PC Engine RGB mod problems (Voultar RGB amp) - part solved!

[BuckoA51]

For some time now I've been wanting to offer PC Engine RGB mods for the community. Towards that end I got hold of two of Voultars PC Engine RGB boards and had them installed, one in a Supergrafx and one in a Core Grafx 2. The installation included the recommended Jailbar fix as well as the RGB amp.

At first everything seemed fine, however as I tried out the Supergrafx a little more, I noticed more and more picture noise. Firing up the 240P test suite, I could clearly see a lot of picture noise, sparking dots, in grey areas of the image. We're not talking a little noise here, in fact if I disconnect the RGB mod and hook up my SD System 3 and use the RGB output from that, the noise is all but gone. Keeping in mind I have one of the early SD System 3 units which is supposedly being recalled to fix picture noise issues, so that's pretty disappointing performance from the mod.

The Core Grafx 2 on the other hand was a total bust, the machine has really, really bad jailbars:-

pc-engine-jailbar by videogameperfection, on Flickr

As you can see Again, switching to the RGB output from the SD System 3, with the same PSU and everything, made the jailbars go away.

Anyone any ideas? I mean I know Voultar's board is good because others have had good success with it. I don't doubt the modder's work because he's done a stellar job for me on other work (Atari 800 RGB mod, Game Gear and Lynx mods) so I'm not really sure where to begin trying to troubleshoot this. Currently my only lead is that he told me he tapped Csync "direct from the Video Chip" rather than, I assume, using the csync on the RGB amp. Could that cause these issues?

Edit - I got clarification on this, the Clean Sync direct from the video chip is fed to the Buffer Amp input, The 75Ohm output from the Amp is then fed to the DIN Socket, so that sounds perfectly correct to me.

[Syntax]

The white snow sounds like a similar issue NES has until you cut the composite feed. So a sync interference issue. Could also be RF box interference.

Jailbars would be power or LPF settings as it seems your using these systems on an LCD.

You 1st gen SSDS3 builds csync from H and V sync, If you can get a decent picture from both systems using the SSDS3 then you need to source sync for your bypass somewhere else.

The H V sync method is not recommended, I'm pretty sure the new SSDS3 strips sync from composite like voultars board.

**EDIT**

Seems Voultars board does not strip sync from composite. This is the advice he gave the Terraonion team for their 2nd revision.

I have a question,

As I understand it (I think); You are taking horizontal and vertical sync pulses and using combinational logic to shape up a C-Sync signal. Probably XORing and inverting, or something to that effect. But why? If you're doing this in the analog space, there's virtually no benefit in doing that. The same wonky patterns in the C-Sync output exist in the horizontal and vertical pins. You're just making more work for yourself than you need to, and run the risk of mucking up the pulses if not done absolutely precisely.

Buffer C-sync by a 6dB gain factor (THS7374), attenuate it, and then ac couple it to remove that odd 1vPP DC offset. I bet it will work much better and be a hella less headache for you guys.

I would let the C-Sync live between 330mV and 900mV. Some equipment may have trouble triggering off of it depending where it "tries" to slice it. So 330mV is where I'd put it @ minimum.

Glad to help.

I'm using a PCE RGB board from Zeruel that strips sync from composite.
viewtopic.php?f=4&t=60272

[Kez]

When I first did the jailbar fix on my CoreGrafx, I found the capacitor locations somewhere on this forum and I was still getting some pretty bad interference. In the end I noticed on the console5 wiki that they recommended different locations, so I moved them and immediately got a pretty much flawless picture. So I'd double check the cap locations and, as Syntax suggested, look into whether the LPF is enabled/disabled on the 7374.

[ASDR]

Bummer!

I have a CoreGrafx which has the SMD cap replacements, done as recommended on the Console5 wiki for my unit. Jailbars are ~95% gone. I hardly ever see them in games, there are only faint jailbars visible in dark shades of gray.

My 7316 RGB mod taps RGB from the ext. port connectors and sync is just the system's composite output. I'm not familiar with Voultar's mod, but I assume the main difference would be how it obtains / builds csync. You could try just using the Voultar RGB with composite video as sync and see if that makes a difference?

Strange that you have less noise with the SSDS3. For me audio & video noise was just massively worse with the unfixed board.

Regarding the LPF, my CoreGrafx is one of those consoles that look like crap with the OSSC's LPF off. I also have two TVs where one doesn't seem to filter very aggressively. The CoreGrafx looks bad directly connected on that one. With the OSSC's LPF turned on everything is peachy, though! Image is razor sharp, very little noise. I only notice some subtle very low-frequency distortion that's visible when you have very large areas of uniform color. Looks a bit like a display uniformity issues. But it's hardly an issue.

Hope some of this was useful and you can figure things out

[Syntax]

When I first did the jailbar fix on my CoreGrafx, I found the capacitor locations somewhere on this forum and I was still getting some pretty bad interference. In the end I noticed on the console5 wiki that they recommended different locations, so I moved them and immediately got a pretty much flawless picture. So I'd double check the cap locations and, as Syntax suggested, look into whether the LPF is enabled/disabled on the 7374.

What would happen if you just replaced all 8 capacitors with the higher value? More load on the 7805?

[BuckoA51]

These are heading back to the lab this week so I'll let you know how we get on...

[BuckoA51]

So an update on this:-

The Core Grafx had a new voltage regulator installed and we tried double the value of the caps that Console 5 wiki recommended. Still jailbars from hell, barely any improvement.

The Super Grafx had a smoothing capacitor added to its power input, this has reduced the sparklies to a point where you can barely notice them, but they go away entirely when the Super SD System 3 is used. EDIT scratch that to be fair noise moves to other colours.

My technician is now out of ideas, can anyone think of anything else? I'm pretty happy with the Super (especially as the Super SD System 3 seems almost perfect with it, contrary to a lot of peoples reports) but the Core isn't in a state that I'd be happy to offer this mod to paying customers.

[Kez]

Sounds like you just got unlucky with your CoreGrafx, most of the old PCE and TG16 known for being fairly noisy so perhaps yours is just on the higher end of this.

When I use mickcris' RGB board the OSSC's LPF takes care of the noise on my CoreGrafx (but it is still very obviously present with the LPF off), however this has the mod board installed in an IFU-30 rather than directly in the CoreGrafx itself so doesn't directly drain power from it.

You could try doing a complete recap if you haven't already.

[Hoagtech]

Can you take “disappointment with Voultars mod” out of your title?

I have a lot of respect for the man and you even said yourself there is probably nothing wrong with the board.

It’s direspectful to his work which is flawless and your title makes it seem like voultars board was defective.

[leonk]

Sounds like you just got unlucky with your CoreGrafx, most of the old PCE and TG16 known for being fairly noisy so perhaps yours is just on the higher end of this.

When I use mickcris' RGB board the OSSC's LPF takes care of the noise on my CoreGrafx (but it is still very obviously present with the LPF off), however this has the mod board installed in an IFU-30 rather than directly in the CoreGrafx itself so doesn't directly drain power from it.

You could try doing a complete recap if you haven't already.

I've installed many of Mickcris' RGB boards. Both the older 7314 and newer 7374 based ones. They all worked great for me in TurboDuo / Turbo PCEngine consoles.

On the other hand, when I installed one in an IFU-30, I was disappointed in the results. PVM looked great, but faint noise/jail bars were visible on the XRGB mini.

[BuckoA51]

Can you take “disappointment with Voultars mod” out of your title?

I have a lot of respect for the man and you even said yourself there is probably nothing wrong with the board.

It’s direspectful to his work which is flawless and your title makes it seem like voultars board was defective.

I've nothing but respect for him and his work either, but that's the board we used and that's the problems we're having. I have nothing but good things to say about the UltraHDMI mod either, but if I'm creating a forum thread discussing one I wouldn't remove UltraHDMI from the title.

[Voultar]

Can you take “disappointment with Voultars mod” out of your title?

I have a lot of respect for the man and you even said yourself there is probably nothing wrong with the board.

It’s direspectful to his work which is flawless and your title makes it seem like voultars board was defective.

I've nothing but respect for him and his work either, but that's the board we used and that's the problems we're having. I have nothing but good things to say about the UltraHDMI mod either, but if I'm creating a forum thread discussing one I wouldn't remove UltraHDMI from the title.

What's remarkable is that you just recently sent me an e-mail to me and asked if I'd be willing fix all of the broken OSSC's here in the States, yet you don't ask me about this?

Nonetheless, the title of your thread here is kinda crappy as it implies that there's something inherently wrong with the board, which there isn't.

Also, it's kind of hard for anyone to offer you any meaningful help if you don't post pictures of the installation.

[BuckoA51]

You're able to send an e-mail to me and ask if I'll fix all of the broken OSSC's here in the states, yet you can't ask me this??

I thought asking the community would be better, anyway I know you post here. Any discussion here benefits the community, rather than just me as would be the case in a 1-1 e-mail exchange.

If it upsets you I'll change it, genuinely didn't think it would. I don't know what else to call it other than "Voultar's board" though.

It's kind of hard for anyone to offer you any meaningful help if you don't post pictures of the installation.

Ok I'll get some pictures sorted.

[BuckoA51]

IMG_0696 by videogameperfection, on Flickr

IMG_0697 by videogameperfection, on Flickr

Hi-res version if you click through to my Flickr, let me know if you want to see anything else.

[Voultar]

1) Your placement is right on top of the 6270. When you "pick up" the board off of the GPU, do the speckles go away? My guess would be yes.

2) Why is your installer/technician using electrolytic capacitors? These are not a suitable substitute for a high performing ceramic. Of course the noise isn't going away with those.

[BuckoA51]

I'll pass that along, the noise is more on the Supergrafx though the Core Grafx here is the one with the really bad jail bars. On the Supergrafx I was going to try a different/better PSU first.

[BuckoA51]

On the caps for the Jailbar fix, electrolytics were chosen because (and this is beyond my level of electronics expertise like most things)

The caps are for jailbar fix which according to Console 5 wiki, the purpose of these caps is to improve the AC decoupling. In this case electrolytics do a better job than ceramics hence why they are used exclusively for that job in Amplifier circuits.

Anyway, if you recommend ceramics that's good enough to warrant giving it a try. Here's the plan at the moment:-

Coregrafx (Jailbar hell machine)

1 - Try full re-cap
2 - Add additional shielding
3 - Swap electrolytics for ceramic caps as provided in the Console 5 wiki (if required)
4 - If still Jailbars, give up and throw it out the window.

Supergrafx (minor noise)

1 - Find better PSU (linear) and go from there.

We'll let you know how we get on.

[BuckoA51]

Well well, so I have an update on the Supergrafx.

Today I got through the mail an adapter so that I could connect my Megadrive/Genesis PSU directly to the Supergrafx and....

The difference to the picture noise was incredible!

The noise is now down to the point where, going from Voultar's mod I couldn't honestly complain about it (there's maybe a tiny, tiny bit of noise in some greys if you really stick your nose against the screen). The noise on the Super SD System 3 is now reduced to what everyone else is seeing (tiny bit in some greens).

I never expected that just switching to a linear PSU would have such a big effect, I was expecting to have to be getting this sucker on scopes etc to figure it out but nope... all down to using a switched PSU. I was using the one from RetroGameSupply.com and my guess is he only tested it with composite video.

That just leaves the Jailbars on the Coregrafx which seems to be a more difficult issue to resolve. From what I've learned there's just some systems that seem to persist with heavy jailbars. We're going to try re-capping the unit anyway, see if it makes any difference.

[ASDR]

Interesting, I use a SMPS with my CoreGrafx and have absolutely no issues. I did not open the PSU to see what kind of filtering it does, maybe the seller I got it from simply picked a very nice unit! But for my 1-CHIP-02 SFC I tried using some generic, cheap SMPS and boy did that look like shit. Tons of noise and wavy lines. For debugging, I tried powered the SFC with a higher quality bench PSU (still a SMPS), noise went down noticeably. Finally, using a linear PSU fixed it completely. Lesson learned, I now have a bunch of linear PSUs around and checking with one is very high up on my list of A/V troubleshooting steps.

And absolutely try the CoreGrafx with the right caps! It's like 3 cents in parts and a pretty easy solder job, 30s with a hot air station if you're in a hurry

[thebigcheese]

If you haven't already, I'd give Voultar's suggestion to switch to ceramic caps a try. He's usually got pretty good ideas about things. I notice Kez said they had moved the caps for the fix to a slightly different location. Per Tim Worthington, which of the digital and analog caps you choose to apply the fix to shouldn't really matter, but it might be worth moving them around anyway to see what happens. You could also try a different PSU since that seemed to help with your SuperGrafx. Finally, not sure how you have the LPF set, but I usually just leave that on auto because some consoles get horrible, horrible jailbars without it (like the SNES). Once it's back on, everything looks great. I don't profess to be an expert on these things, but those are all the suggestions I've found that might apply.

[BuckoA51]

Interesting, I use a SMPS with my CoreGrafx and have absolutely no issues. I did not open the PSU to see what kind of filtering it does, maybe the seller I got it from simply picked a very nice unit! But for my 1-CHIP-02 SFC I tried using some generic, cheap SMPS and boy did that look like shit.

The mains in this house is pretty crappy too, I managed to clear that up using some of those Tacima mains filters (https://www.amazon.co.uk/dp/B00UB0G4DQ/) but it does seem strange that some systems are more susceptible to switch mode PSU interference than others. I used a switched PSU with my RGB modded 2600 and that's fine as far as I can tell, and I'm fairly certain I was using one with my SNES Mini with no ill effects (can't find it at the moment though, so using a stepdown and it's original PSU).

If you haven't already, I'd give Voultar's suggestion to switch to ceramic caps a try.

Yes that will definitely be tried when the caps finally get here to do the full recap at the same time.

You could also try a different PSU since that seemed to help with your SuperGrafx.

On the CoreGrafx I was using the Genesis PSU anyway, since it already fit the machine.

[ASDR]

The mains in this house is pretty crappy too, I managed to clear that up using some of those Tacima mains filters (https://www.amazon.co.uk/dp/B00UB0G4DQ/) but it does seem strange that some systems are more susceptible to switch mode PSU interference than others.

If it makes you feel better about the state of your dwelling, mine has neutral & earth bridged at the outlet. If the neutral wire breaks inside the wall I'll fry when I touch my fridge / soldering iron / stove. Noise on your SNES is such a first-world problem

I always thought it would just be wasteful for a manufacturer to spend money on power filtering when they ship their console with a linear PSU that does not introduce any high frequency switching noise. Maybe some consoles are simply pleasantly over engineered and use a regulator with superior ripple rejection or additional filtering capacitors etc.

Per Tim Worthington, which of the digital and analog caps you choose to apply the fix to shouldn't really matter, but it might be worth moving them around anyway to see what happens

Wild speculation: The advice I always read is to place bypass capacitors as close as possible to the component, but the replacement locations for the jail bar capacitors have been choose by ease of replacement, i.e. the less stuff around them, the better. Maybe you can get better results by placing the new, higher capacity, better performing capacitor closer to the relevant IC instead of just replacing the most convenient of the bypass caps.

[thebigcheese]

Wild speculation: The advice I always read is to place bypass capacitors as close as possible to the component, but the replacement locations for the jail bar capacitors have been choose by ease of replacement, i.e. the less stuff around them, the better. Maybe you can get better results by placing the new, higher capacity, better performing capacitor closer to the relevant IC instead of just replacing the most convenient of the bypass caps.

There are only about 3 to choose from for the mod and they are all very close together anyway, so if that were the case, it is still very unlikely that it would make much difference which one you choose: https://etim.net.au/av-driver/pcebars/.

[BuckoA51]

Moved discussion of the jailbar issue to viewtopic.php?f=6&t=62817