Urgent help regarding CSYNC TTL

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AaronSR
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Urgent help regarding CSYNC TTL

Post by AaronSR »

So I got myself a pre modded SFC Jr. off ebay which has the Voultar RGB bypass, when I bought it I asked the seller which cable from RGC to buy and they recommended the CSYNC TTL (or pass thru as they call it). I was using it on one of those cheap Scart to HDMI boxes for about a week until last night when I was playing my PS2 (Sync on Luma - had it a few years with no issues) and switched to the SFC Jr. with this cable and suddenly the device starts switching modes and all kinds of weird stuff. At that point I was curious because the TTL thing was all I could think of and from my understanding its only for professional/non consumer equipment and even the OSSC says to not use TTL scart.

The thing is doesn't the Voultar board have the resistors built in so TTL should be safe, right? If not I'm glad it was just this $20 scaler box I destroyed rather than an OSSC or even a retrotink. Anyway RGC has accepted my return request but before I do send it back I'm wondering if like I said TTL is safe to use with this RGB bypass board and maybe its just the cheap scaler being garbage and it would be fine on an OSSC? Otherwise I should return it and get the CSYNC 470Ω cable which they recommend. Just wondering though would that degrade performance or anything if there's resistors in the board and in the scart at the same time.

Thanks.
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NewSchoolBoxer
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Re: Urgent help regarding CSYNC TTL

Post by NewSchoolBoxer »

Much more knowledgeable people about this than me who post here but I can answer your questions.
AaronSR wrote:The thing is doesn't the Voultar board have the resistors built in so TTL should be safe, right?
Per the RetroRGB guide that Voultar's shop links:
TTL Sync Jumper (Voultar’s board only)

If you purchased Voultar’s board, you’ll notice a jumper labeled “TTL” on it. That jumper will set the sync type.
The mod can output either TTL or 75 ohm sync. Yes, it has the sync resistor but you have to enable it to drop the voltage from TTL to 75 ohm level. Instructions explain in more detail, assuming you have basic soldering ability. Local retro game store SNES and Pokemon battery changer person can do this.
AaronSR wrote:from my understanding its only for professional/non consumer equipment and even the OSSC says to not use TTL scart.
Not what I would say. Sorry if this runs long but I'll skip over negative polarity, CMOS TTL, H+V and peak to peak terminology. SCART came about by using the existing composite video (yellow plug) as the sync signal. Luma is a cleaner version of composite video to use as sync. Just the sync signal itself we call "csync" (means "composite sync" for being a composite/combination of horizontal and vertical sync on the same wire) is 0.3V. With composite video, the total signal gets as high as 1V I think.

TTL sync is 5V for high logic and 0V for low logic. Obviously, sending 5V to a circuit expecting 1V can destroy it. In practice, TTL level can be 3.5V or even less and still work. This is a big advantage of TTL - it is resistant to electrical noise much better than 0 low and 0.3V high because you have several volts of tolerance to not mix up low with high.

Every computer monitor taking VGA I'm aware of uses TTL sync and probably won't work with 75 ohm level. Every retro console that natively outputs csync does so at TTL level. Every RGB capture card will take it, as will every PVM I've read a datasheet for and sync stripping chips take composite video or luma and output TTL by default.

It's really the European adoption of SCART that expects a 0.3V sync signal that brings us into this screwy situation today. Upscalers and switchers are slightly more expensive to create if they accept both 75 ohm and TTL sync. I think it's dumb not supporting both to prevent a situation like yours but I'm not creating devices myself.
AaronSR wrote:Just wondering though would that degrade performance or anything if there's resistors in the board and in the scart at the same time.
Yes. You drop 5V to 0.3V with the resistor active in the console. Voltage drops too low on resistor in the cable and now all logic is low 0V level and video doesn't display. Have the resistor working in the console or cable but not both. I think SCART cables more commonly have the resistor in order for consoles and sync strippers to output TTL than the reverse.
AaronSR
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Re: Urgent help regarding CSYNC TTL

Post by AaronSR »

Would it destroy equipment immediately or could it take days? Because for a week it was perfectly fine, so I'm wondering if its just this crappy upscaler and the cable is actually fine, and switching cables somehow messed it up. That said I'd hate to buy a more expensive device someday and it destroy it (or even a scart switcher which I should probably do anyway instead of constantly switching cables as I am right now).
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Kez
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Re: Urgent help regarding CSYNC TTL

Post by Kez »

Yeah, TTL damage can certainly take a while to accumulate.. components tend to get hotter than they should and eventually fail. Better designed devices will factor in the possiblility for TTL to some extent, and make it so that only a cheap component or a fuse is blown rather than totally writing it off. Not sure about your SCART box.

Ultimately we can't tell you the right answer because we need to know how the mod is configured. If you can take the SNES apart and get a picture of the mod PCB we can tell you which cable you need, or if you know anyone with even very basic soldering knowledge they should be able to very quickly configure the mod to work with your cable.
AaronSR
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Re: Urgent help regarding CSYNC TTL

Post by AaronSR »

I see. According to the installation video, by default its setup to use pass through cables unless you short the TTL jumper (11:03):

https://youtu.be/YTFGz8CH7lk?t=663

I'm assuming the modder just left it as is but regardless I've ordered a gamebit to open it and check so I'll update when it arrives.

For the upscaler, basically it still "works", I opened it and nothing was fried or smelt weird and it still powers on, the weird thing was that it started switching modes (NTSC, PAL, HDMI) and basically I unplugged it while it was doing this thinking it needed a power cycle, well, it got stuck in its HDMI mode lol (this one only has scart input but there are cheap scart to HDMIs that also have a HDMI input), it still powers on but yeah its stuck on HDMI now unless I somehow glitch it out again switching from PS1 to SFC

https://www.youtube.com/watch?v=m2oR2Vm0Sxw

These are cheap enough so eh, just glad it was only one of these really.
AaronSR
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Re: Urgent help regarding CSYNC TTL

Post by AaronSR »

Okay so my board looks a tad different to the one in the video (I dont see that TTL thing at all)

https://i.imgur.com/nc4i3rn.jpg

https://i.imgur.com/SaTI4Mf.png

So guessing just get the other cable after all?
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Kez
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Re: Urgent help regarding CSYNC TTL

Post by Kez »

Ah okay, well that actually looks like it could be this board:

https://voultar.com/index.php?route=pro ... duct_id=88

Assuming it is, this is what it says in the description:
C-Sync signal is automatically shaped for either 75Ω equipment or TTL based on the cable you use.
So in that case, either cable should work? It may be that your equipment malfunction was a coincidence? Although, some people prefer to have the cables with csync attenuated - which would also work with the above mod - as there is no chance of accidentally connecting a high voltage TTL signal by mistake. So if you have an exchange planned I guess it wouldn't hurt!

I will say, the installation looks pretty bad here. The way all the solder is kinda balled and spherical, is called a "cold" solder joint and often results in bad connections and issues. I'm not sure if would have caused your issue in particular.. but that is a very sloppy installation.

EDIT: Added image to highlight what I'm talking about
Image
Last edited by Kez on Sat Jan 15, 2022 10:11 pm, edited 1 time in total.
AaronSR
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Re: Urgent help regarding CSYNC TTL

Post by AaronSR »

Yeah they said that it should work and quoted that part too. Well if I get this other cable and the voltage is too low will there be no image or too dark?
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Kez
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Re: Urgent help regarding CSYNC TTL

Post by Kez »

Yeah, if the sync voltage is too low then your device just won't be able to produce a stable image.
AaronSR
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Re: Urgent help regarding CSYNC TTL

Post by AaronSR »

On a side note I think I might also use this opportunity to ditch scart and start using dsub cables (I know these can have the same TTL problem) but I think in terms of the connector and getting a switch for dsub is much better/easier than scart. That said retro access is currently not selling any so I will have to wait, but I would assume these would also work nicely with AV Famicom and N64 when I get those (obviously needing RGB mods too). The only issue is an upscaler that accepts 15khz dsub which from what I can tell, is non existent? So would need to have dsub > scart to send it to an LCD regardless. That is unless something like the OSSC Pro will accept it and I can just ditch scart entirely.

As far as the solder points go, would that be an easy fix? There are no modders locally so I would have to send it away (which to be honest I kinda want a SuperCIC installed too for PAL 50Hz), but this SNES has cost me enough so far (+buying the FXPAK Pro) so that would be sometime in the future.
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Kez
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Re: Urgent help regarding CSYNC TTL

Post by Kez »

AaronSR wrote:As far as the solder points go, would that be an easy fix? There are no modders locally so I would have to send it away (which to be honest I kinda want a SuperCIC installed too for PAL 50Hz), but this SNES has cost me enough so far (+buying the FXPAK Pro) so that would be sometime in the future.
Yeah it's just a case of reflowing the joints with flux. I'm sure if you get any other mod work done the modder would be happy to do it for you at a low cost (as long as you ask them beforehand!).
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