PC Engine RGB picture quality issue, is this normal?

[Restart_Point]

I recently bought a PC Engine Core Grafx II which the seller has pre-modded with a "PCE RGB AMP 2.1" board and it all looks like it's been neatly done. It has had an 8-pin din socket added to replace the original 5-pin, with the labelled R, G and B wires going to it from the 2.1 board, to allow for a "Dans project" based Scart RGB cable to be used which was supplied with it. So allegedly I can use the original 5-pin AV cable for normal composite use or I can use the 8-pin RGB cable for the improved picture that RGB allows. (Just to clarify, I already own a Genesis and a Retro Gaming Cables pack-a-punch-pro cable which works great so I am familiar with how much better an RGB signal looks on my Samsung LCD TV compared to composite)

My problem with the newly-acquired modded PC Engine is, when I compare using the standard AV cable to using the RGB cable, the picture quality is absolutely identical, or so similar that I can't personally tell the difference, and the picture shows the normal issues you'd expect from composite; low brightness, shimmering of scrolling backgrounds and moving objects, noise around the edges and indistinct pixel borders and merging of pixels / colours.

Can anybody tell me if this normal? I have never personally seen an RGB-modded PC Engine running before so I don't know exactly what to expect from it. I am also wondering if it's an issue with my TV, bearing in mind that it works great with my Genesis and a quality RGB cable.

There's probably a ton of information that I haven't given here, so if anyone needs to know more I will try to answer.

I paused a game and took pictures of a sprite as it is displayed by both cables, to me they look identical:

[fernan1234]

At least on a CRT the difference between composite and RGB on a PCE should be night and day (or when using a good upscaler or scan converter, like an OSSC). But you're saying you're hooking it up to an LCD? Maybe your LCD is just bad at displaying this, especially since it's a 240p analogue signal, to the point that it doesn't really make a difference to go RGB.

On that TV can you tell a world of difference between composite and RGB with your Genesis? The difference there is huge too, probably a bit more than on a PCE even.

[Restart_Point]

At least on a CRT the difference between composite and RGB on a PCE should be night and day (or when using a good upscaler or scan converter, like an OSSC). But you're saying you're hooking it up to an LCD? Maybe your LCD is just bad at displaying this, especially since it's a 240p analogue signal, to the point that it doesn't really make a difference to go RGB.

I had considered this but when I hook up my Genesis to the same TV with a quality RGB cable, It works excellently and I can see the benefits, I can see every pixel defined as a clear block with none of the issues that the PC engine has.

[Restart_Point]

UPDATE: Tonight I managed to test this on a Sony CRT. And I have made a big discovery.....it appears that the Scart cable I have is transmitting Composite and RGB at the same time ......when I cycle through the Input modes on the Sony while the PC Engine is hooked up to it via the Scart cable, I get one mode where the image is composite with all the issues composite has, then I can cycle through to what I imagine must be a forced RGB mode and suddenly the picture improves and shows exactly how I hoped, clear, bright, solid colours with no composite fuzz etc!

So this cable is transmitting composite and RGB, and the Sony is capable of differentiating between them and flicking between them but, my Samsung LCD apparently defaults to reading just the composite signal and I have no way I am aware of to 'force' it to show the RGB lines like I can with the Sony. Very confusing as I never had this issue with my Genesis.

Here is a picture of the PC Engine scart cable board, what is the "S" which the yellow wire (nb not the Orange wire) is soldered to? If I was to disconnect that would it ruin the cable or would that maybe force my Samsung to read the RGB lines only? My vague knowledge of RGB tells me that the S line might be the composite sync line which maybe is required for RGB, but for some reason my Samsung is using the composite sync line for the whole image and ignoring the R, G and B lines on the board? All this said, how come the Samsung TV immediately reads and displays RGB fine with my Genesis, but with the PC Engine it thinks the signal is Composite only? All this must be to do with how the cables are wired AND how the Samsung reacts to various types of cable.

[fernan1234]

The Genesis cable most likely is wired for csync/composite sync (as opposed to sync-on-composite/CVBS).

[maxtherabbit]

UPDATE: Tonight I managed to test this on a Sony CRT. And I have made a big discovery.....it appears that the Scart cable I have is transmitting Composite and RGB at the same time ......when I cycle through the Input modes on the Sony while the PC Engine is hooked up to it via the Scart cable, I get one mode where the image is composite with all the issues composite has, then I can cycle through to what I imagine must be a forced RGB mode and suddenly the picture improves and shows exactly how I hoped, clear, bright, solid colours with no composite fuzz etc!

So this cable is transmitting composite and RGB, and the Sony is capable of differentiating between them and flicking between them but, my Samsung LCD apparently defaults to reading just the composite signal and I have no way I am aware of to 'force' it to show the RGB lines like I can with the Sony. Very confusing as I never had this issue with my Genesis.

Here is a picture of the PC Engine scart cable board, what is the "S" which the yellow wire (nb not the Orange wire) is soldered to? If I was to disconnect that would it ruin the cable or would that maybe force my Samsung to read the RGB lines only? My vague knowledge of RGB tells me that the S line might be the composite sync line which maybe is required for RGB, but for some reason my Samsung is using the composite sync line for the whole image and ignoring the R, G and B lines on the board? All this said, how come the Samsung TV immediately reads and displays RGB fine with my Genesis, but with the PC Engine it thinks the signal is Composite only? All this must be to do with how the cables are wired AND how the Samsung reacts to various types of cable.

"transmitting RGB and composite at the same time" is how SCART is designed to function, it uses the composite video as a sync source and should not be disconnected

there is meant to be a 1-3VDC signal on pin 16 that tells the monitor to switch over to RGB - your cable may be lacking this which is why the samsung displays composite video

[Mobiusstriptech]

A few notes. 1 that amp board has a 4th channel that is not used, but is driving signal into ground. This will cause excess heat in the chip and premature wear and tear. 2 that amp does not provide csync,it relies on composite video as sync, so if you did disconnect the S line, you will no longer have a picture. 3 you need to put a 180ohm resistor between the 5v pin and the switching pin to force RGB mode. This isn't an issue unless you have a tv that is capable of natively displaying rgb and composite video via scart. Which obviously you do.

Now once you make a couple tweaks, the overall experience will improve. However there are higher quality amp circuits if you want a better experience after that, but it's totally up to you. The install is very neat, which is a definite plus compared to what normally shows up on these premodded systems. Good luck with it.

[Restart_Point]

A few notes. 1 that amp board has a 4th channel that is not used, but is driving signal into ground. This will cause excess heat in the chip and premature wear and tear. 2 that amp does not provide csync,it relies on composite video as sync, so if you did disconnect the S line, you will no longer have a picture. 3 you need to put a 180ohm resistor between the 5v pin and the switching pin to force RGB mode. This isn't an issue unless you have a tv that is capable of natively displaying rgb and composite video via scart. Which obviously you do.

Thanks very much to you and maxtherabbit and fernan1234. This is all extremely useful information! On your point 1, which pad / wire on the board is the 4th channel? How do I stop it driving signal into ground? On point 3, which pins are 5v pin and the switching pin? Pin 16 is the switching pin? And what type of 180 Ohm resistor is best for this situation (carbon / metal film etc) ? My soldering skills should just about be able to do this. Thanks again

[makar1]

On your point 1, which pad / wire on the board is the 4th channel? How do I stop it driving signal into ground? On point 3, which pins are 5v pin and the switching pin? And what type of 180 Ohm resistor is best for this situation (carbon film / metal film etc) ? My soldering skills just about be able to do this. Thanks again

The spec for the THS 7374 amplifier is here: http://www.ti.com/lit/ds/symlink/ths7374.pdf

You should refer to a SCART specification diagram to learn the functions of the individual pins before attempting to modify the connector.
https://en.wikipedia.org/wiki/SCART

[Restart_Point]

You should refer to a SCART specification diagram to learn the functions of the individual pins before attempting to modify the connector.
https://en.wikipedia.org/wiki/SCART

As far as I can see, I need to connect the resistor between Scart pin 16 and the 5v wire coming from the PC Engine , is this correct?

I have also seen recommendations to bridge pin 8 and pin 16 with the resistor, is that best?

[Fudoh]

I have also seen recommendations to bridge pin 8 and pin 16 with the resistor, is that best?

best is not to power pin 8 at all, since it usually tells your TV to switch into 16:9 mode. Widescreen LCDs probably default to 16:9 anyway, but autoswitching usually doesn't help. If you put your TV manually into 4:3 mode and switch a HuCard, your TV will be back on 16:9 with pin 8 being "hot".

[Restart_Point]

3 you need to put a 180ohm resistor between the 5v pin and the switching pin to force RGB mode. This isn't an issue unless you have a tv that is capable of natively displaying rgb and composite video via scart. Which obviously you do.

Are the two points highlighted in pic 1 and 2 (they are on opposite sides of the board) the best points to connect together with the 180 Ohm resistor? (pic 2 shows pin 16)

[maxtherabbit]

3 you need to put a 180ohm resistor between the 5v pin and the switching pin to force RGB mode. This isn't an issue unless you have a tv that is capable of natively displaying rgb and composite video via scart. Which obviously you do.

Are the two points highlighted in pic 1 and 2 (they are on opposite sides of the board) the best points to connect together with the 180 Ohm resistor? (pic 2 shows pin 16)

yes

[Kez]

That should work fine, but you could also check for continuity between that 5V input and some of the other SCART pins.. it might be connected to pin 8 which is closer.

[Restart_Point]

Everyone has been very helpful and I appreciate it! I still have no idea how to stop the un-needed fourth channel on the AMP from driving signal into ground, as Mobiusstriptech mentions, or how much of a concern it is. Why would the board be designed that way if it's unnecessary, or is it the way the amp has been installed that is causing that issue?

[Mobiusstriptech]

Sorry I don't visit this forum very often anymore. The 4th channel was connected to ground because the original board designer didn't know any better and likely didn't read in the datasheet that the input should be grounded and output should float. In his defense, floating signal pins is more commonly a bad thing.

To stop it you have 2 choices, cut the output pin, or lift it. Either one will work but lifting a pin on a ths7374 might not be easy if you aren't great at soldering. I don't know who is selling these boards now but it's sad that they didn't bother to fix that issue.

The pin in question is pin 11. As for how much of a concern, that's hard to say. Ultimately the issue could affect the image quality and will eventually cause the ths7374 to fail prematurely. How long will that take? No idea. There are too many factors that go into calculating that. My personal opinion is always to fix a problem before it starts. Obviously it's easier to say that in my case since this is the type of thing I can fix myself without much effort.

[Restart_Point]

The pin in question is pin 11.

Great, I have found that pin.

The IC and its pins are so small, I don't have any tools that can safely cut such a small pin without risking damaging to neighboring pins , it would require the smallest pair of wire snippers known to man-kind haha. So i'd better not try for now. Can anyone recommend a way to cut such a small pin on a board that is already installed so not super easy to access?

[Mobiusstriptech]

This is going to sound silly but fingernail clippers.

[Restart_Point]

This is going to sound silly but fingernail clippers.

I did try some believe it or not, but they were still a bit too big / blunt-ended to be accurate. Eventually I did it very carefully with an x-acto knife and it's still working good! Thanks for all the tips, my PC Engine is now looking good !!

[Neo-Alec]

I bought a PCE scart cable with a sync stripper built in. I wanted csync but I also wanted the old composite cable to still work.