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Atari 7800 composite video mod


thevnaguy

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Possibly, Looks like the simple video upgrade that you can find in these forums. Costs a couple of bux for the parts. I did that mod on my ntsc console. Results were not as good as I expected, colours washed out and lots of ghosting. I ripped it out and installed the v1 longhorn mod. Much better around but sadly no longer available. Much better than the problematic v2 mod imo

you could try the mod at circuit-board.de for pal systems.

Works great on my pal system, on crt anyway, like most of these mods on lcd and plasma screens its hit and miss

Edited by mimo
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  • 2 weeks later...

OK, I've had this for about a week and a half, but I finally got around to installing it.

Don't judge image quality by picture quality.

I took a really bad pic (this was the best of the ones I took. ;-) ). But I wasn't bothering with lighting and macro and such; just wanted to get a pic.

 

7800_mod.jpg

 

I decided to take out the RF modulator (and channel switch) and since I have so many holes there, I mounted the RCA jacks there.

I just cut out the piece of plastic between where the switch and the RF jack was.

Then I cut a little piece of plastic I had lying around and put some holes in it.

That plastic I have there now isn't permanent (I got the red jack a bit higher than the others), but it works.

Nothing is glue'd or screwed in yet, so I can fix it pretty easily.

 

All in all, I'm pretty happy...

 

This means I'll be able to move my 7800 upstairs and use it a bit more...

 

desiv

p.s. Funny story (and I can't believe I didn't remember). When I got it working, I wanted to test the pokey sound. I have a CC2 cart. As the 7800 is downstairs (RF only), I haven't used it much recently. But, knowing I was going to mod it, I also bought a BallBlazer cart so I could remove the pokey and put it in my CC2. So, I get the mod done, and I try BB.. I have music! Yay..

Hmm.. What does it sound like without a pokey? I pop in my CC2 and try it... er... um.. The same?? Uh.. um..

I open my CC2.. Yep.. Apparently when I got it, I put in a pokey and forgot in the mean time.. D'oh!! ;-)

Edited by desiv
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  • 3 months later...

Just a heads up if anyone else reads this thread and gets this mod.

 

I'm still happy with it, but when I was trying Pokey games "other" than BallBlazer, I noticed that the Pokey volume level was too low.

When I had the volume up high enough to hear the Pokey sounds, the game (TIA) sounds were way too loud.

It was especially painful with Commando....

 

What I ended up doing was adding a 10k trim pot on the line going from the TIA audio to the RCA jacks.

I have my trim pot set at about 7.80 (according to the multimeter).

 

Judging by some youtube vids, I still have the TIA louder than Pokey, but I kind of like the music (Pokey) quieter than the game sounds (TIA). I'm not "an electronics guy" so don't quote me on whether this is a good idea or if the values are right.

 

Just a heads up in case you get this mod.

 

desiv

p.s. Lesson learned. Test with more than just one game (BallBlazer in this case). :-)

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Its a 1701, but sure..

However I'm a terrible one to ask. My wife always says I have an 8 color palette.

 

To the point, I can't really tell your 3 pics apart. They look the same to me.

But I can tell you they don't look like my screen.

The maze in mine looks much more orange (or peach or ???).

 

The more I look at them (especially looking at all 3 at the same time), the more I think I can tell them apart. They appear to be getting lighter, left to right.

But it looks like they would have to keep going before they match what I'm seeing.

 

Of course, I could have my 1701 set wrong....

I don't think I've tweaked the dials on it since I got it..

 

desiv

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Its a 1701, but sure..

However I'm a terrible one to ask. My wife always says I have an 8 color palette.

 

To the point, I can't really tell your 3 pics apart. They look the same to me.

But I can tell you they don't look like my screen.

The maze in mine looks much more orange (or peach or ???).

 

The more I look at them (especially looking at all 3 at the same time), the more I think I can tell them apart. They appear to be getting lighter, left to right.

But it looks like they would have to keep going before they match what I'm seeing.

 

Of course, I could have my 1701 set wrong....

I don't think I've tweaked the dials on it since I got it..

 

desiv

 

No biggie...Just curious...Thanks for checking. Happy gaming! :grin:

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I'll try to get a good pic tomorrow.

Basically, the trim pot is a small device with a knob on top and 3 pins on the bottom.

I disconnected the TIA wire at the RCA center post.

I soldered the "center" pin of the trim pot to the RCA center post.

Then I soldered the TIA wire to one of the other two pins on the trim pot.

(Actually I soldered the wire to the trim pot first and then the trim pot to the RCA center post.)

 

desiv

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OK, here it goes.

I tinned both the wire and the pins on the trim pot before I attached them.

Now that I look at it, that wire attached to the trim pot might need a better solder, but it felt solid.. Oh well, I'm still learning the soldering well thing. ;-)

 

trimpot.jpg

 

Basically, the white wire is the TIA audio out from the 7800 comp mod board (middle wire, it was red originally but I replaced the whole wire).

The red wire you see is the Pokey feed (from the top of C10). So they both go to the RCA audio center post, but the wire from the mod board goes to the trim pot first.

 

You should be able to replace the trim pot with a resistor of the right rating. My trim pot is set at 7.8K OHMs currently.

I still think it's not quite right based on some youtube vids of Commando. The TIA is still a bit loud, but I prefer my game sounds a bit louder than the music anyway. Nice thing about the trim pot is I can go up to about 10K OHMs if I need to.

 

Remember tho, trim pots aren't designed for a lot of twisting. They dial has a limited number of turns. It's not as robust as a volume control. My trim pot is only accessible when the 7800 is opened up...

As you can see, I mounted my RCA jacks where the RF modulator was and not on the side of the case....

 

Good luck,

 

desiv

p.s. I still wouldn't mind someone who understands ratings on resistors and such suggesting actual values. I have no idea what the wattage should be???

The trim pot I have is a 0.1 watts.

Edited by desiv
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Okay, so it doesn't matter which leg of the pot gets soldered then, right?

 

I think I might go the pot route just so I can adjust the sound. I actually do want POKEY and TIA to be about equal, mainly because on Beef Drop the "you're out of pepper" indicator is via POKEY and dammit, I need to know. :)

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Okay, so it doesn't matter which leg of the pot gets soldered then, right?

Well, kind of. There are 3 legs. One is generally called the "center leg" (I did a lot of googling).

You want one end to be on the "center leg" and the other end to be either of the other 2 legs.

So, it almost doesn't matter, but you don't want to attach one end to each of those 2 legs. One needs to be on the "center leg."

 

If you have a multimeter, measure the resistance before you hook it up. You probably want yours all the way up to 10K.

I might try mine there (now that I have it open again), just to see...

It's possible that 10K will still be to low for you, in which case you'd need a bigger trim pot.

 

Also, I just measured resistance again, and I'm getting different numbers (around 5K??)... Not sure if it's because something is different when everything is connected (not powered on tho) or not.

**Based on the info below, it makes sense now..

 

However, I did twist it so that the TIA volume is much more even to the Pokey, and I see what you mean..

I don't think I ever heard the "out of pepper" sound before.. ;-) :-)

Thanx,

 

I wonder if that means that a 10k OHM resistor would be all it needs???

 

desiv

OK, just found this online:

 

Measure resistance when components are not connected in a circuit: It is always advisable not to measure the resistance of an item that is in a circuit. It is always best to make the measurement of the component on its own out of the circuit. If a measurement is made in-circuit, then all the other components around it will have an effect. Any other paths that will allow current to pass will affect the readings, making them inaccurate to some degree.

 

 

So, yeah it appears that my numbers are going to be "off" now that it's installed (unless I desolder the trim pot, which I am not planning on doing. ;-) ).

Edited by desiv
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If you've got a separate wire for pokey, how about setting up stereo sound from the TIA and then splitting the pokey to the L & R jacks? I'm wanting to do this with mine, but I'm not sure what I'll need (as for resistors & caps). There was someone who did it in a past thread, but never responded back with how he did it (he was a "hit it and quit it" poster).

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If you've got a separate wire for pokey, how about setting up stereo sound from the TIA and then splitting the pokey to the L & R jacks?

You mean like actual stereo from the TIA?

 

I've not looked into that. Are there any games that use actual stereo sound?

I suppose you could, but I'm not sure of the benefit. And if you're splitting game sounds to L/R that weren't designed for it, it might make those games sound off. I suppose if you did that, you'd want a switch to allow the TIA to be stereo OR mono on both channels.

Assuming you can get the stereo, the connections shouldn't be difficult. Although I'm not sure if you'd need some diodes to keep the channels separate once they were tied together.

 

There's only 1 audio line from the cart port, so the pokey (and or XM pokey/audio) will only be mono. (Unless you somehow pull the audio from the XM itself and not from the 7800..)

 

Interesting tho..

 

desiv

p.s. Although, my 7800 audio is going to the 1701 monitor, which is mono itself. I'd have to move it to one of my 1804s if I did that. ;-)

Edited by desiv
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Are there any games that use actual stereo sound?

 

Yep. Some commercial games and several homebrews (Medieval Mayhem for example). It's a known mod for the 2600, but everyone does mono for the 7800 because of the pokey.

 

Here's where the guy said he had it working for the 7800, but it sounded like he hadn't gone through with splitting the pokey. I'd like to know how to do that. Otherwise, I can only imagine having pokey through one side.

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Here's where the guy said he had it working for the 7800, but it sounded like he hadn't gone through with splitting the pokey. I'd like to know how to do that. Otherwise, I can only imagine having pokey through one side.

 

Interesting...

If that's the case, splitting the pokey should be simple, in theory. You might want to run each wire thru a diode as it attaches to the RCA so it doesn't use the pokey feeds to send TIA audio to the other channel.

In fact, you might need to add diodes to the TIA side as well, if you don't want the new pokey audio to go back down the TIA side. Not sure you'd need that, but possibly.

 

I say "in theory" tho because of the resistance.

I noticed when I was working on mine that disconnecting the TIA automatically increased the volume of the pokey. I'm thinking that's related to overal resistance in the circuit.

 

So this might also affect that in a similar way. No idea how to figure that out, other than hooking it up and seeing which side might need some resistance.

 

But I really only have a very basic understanding of this stuff..

 

desiv

Edited by desiv
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You might want to run each wire thru a diode as it attaches to the RCA so it doesn't use the pokey feeds to send TIA audio to the other channel.

In fact, you might need to add diodes to the TIA side as well, if you don't want the new pokey audio to go back down the TIA side. Not sure you'd need that, but possibly.

 

...But I really only have a very basic understanding of this stuff..

 

That's more understanding than I have on the subject. I'm going to really show my ignorance here: I only ever thought of diodes for power purposes. I never thought of them in audio. I'm skilled at installing things, but often not very knowledgeable in the "why."

 

Would these work?

Mouser general purpose diodes

Mouser current regulator diodes

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Diodes basically let whatever is in the line (it's all voltage really) go in only one direction.

So if you want to make sure that your left channel audio stays separate from your right and you hook up pokey to left and right, I think you might want a diode or two to keep the TIA audio from traveling along the pokey wiring and over to the other channel.

 

But, I could be wrong.. I just was thinking that its possible that the pokey line might bridge it... I'm not an electronics guy tho...

 

I do keep hoping that as I ramble about this stuff, someone who actually knows what he's talking about will step in, tell me where I'm totally wrong (as opposed to the rest which is only mostly wrong) and give some better pointers..

I know there's people on here who are good with electronics..

 

desiv

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  • 3 years later...

Sorry to necrobump this, but....FINALLY I got around to doing this. What I did:

 

- Cut the TIA wire between the mod and the RCA port

- Soldered the end of each of the two parts to a 10k trim pot

- Turned the trim pot to the right as far as it would go

 

Aaaand....success! POKEY and TIA sound perfectly balanced in Beef Drop! woohoo!

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  • 2 weeks later...

Sorry to necrobump this, but....FINALLY I got around to doing this. What I did:

 

- Cut the TIA wire between the mod and the RCA port

- Soldered the end of each of the two parts to a 10k trim pot

- Turned the trim pot to the right as far as it would go

 

Aaaand....success! POKEY and TIA sound perfectly balanced in Beef Drop! woohoo!

 

Lets see some pics :)

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  • 4 weeks later...

Happened to have a 10k pot laying sound and did the same to my 7800 the other day. Soldered one of the legs of the potentiometer directly to the RCA jack and works perfectly in balancing the sound. :love:

 

I've seen some mods now that include an extra resistor that do the same thing, but having a potentiometer is nice because you can tailor the balance to your prefs.

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