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Atari 7800 mod board using LHE and Stereo audio out


ReilyReed91218

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With LHE's board on Electronic Sentimentalities is finally not restocked and apparently not being sold any longer, I decided to design a 7800 Mod Board out of drunkenness since I wanted to mod my 7800, and since LHE's idea of dropping the board into a chip socket was ingenious, I took the idea and ran. This 7800 Mod board will do the same, however, it's SMD. And I noticed a discrepancy when testing an LHE mod board before in the TS5. Which, to sum up, he swapped the two connections on NC and NO of the TS5... I think any ways since I get vertical bars on my other 7800 that uses LHE's board design. So that's swapped. Also, as some may not know the TIA chip is entirely responsible for audio output in the 7800 and there is no MARIA output on sound. So I'm grabbing TIA13 & TIA12 directly from the TIA chip. This also allows for stereo mixing with a pot, and I overlayed the potential for POKEY sound on top of both audio lines with some simple 47K resistors (did no testing but the values should work). This was really just a night project that I designed because I was drunk, bored, and trying to kill an evening.

Need user feedback on the board just to see if I should release at all. Thanks.

 

 

Screenshot 2021-09-13 022846.png

untitled 2.png

Edited by ReilyReed91218
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If anyone wishes for the EAGLE parts I made for this project, you can find them attached below. If you don't understand the TS5 symbol, then read the datasheet. Still dubios on releasing board or shchematic. But I'll definitely think about it. If anyone could, they could try hooking me up with a manufacturer, don't want to govern or make money from it terribly badly, but it might serve the community. Let me know and do look at the board. I need feedback on it's design.  

74_Logic_Series.lbr FMS64XX (contains all FMS derivatives).lbr Texas_Instruments_Logic.lbr

Edited by ReilyReed91218
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Just remembered this piece, there is no 75 ohm termination or pulldown on output of video. I did this, to save space pretty much. If you feel your picture is a tad too bright or needs these resistors. Then, just put the impedance in-line with the output of the board and bend the resistors down between grounding and input on the RCA jacks. 

Just remembered this revision btw, it was just a few capacitors changed to 1uF and DIP. But, it still was a good revision. Just wanted to post about it. Was slightly different than the latest. AND I also was going to make a DIP version because some of us hobbyists aren't trained in SMD soldering. That to come later. Just need feedback, to see what peoples interest in these Atari boards with schematics that are a little older. Not many alts are made anyways. 1060749597_board2.thumb.png.09b5d599da04d049e18658e7565b7281.png

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I never liked the LHE design as it never addressed the bleed over from the TIA colorburst interfering with the Maria color when playing 7800 games. As a result, it required installing a switch inline of that TIA9 pad so that when playing 7800 games you could completely kill the color signal from the 2600 causing the issue. But worse was the severe color bleeding from the LHE on darker hues on 7800 games and the odd doubling of images/ghosting what have you on the edges of many 2600 games. 

 

The UAV corrects for nearly 95% of these issues with the remaining issue being the still slight color bleed on darker hues. Now almost completely corrected with an additional 4050 added to slightly delay the Maria color input to correct its timing better.

 

The audio portion of this is what really needs to be tested, because the common stereo conversion will either require the pokey to be hard set to left or right or doesn't work properly with the Dragon Fly cart. Additionally, if you are going to create a board with the Stereo mod in place for the TIA chips, then you need to include a method for mono for those that either don't like the way the stereo sounds (Such as myself), or for those in PAL land whose TIA chips only have a single audio output line from the chip.

 

Also, doing a MOD like this requires you to remove the RF and other components which, the UAV does not require thus allowing you to keep the RF intact and fully working along with the composite and s-video it can provide. It is really handy to still have the RF on hand should you run into issues with the upgraded video board during installation or in the future.

 

 

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  • 2 weeks later...
On 9/13/2021 at 8:22 AM, -^CrossBow^- said:

I never liked the LHE design as it never addressed the bleed over from the TIA colorburst interfering with the Maria color when playing 7800 games. As a result, it required installing a switch inline of that TIA9 pad so that when playing 7800 games you could completely kill the color signal from the 2600 causing the issue. But worse was the severe color bleeding from the LHE on darker hues on 7800 games and the odd doubling of images/ghosting what have you on the edges of many 2600 games. 

 

The UAV corrects for nearly 95% of these issues with the remaining issue being the still slight color bleed on darker hues. Now almost completely corrected with an additional 4050 added to slightly delay the Maria color input to correct its timing better.

 

The audio portion of this is what really needs to be tested, because the common stereo conversion will either require the pokey to be hard set to left or right or doesn't work properly with the Dragon Fly cart. Additionally, if you are going to create a board with the Stereo mod in place for the TIA chips, then you need to include a method for mono for those that either don't like the way the stereo sounds (Such as myself), or for those in PAL land whose TIA chips only have a single audio output line from the chip.

 

Also, doing a MOD like this requires you to remove the RF and other components which, the UAV does not require thus allowing you to keep the RF intact and fully working along with the composite and s-video it can provide. It is really handy to still have the RF on hand should you run into issues with the upgraded video board during installation or in the future.

 

 

Thanks for the info. I swapped around the inputs on the TS5 switching chip, and that, theoretically, should prevent the need for a switch between TIA pin 9 and the board. Technically, according to the datasheet, the most common connection should be connected to NC (or normally closed) when inputting on the TS5. But I didn't know if output on the 74LS174 Pin 5 was high or low when in 7800/2600 mode. So I needed someone to test that for me. I thought LHE had gotten it wrong due to the datasheet though so I swapped it.

 

Also, you mention Stereo to Mono output. I'd just use a potentiometer, input and output on same pin, to short the connection between stereo and mono. And, just as with LHE's board, you won't get any output on the RF modulator, once the 74LS32 is gone. 

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Ahh but see I like to keep the Rf intact whenever possible and I prefer something doesn't require removing anything off the board to use it. The UAV is that. Additionally, the LHE design boards of which one is still being sold on Ebay under Winzmod is still more expensive than the UAV cost wise and doesn't produce nearly as good of a result.

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