7800 video mod - Which One?

[PSW]

I'm currently in the process of modding a 7800 using the procedure posted by puppetmark; however, I'm having some problems, and scouring this forum (as well as the internet) I've discovered that there are several "versions" of video mods for the 7800. I would like to know which of the several mods reported for the 7800 is the best version to pursue from two perspectives: 1.) ease of build, and 2.) quality of output. Can anyone shed some light on this? FYI, I'm simply trying to hook up my 7800 to a television with composite video input.

[Rex Dart]

This 'un.

[Underball]

This 'un.

That's puppetmark's. (sort of, he posted it, but a few of us have added to it).

 

It's definitely the easiest, and quality-wise, they're really all about the same, unless you do a more complicated (and expensive) one with S-video, which may or may not produce better results. I've heard both great and terrible things about the other two (8bitdomain's and Longhorn's).

 

What's the trouble you're having, I'm sure we can sort it out.

[PSW]

I have audio so I'm confident my audio circuit is complete. The issue is that i'm not getting any video at all. After reading through the extremely long puppetmark post, I have some basic questions. 1.) does the RF modulator have to be removed. 2.) Can the RCA jacks for audio and video be run off the same ground? 3.) Do I need to change the R11 resistor or not? 4.) Do I need to keep the 75 ohm resistor in the video circuit?

[Underball]

1.) no.

2.) yes.

3.) no, it's a matter of what looks better to your eyes.

4.) no. In every 7800 I've nodded it absolutely looks better without it.

[PSW]

Thanks - that certainly helps when someone gives definite answers. Now, after reading deeper into the puppetmark mod, I noticed that there is some differences in how the audio circuit can be performed. I followed the original mod; however, it seems that some people are soldering R5 and R6 together with a microcapacitor. Why the change? Do both methods provide identical results? Is one method better than the other?

[Underball]

Either is fine. They essentially produce the same result.

[yelever]

I did the mod over a couple days due to soldering skills. I did the sound with R5 and R6 and sounds good. The only thing I`ve noticed is my picture is very dark and fuzzy.

[PSW]

So, if I omit the 75 ohm resistor from the video circuit, does the final circuit have the ground, video out, 3.3 k resistor, and the capacitor all connected at the same point?

[yelever]

So, if I omit the 75 ohm resistor from the video circuit, does the final circuit have the ground, video out, 3.3 k resistor, and the capacitor all connected at the same point?

Sorry but new to this myself but I`m sure someone can help

[Underball]

So, if I omit the 75 ohm resistor from the video circuit, does the final circuit have the ground, video out, 3.3 k resistor, and the capacitor all connected at the same point?

Here take a look at this. This should make more sense. The piece in the center is the Transistor. Transistors are pin-specific, you have to pay attention to which pin goes where. If you're looking at the Transistor, label facing you:

 

1. The RIGHT pin gets soldered to +5v and one leg of the 2.2k resistor.

 

2. The CENTER pole of the Transistor gets solderd to the other leg of the 2.2k, the video in from teh 7800 mohtherboard RF, and one leg of the 3.3k resistor. The other leg of the 3.3k goes to ground.

 

3. The LEFT leg of the Transistor is your video output. This goes to the center pole on the RCA Video output jack. You can take the ground connection for the outer ring of teh RCA jack straight from the 7800 Motherboard Ground.

[Jinks]

So do these mods make a big difference? I run my 7800 with a monster heavy gauge rca cable on the female rf connector to an adapter to go into the coax on my vcr then from the vcr left right and video outputs to my 7.1 surround system and then to a 50"plasma for picture. I play with the bass sub cranked to 10 and the picutre and sound seems flawless. After you guys have done these mods in comparision to your setup was it a big upgrade? I only have one 7800 and by the sounds of things the mod seems far from flawless with mixed results, with the problem of several types of systems and pictures that are too bright or too dark.

[yelever]

So, if I omit the 75 ohm resistor from the video circuit, does the final circuit have the ground, video out, 3.3 k resistor, and the capacitor all connected at the same point?

Here take a look at this. This should make more sense. The piece in the center is the Transistor. Transistors are pin-specific, you have to pay attention to which pin goes where. If you're looking at the Transistor, label facing you:

 

1. The RIGHT pin gets soldered to +5v and one leg of the 2.2k resistor.

 

2. The CENTER pole of the Transistor gets solderd to the other leg of the 2.2k, the video in from teh 7800 mohtherboard RF, and one leg of the 3.3k resistor. The other leg of the 3.3k goes to ground.

 

3. The LEFT leg of the Transistor is your video output. This goes to the center pole on the RCA Video output jack. You can take the ground connection for the outer ring of teh RCA jack straight from the 7800 Motherboard Ground.

This may sound like a stupid question but say if the pins are soldered the wrong way round then would it effect the display say make it darker?

[yelever]

So do these mods make a big difference? I run my 7800 with a monster heavy gauge rca cable on the female rf connector to an adapter to go into the coax on my vcr then from the vcr left right and video outputs to my 7.1 surround system and then to a 50"plasma for picture. I play with the bass sub cranked to 10 and the picutre and sound seems flawless. After you guys have done these mods in comparision to your setup was it a big upgrade? I only have one 7800 and by the sounds of things the mod seems far from flawless with mixed results, with the problem of several types of systems and pictures that are too bright or too dark.

I have noticed the colour alot darker and a little fuzzy but hoping the guys here can help me get it perfect but it was my first time modding.

[PSW]

So, if I omit the 75 ohm resistor from the video circuit, does the final circuit have the ground, video out, 3.3 k resistor, and the capacitor all connected at the same point?

Here take a look at this. This should make more sense. The piece in the center is the Transistor. Transistors are pin-specific, you have to pay attention to which pin goes where. If you're looking at the Transistor, label facing you:

 

1. The RIGHT pin gets soldered to +5v and one leg of the 2.2k resistor.

 

2. The CENTER pole of the Transistor gets solderd to the other leg of the 2.2k, the video in from teh 7800 mohtherboard RF, and one leg of the 3.3k resistor. The other leg of the 3.3k goes to ground.

 

3. The LEFT leg of the Transistor is your video output. This goes to the center pole on the RCA Video output jack. You can take the ground connection for the outer ring of teh RCA jack straight from the 7800 Motherboard Ground.

 

Thanks, your revised schematic was exactly what I needed. I'll give it a whack this weekend and let you know how it went. Again, a million thanks as you cleared up all of my questions.

[PSW]

So, if I omit the 75 ohm resistor from the video circuit, does the final circuit have the ground, video out, 3.3 k resistor, and the capacitor all connected at the same point?

Here take a look at this. This should make more sense. The piece in the center is the Transistor. Transistors are pin-specific, you have to pay attention to which pin goes where. If you're looking at the Transistor, label facing you:

 

1. The RIGHT pin gets soldered to +5v and one leg of the 2.2k resistor.

 

2. The CENTER pole of the Transistor gets solderd to the other leg of the 2.2k, the video in from teh 7800 mohtherboard RF, and one leg of the 3.3k resistor. The other leg of the 3.3k goes to ground.

 

3. The LEFT leg of the Transistor is your video output. This goes to the center pole on the RCA Video output jack. You can take the ground connection for the outer ring of teh RCA jack straight from the 7800 Motherboard Ground.

This may sound like a stupid question but say if the pins are soldered the wrong way round then would it effect the display say make it darker?

 

If I'm not mistaken, the transistor is directional, meaning that if the pins are soldered "backwards" then you will not receive a signal at all. If you have video, then I think you have your circuit built correctly; however, there may be a bad solder somewhere in the circuit or on the board. Did you change the resistor at R11 to a 47k Ohm? If so, a bad solder at this point could definitely cause you mucho problemos. Also, after pouring through the original puppetmark post, it appears that keeping or removing the Rf modulator is motherboard specific. If your connection at R11 is good, and it appears that your video circuit is properly soldered, then you may have to remove the Rf modulator to eliminate all Rf interference with your circuit. Again, I haven't even gotten my circuit built yet, so everything I've written could be complete hogwash and I wouldn't know it.

[Underball]

So do these mods make a big difference? I run my 7800 with a monster heavy gauge rca cable on the female rf connector to an adapter to go into the coax on my vcr then from the vcr left right and video outputs to my 7.1 surround system and then to a 50"plasma for picture. I play with the bass sub cranked to 10 and the picutre and sound seems flawless. After you guys have done these mods in comparision to your setup was it a big upgrade? I only have one 7800 and by the sounds of things the mod seems far from flawless with mixed results, with the problem of several types of systems and pictures that are too bright or too dark.

You have to use a a VCR to connect it. This mod eliminates that need. It allows people to connect their 7800's to newer TV's that lack RF connections, without having to keep a big klunky VHS machine around just for that. It also eliminates 100% of the RF noise/interference you would get from using the standard 7800 RF out (which you still get going through a VCR). It also tightens up the picture so colors aren't smeared like they are using RF.

 

I have mine connected to a 65" DLP and it looks glorious. before I modded it I used the RF connection and it was absolutely terrible.

 

So yeah, it's worth not having to keep 3 other outdated TV/Stereo components laying around my gaming room, just to be able to connect it to my TV.

[Underball]

So, if I omit the 75 ohm resistor from the video circuit, does the final circuit have the ground, video out, 3.3 k resistor, and the capacitor all connected at the same point?

Here take a look at this. This should make more sense. The piece in the center is the Transistor. Transistors are pin-specific, you have to pay attention to which pin goes where. If you're looking at the Transistor, label facing you:

 

1. The RIGHT pin gets soldered to +5v and one leg of the 2.2k resistor.

 

2. The CENTER pole of the Transistor gets solderd to the other leg of the 2.2k, the video in from teh 7800 mohtherboard RF, and one leg of the 3.3k resistor. The other leg of the 3.3k goes to ground.

 

3. The LEFT leg of the Transistor is your video output. This goes to the center pole on the RCA Video output jack. You can take the ground connection for the outer ring of teh RCA jack straight from the 7800 Motherboard Ground.

This may sound like a stupid question but say if the pins are soldered the wrong way round then would it effect the display say make it darker?

 

If I'm not mistaken, the transistor is directional, meaning that if the pins are soldered "backwards" then you will not receive a signal at all. If you have video, then I think you have your circuit built correctly; however, there may be a bad solder somewhere in the circuit or on the board. Did you change the resistor at R11 to a 47k Ohm? If so, a bad solder at this point could definitely cause you mucho problemos. Also, after pouring through the original puppetmark post, it appears that keeping or removing the Rf modulator is motherboard specific. If your connection at R11 is good, and it appears that your video circuit is properly soldered, then you may have to remove the Rf modulator to eliminate all Rf interference with your circuit. Again, I haven't even gotten my circuit built yet, so everything I've written could be complete hogwash and I wouldn't know it.

TThis is all correct, and likely the problem. My first few times doing it, I had similar problems. I was clumsy with the soldering iron, and contacts go smeared too close to others. This is especially important on that Luma Resistor Ladder area of the board.

[yelever]

The rf module has been removed. I`ll have to go over the solder points sometime this week due to work. Didn`t change R11 as I went with the modified version of the mod. Just got 2 7800`s of ebay for 6 bucks and not sure if they work so I can mess about with them when they arrive. Will keep you guys updated when I check out the solder connections. I didn`t build the circuit on a board and just soldered to the motherboard which may make a difference which I may do on the next 7800. Also does the metal sheilding need to go back into 7800?

Edited September 13, 2010 by yelever

[Rex Dart]

I just modded two last night, and the metal shielding makes no difference.

[PSW]

Does the length of the hookup wire that i use to connect to the video input, the ground, and the +5V to the video circuit matter? I want to place the video circuit in the bottom left hand corner of the case, directly below the audio jacks.

[Underball]

Does the length of the hookup wire that i use to connect to the video input, the ground, and the +5V to the video circuit matter? I want to place the video circuit in the bottom left hand corner of the case, directly below the audio jacks.

not at all.

[yelever]

Just modded a second 7800 and still have the dark issue and it`s a different motherboard i.e. one with the exspantion port so not sure what to do. Still have an unmodded 7800 that shows the colours bright and clear. May just have to buy a tv monitor combo to play the unmodded 7800 lol

[Rex Dart]

Have you tried replacing that one resistor (R11 I think?) with a 100k potentiometer & adjusting the brightness? Not sure if it's R11, but it's discussed in that topic.

[yelever]

I went with the modified version of the mod where R11 was untouched. Would it have anything to do with motherboard versions?