27 replies to this topic

[atari2atari]

Greetings, Atarians.  I have a vexing problem I would appreciate some assistance on.


I've been having myself a good time installing a batari/longhorn engineer designed 7800 video board into my personal "keeper" 7800 unit.





I purchased it from "electronicsentimentalities," a member here who has taken batari/longhorn's open-source design and crafted some nice boards:

http://electronicsen...led%20Mods.html

And, his instructions are quite easy, too:

http://electronicsen...structions.html


The installation is done, and sound and video head on out the composite and S-video jacks as expected . . .

. . . but I'm getting those pesky, rolling diagonal lines that others have talked about in the past!


The diagonal rollers show up in both the composite AND the S-video outputs.  It DOESN'T show up in 2600 mode, only 7800.


I have done my research, and tried multiple things in an attempt to solve the problem - -

• Detached the 4-pins that go to the RF modulator (the above picture shows them as attached; they are no longer)
  
• Removed the Q8 transistor (as was suggested here: http://www.made-by-b...101&t=842#p3415 )
  
• Removed the Q1 transistor (from the AtariAge 7800 FAQ: "In order to prevent the audio from interfering with the video signal, the mixing oscillator must be disabled on the main circuit board. On a 7800, remove the base lead of Q1. It is located near the RF modulator." [click on text to link to page]

So far, no luck!


This post cryptically offers some advice - -

http://www.atariage....ost__p__1543423

"I disconnected the audio from the video in order clear up the diagonal lines. Where it is disconnected I added a cap to amplify the audio. Where did you get the audio signal?"

But I could not determine exactly what was meant . . . !  Maybe I already did that by removing some of the transistors


And, this post also offers some hope . . .

http://www.atariage....ost__p__1524023

"I had to disconnect at R3 to remove all interference to the composite signal."

But again, I am not certain what is meant?  I am going to have to go look for "R3" on the board after I post this!



Does anyone have some advice?

The picture is great - - nice and crisp, no shadows, but those diagonal rollers, especially on a dark background, are VERY noticeable!

Thanks SO much for any and all ideas!!

-a2a

Edited by atari2atari, Tue Feb 28, 2012 11:07 PM.

[Lendorien]

I had some issues with my Longhorn mod when I first got it. I can't recall exactly what it was, but it ended up being a chip on the board itself was not soldered correctly.

[LittleJoe]

The best way I know how to get rid of the 7800 mode diagonal interfence is to cut the wire (install a manual swtich) from the TIA 9 connection to the mod board.   Disconnect it temporarily and give it a try.

[atari2atari]

Thanks!

I will try disconnecting the TIA 9 wire and report back with the results!

Over here at the famous "Saundby mod" page, he discusses buffering the TIA 9 with a resistor - -


http://saundby.com/a...mod_theory.html

He uses a 1.2Kohm resistor, to be exact.

I might try that buffer first before resorting to a physical switch, and see if that cleans it up!

-a2a

[evg2000]

Don't want to hijack the thread but has anyone had an issue with some home-brews not working with the LH7800 video mod?  A few games I have don't work on my longhorn 7800 but work on others.

[atari2atari]

evg2000, on Wed Feb 29, 2012 7:08 PM, said:

Don't want to hijack the thread but has anyone had an issue with some home-brews not working with the LH7800 video mod?  A few games I have don't work on my longhorn 7800 but work on others.

Any and all are welcome!  Don't worry, I won't go all Harrison Ford "Airforce One" on you for hijacking . . .



I have not tried homebrews on my 7800 - - are you referring to 7800 'brews, or 2600, and which ones?  There is indeed a LONG history of various 2600 games not working with the 7800.  Some have to do with the placement of certain resistors and capacitors, which can be fixed and compatibility restored (DECATHALON, SPACE SHUTTLE, etc.) and some have to do with incompatibilities with the "late model" 2600 TIA chips used in the 7800, such as KOOL-AID MAN!

Don't know about 7800 compatibility, tho . . .

ANYways - -

LittleJoe, on Wed Feb 29, 2012 10:22 AM, said:

The best way I know how to get rid of the 7800 mode diagonal interfence is to cut the wire (install a manual swtich) from the TIA 9 connection to the mod board.   Disconnect it temporarily and give it a try.

I clipped the TIA 9 line on the board tonight, and, yes, no interference in 7800 mode anymore.

Not wanting to have ANOTHER switch to flip on the unit (I already have one on the back to flip on/off the capacitor for 2600 DARK CHAMBERS / certain ACTIVISION title compatibility), I decided to try a few resistors as was mentioned here - -

atari2atari, on Wed Feb 29, 2012 10:32 AM, said:

Thanks!

I will try disconnecting the TIA 9 wire and report back with the results!

Over here at the famous "Saundby mod" page, he discusses buffering the TIA 9 with a resistor - -

Capture.JPG
http://saundby.com/a...mod_theory.html

He uses a 1.2Kohm resistor, to be exact.

I might try that buffer first before resorting to a physical switch, and see if that cleans it up!

-a2a

- - and see what happened.


- So, the 1k-ohm resistor on the TIA 9 line made for some strange hues and washed out colors in 2600 mode - - but no diagonal lines in 7800 mode!

- The 2k-ohm resistor made the 2600 mode black and white

- And, a 330 ohm resistor looked somewhat normal in 2600 mode, and no diagonal lines in 7800 mode!

That was all the resistors I had on hand, so I will obtain some more very low resistance ones tomorrow and keep trying.  Looks like just a minimal buffer is all that is needed to clean up that interference and carry on without adding in extra switches and levers!



Thanks, everyone, keep the ideas flowing, if you have them!

-a2a

Attached Thumbnails

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Edited by atari2atari, Wed Feb 29, 2012 9:14 PM.

[evg2000]

atari2atari, on Wed Feb 29, 2012 9:13 PM, said:

I have not tried homebrews on my 7800 - - are you referring to 7800 'brews, or 2600, and which ones?  There is indeed a LONG history of various 2600 games not working with the 7800.  Some have to do with the placement of certain resistors and capacitors, which can be fixed and compatibility restored (DECATHALON, SPACE SHUTTLE, etc.) and some have to do with incompatibilities with the "late model" 2600 TIA chips used in the 7800, such as KOOL-AID MAN!

Don't know about 7800 compatibility, tho . . .

Games that don't work for me:
Space Duel, Super Pac-Man, Jr. Pac-Man, and Pac-Man collection

Edited by evg2000, Wed Feb 29, 2012 11:44 PM.

[Deteacher]

I just picked up this mod from electronicsentimentalities today.  I plan on putting it in this weekend.  Hopefully I won't have the issue with the diagonal lines because I won't know how to change/add resistors/transistors.  I'll post my results once I get it installed.

[atari2atari]

Deteacher, on Thu Mar 1, 2012 10:01 PM, said:

I just picked up this mod from electronicsentimentalities today.  I plan on putting it in this weekend.  Hopefully I won't have the issue with the diagonal lines because I won't know how to change/add resistors/transistors.  I'll post my results once I get it installed.

Yes, please do let me know!

I was VERY happy with the quality of the board, the online instructions, and the ease of installation - - I think you will be, too.

The diagonal lines might not be noticeable to some people, but once I personally saw them, I couldn't stop seeing them!


This weekend I have to pick up some low-resistance (like, 100 Ohm and 10 Ohm or even less) resistors  from my local electronics shop, and I will report back with how that works.


If that DOES prove to be the fix, it will be VERY simple to do, Deteacher - - no more complex than the desoldering of resistors from the 7800's motherboard that are required to install the board in the first place.  The additional resistor will just attach at the "TIA 9" point on the video mod board, and then you will attach the TIA 9 wire to that resistor!  Simple!

I'll post my results on Sunday or Monday.

-a2a

[Deteacher]

atari2atari, on Fri Mar 2, 2012 6:58 AM, said:

Deteacher, on Thu Mar 1, 2012 10:01 PM, said:

I just picked up this mod from electronicsentimentalities today.  I plan on putting it in this weekend.  Hopefully I won't have the issue with the diagonal lines because I won't know how to change/add resistors/transistors.  I'll post my results once I get it installed.

Yes, please do let me know!

I was VERY happy with the quality of the board, the online instructions, and the ease of installation - - I think you will be, too.

The diagonal lines might not be noticeable to some people, but once I personally saw them, I couldn't stop seeing them!


This weekend I have to pick up some low-resistance (like, 100 Ohm and 10 Ohm or even less) resistors  from my local electronics shop, and I will report back with how that works.


If that DOES prove to be the fix, it will be VERY simple to do, Deteacher - - no more complex than the desoldering of resistors from the 7800's motherboard that are required to install the board in the first place.  The additional resistor will just attach at the "TIA 9" point on the video mod board, and then you will attach the TIA 9 wire to that resistor!  Simple!

I'll post my results on Sunday or Monday.

-a2a

That's good to know.  Can't wait to dig into the project.  

Actually, I have a 7800 with this mod installed (did it myself about a year ago) but the 7800 games only show up in B/W (2600 games look GREAT!)  I contacted Parker (LH, himself) and he offered to fix it for me, since it appears to be a problem with the board.  I'm going to swap that out with this new one and see if that brings color to the 7800 games.  Then I can simply send the bad board back to him for repair (rather than send the whole console to him.)  If I still get B/W with the new board, then I know there's something screwy with the console and I'll install the new board in my other 7800.

I love tinkering, so it's going to be a fun weekend for me.  

[atari2atari]

Deteacher, on Fri Mar 2, 2012 9:57 AM, said:

That's good to know.  Can't wait to dig into the project.  

Actually, I have a 7800 with this mod installed (did it myself about a year ago) but the 7800 games only show up in B/W (2600 games look GREAT!)  I contacted Parker (LH, himself) and he offered to fix it for me, since it appears to be a problem with the board.  I'm going to swap that out with this new one and see if that brings color to the 7800 games.  Then I can simply send the bad board back to him for repair (rather than send the whole console to him.)  If I still get B/W with the new board, then I know there's something screwy with the console and I'll install the new board in my other 7800.

I love tinkering, so it's going to be a fun weekend for me.  

So, how did your modding go, Deteacher?



Sadly, it's GAME OVER for me and the electronicsentimentalities board.

I think that right off the bat the board was having video output issues due to a defective solder point or trace - - I could always get sound out output of the card, but the video output would only pop into view when I slightly bent the board in a certain way!

I checked all my solder points on the motherboard and my IC socket, but since I could always reproduce the video on/video off by slightly flexing the board, I think it was the board.

Now, with this last round of soldering and tinkering, I think I fiddled the board to death or finally completely broke whatever trace was bad.  No matter what I do, I get zero video output, on either the 7800 or 2600 mode.  I get sound, though, so something is making it through!

Bummer!

I will have to get in touch with LittleJoe and see what he would charge for a repair of this board.  Seems a pity to have come this far and then stop!



Was your setup okay?  Do you see diagonal lines?

-a2a

Edited by atari2atari, Tue Mar 6, 2012 11:42 AM.

[Deteacher]

I just got around to working on it today at work...I installed the board, but I forgot to bring a test cart with me (duh!)  I will bring it home and fire it up and post my results.

BTW, I've never tried before, but should I get any output on a 7800 with no cart in the slot?  Will the Atari logo screen come up?

[atari2atari]

Deteacher, on Tue Mar 6, 2012 12:50 PM, said:

I just got around to working on it today at work...I installed the board, but I forgot to bring a test cart with me (duh!)  I will bring it home and fire it up and post my results.

BTW, I've never tried before, but should I get any output on a 7800 with no cart in the slot?  Will the Atari logo screen come up?

Hey that's nifty, glad you get to do that at work!

Someone else may chime in, but I think you get the usual black screen on the 7800 with no cartridge.

I also installed this EXCELLENT European mod from BEST ELECTRONICS, though, and so now when I boot with no cartridge, I get ASTEROIDS!

http://www.best-elec...m/7800.htm#Euro

I was (relatively) easy to install, and worked amazingly well!  I was able to confirm that before the video output on the mod board went out . . .  

Cool, well, let us all know how it goes once you get it home and test it!

-a2a

Edited by atari2atari, Tue Mar 6, 2012 1:16 PM.

[iesposta]

I started my 7800 Longhorn mod from LittleJoe electronicsentimentalities today Tue., May 6, 2012.
This is the first I've heard about this problem.
Sorry to hear your board went.
I'll let you know how mine turns out.
I'll have to look up the resistor values that were removed. Maybe you can use one of those?

Anything will be an improvement.  Compared to all the other ways I have to play 2600, this has the worst output and sound! And yes I adjusted the sound coil and the RF adjustment. I didn't touch those pots that are glued in place though.

[Deteacher]

Well, things are going from bad to worse.  Here's the deal:
1.  I replaced the "what I thought was bad" LHE board with the new one I just got.  Remember, I had perfect color and clarity in 2600 mode, but only b/w in 7800 mode.  After replacing with the new board, now everything is in b/w.  So I'm not so sure that the original board is/was bad.  I must have done something wrong on the motherboard.  Next:

2.  I put the old board back in place...the 7800 powers up, but I get NO VIDEO SIGNAL AT ALL.    Seems the more I mess with it, the worse I make things.  I'll have retrace my steps, but I don't know what I could have done wrong.  Everything is wired properly.

Now, I still have an untouched 7800.  I may try to mod that one with the new board...you know...start from scratch.  But I'm thinking I may have to take this to someone who can do it for me...as much as I hate to do that.  Hey iesposta, I see you're from PA.  How close are you to Northern DE?  

Edited by Deteacher, Tue Mar 6, 2012 6:33 PM.

[Underball]

Not to be a stick in the mud, but in nearly every case I've seen in here, Longhorns mod is plagued with problems.

Why not save yourselves the time and aggravation and jus do the "easier composite mod" from these forums? It's >$5 worth of parts and takes about 10-15 minutes to assemble and install, and the picture quality is stellar. Easily as good if not better than Longhorns.

[Deteacher]

Underball, on Tue Mar 6, 2012 6:49 PM, said:

Not to be a stick in the mud, but in nearly every case I've seen in here, Longhorns mod is plagued with problems.

Why not save yourselves the time and aggravation and jus do the "easier composite mod" from these forums? It's >$5 worth of parts and takes about 10-15 minutes to assemble and install, and the picture quality is stellar. Easily as good if not better than Longhorns.

The only issue I have with that mod is that I don't know how to build the video amplifier from the schematic.  I don't know how to read it.  If someone could post a "for dummies" procedure for building the amplifier, I could probably handle the rest.  

[iesposta]

Just guessing here, but since the motherboard is double sided and the removed chip should have holes that are plated through to both side of the motherboard, maybe it's not 100% soldered to the circuit (top) side. That may explain moving the board to get video / no video.
Removing that chip is potentially damaging and I would check those pin connections in the new socket ( both top and bottom ) visually first. I don't know enough to know if a continuity checker would hurt any chips or not. I have flowed solder to the top by heating the top (under) side of the socket and applying solder just to be a bit  more sure that contact is made with the new socket. I could have caused damage, but it's not finished so I don't know yet.

I just started my 7800 mod, and didn't get to finish it. The socket is in, resistors removed, 4 wires attached so far.
I installed the Longhorn mod from LittleJoe in my 2600a 4 switch no problem, but this 7800 is a little bit harder due to desoldering / removing parts.

[atari2atari]

Underball, on Tue Mar 6, 2012 6:49 PM, said:

Not to be a stick in the mud, but in nearly every case I've seen in here, Longhorns mod is plagued with problems.

Why not save yourselves the time and aggravation and jus do the "easier composite mod" from these forums? It's >$5 worth of parts and takes about 10-15 minutes to assemble and install, and the picture quality is stellar. Easily as good if not better than Longhorns.

I'm almost to that point, Underball, I'm almost there . . .  :-)

iesposta, on Tue Mar 6, 2012 7:20 PM, said:

Just guessing here, but since the motherboard is double sided and the removed chip should have holes that are plated through to both side of the motherboard, maybe it's not 100% soldered to the circuit (top) side. That may explain moving the board to get video / no video.
Removing that chip is potentially damaging and I would check those pin connections in the new socket ( both top and bottom ) visually first. I don't know enough to know if a continuity checker would hurt any chips or not. I have flowed solder to the top by heating the top (under) side of the socket and applying solder just to be a bit  more sure that contact is made with the new socket. I could have caused damage, but it's not finished so I don't know yet.

I just started my 7800 mod, and didn't get to finish it. The socket is in, resistors removed, 4 wires attached so far.
I installed the Longhorn mod from LittleJoe in my 2600a 4 switch no problem, but this 7800 is a little bit harder due to desoldering / removing parts.

Thanks, ieposta!  That was my guess, too, that the solder and/or traces were not exactly "right" and just got damaged somewhere along the way while I was working.

I will talk to LittleJoe and see what he would charge to repair the board, or I may try reflowing it myself.

Glad to hear the 2600 video mod goes smoothly, I have a few of those to do here soon!

-a2a

[iesposta]

I meant the 7800 motherboard and the empty socket, not parts on the mod board. Sorry if I wasn't clear.

[atari2atari]

iesposta, on Tue Mar 6, 2012 8:53 PM, said:

I meant the 7800 motherboard and the empty socket, not parts on the mod board. Sorry if I wasn't clear.

Ah, no worries, I understand!

Sadly, I think it all goes back to the video mod board - - I have been careful with the 7800 motherboard and the traces all are good there.

I'll be able to confirm that soon, however, when I socket back in the 4001 NOR chip and ensure the output still functions as expected.  I'll update the thread when I do!

-a2a

[Deteacher]

Well, I'm sending my unmodded 7800 off to someone to do the easier composite mod for me.  Money well spent!  I'll continue to tinker with the other 7800 and the 2 LHE mod boards.  I think I'll take it all apart and start from scratch.  As of right now, I can't possibly do more damage because I'm getting no signal at all, so there's nowhere to go but up from here.  

[iesposta]

atari2atari,
I finished wiring my mod. The 7800 output S-video is beautiful and rich. Noticed some diagonals on Ballblazer with the brown start screen.
Did you REMOVE Q1!?? That could kill your video output. You are supposed to cut the base (center) lead. I did this and noticed no difference, but when I was wiggling around Q1 the video went out.
Also Q8 is on a PAL board or maybe a different version board. (near the tall red tube coil).  I'm quite sure IT IS Q1 and again, just cut the center lead, don't remove it.
I'm so frustrated that home-brews Beef Drop VE 7800 still has graphic horizontal banding dropout glitches, same before and after this mod, and Scramble doesn't work at all, after a scrambled (ha ha) Atari 7800 boot screen.  I never tried it before I modded this system, so I don't know if it worked stock. Home brew Moon Cresta works just fine, go figure...
Now the 2600 is disappointing. Still better than RF, but not rich like a Heavy Sixer. Very washed out. There is also slight vertical banding, unlike longhorn's 2600 mod board.
If things don't improve with a cart socket cleaning and with the use of the XM when it arrives, I'll have to get another one to mod or just sell all of it off.

[ApolloBoy]

I installed the LHE board on my 7800 and I also had interference problems with mine. In my case, I wired a switch for the TIA chroma so I could disconnect it when playing 7800 games. I'm still getting interference with 2600 games, so I'm thinking installing a switch for the MARIA chroma might help.

[Deteacher]

both of my systems are off in the mail to be modded/fixed by folks who know what they're doing.  I'm so grateful that there are so many people willing to help us not-so-savvy individuals.