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 Post subject: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 4:04 am 


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Joined: 06 Oct 2015
Posts: 1972
Location: Montréal, Canada
Firstly, a disclaimer: I'm not an electrical engineer. Most of the technical details below are going to be stuff I've been told by Ste and am parroting here.

There are not many options for people who want to convert YPbPr signals into RGBS in order to integrate consoles like the Wii into a primarily RGBS setup: the only one that's readily available is the Beharbros Garo. Unfortunately, it has some critical design flaws that prevent it from being used for this purpose in many cases. Its primary problems:

  1. It directly drives the SCART/VGA port with the outputs of the TI LMH1251 chip, despite the datasheet specifically saying you can't do that, which results in various glitches in the video output like blooming in dark areas
  2. It generates an invalid csync signal for the SCART port because it just XNORs the H and V sync together, which is incorrect and won't work properly with many digital devices like the OSSC.
  3. The TI LMH1251 seems to lack a DC restore circuit, so the black level for Pb and Pr moves around, causing the purple flash during some transitions (most notably opening the settings screen on the Wii)

There are also secondary problems, like 90 degree traces being susceptible to EMI, the scanliner being implemented by just shorting the video signal to ground every other scanline, not all the grounds on the video ports being connected, etc. Nothing to be done about those, other than to say, don't use the scanliner, and if you want, you can connect the missing ground pins on the bottom of the board.

I was talking to Ste from HD Retrovision, and the idea came up of trying to do an RGB bypass mod on the Garo to fix these problems. I had the idea that you could avoid having to implement a sync combiner if you just split off the input luma signal and routed it to the sync output, which would give you a clean unmodified sync-on-luma without much effort. Ste then went and designed this circuit to perform the bypass mod using a TI THS7374 chip:

Image

This bypass mod should fix two of the three main issues: it bypasses the Garo's wonky RGB circuitry and properly buffers the signals which fixes the RGB quality issues, and it bypasses the Garo's broken sync generation to solve the invalid sync issues. It does not solve the purple flash issue, as the TI LMH1251 datasheet does not provide enough information to design a DC restore circuit to fix that issue. However, after this mod, the Garo will work perfectly fine with 240p video and the OSSC and gscartsw-lite.

To perform this mod, you'll need the following:

  • A THS7374 chip, preferably on a TSSOP14 breakout board like I'm using, or maybe even on a PCB with all the other components
  • 4x 100nf ceramic capacitors
  • 4x 75ohm resistors
  • 1x 10nf ceramic capacitor
  • 1x 1uf ceramic capacitor

Here are the instructions for the mod:

Part 1 (building the mod circuit):

  1. Connect CH1_IN, CH2_IN, CH3_IN and CH4_IN (pins 1-4) of the THS7374 to the 100nf capacitors and add a wire coming off each one
  2. Connect CH1_OUT, CH2_OUT, CH3_OUT, and CH4_OUT (pins 14-11) of the THS7374 to the 75ohm resistors and add a wire coming off each one
  3. Add a wire to GND (pin 5) of the THS7374 and bridge GND (pin 5) to DISABLE (pin 6)
  4. Add a wire to Vs+ (pin 10) of the THS7374 and bridge Vs+ (pin 10) to BYPASS (pin 9)
  5. Twist the legs of the 10nf and 1uf capacitors together and solder them together, then put them between GND (pin 5) and Vs+ (pin 10). It may be easier to connect them to DISABLE (pin 6) and BYPASS (pin 9) since those pins are bridge to GND (pin 5) and Vs+ (pin 10) anyhow. I had the caps in the wrong orientation so I used a wire to finish the connection. Oh well.

This is what my board looked like after construction. The heatshrink tubing is because I'm not proud of the solder joints on those wires, so I'm not going to let you see them :P

Image

Part 2 (installing into the Garo):

  1. Remove C11/C12/C13 to isolate the R/G/B outputs on the SCART connector and R12 to isolate the sync (pin 19) on the SCART connector. Don't damage the pads, we need them for the rest of the mod.
  2. Connect the CH1_IN (pin 1) wire to the luma signal from the green RCA jack before it goes into any other components. You can get this signal from the input to R8 (left pad), R3 (left pad), and C4 (right pad). I used the input of C4 because it was much easier to get to with a soldering iron.
  3. Connect the CH1_OUT (pin14) wire to the output of R12 (right pad).
  4. Connect the GND (pin 5) wire to a ground point. They're all over, I used the negative side (right pad) of C7.
  5. Connect the Vs+ (pin 10) wire to +5v on the Garo. I connected it directly to the +5v output of the voltage regulator (middle pin) right below the DC barrel jack.
  6. Connect the CH2_IN, CH3_IN, and CH4_IN (pin 2-4) wires to the positive pads of C11, C12, and C13. C11 is the red signal, C12 is the blue signal, and C13 is the greensignal. You may want to rearrange the soldering of steps 3 and 4 to make it easier (I did C13-, C13+, C12-, C12+, C11-, C12+). It doesn't actually matter which channels you connect to which capacitor pads, just make sure that the IN and OUT of each channel are connected to the correct sides of the same pad. They need to stay in pairs, obviously.
  7. Connect the CH2_OUT, CH3_OUT, and CH4_OUT (pin 13-11) wires to the negative pads of C11, C12, and C13.

That's it. I put some kapton tape on the Garo under where the mod was going to be, and some kapton tape on the bottom of the mod to cover the bottom solder joints. The Garo's cover should still fit just fine. The result (LED looks weird because I sharpied it to reduce the brightness, that sucker is way too bright):

Image

Some reference material:

TI LMH1251 datasheet: http://www.ti.com/lit/ds/symlink/lmh1251.pdf
TI THS7374 datasheet: http://www.ti.com/lit/ds/symlink/ths7374.pdf

I've got a before/after shot showing the blooming issue, maybe I'll post that in a reply.


Last edited by Guspaz on Fri Dec 22, 2017 5:29 am, edited 5 times in total.

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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 4:17 am 



Joined: 05 Mar 2017
Posts: 290
Location: Woodinville, WA
Cool. I seem to remember DirkSwizzler stating that he was able to use the Kenzei device to properly combine H+V. Do you know if this is true? If so, what is that device doing properly? Lastly, has beharius commented on a possible Garo V2 that corrects these issues? On the surface, that would seem simpler than everyone needing to mod their own device.


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 5:06 am 


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Location: Montréal, Canada
I've never seen a Kenzei, but DirkSwizzler was using it as a sync combiner to merge the separate H/V sync off the Garo's VGA port. My guess is that the Kenzei combines sync in a less broken manner? That approach doesn't fully avoid the other issue with the Garo, though, namely that it drives the video outputs directly from the LMH1251 chip, which can't handle it.


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 7:01 am 



Joined: 02 Mar 2017
Posts: 565
Guspaz wrote:
There are not many options for people who want to convert YPbPr signals into RGBS in order to integrate consoles like the Wii into a primarily RGBS setup


I could very well be missing something, but what's wrong with models like the Extron CVC 200 or 300 which convert YPbPr (or even RGsB - sync on green) to RGBS or RGBHV? I've seen those for as cheap as $25 +shipping on eBay recently (even on Craigslist near me). A quick google search pulls up some other models from other companies but I've only personally used the Extron.


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 8:02 am 


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Location: Bellevue, Washington, USA
I haven’t used the extron units. But I tried a couple by audio authority, some from Keene, and every unit I tried did something weird or didn’t work with all the formats that I need them to.

Even with the janky sync problems, the Garo did the best job of anything I tried.

I’m currently using the gscartsw_lite to fix the Garo sync. But I’d love to bypass that nonsense and further reduce the length of my video chain for component and svideo systems.

I’m super excited to try this mod once I get the parts. Thanks Adam & Ste.


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 10:57 am 


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Whoa, nice work Guspaz and Ste!


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 2:14 pm 


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Agreed really great work, hopefully Beharbros can take on board some of these improvements for a Garo 2 too.
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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 4:00 pm 



Joined: 05 Mar 2017
Posts: 290
Location: Woodinville, WA
Dochartaigh wrote:
I could very well be missing something, but what's wrong with models like the Extron CVC 200 or 300 which convert YPbPr (or even RGsB - sync on green) to RGBS or RGBHV? I've seen those for as cheap as $25 +shipping on eBay recently (even on Craigslist near me). A quick google search pulls up some other models from other companies but I've only personally used the Extron.


Reading the CVCs' manuals, it seems like you're technically required to switch the input format when switching between 480i/480p. Do you know if this is absolutely necessary? Given how frequently some systems switch between these, that would be a pain. :)


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 6:57 pm 


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strygo wrote:
Dochartaigh wrote:
I could very well be missing something, but what's wrong with models like the Extron CVC 200 or 300 which convert YPbPr (or even RGsB - sync on green) to RGBS or RGBHV? I've seen those for as cheap as $25 +shipping on eBay recently (even on Craigslist near me). A quick google search pulls up some other models from other companies but I've only personally used the Extron.


Reading the CVCs' manuals, it seems like you're technically required to switch the input format when switching between 480i/480p. Do you know if this is absolutely necessary? Given how frequently some systems switch between these, that would be a pain. :)


Yes, you have to use the dial switch on my units. They also lose sync with the Wii's white screens. The outputs are also slightly noisy and jittery on an LCD.

I think they are rubbish. Maybe I have bad units of both CVC models, but that seems unlikely to me. The Garo easily outperforms my CVC devices for RGBHV. I did buy both CVC's used in lots, but it seems unlikely that the CVC units would be the only items to not work properly due to age/use.
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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 8:14 pm 



Joined: 02 Mar 2017
Posts: 565
orange808 wrote:
Yes, you have to use the dial switch on my units. They also lose sync with the Wii's white screens. The outputs are also slightly noisy and jittery on an LCD.

I think they are rubbish. Maybe I have bad units of both CVC models, but that seems unlikely to me. The Garo easily outperforms my CVC devices for RGBHV. I did buy both CVC's used in lots, but it seems unlikely that the CVC units would be the only items to not work properly due to age/use.


Which CVC's do you have - there's 100, 200, 300 models I think? I've been using the 200 and it's been good to me so far (along with my 5 other Extron devices - all have been great even when they're ~20 years old so far).

For the dial I want to say I used setting 7 (could be wrong) which is marked "NTSC/PAL" - no resolution is listed. I'm pretty sure I tested my one single 480i game -Hitman 2- on my original Xbox (which is what I use the CVC 200 for), and I'm pretty sure I didn't have to touch the dial when i switched to a 480p game. I did however have to test each of the 9 settings on the dial to find one which worked properly - what the manual says isn't exactly intuitive in choosing the right one. Some had off color, others were flickery like you mentioned.

Admittedly though, I've barely put the CVC 200 through it's paces at all. I'm currently only using it along with an Extron VSC 700 so I can have my Xbox displayer in 480p on one monitor, and 480i on another at the same time. I even bought Enter the Matrix which can do 720p and 1080i on the original Xbox to test those resolutions when I get some time. I've also been meaning to find my currently lost PS2 component cables so I can see if PS1 games on the PS2, through component converted to RGBS will maintain 240p...so I still have to do quite a bit more testing to get a full impression of this converter - and sadly don't own a Wii like you've tested your CVC with.


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Dec 22, 2017 10:41 pm 


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Dochartaigh wrote:
orange808 wrote:
Yes, you have to use the dial switch on my units. They also lose sync with the Wii's white screens. The outputs are also slightly noisy and jittery on an LCD.

I think they are rubbish. Maybe I have bad units of both CVC models, but that seems unlikely to me. The Garo easily outperforms my CVC devices for RGBHV. I did buy both CVC's used in lots, but it seems unlikely that the CVC units would be the only items to not work properly due to age/use.


Which CVC's do you have - there's 100, 200, 300 models I think? I've been using the 200 and it's been good to me so far (along with my 5 other Extron devices - all have been great even when they're ~20 years old so far).

For the dial I want to say I used setting 7 (could be wrong) which is marked "NTSC/PAL" - no resolution is listed. I'm pretty sure I tested my one single 480i game -Hitman 2- on my original Xbox (which is what I use the CVC 200 for), and I'm pretty sure I didn't have to touch the dial when i switched to a 480p game. I did however have to test each of the 9 settings on the dial to find one which worked properly - what the manual says isn't exactly intuitive in choosing the right one. Some had off color, others were flickery like you mentioned.

Admittedly though, I've barely put the CVC 200 through it's paces at all. I'm currently only using it along with an Extron VSC 700 so I can have my Xbox displayer in 480p on one monitor, and 480i on another at the same time. I even bought Enter the Matrix which can do 720p and 1080i on the original Xbox to test those resolutions when I get some time. I've also been meaning to find my currently lost PS2 component cables so I can see if PS1 games on the PS2, through component converted to RGBS will maintain 240p...so I still have to do quite a bit more testing to get a full impression of this converter - and sadly don't own a Wii like you've tested your CVC with.


I have a CVC 200 and a CVC 300. I will have to break them out again soon and get a refresher. I usually test RGBHV video using a Sony LCD television I use for video. That display makes noise and artifacts stick out like a sore thumb.

The Wii problems were my biggest complaint. Naturally, any time the video completely blinks out, that's a deal breaker.

I never really got to the bottom of the issues. Probably because the Garo plugs right in and gives me much better RGBHV results. I use the Garo to drive CRT's in my setup and it looks pretty good (although it is obviously a flawed device).

------

I do have some mysterious noise (that is very apparent on LCD displays) when I chain the Garo output through my Kramer RGBHV switch. I think this might explain it. Good stuff, Guspaz.
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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Tue Feb 13, 2018 7:53 am 



Joined: 05 Mar 2017
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Location: Woodinville, WA
I recently picked up a CVC 300 and finally received some connectors to incorporate it into my setup. So far, the CVC 300 has proven to be more versatile than the Garo - in addition to handling 240p/480p/480i, it also handles 720p and 1080i.

I've had my few component systems (Xbox, GC, Wii) route through a Garo until now. This has generally worked, except that it hasn't worked with 720p and 1080i from the Xbox. Based on the recommendations from this thread, I got a cheap CVC 300. When I set it to Position 7, all signals (240p/480i/480p/720p/1080i) work to my PVM-20L5. The build quality isn't as nice as the Garo, but its increased compatibility gives it the edge for me.

orange808: I didn't observe any signal degradation via RGBS, so I do wonder if your units were happen to be defective. If there is anything you or others would like me to try, let me know.


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Tue Feb 13, 2018 8:23 am 


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Strange. I use the Garo to get 720p and 1080i from PS2 and XBox and it seems to work well enough.

EDIT: I forgot that these were the modes with goofy sync unless you fix it with the mod, a gscartsw_lite, or a Kenzei.


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Tue Feb 13, 2018 6:03 pm 



Joined: 11 Jan 2018
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The pictures are not viewable, any chance they can be re-added?


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Feb 16, 2018 12:37 am 


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strygo wrote:
I recently picked up a CVC 300 and finally received some connectors to incorporate it into my setup. So far, the CVC 300 has proven to be more versatile than the Garo - in addition to handling 240p/480p/480i, it also handles 720p and 1080i.


The Garo should do 720p and 1080i?

shadowhc wrote:
The pictures are not viewable, any chance they can be re-added?


Not sure what you mean, they're showing up fine here. They're hosted on Imgur.


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Fri Feb 16, 2018 3:04 am 



Joined: 05 Mar 2017
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Location: Woodinville, WA
I haven't had a chance to test the Garo direct to my TV and PVM. However, Garo via a Hydra doesn't handle 720p or 1080i. The Extron CVC does.


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 Post subject: Re: Garo (YPbPr -> RGB converter) RGB & Sync bypass mod
PostPosted: Tue May 15, 2018 6:25 am 


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So I finally got a chance to try this last week.

I originally assembled it with mostly SMD parts because I had them lying around. But that was a giant pain and my results were a bit weird.

On my test case of Xbox 1080i I was seeing a bit of ghosting in high contrast text and the sync would flip out in 720p and 1080i if I had it going into a gscartsw 3.4 port other than 8. And worked fine through the gacartsw_lite with sync regen on.

I assumed that I screwed up one of the tiny tiny SMD parts and ordered through-hole from Digi-Key.

Got my new parts today and assembled a new board. The ghosting is gone but the sync issues are exactly the same.

Moreover, On the gscartsw 3.4 port 8 I see quite a bit more wavy noise going on. But running through a lite first is much cleaner which baffles me a bit.

Going to start double checking my work. But if anyone can hypothesize what to try I’d appreciate it. My skills are only good enough to follow precise directions. After that I’m lost.


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