183 replies to this topic

[Math You]

mimo, on Wed Sep 17, 2008 1:11 PM, said:

pepax, on Wed Sep 17, 2008 12:56 PM, said:

Math You, on Wed Sep 17, 2008 12:21 PM, said:

Bear in mind that the composite signal uses the French SECAM system so you'll need a multi-standard TV if composite is your only option. The RGB signal should work with PAL or SECAM tv's.

Fortunately I'm not stuck with the composite video. I didn't even realize it was there. What I had in mind was a composite video mod of the stock PAL machine.
The RGB video is nice....... on a classic CRT TV. For some reason, it's a lot worse on my LCD with a TV tuner.

Just found that out on my SECAM Colecovision, it really does not like my LCD tv despite the spec for the TV stating that it accepts SECAM and RGB (and a lot of other stuff)
Long live the CRT television

You might need to select SECAM or RGB from the TV's menu.

[Mitch]

Math You, on Wed Sep 17, 2008 3:21 AM, said:

pepax, on Wed Jul 9, 2008 7:36 PM, said:

I'm about to get a French (SCART-equipped) 7800 and I've been told that even the composite video looks better than this French RGB stuff... I wonder if it's really so bad.

The French 7800's use a 13 pin socket that carries both RGB and composite video.

Bear in mind that the composite signal uses the French SECAM system so you'll need a multi-standard TV if composite is your only option. The RGB signal should work with PAL or SECAM tv's.

Have you actually been able to get a composite picture out of it? I thought I had traced it out at one point and it was only composite sync.

Mitch

[Math You]

Mitch, on Wed Sep 17, 2008 5:50 PM, said:

Math You, on Wed Sep 17, 2008 3:21 AM, said:

pepax, on Wed Jul 9, 2008 7:36 PM, said:

I'm about to get a French (SCART-equipped) 7800 and I've been told that even the composite video looks better than this French RGB stuff... I wonder if it's really so bad.

Bear in mind that the composite signal uses the French SECAM system so you'll need a multi-standard TV if composite is your only option. The RGB signal should work with PAL or SECAM tv's.

Have you actually been able to get a composite picture out of it? I thought I had traced it out at one point and it was only composite sync.

Mitch

The picture on my portable colour TV was in black and white (and cyan?) so I assumed it was a composite signal. I found this diagram of the 7800 & ST 13 pin socket. Looks like composite isn't connected:
http://musepat.club.fr/atari78.htm

Edited by Math You, Sat Sep 20, 2008 6:17 AM.

[MrRetroGamer]

After reading through the entire thread, is it safe to assume that the instructions in post #14 are considered the "final" procedure? The reason I ask is that there was some additional fine tuning going on to address some issues after that, so I was just wondering before I started on the project? Thanks!

[PacManPlus]

I think so - I just recently (over this past weekend) did this to my second 7800 and it looks EXCELLENT!!!
The dark red and dark blue colors seem to bleed at bit much and the sound is a little distorted, but I can live with that. Could very well be the resistors I used (I didn't have some exact values so I used values that were close), or it could very well be the TV.

Over all, the mod is very simple and I plan on doing some other mods (like externalizing the 'Select' and 'Start' buttons through another connector & stuff).

I meant to post this earlier, but your post was a great segue.
Great job guys!

Bob

Edited by PacManPlus, Tue Sep 30, 2008 12:14 PM.

[ApolloBoy]

OK, I was able to redo the mod today, and made some changes from last time. This time, I built the whole circuit on a breadboard and replaced R11 with a 100K pot as per puppetmark's suggestion. I'm pleased to say that I'm now getting crystal clear video with no artifacting issues. Thanks for posting the mod puppetmark, this really does work!

[MrRetroGamer]

ApolloBoy, on Sat Oct 4, 2008 9:02 PM, said:

OK, I was able to redo the mod today, and made some changes from last time. This time, I built the whole circuit on a breadboard and replaced R11 with a 100K pot as per puppetmark's suggestion. I'm pleased to say that I'm now getting crystal clear video with no artifacting issues. Thanks for posting the mod puppetmark, this really does work!

Can you post a picture for the electronically challenged like me?

Are all these parts available at Radio Shack?

[puppetmark]

ApolloBoy, on Sat Oct 4, 2008 9:02 PM, said:

OK, I was able to redo the mod today, and made some changes from last time. This time, I built the whole circuit on a breadboard and replaced R11 with a 100K pot as per puppetmark's suggestion. I'm pleased to say that I'm now getting crystal clear video with no artifacting issues. Thanks for posting the mod puppetmark, this really does work!

That's great to hear! I am glad you got it to work. It makes the 7800 a real joy to play. I am sorry I haven't been able to get back to it. I found a bit of time to test a VGA converter on my 8-bits but that's it. I hope to have some more Atari time soon.

[puppetmark]

MrRetroGamer, on Tue Sep 30, 2008 12:35 PM, said:

After reading through the entire thread, is it safe to assume that the instructions in post #14 are considered the "final" procedure? The reason I ask is that there was some additional fine tuning going on to address some issues after that, so I was just wondering before I started on the project? Thanks!

The Instructions in Post 14 are the final procedure. HOWEVER, It looks like some people were having artifacting issues and replacing R11 with a 100K Potentiometer helped fix the problem as it allows for adjustment. The instructions in post 14 call for replacing R11 with a 47K resistor and you may want to just try that first then if you are having color artifacting problems, chnange it to a 100k pot.

I think you can get everything you need at radio shack but the 75 ohm resistors. 68 ohm resistors will work and Radio Shack sells the 1/2 watt version. Its a little big but it should work.

[ApolloBoy]

I guess maybe I spoke too soon, because now I've run into another problem, this time concerning carts with external audio. Whenever I play a game that uses external audio, the picture becomes slightly unstable and eventually the game crashes and goes to a brown screen. I'll see if I can get a pic of my circuit soon.

EDIT: I actually just got through playing Commando (which has external audio) and the game worked perfectly fine. It only seems to do the above with Ballblazer for some odd reason.

Edited by ApolloBoy, Fri Oct 10, 2008 11:02 PM.

[ericaesop]

great mod, it is so easy a caveman could do it(i watch to much tv lol)

[ericaesop]

whch audio mod do i use(i only know of saundby's) i dont have a nonpolar cap rated for 1uF. is there an alternative?

[Spazmonkey]

So, I just finished this, and it worked for a while. So when I went to close it up, I put the shielding back on and I think this may have caused a short or something. I replaced the transistor and still nothing. I checked the power supply with a multimeter, and it's still working fine. Any ideas?

[gdement]

I think the audio hookup can be simplified.
Below is a small section of the 7800 schematic:


Notice that the TIA audio and external (POKEY) audio are mixed through the appropriate resistors before reaching the expansion port connector (J2-17). Wouldn't it be simpler to take audio from there instead? Soldering to an unpopulated through hole at J2 should be much easier than the legs of 2 resistors, except for people who actually have an expansion port installed. You also don't have to duplicate the resistors in your own circuit.
You could almost just run a wire straight from J2-17 to the audio jack, except I suppose you'd still want a 0.1uF cap first.

My ohmmeter readings from J2-17 to C10 and C14 agree with the schematic so I think it's accurate. I haven't tried this yet, but when I mod mine I'm inclined to do it this way.

[Almost Rice]

gdement, on Sun May 31, 2009 5:35 PM, said:

You could almost just run a wire straight from J2-17 to the audio jack, except I suppose you'd still want a 0.1uF cap first.

I wanted to do this too, but I did not disconnect the RF modulator from the board. This leads the sound to interfere with the composite signal for me. Pulling R5 and R6 where it goes to J2-17 disconnects it from the mixing the sound into the RF. That also cleared up my composite signal. My RF signal still works except for the sound. I then solder the R5 and R6 ends together and connect it to the RCA jack.

[Spazmonkey]

Any ideas about my dilemma? Is there something that goes out easily? I would hate to have just finished the mod, had it working, then have been screwed over by that shielding plate.

[Rybags]

I would fear that you might have been screwed over.

I guess if you have an oscilloscope handy, you could check things like Sync output from the video chip to see if the system has any signs of life.

[Almost Rice]

Spazmonkey, on Mon Jun 1, 2009 12:48 AM, said:

Any ideas about my dilemma? Is there something that goes out easily? I would hate to have just finished the mod, had it working, then have been screwed over by that shielding plate.

Probably had something touch ground that should not have. Look at the board and see if anything is sticking out. Pay attention when putting the shielding on to see if any of your work comes close to the shield. Does the system work when you have the board out of the shield?

Edited by Almost Rice, Mon Jun 1, 2009 2:58 PM.

[Spazmonkey]

Almost Rice, on Mon Jun 1, 2009 12:57 PM, said:

Spazmonkey, on Mon Jun 1, 2009 12:48 AM, said:

Any ideas about my dilemma? Is there something that goes out easily? I would hate to have just finished the mod, had it working, then have been screwed over by that shielding plate.

Probably had something touch ground that should not have. Look at the board and see if anything is sticking out. Pay attention when putting the shielding on to see if any of your work comes close to the shield. Does the system work when you have the board out of the shield?

Not anymore, I've taken it out, plugged it into a power supply and the LED doesn't come on. I verified that the power supply is working too.

[Almost Rice]

Spazmonkey, on Tue Jun 2, 2009 4:19 PM, said:

Not anymore, I've taken it out, plugged it into a power supply and the LED doesn't come on. I verified that the power supply is working too.

Ok, I would start by getting a Ohmmeter and checking all your work(5v, video and sound) to see if any of those lines go to ground.

[Spazmonkey]

Almost Rice, on Wed Jun 3, 2009 7:11 AM, said:

Spazmonkey, on Tue Jun 2, 2009 4:19 PM, said:

Not anymore, I've taken it out, plugged it into a power supply and the LED doesn't come on. I verified that the power supply is working too.

Ok, I would start by getting a Ohmmeter and checking all your work(5v, video and sound) to see if any of those lines go to ground.

I've taken out the circuit, and the console still doesn't work.....

I'm just going to proclaim it dead, and get another one I suppose.

[PacManPlus]

gdement, on Sun May 31, 2009 6:35 PM, said:

I think the audio hookup can be simplified.
Below is a small section of the 7800 schematic:
7800audio.png

Notice that the TIA audio and external (POKEY) audio are mixed through the appropriate resistors before reaching the expansion port connector (J2-17). Wouldn't it be simpler to take audio from there instead? Soldering to an unpopulated through hole at J2 should be much easier than the legs of 2 resistors, except for people who actually have an expansion port installed. You also don't have to duplicate the resistors in your own circuit.
You could almost just run a wire straight from J2-17 to the audio jack, except I suppose you'd still want a 0.1uF cap first.

My ohmmeter readings from J2-17 to C10 and C14 agree with the schematic so I think it's accurate. I haven't tried this yet, but when I mod mine I'm inclined to do it this way.

Hi!

I actually tried that circuit and I get no audio. Nothing.

I think, however, that I may have found a slightly easier form of this mod, for people who do not plan on using their RF modulator any more:

• Remove R3 *only*
  
• Remove RF modulator, but leave the connector soldered to the board (see picture)
  
• Obtain a Floppy power connector, or a CD-Rom audio connector
  
• For Audio, solder a wire to *both* R5 and R6 at the bottom of the resistors (closest to the joystick ports)
  
• Ground, +5 Volts, and The Composite signal are all part of the connector to the RF module

Layout of RF connector:

---
|o| - No Connection
|o| - Video Signal
|o| - +5 v
|o| - Ground
---

Use the same circuit as described in the prior posts. I was able to use a 68 ohm resistor instead of a 75 ohm with success (I didn't have a 75 ohm resistor handy)

NOTE - I was lucky enough where didn't have to change R11 to 47K, it looked good to me. Your mileage may vary, though.
For the audio, the Pokey Music will by lower in volume to the TIA sounds. Again, this is acceptable to me, as the background music in a game *should* be lower than the game sounds.





This way, the cable can just be plugged into the jack (the cables can be made first and tested on a known working one).

What do you guys think?

Bob

Edited by PacManPlus, Sat Jul 18, 2009 6:51 PM.

[puppetmark]

PacManPlus, on Sat Jul 18, 2009 7:49 PM, said:

gdement, on Sun May 31, 2009 6:35 PM, said:

I think the audio hookup can be simplified.
Below is a small section of the 7800 schematic:
7800audio.png

Notice that the TIA audio and external (POKEY) audio are mixed through the appropriate resistors before reaching the expansion port connector (J2-17). Wouldn't it be simpler to take audio from there instead? Soldering to an unpopulated through hole at J2 should be much easier than the legs of 2 resistors, except for people who actually have an expansion port installed. You also don't have to duplicate the resistors in your own circuit.
You could almost just run a wire straight from J2-17 to the audio jack, except I suppose you'd still want a 0.1uF cap first.

My ohmmeter readings from J2-17 to C10 and C14 agree with the schematic so I think it's accurate. I haven't tried this yet, but when I mod mine I'm inclined to do it this way.

Hi!

I actually tried that circuit and I get no audio. Nothing.

I think, however, that I may have found a slightly easier form of this mod, for people who do not plan on using their RF modulator any more:

• Remove R3 *only*
  
• Remove RF modulator, but leave the connector soldered to the board (see picture)
  
• Obtain a Floppy power connector, or a CD-Rom audio connector
  
• For Audio, solder a wire to *both* R5 and R6 at the bottom of the resistors (closest to the joystick ports)
  
• Ground, +5 Volts, and The Composite signal are all part of the connector to the RF module

Layout of RF connector:

---
|o| - No Connection
|o| - Video Signal
|o| - +5 v
|o| - Ground
---

Use the same circuit as described in the prior posts. I was able to use a 68 ohm resistor instead of a 75 ohm with success (I didn't have a 75 ohm resistor handy)

NOTE - I was lucky enough where didn't have to change R11 to 47K, it looked good to me. Your mileage may vary, though.
For the audio, the Pokey Music will by lower in volume to the TIA sounds. Again, this is acceptable to me, as the background music in a game *should* be lower than the game sounds.





This way, the cable can just be plugged into the jack (the cables can be made first and tested on a known working one).

What do you guys think?

Bob

I removed R5 and soldered a connection at C10 for Pokey Audio. I know some people have had trouble with the audio but I have done this to two different 7800s and I have full audio. Perhaps its a different board revision that doesn't match the schematic I used. anyway, Keeping R5 is what keeps the Pokey audio lower in your version which is fine if you like that. 68 ohm resistors are fine in place of 75 ohms. I do like your cable idea though

Edit: One more thing, If you do not remove the modulator, R5 and R6 should be removed or the "bottom" legs pulled up from the board because the audio will still be feeding into the RF modulator and cause intereference with the composite video signal. you can actually solder the lifted ends together and take the audio signal from there if you wish. Almost Rice wrote about this in an earlier post.

Edited by puppetmark, Wed Jul 22, 2009 10:02 PM.

[alex_79]

Hi!

I fixed a PAL 7800 with a broken rf modulator using this mod and I can confirm that it works fine on PAL machines.
I couldn't use the PAL schematics here on AtariAge because they refers to a different revision board than mine, but I found the right one on this site. There are some errors but I was able to identify the video circuit component on my console.


I used the instructions on post #14 for the video part and those on post #90 for the audio.
The brightness was ok, so I didn't change the resistor in the luma circuit, while there were some slight interferences in the video in the form of diagonal lines which disappeared after cutting the base of the audio oscillator transistor.
There's still some video noise in 7800 mode. The mod described here will probably fix the problem but I haven't tried it because I basically use the console for 2600 games only.

Here are some pics to help identify the components on the board and the procedure I used:


- remove resistor R62 (or cut one of the lead).
- cut the 4 pins of the rf modulator. The 3 pins from the bottom are Ground, Power (+5V) and Video.
- desolder or cut only the right ends of R33 and R32 from the board, then solder them together and connect to the center pin of the audio rca jack.
- build the circuit posted by puppetmark on post #14 and connect it to the board and to the video rca jack.
- connect the ground wires to the outer housings of the rca jacks
- cut the base of Q8 transistor or remove it (optional. reduces interferences in composite video).

I hope this can help people to mod their PAL consoles.


P.S. sorry for my bad english.

[AdeptRapier]

Hey, thanks for posting this great mod on Atariage.

I am SO doing this mod to both of my 7800's as soon as I get moved into my new place next week and can unpack. I guess I'll probably replace all the caps on my other 7800 too as long as I have the thing open and am screwing around inside it!