easier 7800 Composite video mod

[+chriswhit]

I just did this mod. Wow what a difference my picture is awesome. I put my parts on a board for looks but followed post 14 to a t. Sweet mod.

[+chriswhit]

Is there any way to have sound through the rf module to. I'm only wondering because I have a dev. system and may use this somewhere that doesn't have a composite hookup. The original rf still works but looks terrible compared to the composite video. I probably don't need sound to dump roms but would be cool to have.

[PSW]

Has anyone tried this modification with the original version of the 7800 that has the expansion port installed on the motherboard. My issue is that the expansion port is occupying the spot where the 5V connection is to be made. Is there another 5V spot I can connect to, if so where is it? Does anyone have a solution to this? Furthermore, are there any differences between my motherboard version, and the motherboard used for the modification in this thread that would cause problems once modified? I'm an electronics newbie, so please be gentle with your response.

[+chriswhit]

Has anyone tried this modification with the original version of the 7800 that has the expansion port installed on the motherboard. My issue is that the expansion port is occupying the spot where the 5V connection is to be made. Is there another 5V spot I can connect to, if so where is it? Does anyone have a solution to this? Furthermore, are there any differences between my motherboard version, and the motherboard used for the modification in this thread that would cause problems once modified? I'm an electronics newbie, so please be gentle with your response.

 

Mine has the expansion port. I hook the 5v off the rf input. There are 4 metal prongs side by side that hook into the rf module. the one on the top is what I used. Post #16 third pic down. I followed post 14 to a t except I took the 5volts where they did in post 16 and I also took my vidio from there to. It worked great. The pic is not so clearin the post. if you cant make it out let me know. I have a nice digital camera that's made for doing photos like that.

[PSW]

Has anyone tried this modification with the original version of the 7800 that has the expansion port installed on the motherboard. My issue is that the expansion port is occupying the spot where the 5V connection is to be made. Is there another 5V spot I can connect to, if so where is it? Does anyone have a solution to this? Furthermore, are there any differences between my motherboard version, and the motherboard used for the modification in this thread that would cause problems once modified? I'm an electronics newbie, so please be gentle with your response.

 

Mine has the expansion port. I hook the 5v off the rf input. There are 4 metal prongs side by side that hook into the rf module. the one on the top is what I used. Post #16 third pic down. I followed post 14 to a t except I took the 5volts where they did in post 16 and I also took my vidio from there to. It worked great. The pic is not so clearin the post. if you cant make it out let me know. I have a nice digital camera that's made for doing photos like that.

 

I guess I should have read a little further. Did you keep the Rf connectors intact (did not cut them), and simple solder onto those connections? Also, did you use the ground on the Rf or did you use the side tracer? Could you post some pictures? Unfortunately, I'm so new to electronics, that I need a good picture to reference, or I'll screw this thing up pretty good.

[+chriswhit]

I left the rf connectors intact on mine so at a later date I can still use the rf if I need to. Just solder the connection to them. I used the ground on the side trace but you can use ether. To me it was easier to solder the ground there (more room). I will post some pics some time tomorrow.

[Shawn]

Nevermind, it was a junk transistor.

[Underball]

Ok,

 

So I just got a new Samsung LCD TV for gaming and hooked up my "easier composite modded" 7800 to it and it looked like crapola.

 

So I went ahead and changed out r11 from the suggested 47k resistor to a 100k pot. Better, the lines got tighter and most of the ghosting went away, but my issues now are color saturation and tint/hue issues.

 

When I turn the 100k pot to the point where ghosting goes away and lines (specifically Pac-Man collection) tighten up nicely, the color saturation starts to fade away. Also the tint appears to skew a bit green. I'm assuming this is because cranking up the 100k pot is allowing more luma into the signal. I'm wondering is there is somewhere else in this mod or on the 7800 board itself where I can replace a chroma/color saturation resistor with a potentiometer to adjust the chroma now back up to compensate for the loss of color?

 

Puppetmark? Almost Rice? Anyone? Bueller?

Edited February 16, 2010 by Underball

[Underball]

Ok,

 

So I just got a new Samsung LCD TV for gaming and hooked up my "easier composite modded" 7800 to it and it looked like crapola.

 

So I went ahead and changed out r11 from the suggested 47k resistor to a 100k pot. Better, the lines got tighter and most of the ghosting went away, but my issues now are color saturation and tint/hue issues.

 

When I turn the 100k pot to the point where ghosting goes away and lines (specifically Pac-Man collection) tighten up nicely, the color saturation starts to fade away. Also the tint appears to skew a bit green. I'm assuming this is because cranking up the 100k pot is allowing more luma into the signal. I'm wondering is there is somewhere else in this mod or on the 7800 board itself where I can replace a chroma/color saturation resistor with a potentiometer to adjust the chroma now back up to compensate for the loss of color?

 

Puppetmark? Almost Rice? Anyone? Bueller?

 

So after a little digging I found another old 7800 video mod sight which details which resistors are which signals on the 7800 mobo. Apparently, the 7th resistor from the left is the 7800 chroma signal at 4.3k, and the 8th is the 2600 chroma at 4.7k.

 

I'm going to experiment and replace each of them with a 10k pot and adjust it to see if any added chroma will even things out.

 

I'll let you know tonight whether it works out.

[Underball]

Ok,

 

So I just got a new Samsung LCD TV for gaming and hooked up my "easier composite modded" 7800 to it and it looked like crapola.

 

So I went ahead and changed out r11 from the suggested 47k resistor to a 100k pot. Better, the lines got tighter and most of the ghosting went away, but my issues now are color saturation and tint/hue issues.

 

When I turn the 100k pot to the point where ghosting goes away and lines (specifically Pac-Man collection) tighten up nicely, the color saturation starts to fade away. Also the tint appears to skew a bit green. I'm assuming this is because cranking up the 100k pot is allowing more luma into the signal. I'm wondering is there is somewhere else in this mod or on the 7800 board itself where I can replace a chroma/color saturation resistor with a potentiometer to adjust the chroma now back up to compensate for the loss of color?

 

Puppetmark? Almost Rice? Anyone? Bueller?

 

So after a little digging I found another old 7800 video mod sight which details which resistors are which signals on the 7800 mobo. Apparently, the 7th resistor from the left is the 7800 chroma signal at 4.3k, and the 8th is the 2600 chroma at 4.7k.

 

I'm going to experiment and replace each of them with a 10k pot and adjust it to see if any added chroma will even things out.

 

I'll let you know tonight whether it works out.

 

this definitely helped. much like putting a 100k pot instead of the 47k resistor on R11, adding a 10k pot instead of the 4.4k resistor on the 7800 chroma (R16) and adjusting cleaned the signal up even more.

 

I just wish I could squeeze a little more color saturation out of it.

[Underball]

Figured the color saturation bit. Not a big deal just needed to find the right luma/chroma balance with the two pots.

 

Now what I'd like to be able to add is a tint/hue control to this video amp circuit. As it is, the red/green ratio is off by about 25% toward green. On any set I connect it to, if I put the tint setting at 75%/25% adjustment towards red (to the right), everything looks perfect. but at 50%/50% dead even, it skews very green on some games, especially Commando and Pitfall II. The Browns appear more green than brown.

 

What would I need to do to add basic tint/hue control to this circuit so that I don't have to adjust it on my TV? I ask this because I have all of my old game systems connected using composite video on a switch box, and when I switch over to my Sega Master System, all the reds are too pink, and greens are washed out.

 

and no - the tint control pot already on the 7800 motherboard doesn't help. That pot adjusts overall Blue/Yellow hue control, and has no effect on Red/Green bias.

[primeform]

Are any of you guys that, whom have done this mod a few times already, willing to do mine for a fee? If so please hit me up with a private message thanks!

Edited February 20, 2010 by primeform

[vb_master]

I decided to start on this project today while I had my 7800 open to replace the BIOS or whatever with a DevOS v0.2 EPROM. Here's my results of the board. I used 1/4" Forstner bits to drill holes for the RCA ports onto the case, plus plugged the RF hole up with a section of plastic carved to fit. I took a quick picture of the mobo for now until my 74LS04 and 28 pin machined DIP socket arrive.

[vb_master]

Sorry for the double post, got my DIP socket and 74LS04 today, put them together and found the video scrolling as described in some other posts. I moved the video input and the +5v over to the RF pins and it works absolutely perfectly. I had one of the third gen models with the expansion totally missing and the hole in the case gone, so that might explain it?

 

Also in the pic you can see the plugged in RF section I made out of spare 7800 textured plastic.

 

Thanks everyone in the thread - got my 7800 modded just the way I want.

 

Just waiting on the SRAM and 74LS02 from Jameco and a Hat Trick cart to make into a flashcart.

Edited March 1, 2010 by vb_master

[NeilTheDruid]

I just did this mod on a PAL model just like in alex_79's post. Everything seems to have gone fine except for on major issue. My cart slot doesn't work anymore! :/ I get either complete blackness of may be slight diagonal fuzz. Anyone got any idea what I've done?

[unhuman]

Just waiting on the SRAM and 74LS02 from Jameco and a Hat Trick cart to make into a flashcart.

 

Ummm... I don't know about this.... Could you link me to the right place? Thanks!!!!

[NeilTheDruid]

I just did this mod on a PAL model just like in alex_79's post. Everything seems to have gone fine except for on major issue. My cart slot doesn't work anymore! :/ I get either complete blackness of may be slight diagonal fuzz. Anyone got any idea what I've done?

 

Nevermind, I figured it out

[robertski]

FROM UNDERBALL

Now what I'd like to be able to add is a tint/hue control to this video amp circuit. As it is, the red/green ratio is off by about 25% toward green. On any set I connect it to, if I put the tint setting at 75%/25% adjustment towards red (to the right), everything looks perfect. but at 50%/50% dead even, it skews very green on some games, especially Commando and Pitfall II. The Browns appear more green than brown.

 

 

----------------------------

 

If anyone wants to see this mod really shine, here is

what I did./

 

I ran the signal through a Sima Go-Video and Radio Shack

Video color processor.

 

Setting the Burst level a little low, I can then

Play games which are too bright by setting the Sima

for Lowered brightness, OR play games that are too

dark on the BRIGHTEN setting...

 

Both units should be available on the E6ay ..

 

Hope that helps someone who has these units around

and never thought to use them,

 

Rob/

[jmetal88]

I just tried this out. It looks decent on 7800 games for me, but on 2600 games I get 'ripples' through the video. Any idea what might be causing that?

 

EDIT: Actually, I get the ripples on the 7800 video as well, they just move more slowly and are much less noticeable.

Edited May 15, 2010 by jmetal88

[Curt Vendel]

Anyone try tapping the CVIDEO signal on Pin 31 on the cartridge port?

[Almost Rice]

I just tried this out. It looks decent on 7800 games for me, but on 2600 games I get 'ripples' through the video. Any idea what might be causing that?

 

EDIT: Actually, I get the ripples on the 7800 video as well, they just move more slowly and are much lesIs noticeable.

 

 

Did you disconnect the audio signal from the rf modulator? That was one of the first problems I encountered

Edited May 15, 2010 by Almost Rice

[jmetal88]

I just tried this out. It looks decent on 7800 games for me, but on 2600 games I get 'ripples' through the video. Any idea what might be causing that?

 

EDIT: Actually, I get the ripples on the 7800 video as well, they just move more slowly and are much lesIs noticeable.

 

 

Did you disconnect the audio signal from the rf modulator? That was one of the first problems I encountered

 

I removed R3, if that's what you mean. I also completely removed the modulator from the circuit board, as I wanted to mount the composite jack in its place.

 

IIRC, the audio causes diagonal lines, right? I'm not getting those. On my capture card, it looks like the video is gently swaying back and forth, and on my TV I see horizontal bands of varying brightness moving up the screen, with the video 'bending' at the brighter parts of the picture.

 

EDIT: I took a short video of Dig Dug doing this with my capture card. I could try to upload it somewhere if you're struggling to picture what I'm trying to describe

 

EDIT 2: I screwed around with the resistors a little and got a slightly more stable picture out of the 2600 side, but the 7800 side still looks the same. What I did was remove the 75 ohm and 2.2k resistors, and moved the 3.3k resistor so it connects between the base and the collector.

Edited May 15, 2010 by jmetal88

[jmetal88]

Actually I just hooked it up to a cheaper capture device with an entirely different result. Perhaps my 7800 is putting out a bad horizontal sync signal or something?

 

Anyway, on the cheaper device I get what appears to be a stable picture, overlaid with a diagonal outline of the same picture that cycles quickly so as to appear that it's constantly moving to the left.

 

EDIT: Sorry, it's actually moving to the right.

 

So, you experts out there, what part of my 7800 needs fixing, and why was the picture stable when hooked to RF tuners?

Edited May 15, 2010 by jmetal88

[jmetal88]

So apparently, I have to re-post rather than being able to edit my old posts after a certain period of time.

 

I'm beginning to suspect my power supply may be the issue. I'm using a rather cheap 3rd-party 2600 power adapter I have hooked up to the board through an earphone cable, which might be causing problems in the video amplification circuit or perhaps somewhere else on the motherboard. I guess I'll have to do some testing to see if that's the issue.

 

EDIT: Yep, that was totally the problem. I just stole a power cord off my other 2600, an official Atari-branded AC adapter, and the video problems went away like magic.

 

I'll have to put the circuit back together in the original way now I guess to see which way I like better, 3 resistors or 1.

 

EDIT 2: On my TV, the 1-resistor version looks better, oddly enough, but on my capture card the 3-resistor version looks best. Since I'll probably be playing using my capture card more often than using my portable TV, I'll build the original version of the amp.

Edited May 15, 2010 by jmetal88

[gdement]

Glad you've pretty much sorted it out. Actually I think you're lucky it works as well as it does on your capture card.

My capture card has major "dot crawl" problems with my NES, and it couldn't sync to an svideo 7800 I was experimenting with.

 

The signal from old game consoles probably violates NTSC spec, and I think some modern devices don't tolerate it as well as an old CRT television. If something doesn't work on a capture card, don't worry too much until you've tried a TV.