composite video mod - what's wrong?

[SignGuy81]

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

no, don't jump across the 3.3k you will leave that open(it won't technically be open because there is a 15k ohm on the main board that is across that same spot), so on the mod board it is simply just removing that resistor, not jumping it.

[dphirschler]

I don't have any 10k ohm resistors, so I tried three 3.3k ohm resistors in-line. I left the other spot empty. Still got b/w. :-(

 

Darryl

[SignGuy81]

I don't have any 10k ohm resistors, so I tried three 3.3k ohm resistors in-line. I left the other spot empty. Still got b/w. :-(

 

 

 

Still must not be quite high enough signal, like I said it was 800mV peak to peak when I did this which is technically still too low. To get higher you would have to remove the 15k ohm and put a higher one in its place either in that spot or on the mod board where the 3.3k goes in place of it. Do you have anything around 22k ohm? I would try putting that in place of the 15k ohm and then put the 15k ohm where the 2.2k goes, and still leave the spot on the mod board empty where the 3.3k goes.

 

Sorry to put you through all those steps but was trying to gradually bring your signal up to see when it is good enough for your TV.

 

Also you did leave the 75 ohm in place from output to ground right?

Edited May 17, 2017 by SignGuy81

[dphirschler]

The 75 ohm one is still in place. I'll have to look for the others.

 

And I don't mind all the steps. I figure I am like a guinea pig. My success is everybody's success because the mod ultimately gets improved.

 

Darryl

[+DrVenkman]

Contact user 'Bryan' - he's considering another run of his UAV boards. Dead simple installation (five wires soldered directly to the shoulders of TIA or the pins under the board - Sync, LUM1 - 3, Color) plus whatever you want to do for audio. And yes, it works great with modern LCD sets.

 

[+DrVenkman]

ALSO: Looks like Bryan is doing another run this month.

 

http://atariage.com/forums/topic/260267-the-uav-rev-d-video-upgrade-thread/?p=3763891

[dphirschler]

Thanks, I PMed him.

 

Darryl

[dphirschler]

BTW, in the mean time, I do not have a 22k ohm resistor. So now we have to wait for my bag of 1500 various resistors to arrive. I'd really like to perfect this circuit. Eventually though, I will probably desolder the resistors necessary to do Ben Heck's reloaded mod. But I am also going to buy Bryan's circuit board... which is what will ultimately be installed.

[Atari-Collector]

Those mod boards are so over priced for what they are. There's about $1 worth of parts there. I built a couple just out of parts I keep around for everyday use.

The one thing I notice in the video wire (yellow) is not shielded. It should have something like RG174 coax even for short hops, or at least have a ground wire wrapped around it to to cut interference down. The circuit isn't just amplifying the signal, it'll amplify signal noise too. That's why they have the shielding in there in the first place.

[dphirschler]

Question. I am not sure which resistor I need to remove. I believe I've identified the only 15k ohm resistor using this website, however I just want to be sure. I've attached a photo where I marked the resistors that I think I know. So, please tell me, is the 15k I need to remove the one in the lower right corner (between the green resistors)?

 

 

The plan then is to put the 15k on the mod board in place of the 2.2k. And put the 22k where the 3.3k is.

 

 

Darryl

[SignGuy81]

It should be the second one over going to the left from the right side on the bottom. brown, green, orange is 15k, and it is only one i see

[dphirschler]

Well, after installing the 15k and 22k resistors, the picture is still b/w on the Sharp TV. Looks ok on the Samsung. Here is a bit of a clue. Last time (10k and none), I got a brief flash of color before it went b/w. This time, however, it did NOT do that. It was just b/w.

 

At this point, I am waiting for my transistors so I can build Ben Heck's "reloaded" circuit.

 

But I am willing to try other ideas if you have any.

 

 

Darryl

[dphirschler]

It will be end of June before I get my Bryan mod board, so I continue to experiment. I just removed the 75ohm resistor between composite out and ground. Picture is now color on the Sharp TV, but it now bounces.

 

Darryl

[mrkite]

On 5/15/2017 at 4:07 PM, SignGuy81 said:

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

Sorry for the necro, but I just wanted to highlight this for others.  I used the 1 transistor/2 resistor composite mod (no motherboard changes except for clipping that one transistor) on my 4 switcher, and the video was far too dark.  The signal was around 300mV peak to peak, color burst was around 140mV.  Changing the resistors in the mod to 9.1k and 4.7k boosted the signal up to around 600-700 mV peak to peak (color burst now where it should be at ~300mV) and brightened the picture up considerably.  It now looks amazing, even after being passed through an Extron switch.