I will have so many, I may also try Ben Heck's composite mod "reloaded". Of course that means I need to get some perf board and a transistor..

 

Darryl

Edited May 7, 2017 by dphirschler

[dphirschler]

My apologies. The "before" pitfall image is incorrect. Here it is:

 

 

And for comparison's sake, here is the after shot:

 

 

I wanted to ask about the ghosting I see on the white numbers in the upper left corner? What could be causing that? Is it all because of the weak video signal coming out of the circuit?

 

Here is just a shot showing the garbledness that is the tree.

 

Darryl

[SignGuy81]

Probably be best to get it working on both TVs then see if it still exists and go from there.

[dphirschler]

OK, I put the new resistors in place. My picture is better on the Sharp TV, but still b/w. I'll post a pic later after the sun goes down. No window reflections. Ideas?

 

 

Darryl

[SignGuy81]

It could still just be not strong enough signal for the Sharp TV. Not the TVs fault really though. An NTSC composite signal is supposed to be around 1V peak to peak. I tested two Atari 2600s with the 2 resistor/transistor mod as it comes and the signal was around 200mV to 300mV peak to peak which is way too low. Both Ataris played fine on my Hisense TV, however on a GPX TV they would not.

 

After increasing the resistance values I mentioned my GPX then played both Ataris just fine. However, the signal coming out was around 600mV peak to peak, still not where it needs to be for a proper composite video signal.

 

It probably did help it become more compatible with more TVs though now that you've done the resistor changes. But if you really want it to work on the Sharp TV you already have really the best solution is a different mod.

 

There are probably users here that could sell you a premade board to install.

 

 

EDIT:

I wasn't thinking when I originally did testing and increased the resistor values about there being a 15k ohm already in place on the board from the mixed signals to ground. When increasing the values I was trying to keep it about the same ratio as before by just doubling or about doubling the values which is why I went with 4.7k and 6.8k. So originally I thought it was 2.2k/3.3k but because of the 15k already in place in parallel with the 3.3k it instead makes it 2.2k/2.7k in which case I would want to go with instead 4.7k/5.6k but keeping in mind that 5.6k will not work I would have to either clip or desolder the 15k and use a 5.6k or put in a value that will make it around that while leaving the 15k in place.

 

So in that case to keep it same ratio as original mod and not clipping the 15k ohm the values would be 4.7k ohm and 9.1k ohm(9.1k and 15k in parallel is around 5.6k). But if clipping the 15k ohm out and sticking in 5.6k in place of the 3.3k would be okay as well.

 

I'm not saying either of these will work but it would be worth a try to see if it helps increases the signal enough for your TV. I'm going to later on try this myself and recheck the signal output on my scope and go back to my original topic I started on the issue.

 

Also you may even want to try going higher and instead try 6.2k ohm and 9.1k ohm(clip or desolder the 15k ohm on main board) instead and you may get a stronger signal. These are just things to try no guarantee, like I say I'm going to go back and try these specific values myself later on. I did get a stronger signal I believe the first time I tried increasing resistance values but I got a little bit of ghosting but also at the time like I said I wasn't thinking about the 15k ohm resistor(R222) on the main board so maybe keeping the same ratio will help.

Edited May 15, 2017 by SignGuy81

[dphirschler]

Here is the pic after the new resistors have been put in place. Much improved on the Sharp, but still b/w.

 

 

And here it is on the upstairs TV (Samsung). It may appear brighter, but I think I used different camera settings. And there are reflections from the kitchen. ignore that.

 

 

 

Darryl

[dphirschler]

I will await your findings. I may try Ben Heck's reloaded AV mod (linked above). Anybody here have any experience with that one? I am not sure where to connect ground on that one. What I mean is, there is ground to the mainboard, and ground to the composite video connector.

 

Darryl

[SignGuy81]

I will await your findings. I may try Ben Heck's reloaded AV mod (linked above). Anybody here have any experience with that one? I am not sure where to connect ground on that one. What I mean is, there is ground to the mainboard, and ground to the composite video connector.

 

Darryl

 

I tried to think of the simplest solution to get a stronger signal to work for you and the other guy.

 

Going back to the 2 resistor/transistor mod what I did was just completely eliminate the 3.3k ohm resistor altogether on the mod board(like I say there is a 15k ohm resistor across that same path and trying to use higher values anyway so will just let this be the value for that one) and for the 2.2k ohm resistor put in a 10k ohm or slightly higher. I used 10k ohm because it was the easiest to find in my junk pile that I need to get organized. I then hooked my scope to the output while playing game and I had an 800mV peak to peak signal this time, the highest I've had. With my previous resistor adjustment I had 600mV peak to peak.

 

Doing this may very likely bring you color. All it is is putting the mod board back on and changing out the resistor(the one that is supposed to be 2.2k) with a 10k and then removing the other resistor(the one that is supposed to be 3.3k). That simple and gives you much stronger signal.

Edited May 16, 2017 by SignGuy81

[dphirschler]

So, let me make sure I understand this. The top resistor (which used to be 2.2k) gets replaced with a 10k. And do I just jump across where the 3.3k was?

 

Darryl