Jump to content
shear_xear

7800 with flickering interference

Recommended Posts

Hi everyone!  I have an Atari 7800 which I have installed a UAV mod on, and when I went to test the mod the 2600 games looks great, but when I turned on Pole Position II there is a flickering horizontal “rainbow” that seems to be interference of some kind.  I had recapped the three caps and replaced the power regulator.  I’ve noticed this before on previous composite mods with the “simple” mod kit, but it is more pronounced with the UAV.  I did check voltage across the board and everything appears normal.  Anyone have any ideas what might be happening here?  

B178ED55-9567-4502-AC79-0A29B961D94F.jpeg

Share this post


Link to post
Share on other sites

Can you provide a video to perhaps show this better?

 

Is it present on all 7800 games or just noticed with Pole Position II?

 

Also be curious to know if that rainbow you see is still present if you remove the TIA color wire off the UAV?

 

Can you also show pics of the UAV installation?

 

  • Like 1

Share this post


Link to post
Share on other sites

For some reason the videos don’t seem to show up.  Odd.  As far as other games, Ballblazer and Asteroids are wonky too.  Donkey Kong Jr seems fine.  Those are the only others I have tested so far.  

Share this post


Link to post
Share on other sites

No I can see the flickering line. I've not seen anything like that before. You've soldered to the correct alternate points just as I have been doing for the past year now instead of along the resistors but that doesn't matter in this case. You changed out the voltage regulator so that rules out power, removed the TIA color to verify that wasn't causing any interference. Does it do it with 2600 games? (have to attach the TIA color back in of course).

 

I wonder if the buffer IC above the maria is faulty? As I've never installed any of the other composite mods in 7800s, I've never seen this before in any of the ones I've done. Do you have another UAV board to slap in there in case that is the issue? It is rare, but I've had 3 UAV boards over the past few years give me some issues. One didn't produce any color and I was able to resolve it with some fresh solder to the SMD ICs on the UAV. Another gave me a darker colored band in the middle of the picture. That too was corrected with some fresh heat to the IC pins on the UAV and other places that looked like they could use a little more solder and the 3rd one I have now that produces a very dark overall picture that I've not figured out what is wrong with it but have spoken to MacRorie about it.

 

Share this post


Link to post
Share on other sites

Okay, so it’s definitely the 7800.  The new UAV gave the same results.  2600 games look great.  I also already swapped out every socketed IC on the board (which is everything including RAM and BIOS) just to be sure those were all good.  Which of the two ICs is the buffer (or is it both)?  

Share this post


Link to post
Share on other sites

It is the one on the left above the Maria and it isn't socketed. It is the 74LS32 chip and is actually a quad OR gate but I've had that go bad and cause some sync like issues before in the 7800. But if that didn't take care of it and a second UAV is doing it...

 

You swapped all the chips? What about the Maria if you have a spare? You said 2600 looks good and the Maria is really the only IC that is unique to 7800 game use. 

 

And last...have you tried a different TV?

Share this post


Link to post
Share on other sites

The Maria was the first one I swapped.  I will try another Maria just to be positive there.  Like I said, I have seen this before to a lesser degree with the simple mod, but probably only two times in four or five years, so out of dozens of 7800’s.  
 

Share this post


Link to post
Share on other sites

So new TV.  Same.  Replaced the buffer.  Same.  Swapped in a different Maria.  Same.  I even ran everything off the resistors to the UAV just to be sure.  This is the second one of these early 7800s that has some weird issue.  

Share this post


Link to post
Share on other sites

Well I've not had that be an issue but I guess you can't rule that out either. Try spritzing it with some contact cleaner and rotate it back and forth to the limits and then try to dial back in to see if it changes anything? Would be awesome if it was that simple, but with the exception of having to adjust that a few times for client consoles that were out of adjustment, I've not had to replace either color trimmer on the 7800.

 

  • Like 1

Share this post


Link to post
Share on other sites

I feel like this might still be power-related. . . you replaced the 7805 and the capacitors. . . if you haven't already, try a different power supply.

Share this post


Link to post
Share on other sites

I actually have tried two power supplies and had the same results.  I think it is somehow power related as well, but finding the source of the problem is becoming a pain.  Thanks!

Share this post


Link to post
Share on other sites

Is it possible you have a loose ground on the s-video jack itself in someway or it isn't making a good connection to the cable pins? I can sorta replicate the issue if I loosen the connections at the UAV to the s-video jack.

Share this post


Link to post
Share on other sites

Unfortunately this happens when using composite too.  Actually it’s worse when the composite is being used.  I have removed and then replaced all of the UAV leads as well and had the same results.  

Share this post


Link to post
Share on other sites

Sorry for my ignorance but I will ask.

Did this console use a RF modulator before AV mode ??

Did it haves this issue in RF mode?

Share this post


Link to post
Share on other sites

It did have the RF output before the mod, but that was removed during modding.  I am not sure if this happened before the mod as I only loaded the game up to the second screen briefly to verify it worked.  I would guess that it did have the problem as the UAV takes the image from the same source (I think).  The RF image is so muddy in comparison I would have needed to really pay attention to the image displayed to notice it (wish I had).

Share this post


Link to post
Share on other sites

I am asking because it would be a valued information to know if the issue appeared after or before the AV Mod. If the  issue were before the av mode, the matter is in the console but If the issue appeared after the mod, the matter is in the AV mod.

Share this post


Link to post
Share on other sites

Well, the fact that the same UAV kit worked without problems on a different board, and a second UAV kit had the same issue with the problem board and also gave a perfect picture on a second board, it seems unlikely it is the mod kit itself, unless this specific version of the board is just incompatible with the UAV kit.  

Share this post


Link to post
Share on other sites

I've installed the UAV into an all socketed early made 7800 before and it didn't exhibit this issue. In fact it was just this past June that I installed one into an early model like this. It still had Atari Inc on the serial number label in fact.

 

Share this post


Link to post
Share on other sites

Well.... I received another fully socketed Rev A 7800 yesterday and tested it out.  There was no flickering through the RF output and everything looked great.  Then I swapped in the new board and got the same flickering problem.  I had recapped and replaced the PR and the Power and Reset switches.  I went back and reinstalled the original caps and PR and still have the flicker.  Could it be the switches causing this, because otherwise there seems to be something in this revision that doesn’t like the UAV.  I really don’t want to pull those new switches off if there is no way that’s the problem.  Any thoughts??  Thanks!

Share this post


Link to post
Share on other sites

Well I swapped in some original 7800 switches and it’s still there.  The only other thing I can think of (other than it being the version of 7800 board) is that it is the batch of UAV?  There definitely wasn’t any issue through the RF.  

Share this post


Link to post
Share on other sites

Only way to know that is to take a UAV that you KNOW doesn't have any issues and install that into place. But I thought you said you did that already and still had the issues leading you to believe it to be an issue with the 7800 at that point? When did you get in this batch of UAV boards? I just got some in about 2 weeks ago I think but haven't used any of them yet.

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...