AES - picture off center after RGB mod

[edd_jedi]

As per this thread I just had an 3-5 revision AES console RGB modded. I have just noticed that while the picture is now much clearer, it is now off center to the left, which it wasn't before. As you can see in the attached screenshot there is approx 1 inch of the left side being cropped off, and it's displaying too much of the right hand side (in some games it shows a white border or other artifacts.) This is using an RGB SCART cable direct into an LCD TV with SCART socket.

Any suggestions on how I might be able to remedy this?

 

[Neo Alec]

It could be normal; it could be only that TV. It might be incosistent caps across the RGB and sync lines, although I didn't thinks could make that dramatic of a difference.

 

[maki]

thats "normal" if a TV expects Composite Video as sync signal, instead of CSYNC

composite video is delayed, if the TV assumes thats whats its going to get, its going to assume a delay
CSYNC has no delay, add a capacitor to delay the signal (caused by the phase shift), 470uF is a common value, the data sheeting for the THS7374 mentions values up to 1000uF

my favourite RGB mod PCB for the MVS has that cap, btw. extra for the delay:

OSH Park ~

oshpark.com

so, I'd say your TV expects composite video as sync source, feeding it CSYNC works but its "too fast", needs an extra delay

edit:
just to be clear, there is nothing wrong with your AES, its your TV

I do not recommend changes to your AES for this issues

 

[SignOfGoob]

Doesn’t someone (a German company maybe?) sell an in-line device that essentially gives you trim pots to adjust this as if it were a CRT? I think Tempest has one.

 

[edd_jedi]

Doesn’t someone (a German company maybe?) sell an in-line device that essentially gives you trim pots to adjust this as if it were a CRT? I think Tempest has one.

Yes, something like this: https://www.aliexpress.com/item/4001070254969.html

 

[edd_jedi]

I just opened up the SCART connector, and it currently has a 220 uF capacitor on pin 20. So do I need to remove that and replace with a 470?

 

[edd_jedi]

OK I have tried both 820 and 1000uF caps on the sync line, but it makes no difference to the horizontal shift. The resistor is a 75ohm one which was there already, so I didn't remove it. Would this make any difference?

 

[Neo Alec]

OK I have tried both 820 and 1000uF caps on the sync line, but it makes no difference to the horizontal shift. The resistor is a 75ohm one which was there already, so I didn't remove it. Would this make any difference?

Not surprised it had no effect honestly. I tried the same thing on my CRT mod with the image too far left and there was no change.

 

[awbacon]

That’s really not surprising. Since you are on LCD I’d say just let it be since you have borders

On CRT it’s the same story. Usually I deal with it in the service menu. All my consoles on RGB all center differently. Bit maddening

 

[edd_jedi]

It's not a big deal for some games (like fighters) but on Puzzle Bobble for example, it cuts off the entire left column making the game unplayable

 

[awbacon]

It's not a big deal for some games (like fighters) but on Puzzle Bobble for example, it cuts off the entire left column making the game unplayable

Oof. That’s a diff story

 

[maki]

OK I have tried both 820 and 1000uF caps on the sync line, but it makes no difference to the horizontal shift. The resistor is a 75ohm one which was there already, so I didn't remove it. Would this make any difference?

Thats not how capacitors work.

In parallel, they'll add their capacity, but in series they will reduce the total capacity!

Series and Parallel Capacitors | Capacitors | Electronics Textbook

Read about Series and Parallel Capacitors (Capacitors) in our free Electronics Textbook

www.allaboutcircuits.com

When capacitors are connected in series, the total capacitance is less than any one of the series capacitors’ individual capacitances. If two or more capacitors are connected in series, the overall effect is that of a single (equivalent) capacitor having the sum total of the plate spacings of the individual capacitors. As we’ve just seen, an increase in plate spacing, with all other factors unchanged, results in decreased capacitance.

In the AES there is a cap already on the output (and a resistor, thats why the AES cable needs no extra components), so you adding another(!) capacitor in the SCART head reduces the total capacity, instead of increasing it.

You'd have to replace the cap in your AES, but its your TV that is causing the issue, using composite video for sync is totally fine IMO.

 

[edd_jedi]

Sorry I'm confused, in your original post it says "add a capacitor to delay the signal" and "I do not recommend changes to your AES for this issues." So what exactly am I supposed to modify then if not the console or the cable?

 

[maki]

Sorry I'm confused, in your original post it says "add a capacitor to delay the signal" and "I do not recommend changes to your AES for this issues." So what exactly am I supposed to modify then if not the console or the cable?

You're right, I did say that, but thats wrong, so thats on me.

If you swap the cap in the AES, it should center the pic, but its actually due to your TV.

"Composite Video as Sync" thats when I mixed up this thread with another one, sorry for the confusion

 

[edd_jedi]

No worries, thanks for clarifying