2600 DIY AV mod quesiton

[eizner23]

I am receiving the same results on a different LCD TV and with different cables and power strip. Even tried a 75ohm cable. There isn't really anything else plugged in the room the atari is residing to cause interference.

 

Looking at schematic I'm curious if c215 is still neccessary? 

[Voxel]

Okay, it's the VCS.

 

Some spurious interference is leaking into the signal from somewhere into the cabling, still...

 

I've reviewed your wiring on your recent images.  Would you be able to use a shielded cable tapping the audio and video signals from the board to the AV mod then again shielded cables from the AV mod to the RCA chassis connectors, connecting the outer shielding to a common earth on the AV board as well as the earth on the RCA sockets on the chassis.  Sorry to ask this I'm still not a fan of your wiring set up with that choke, with the wires going around it acting like an inductor could be distorting the signal at the output end.

[eizner23]

There is no wiring for video between the VCS and av board, I'm using header pins soldered to the two.

 

Not sure where I can salvage shielded cable but I'll look around. Could I temporarily tack the video rca using a tiny bit of wire right next to the av board to determine if this is the cause? 

 

 

 

[Voxel]

Apologies I was thinking about your original wiring and not your amendment on post #14, when I looked at your most recent images.

 

I've taken the liberty of using one of your images, and have boxed in the area of wiring I was referring to with regards to the use of shielded cables.

 

However, as shielded cabling is not immediately available, we can put that aside and focus on the other aspect, which is what I'm most suspicious of in relation to your current video blurring.

 

In you image below I've pointed to what looks like a choke, which I'm looking at as acting like an inductor with the wires going around it.  Could I ask you please to remove it and advise back on the image quality.

 

 

[eizner23]

Thank you for the further advice. I got rid of the wiring I had in exchange for shielded cabling for a cnc machine. I followed your instructions by soldering the shield (bare wire) to ground on both ends. Unfortunately I am confronted with the same video issue.

 

 

 

[Voxel]

Thank you for the update and I appreciate the new images.  Could I please ask for an image of the entire screen, so I can see the scope of the blurring.

 

On 4/29/2020 at 7:11 PM, eizner23 said:

Looking at schematic I'm curious if c215 is still neccessary?

I've not studied the video mod you've done in enough detail to comment.  It would not hurt to remove it in case it is affecting the output. If you do remove it, then it may be a good idea to have a replacement, in case it has gone out of spec, should one need to be put back in.

 

From your previous image of the blurring I'm still looking at some bleeding into the video signal.  I've been looking at RF interference so far only because I assume the work you've done on the board and the circuit you've assembled is tried and tested, which it appears to be very good.  However I've not considered much of the components upstream providing the video signal and as most people choose an AV mod because they are not happy with the RF out, it would bring into question components that may have aged badly.

 

I am asking for an image because usually when there is blurring there is some incompatability between the TV and the device.  In this case it's consistently the VCS and I'd like to rule out a possible sync issue.

 

The two possibilities I'm considering are shielding, while you've been kind enough to rule out the wiring and that of a component being faulty (or be that from soldering from work done i.e. a solder blob causing junction).

[eizner23]

Thank you for the kind help Voxel during this saga. 

I analyzed video output on my scope of video out rca and before it enters the amplifier I assembled (pin 4). Waveforms look the same on the scope. I'm curious if we can see any anomalies here. Its Barnstormer on the intro screen when you first turn the game on, no motion. I may see what the output looks like on another unit out of curiosity.

 

 

 

This is the blurring I'm seeing, notice the yellow fence posts spilling over.

 

 

Not much solder was done to the board to cause any blobbing really. I've been reading the video troubleshooting in atari field service guide for clues I will post if I find anything out.

 

[ApolloBoy]

On 4/29/2020 at 9:15 AM, eizner23 said:

Is it true these light 4 switchers are finicky with composite mods?

TBH I would replace your AV mod with a UAV board at this point. I've tried a few homemade AV mods and never got consistent (or good) results with them. The last straw came when I did a simple AV mod on a Vader and got a really dim picture which nothing was able to fix. That same Vader now has a UAV installed and the picture quality is gorgeous, even through composite.

[Voxel]

Thanks for the screen shot and the scope was interesting viewing.

 

If we take a step back we can see the voltage supply was causing a ripple on the display side.  You've corrected that with a replacement supply.  In your early work you replaced the AV mod for what apprears to be a superior one, however this was when the localised blurring was also introduced.  You've been kind enough to oblige and change the wiring, so I've no doubt in the wires.  This leaves work done on board, or the replacement mod.

 

I'm working form a dull memory, when I type this so please bare with me.  The old CRT was made to accept a TV signal and there was a bandwidth for it's operational frequency range.  The VCS was set up to provide a signal operating in that requency range (as limited as it was).  Previously I mentioned a sync signal, I'm of the opinion that the blurring is caused by the signal output for that blurry area deviating outside of the bandwidth of the frequency that is required for a clear image to be displayed.

 

So as indicated previously there is an indication for a soldering anomaly, or that a component is outside of spec.  If you removed or introduced a component please check again, against the method advised on the thread for where you followed your instructions.  Please also examine your work done on the AV circuit you made please pay particular attention to the reverse and try to tidy up the soldering to remove heavy blobs (this would remove any junction).

 

I'll just add that the original DIY AV mod was of a tried design and now the voltage has been corrected, it may be an idea to add back the original AV mod to compare and confirm if the replacement AV board is suspect if the blurring goes away, if the blurring remains then the issue would be on board with the work done.  By swapping out the AV mods via a process of elimination the issue can be localised.  (It's a big ask, so I'll not feel insulted if you'd rather not).

 

I've heard good praise for the UAV board as mentioned.  There is a possibilty that the current AV mod has an issue which needs correcting.  However the issue needs to be localised to the main circuit or AV mod before changing to a new AV mod for a third time without a resolution to the issue.

 

 

[Voxel]

15 hours ago, eizner23 said:

Not much solder was done to the board to cause any blobbing really.

Thanks for confirming.  I'm not sure if it was the angle of the image, but on the reverse the soldering looks a little heavy.  If it's an optical distortion then you've not to worry about the reverse of the AV mod.  I've borrowed one of your images below to illustrate the view I'm looking at.

[eizner23]

The blurring was also present on the original AV mod i tried, just not as bad- so I dont think its the cause of blurring. I am reading about the UAV and it has circuitry to align the 4 luminescence signals into a perfect pixel edge, perhaps that is what I am lacking on this VCS model.

 

At this point I may chalk this up as a learning experience and integrate the UAV into the unit. It was a fun experiment anyways.

[Voxel]

On 5/11/2020 at 6:47 PM, eizner23 said:

It was a fun experiment anyways.

I'm glad you're being positive.