easier 7800 Composite video mod

[Underball]

Also - this seems like a problem more ont eh PAL consoles than NTSC. I haven't seen any of that.

 

Ok, I had a 4 x 2 input NAND chip lying around, so I made a buffer out of that. The vertical banding has gone, now just the dot crawl remains. This might be due to my LCD tv (though I've not experienced it on other consoles to the same extent).

can you post part numbers and a circuit layout/picture of this?

 

I'm curious how this would behave in an NTSC 7800.

[CongoZombie]

Also - this seems like a problem more ont eh PAL consoles than NTSC. I haven't seen any of that.

 

Ok, I had a 4 x 2 input NAND chip lying around, so I made a buffer out of that. The vertical banding has gone, now just the dot crawl remains. This might be due to my LCD tv (though I've not experienced it on other consoles to the same extent).

can you post part numbers and a circuit layout/picture of this?

 

I'm curious how this would behave in an NTSC 7800.

 

I'll try, but the board layout of the PAL rev C 7800 is quite a bit different to the NTSC layout

[Rex Dart]

Just got a new 7800 this week, and after having experimented the living crap out of this mod on my old one, I'v posted some updates to Puppetmark's instructions for this mod that make it both EVEN EASIER, and much clearer video:

 

 

Just to make sure I've got this correct before I start soldering... you've left out both of the original mod's 47K to 68K resistors, and where it originally included a 75 ohm resistor, you're simply not making that connection?

[alex_79]

can you post part numbers and a circuit layout/picture of this?

 

I'm curious how this would behave in an NTSC 7800.

 

I'll try, but the board layout of the PAL rev C 7800 is quite a bit different to the NTSC layout

The mod (which is described here) consists in buffering the pal color clock signal which goes from TIA pin 8 to MARIA pin 3 (PAL consoles have 2 oscillators, while NTSC only have one). This is done by removing resistor R74 and connceting TIA pin 8 to a buffer and then through a 1k resistor to MARIA pin 3.

 

PS

In my previous post about the mod on PAL 7800 there's an error: you must desolder or cut the LEFT (not right) ends or R33 and R32 from the board. (The picture is correct, anyway).

[ApolloBoy]

For those that have performed this mod, have any of you had problems with Ballblazer? The last time I did this mod, Ballblazer would crash on me and I still don't know why. I ask since I'm thinking of doing this mod again, this time on my unmodded 7800.

[Underball]

Just got a new 7800 this week, and after having experimented the living crap out of this mod on my old one, I'v posted some updates to Puppetmark's instructions for this mod that make it both EVEN EASIER, and much clearer video:

 

 

Just to make sure I've got this correct before I start soldering... you've left out both of the original mod's 47K to 68K resistors, and where it originally included a 75 ohm resistor, you're simply not making that connection?

No.

 

What I did was not change anything on R11 at all.

 

You need to remove R3 to clear up the static of the audio in the video signal, but you don't need to change R11 at all. You will get the exact same color/brightness values as those from the factory RF connection (therefore it's a more accurate mod) by doing this, but with none of the RF noise.

[Rex Dart]

 

What I did was not change anything on R11 at all.

 

You need to remove R3 to clear up the static of the audio in the video signal, but you don't need to change R11 at all. You will get the exact same color/brightness values as those from the factory RF connection (therefore it's a more accurate mod) by doing this, but with none of the RF noise.

 

 

Right right, bad choice of words on my part. I was trying to ask if instead of replacing R11 with a 47K Ohm (step 3) and connecting a 47K Ohm to C14 (step 6), you simply did nothing & left both 47K resistors out of your mod.

 

As far as the the 75 Ohm on the video plug though... what's going on with your revision? No connection there, right? That's what I assume, as it seems it would short out the video signal to ground, but I only have a basic understanding of A/V electronics.

Edited August 31, 2010 by Rex Dart

[Underball]

 

What I did was not change anything on R11 at all.

 

You need to remove R3 to clear up the static of the audio in the video signal, but you don't need to change R11 at all. You will get the exact same color/brightness values as those from the factory RF connection (therefore it's a more accurate mod) by doing this, but with none of the RF noise.

 

 

Right right, bad choice of words on my part. I was trying to ask if instead of replacing R11 with a 47K Ohm (step 3) and connecting a 47K Ohm to C14 (step 6), you simply did nothing & left both 47K resistors out of your mod.

 

As far as the the 75 Ohm on the video plug though... what's going on with your revision? No connection there, right? That's what I assume, as it seems it would short out the video signal to ground, but I only have a basic understanding of A/V electronics.

 

Correct. No need for the 47K at all.

 

and the 75ohm doesn't short out the signal, but it introduces a bunch of ghosting/smearing, especially on games with solid filled backgrounds like Pole Position II. It's better left out, and if you want to tweak the brightness down a touch, just put a 15ohm (or thereabouts) resistor after the transistor output on it's way to the center contact of the Video out RCA jack.

[yelever]

Just got a new 7800 this week, and after having experimented the living crap out of this mod on my old one, I'v posted some updates to Puppetmark's instructions for this mod that make it both EVEN EASIER, and much clearer video:

 

 

*UPDATE*

7-8-2008; I have updated the instructions to include the POKEY audio fix and a resistor change that will bring down the brightness so light collored objects are not over-driven. Here is the info for the mod:

 

Parts List:

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

2.2k 1/4 watt resistor

3.3k 1/4 watt resistor

75 ohm 1/4 watt resistor No longer needed.

47K to 68K 1/4 watt resistor

47K resistor (optional) No longer needed.

2n2222 or 2n3904 transistor

1uf capacitor.

2 RCA jacks

hook up wire

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

 

Procedure:

 

1. Open up the 7800 and remove the metal shield.

2. Locate R3 and remove it. This is a good time to drill two holes and install the RCA Jacks. I installed mine facing down on the edge of the case.

3. Locate R11 and replace it with a 47K resistor. This is optional but it cuts down the brightness a bit. I didn't have this problem on my magnavox monitor but on my TV some light collored characters were over-driven. I found that this was counterproductive, and made tme mod more susceptible to minor interference. Leave the original 38k Resistor at R11 where it is.

4. Cut the pins that connect the Video modulator to the board. (don't do this if you ever think you will use the RF out in the future) De-solder the pins from the RF unit's connecting board and bend them back using pliers. leave them intact. Then, de-solder the RF unit from the bottom of the board and remove it. (again, less interference is the goal, plus more room to work.)

5. Build the circuit in the schematic.* Edit: DO NOT include the 75ohm resistor between the ground and the video output from the transistor. This causes severe ghosting on certain games with solid, light color-filled backgrounds like the grey roadway in Pole Position II and the blue water in Frostbite. I just soldered the parts together then soldered the transistor's collector to the 5V connection on the expansion bus connector. The connection is the third point from the bottom on the right side. I made my ground connection by soldering the resistors to the edge of the board. I then ran a small wire to the video connection on the expansion bus connector. It is much cleaner and easier to get +5v and video input from the middle two pins on the RF unit. Pin 2 (closer to where the RF unit was) is video input. Pin 3 is +5v. As PacManPlus pointed out, using an old floppy connector is great here, since you won't have to solder to the pins, just plug it in. Makes for easier removal of the motherboard later on too, for cleaning or more mods/work. Finally I ran a yellow wire to the RCA jack. this worked well for me but it may be easier for some to build the circuit on a small piece of PC board such as Almost Rice did. (I built mine on a board as well.)

6. I connected a resistor to the bottom of C14. This is the audio out. Any resistor value between 47K and 68K should be fine. The other end of the resistor goes to the RCA connector Now clip the top connection (towards the back of the unit/cart cup) of R5 and R6, but leave the bottom connected to the motherboard. Solder the two clipped end together, and then attach a 1uf capacitor between the two soldered together ends and the center pole of the audio RCA jack. This will give you both standard TIA audio and Pokey audio for games that have that.

7. Run a wire from the top of C10 to the audio jack. This is the POKEY audio. I actually made the connection by running a wire from C10 to where the audio jack connects to the resistor I added for the audio output.

8. I connected the ground wires to the RCA jacks and connected the other end to the ground trace on the edge of the board.

9. Put the 7800 back together and enjoy the clean video and audio!

 

Here are some pics that will help explain:

 

Here is the upgrade. You can also see where I cut the RF modulator pins:

 

Here is a close up of the resistors to be removed:

 

 

Here is the Amplifier Schematic:

 

Here is the amplifier installed in the 7800. The only solder points to the board are the 5V, ground, and the video in signal:

 

Here is the audio connection:

 

Here is where to make the POKEY connections:

 

Here is a close up of the C10 connection:

 

Here is a close up of the connection point to the RCA jack:

 

Here is a closeup of the RCA connectors:

 

Here is another view of the RCA connectors:

 

 

Enjoy!

 

Doing this mod right now but getting confused on the where R6 is located. Also read somewhere that +5v is located on pin 1 and not pin 3 as want to make sure and not mess the board up. Thanks in advance.

[yelever]

Found where R6 is but still not sure about the +5v pin is

[Rex Dart]

Got a multitester/voltmeter?

[yelever]

Got a multitester/voltmeter?

A friend has

[yelever]

Does the board have to plugged in and turned on? Sorry for the newbie questions.

[CongoZombie]

Does the board have to plugged in and turned on? Sorry for the newbie questions.

 

Yes. Plug in the 7800 board, then put the ground probe (the black one) onto a ground source. (The easiest is probably the thick silver line around the board that connected to the shielding). Then just test each pin with the red probe.

[Underball]

I have two 7800's and they are different motherboard revisions, and I get different results depending upon where I take +5v from. My newer one takes it from pin 3 of the RF connector. Picture is beautiful. My older one takes it from the expansion connector. When I tried to take it from the expansion connector in my new one, I got a weak, static-y picture. Same thing on me old one when I tried it on pin 3 of the RF.

 

Using a multimeter might be less than effective in testing how the mod will perform. My suggestion would be to put ti all together, and solder all the relevant connections to the board except for the +5v. Use a decent enough length of wire for the +5v connection, and simply test both connection points to see which gives better results. Your'e not going to hurt anything by trying different options.

[yelever]

Thanks for the help. I`m personally not doing the mod as my soldering skills arent up to standard so getting a friend doing mine. All the resistors have been removed or clipped so just waiting to build the the stuff and get it in there nut he didn`t want to solder anything until he knew which pin was the +5v.

[Underball]

Thanks for the help. I`m personally not doing the mod as my soldering skills arent up to standard so getting a friend doing mine. All the resistors have been removed or clipped so just waiting to build the the stuff and get it in there nut he didn`t want to solder anything until he knew which pin was the +5v.

doesn't need to be soldered to the board to test it. just touch the bare wire end from where +5v should connect tot eh mod circuit to the two differnt points on the mobo, and see which one produces better results. trial and error.

[yelever]

Ok mod installed but for some reason the picture is very dark and murky. Tried pin 1 for the +5v and got nothing but get the dark and murky picture on pin 3.

[Rex Dart]

Man, I just completed (the revised version of) this mod and I've got mixed results. Solid colors look great, nice and solid and consistent, but edges between colors are pretty ghost-like. Also, the picture seems extremely motion-blurred. Ballblazer exhibits the blurring and ghosting pretty badly. Pixel colors seem to bleed over 2 to 3 pixels to the right. I can post a photo of my solderwork later, but does anybody have any ideas as to what's going on?

[Underball]

Man, I just completed (the revised version of) this mod and I've got mixed results. Solid colors look great, nice and solid and consistent, but edges between colors are pretty ghost-like. Also, the picture seems extremely motion-blurred. Ballblazer exhibits the blurring and ghosting pretty badly. Pixel colors seem to bleed over 2 to 3 pixels to the right. I can post a photo of my solderwork later, but does anybody have any ideas as to what's going on?

LCD, or CRT TV?

[Rex Dart]

LCD, or CRT TV?

 

Both, actually. 25" CRT and 42" LCD.

[Underball]

LCD, or CRT TV?

 

Both, actually. 25" CRT and 42" LCD.

Ok, well with this composite mod you will still see a tiny bit of smearing around some objects, and some NTSC artifacting with color going on (white lettering in One on One has green and red artifacts) but those are inherent to NTSC composite video. It should look better than the RF output did, re: color bleed/smearing. If it doesn't, there may be an errant solder blob somewhere making a bad connection.

[Rex Dart]

Well... crap. I guess it's time to pull out the magnifying glass and fluorescent lamp. Good thing I only put the RF shield back on one of the two systems I modded. Isn't it funny, though, that two systems with this mod are showing the same graphical problems on two different TVs? The only bit that looks better than RF are the nice solid interference-free colors, until you get to the edge & it bleeds onto the next color.

 

I'll check this when I get home, but what're the chances of faulty resistors in my mod causing this? I didn't actually test them before soldering, just assumed the color codes were accurate. Maybe I've got off-brand transistors? I'd like to post the parts I used & a photo maybe, if anybody could take a look later.

Edited September 14, 2010 by Rex Dart

[Underball]

Well... crap. I guess it's time to pull out the magnifying glass and fluorescent lamp. Good thing I only put the RF shield back on one of the two systems I modded. Isn't it funny, though, that two systems with this mod are showing the same graphical problems on two different TVs? The only bit that looks better than RF are the nice solid interference-free colors, until you get to the edge & it bleeds onto the next color.

 

I'll check this when I get home, but what're the chances of faulty resistors in my mod causing this? I didn't actually test them before soldering, just assumed the color codes were accurate. Maybe I've got off-brand transistors? I'd like to post the parts I used & a photo maybe, if anybody could take a look later.

post photos.

 

I doubt it's the resistors.

[ramdass]

HELP!

 

I tried doing the Underball mod on my 7800. Didn't get any output at all. Tracing back my steps I found a mistake on the video side. So I tried to see if I could just get audio output first. I don't see that I've done anything wrong here. Here's a pic:

 

 

I removed R3 by desoldering; lifted the rear legs of R5 and R6, soldered them to one lead of the capacitor and ran the other lead to the tip of the audio out jack, with the sleeve soldered to the ground on the edge of the board. Anybody see anything wrong here? I've checked the underside of the board for solder problems, and tried pulling signal from the back lead of the capacitor, from the bottom legs of R5 & 6. Nothing. In the pic it looks like the capacitor lead might be touching the top leads of the yellow resistors, but its not.

 

As you can see, I removed the RF modulator, but I hooked it back up via a short cable with a floppy connector (c.f. PacManPlus). I still get video out via RF, but no audio either via RF or the line out mod.

 

I have not yet tried returning R3 R5 and R6 to original config, and seeing if that yields audio at the RF out. I may have lost R3.

 

Can anybody give me more info on the audio circuit of this mod? What does removing R3 do? What does detaching the upper legs of R5 and R6 do? (That disconnects the audio from the RF modulator among other things, right? Anything else?)

 

Of course, any other tips on how I might get line audio out working would be welcome. This is an NTSC 7800. Board model C025233-002 REV A. There is no expansion port, though there are unused solder points labeled J2 forward of the RF modulator.

 

Thanks for reading, and more thanks if you have suggestions.