PC Engine RGB jailbars, let us find a working solution

[rtw]

could someone please do the following:

. describe the 3 channel amp
. provide a picture of the symptom

[keropi]

I believe the 3 channel amp is the THS7314 chip

[rtw]

I believe the 3 channel amp is the THS7314 chip

Thank you, now I'm only missing an image of the symptom.

[CkRtech]

I don't think our search engine on shmups likes terms less than 3 characters (which hurts when searching for "RGB" and "PCE"), but here is an example thread (with pictures) from our forum: http://shmups.system11.org/viewtopic.php?f=6&t=44262

[Artemio]

Here is a video of the issue, displayed on a PVM 2530. The NJM mod doesn't show this in the same display and cables on a TG-16 as previsouly described. The same NJM mod was tested on this Duo before changing it to a THS one. it has the capacitor mod described above, which I made yesterday.

This is the THS7414 schematic I used: http://i.imgur.com/qB71l.png

Video: http://youtu.be/Fdnrl2qm1Gw (Direct download form DB while yt processes the video: https://dl.dropboxusercontent.com/u/140 ... 200004.mp4)

On a side note, the bars don't show up in the above setup when using the pce rom I made. In other words, the jailbars are not visible in primary RGB colors.

[rtw]

Thanks for the schematics, video and information Is there a specific game which exhibits this more than others or should I wait for an updated 240p Suite ?

[kamiboy]

Super Raiden, first level when you get to the part in the screens from the other thread you can see them pretty well in the brown colours.

Currently I am using Dragons's Curse/Adventure Island to test. In town and the desert the sky shows them well enough.

[CkRtech]

In other words, the jailbars are not visible in primary RGB colors.

Well now that is interesting.

[Artemio]

You are welcome.

I'll try to make a rom that shows the behaviour in the next 24 hours.

The games I've seen them most are the soldier blade intro, as shown in the video; and magical chase, during the boss presentation screens that show before each stage. Can't remember others from the ones I have.

[keropi]

I always use monsterland 2 to see this, the blue background of the 1st level shows these jailbars
the jailbars I am getting are much thicker , one thinks that there is dirt on the screen or something

[Fudoh]

easiest to notice on horizontally scrolling games with bright colors. My test HuCard is New Adventure Island, first level. Another benefit is that this Card quickly produces dropouts (e.g. on the XRGB-3) if the sync signal isn't handled right.

the jailbars I am getting are much thicker , one thinks that there is dirt on the screen or something

jail bars certainly isn't the best description for the PCE problem. Especially if you dealt with jail bars on the Mega Drive before (one pixel column wide). The problem on the PCE is best described as vertical banding.

[keropi]

^ yes, my thoughts exactly... I don't like jailbars term as well on the pce but since people get what it means it works good enough for me
the first time I noticed them on monsterland 2 I thought my screen was dirty and tried to clean it

[kamiboy]

Wish I had money to throw around as I would then invest in an original PC Engine as well as a Core Grafx II.

Doing the RGB mod would take next to no time and I could do a comparison of them all since my amp is housed inside the SCART cable.

[Artemio]

Here is a ROM I just compiled that will hopefully help:

PCE banding

It has a few full screen images and patterns that show banding in my setup, and mentioned above. You can switch between them with button "I". The first is from the Soldier Blade intro, banding shows at the top and bottom. The next is the most obvious in my PVMs, it is from Magical Chase, and it has automatic scrolling between one of the solid colors and the pattern from the stage introduction.

The next one scrolls as well, taking some tiles and colors from new adventure island. And finally, some solid colors. First it is the bg color from soldier blade (0, 148, 33), next the sky form new adventure island (it isn't noticeable in my current setup) and some misc RGB colors over solid background.

[kamiboy]

Anyone had time to experiment with their machines?

I am considering buying a white PCE just to confirm whether a 3 channel amp is artefact free on said revision or if there is some other factor involved.

[kamiboy]

Oh, and worth mentioning. The reason why I in the previous thread stated that my Core Grafx appeared to be artefact free has now become clear.

I used to play that unit on a PVM monitor. Since then I've moved to mainly play on a 25" B&O CRT. Just now I moved the Core Grafx over and hooked it up to my recently purchased 20" BVM and traces of the artefact has diminished in Adventure Island. The sky of the town and beach levels no longer show banding but the banding in the desert still persist.

I guess a pro monitor will filter away some of the banding that show up on consumer sets.

[speedlolita]

I bought one of these (http://www.neo-geo.com/forums/showthread.php?249063) recently. Don't get any jailbars - they used to be especially visible on Twinbee's blue sky.

http://i.imgur.com/rWpnw9Y.jpg
http://i.imgur.com/vjsxoJL.jpg
http://i.imgur.com/wpjfNlD.jpg

Using a PlayStation 2 slim PSU for power.

[kamiboy]

The 3 channel amp I have in my SCART cable is based on the same TI chip. So unless the extra components he has on the board make the difference it should give me the same picture that I have right now.

I actually have a couple of TI 3 channel chips here, if I had the full exact schematics of what he is selling I could try to replicate his design to see whether that makes a difference.

[speedlolita]

Think you'll find information here. http://nfggames.com/forum2/index.php?topic=4822.40

Worth noting that the SCART lead I got with this is properly shielded too.

[rtw]

I bought one of these (http://www.neo-geo.com/forums/showthread.php?249063)

Do you have a public link ? Not everyone has an account an neo-geo...

[kamiboy]

Bah, humbug! I am two parts short of being able to build that circuit, so I am out.

Here are images of the diagram:

[speedlolita]

Believe broken changed the output to 100 Ohm resistors over the 75 Ohm as he felt them a little bright.

[kamiboy]

I believe he does mention that in the thread, I have both 75 and 100ohm resistors here so if I can manage to get my hands on the missing parts I can try both.

[Artemio]

Here is the current build of the PC Engine/TG-16 240p Suite, for Hu Card and Super CDROM2 (the System Card 2.0 and 1.0 versions are not working completely yet). It is still missing a lot of the help and a few patterns and tests, but it should help those willing to measure levels:

https://sourceforge.net/projects/testsu ... -TG16-SCD/

[kamiboy]

Good news everyone!

I think I may have happened upon a way to uproot the banding issue, at least on my PC Engine Core Grafx.

I had my pappy, who unlike me knows what he is talking about, look over the digram for the THS7314 amp above and he told me the 100nf and 22uf caps between +5v and GND were of special importance for filtering out noise.

I opened up the SCART housing for my amped cable and, true enough, these caps were not there. I soldered them on, and somehow managed to get everything to fit back into the housing and viola! I no longer see the banding. Neither in the desert sky of Adventure Island nor in the Soldier Blade intro.

I should mention that my PCE also has those two additional caps on the PPU, so they might be necessary as well.

In short, it seems like a THS7314 amp with those filtering capacitors might just do the trick.

[Artemio]

In my particular case I have the filtering caps. I guess the issue is worse without them.

[kamiboy]

I need to connect my PC Engine to my B&O and see whether the artefacts are gone for good or not. The Banding is more prominent on the B&O. I'll do it when it gets darker outside so there is no glare.

Also bear in mind that my system is also modded with the caps on the two PPU legs, so that might make the difference.

[kamiboy]

So, I connected it to the B&O and the banding is still there. So I guess it just does not show up on the BVM.

I used the same cable to test both a Core Grafx with the two caps on the PPU pins and a Duo without them and the banding is much more prominent on the Duo. So the additional caps on the pins most certainly help to reduce the banding.

I will have to get hold of some flat caps and attach the additional 3 mentioned in the Otaku store mod to see if that improves things further or not.

Last resort is I take the PC Engine down to my pappy and we use an oscilloscope to try and find the source of the noise if possible.

[Voultar]

I'm brand spankin' new to the PC-Engine scene, so I'm quite interested in seeing a resolution to this problem.

I have a Duo-R coming over from Japan that's in seriously rough shape, I'll be restoring it.

[Pasky]

Putting additional bypass caps on each of the 6280's vcc pins usually removes any jailbars. Doesn't hurt to put a single 220uF on one of them either.