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800XL Vertical Bars


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#1 TroyQ OFFLINE  

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Posted Tue Jan 2, 2018 12:42 AM

I've got an 800XL that produces vertical bars that I've been trying to get rid of.  Currently, I'm using SVideo (Chroma/Luma) -> VGA Converter -> LCD Monitor.

 

Initially I added the missing chroma line and lifted a single cap so that chroma was output on the 5-pin din.

I've removed the RF modulator

Installed a UAV rev D

 

I thought it might be some kind of cross talk/interference in the cable itself - the cable is one I hacked together using an AT KB Extension + SVideo cable.  To eliminate the cable as the issue, I wired in a second 5 pin din (the female side of the AT KB extension) directly to the UAV and the result was no bars - clean solid blue background.  I've checked the cable for continuity or even some level of resistance between between the pins on the cable and didn't get anything so I don't think its the cable.

 

The problem only happens when I try to use the built in 5pin din port.  If I go directly from the UAV, everything is fine but when wiring the UAV output back into the motherboard, the problem reappears.  I've narrowed it down to be something with the composite line.  If I don't connect that line from the UAV to the motherboard (UAV Pin 2 -> L7), then everything looks fine.  (The attached pic shows the ground wire hanging - that was part of testing; connected vs not connected didn't change anything).

 

Is there some kind of back-feed happening from the composite line onto the Chroma/Luma lines on the motherboard?  Is that possible?  I've removed the original Chroma wire (used pre UAV) - no effect.  I put the 1 lifted cap back into the circuit - also no effect; i've since lifted it again.

 

Any ideas?  Any other components that can be removed that will separate the composite line from the C/L lines on the motherboard?

Attached Thumbnails

  • 800XL_Bars.jpg
  • UAVrD.jpg

Edited by TroyQ, Tue Jan 2, 2018 12:44 AM.


#2 brenski OFFLINE  

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Posted Tue Jan 2, 2018 7:20 AM

you could try Nir Dary's simple video fix by removing capacitor C56 on the 800XL



#3 TroyQ OFFLINE  

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Posted Tue Jan 2, 2018 4:52 PM

you could try Nir Dary's simple video fix by removing capacitor C56 on the 800XL

 

Yep, that's the cap I lifted before I did the UAV upgrade when I was just wiring up the Chroma line to the 5 pin din.  After the UAV upgrade, I've experimented with putting C56 back in circuit and lifting it and it had no effect on the bars,,,



#4 Bryan OFFLINE  

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Posted Tue Jan 2, 2018 5:07 PM

Can you post a picture of where the chroma wire connects to the DIN?



#5 TroyQ OFFLINE  

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Posted Tue Jan 2, 2018 5:41 PM

Can you post a picture of where the chroma wire connects to the DIN?

 

Here you go.  The one with white wires was as I was testing and I had just cut the original chroma wire (pre uav).  The one with the blue wire is how it is now - completely removed the original chroma mod.

 

 

Attached Thumbnails

  • 800XL_Bottom.jpg
  • 800XL_Bottom2.jpg

Edited by TroyQ, Tue Jan 2, 2018 5:46 PM.


#6 Bryan OFFLINE  

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Posted Tue Jan 2, 2018 5:54 PM

Weird. Once you lift the 2 inductors, the DIN jack is completely isolated except for the audio pin.

 

So, are you saying that if you take the composite line out of the UAV terminal that the noise stops?

 

Here are a few things off the top of my head.

 

If you take the Composite and Luma wires out of the UAV and measure resistance across them, do you get anything (unplug the other end of the cable from any video devices, of course). If the circuit is open, then it may be the result of crosstalk in the cable. I don't know how long the keyboard cable part is, but 75-ohm video cable is a special kind of wire specifically for this purpose and I doubt a keyboard cable has individually shielded conductors.



#7 TroyQ OFFLINE  

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Posted Tue Jan 2, 2018 8:32 PM

If you take the Composite and Luma wires out of the UAV and measure resistance across them, do you get anything (unplug the other end of the cable from any video devices, of course). If the circuit is open, then it may be the result of crosstalk in the cable. I don't know how long the keyboard cable part is, but 75-ohm video cable is a special kind of wire specifically for this purpose and I doubt a keyboard cable has individually shielded conductors.

 

Thanks for pointing me in the right direction! Yep, looks like it was the cable.  I shortened the KB side to just a few inches and most of the problem is gone. 

 

Any suggestions on a good 5 din cable with an SVID connector?  I haven't found any RCA -> SVID adapters that are wired correctly to work with the "standard" Atari 4-RCA cable.


Edited by TroyQ, Tue Jan 2, 2018 8:34 PM.


#8 ACML OFFLINE  

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Posted Tue Jan 2, 2018 8:35 PM

 

Thanks for pointing me in the right direction! Yep, looks like it was the cable.  I shortened the KB side to just a few inches and most of the problem is gone. 

 

Any suggestions on a good 5 din cable with an SVID connector?  I haven't found any RCA -> SVID adapters that are wired correctly to work with the "standard" Atari 4-RCA cable.

I highly recommend this one.

https://www.8bitclas...ideo-Cable.html

Cory makes a great cable.  It has chroma, luma, composite and L&R audio.  The chroma and luma are already on an s-video plug.

70a74eec7083f321b4ee03954297deb8-500x500


Edited by ACML, Tue Jan 2, 2018 8:36 PM.


#9 Bryan OFFLINE  

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Posted Tue Jan 2, 2018 8:36 PM

My suggestion is to get a 5-pin DIN connector and make a breakout cable, or remove the RF modulator and install one of these in its place:

 

https://www.mouser.c...50W7KPmarOzRw==

 

Also, these can be easily modified to adapt to an S-Video connector:

 

https://www.ebay.com...le/272415776125






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