800 XL UAV help

[GMorin]

I recently installed a UAV in my socketed Hong Kong Atari 800XL. The clarity is much improved, and I have the Chroma/Luma pot dialed in perfectly, However, I still have some very fine jailbars and a little noise in both composite and S-video. It's likely a grounding issue, as the bars go away when I pull the chroma wire out of the UAV. The manual recommends splitting the ground pad on top of the UAV to sever the 4050's ground connection and soldering an additional ground wire to the right half of the pad, or just using the second ground pin on the UAV terminal. What I'm unclear on is the best place to soler this ground wire TO. Any help or pictures would be greatly appreciated.

[+Stephen]

15 minutes ago, GMorin said:

I recently installed a UAV in my socketed Hong Kong Atari 800XL. The clarity is much improved, and I have the Chroma/Luma pot dialed in perfectly, However, I still have some very fine jailbars and a little noise in both composite and S-video. It's likely a grounding issue, as the bars go away when I pull the chroma wire out of the UAV. The manual recommends splitting the ground pad on top of the UAV to sever the 4050's ground connection and soldering an additional ground wire to the right half of the pad, or just using the second ground pin on the UAV terminal. What I'm unclear on is the best place to soler this ground wire TO. Any help or pictures would be greatly appreciated.

Before you do that, do you have another cable to test?  It sounds like the luma & chroma wires are not properly shielded which is causing the issue.

[+x=usr(1536)]

11 minutes ago, GMorin said:

I recently installed a UAV in my socketed Hong Kong Atari 800XL. The clarity is much improved, and I have the Chroma/Luma pot dialed in perfectly, However, I still have some very fine jailbars and a little noise in both composite and S-video.

This can also happen with unshielded video cables.  Try moving the cable relative to the display and see if anything changes.

11 minutes ago, GMorin said:

It's likely a grounding issue, as the bars go away when I pull the chroma wire out of the UAV.

That doesn't sound like grounding, necessarily - that sounds as though the noise is being introduced in the colour circuit.

11 minutes ago, GMorin said:

The manual recommends splitting the ground pad on top of the UAV to sever the 4050's ground connection and soldering an additional ground wire to the right half of the pad, or just using the second ground pin on the UAV terminal. What I'm unclear on is the best place to soler this ground wire TO. Any help or pictures would be greatly appreciated.

Anywhere on the wide track on top of the PCB that the RF shield would normally sit against.

[+tf_hh]

9 hours ago, GMorin said:

I recently installed a UAV in my socketed Hong Kong Atari 800XL. The clarity is much improved, and I have the Chroma/Luma pot dialed in perfectly, However, I still have some very fine jailbars and a little noise in both composite and S-video. It's likely a grounding issue, as the bars go away when I pull the chroma wire out of the UAV. The manual recommends splitting the ground pad on top of the UAV to sever the 4050's ground connection and soldering an additional ground wire to the right half of the pad, or just using the second ground pin on the UAV terminal. What I'm unclear on is the best place to soler this ground wire TO. Any help or pictures would be greatly appreciated.

 

Beside already given hints, if you check the others out, try to replace the inductor L5 with a simple wire. This inductor reduces the 5 volts voltage a little bit. When you feed the system with 5.0...5.2 volts, normally the +5 volts at the 4050 chip (where you have installed UAV) is around 4.75 - 4.9 volts. Enough for the LDO voltage regulator on the UAV board. But when the main input voltage is already below 5.0 volts under load, it may happen that less than 4.7 volts reach the UAV. And this is too less for proper function. So removing the inductor L5 might fix this problem.

 

Red rectangle shows the L5 inductor. When you already working on the board, it´s also a good idea to change the electrolytic cap in the yellow circle with 100uF instead of only 10uF. Helps to stabilize the video power.