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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 12:07 am 



Joined: 08 Mar 2017
Posts: 569
The 100 Ohms are necessary still, yes. And yea, just replacing the 2 SOG capacitors removes the need for a sync stripper.
Doing this, the internal stripper works great!
A single 750pF should work, I think.
The PSU is 5V at 1A? If so, it probably is overloaded. The GBS + ESP8266 draw about 500mA at 5V, so 2.5W.

NoAffinity:
It tries to work, but other than seeing a faint VSync signal sometimes, there's not much happening.
You can't control RGBHV bypass with the preset buttons. It either works automatically, or not at all.
Do you have the 100 Ohm resistor connected? It may have to go for VGA inputs (it depends on the output of the Dreamcast).
Also, is the console definitely putting out real VGA?
There is a "print infos" button in the web ui. If you enable that, it spews out status information continuously.
Try to capture what happens when it goes into RGBHV bypass.


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 10:38 am 



Joined: 08 Mar 2017
Posts: 569
I modified a second (slightly different) GBS with the 2 x 1nF SOG caps and it works nicely as well.
I'd say it is on par, maybe a little better even, than the LM1881 solution.
With the internal stripper doing all the work, the H-PLL stays locked over a wider range it seems.
This hints at less jitter in the system, which makes sense.
Before, it was working with basically 2 strippers in a chain. Now it's just one.

Regarding Dreamcast, does anyone know for sure what it's VGA mode is like?
Particularly I wonder if it outputs pure HSync, or if it uses CSync on H + VSync on V.
Also, are the sync tips negative? So basically this modeline:
Code:
640 480 60Hz 31.475 kHz ModeLine "640x480" 25.18 640 656 752 800 480 490 492 525 -HSync -VSync


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 11:22 am 


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Location: Australia
Pure h v sync. Not sure about polarity.


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 11:34 am 



Joined: 09 Jun 2018
Posts: 35
when i have modded my DC to vga, only one monitor worked with it, and it supported sync on green and all that good stuff. Samsung older tv and benq tv didn't show anything at all.


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 1:24 pm 


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Did you try switching between the 3 video modes?

The select pins are 6 and 7. Ground either one for two kinds of 15kHz RGB, ground both for VGA.

https://gamesx.com/wiki/doku.php?id=av:dreamcastav


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 2:05 pm 



Joined: 11 Oct 2018
Posts: 2
Hello,
Just a question please.
When i connect a console with composite video sync, i have to use the 100ohm resistor between Sync and ground on gbs8200 driven by gbs conbtrol.
And when the console has csync, i have to remove this resistor ?
Thank you !
Next step for me, replacement of the capacitor


Last edited by crossmanbx on Fri Oct 12, 2018 4:09 am, edited 1 time in total.

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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 2:30 pm 


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Posts: 335
@rama

this is a little out of scope, but how feasible do you think it would be to grab the digital RGB signals right out of the scaler chip? might require changing registers to enable them I'm not sure...

I think a cool project would be to route them to a HDMI tx chip to get a real HDMI gbs without the ADC


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 2:35 pm 



Joined: 09 Jun 2018
Posts: 35
@Syntax, yeah i tried, it was normal vga from dc. Everything was fine, but maybe my board was wrong. I did diy solution with caps and resistors


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 4:44 pm 


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redcatex wrote:
@Syntax, yeah i tried, it was normal vga from dc. Everything was fine, but maybe my board was wrong. I did diy solution with caps and resistors


This without the buffer?

https://www.raphnet.net/electronique/dr ... dricas.gif


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 5:09 pm 



Joined: 09 Jun 2018
Posts: 35
Yep. It was from mmonkeys website


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 5:29 pm 



Joined: 08 Mar 2017
Posts: 569
@maxtherabbit:
The digital output pins are all on the left side of the chip. If you have some technique to get the connections down, then the rest shouldn't be too hard.
Though it might be easier to remove the IC and put it on a new board ;p
Such a mod would be great for tuning the picture quality though!
Image

There's one issue:
Pin VB3 (or so) is also the debug pin. If this is used for display, I won't be able to measure the frame time anymore.
Getting the output timing close to the source will be harder then, but still possible via a new wire VSync out > ESP8266 input.


Last edited by rama on Thu Oct 11, 2018 5:34 pm, edited 1 time in total.

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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 5:30 pm 



Joined: 12 Jun 2017
Posts: 89
Went ahead and removed LM1881 circuitery (kept the 100R to ground), used 750pF (measured around 800pF before installing) for C33 and C35, had to be a bit creative since they were larger SMDs, installed them sideways lol. Using latest dev branch.


Using a VGA CRT monitor, everything worked, so plugged PS2 in component, and also no problem, in either 480i or 480p. Stayed in sync even during 1 frame flashes.

BTW, does the chip have deinterlacing.


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 5:38 pm 



Joined: 08 Mar 2017
Posts: 569
Heh, I also do the sideways installation sometimes. If it works, it works! ;p

The chip prides itself on its deinterlacing engine, but I won't work on it anytime soon.
It'll mean some lag, it'll require tighter timing control, there'll be RAM constraints, etc.

But yeah, the chip has it. They waste half the programming guide on it ><


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Thu Oct 11, 2018 10:58 pm 


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rama wrote:
Do you have the 100 Ohm resistor connected? It may have to go for VGA inputs (it depends on the output of the Dreamcast).

I do have the 100 ohm resistor between ground and sync, on the 5-pin RGBS input. Based on what was said above, about the DC's output, do you recommend resistors at the DB-15 input as well? If so, between HS->ground and VS->ground?


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Fri Oct 12, 2018 8:28 am 



Joined: 08 Mar 2017
Posts: 569
Try removing it first.
Most VGA sources expect high impedance termination, such as is already installed on the GBS.


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Fri Oct 12, 2018 8:22 pm 


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I remember you saying a long time ago that this chip cannot accept TTL level sync Rama, and as such i placed a 470R resistor on the VGA sync inputs of my GBS way back then.

This would effect passthru right?


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Fri Oct 12, 2018 9:56 pm 



Joined: 08 Mar 2017
Posts: 569
It doesn't like 5Vpp, that's for sure.
I'm pretty certain now that the maximum for all inputs (SOG and HS/VS) is Vcc + 0.3V, so 3.6Vpp is acceptable.
A 5Vpp signal will be attenuated a little by the existing 1k (VS) and ~560 Ohm (HS) termination resistors.
It will be around 4Vpp when it reaches the pins, just outside specs.
It'll be fine for a while.
Also consider that they built it like this, with a VGA input and all, so eh? ;p

For permanent use, series resistors would be the best fix, I suppose.

Edit:
Passthrough modes don't electrically connect source to display. All signals get either sampled (RGB) or mirrored (Sync).
The difference is that passthrough modes don't do anything significant to the raw data, ie: no digital processing on it.
Even the memory bus is disabled now. You could desolder the memory chip and it'll work! ( I think! :p)


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Sun Oct 14, 2018 11:13 pm 



Joined: 27 Jul 2018
Posts: 2
Please, can someone draw an schematic for the final mod? :cry:

I tried to figure it out reading all the latest posts, but I can´t imagine/understand the mod.
I preffer an schematic draw, it's more clear and universal. :wink:

This project is awesome!!
Greetings!


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Mon Oct 15, 2018 12:45 am 



Joined: 08 Mar 2017
Posts: 569
Hey,
there isn't much to do. The Wiki should help you figure it out:
https://github.com/ramapcsx2/gbs-contro ... e-Hardware


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Mon Oct 15, 2018 2:58 pm 


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rama wrote:
It doesn't like 5Vpp, that's for sure.
I'm pretty certain now that the maximum for all inputs (SOG and HS/VS) is Vcc + 0.3V, so 3.6Vpp is acceptable.
A 5Vpp signal will be attenuated a little by the existing 1k (VS) and ~560 Ohm (HS) termination resistors.
It will be around 4Vpp when it reaches the pins, just outside specs.
It'll be fine for a while.
Also consider that they built it like this, with a VGA input and all, so eh? ;p

For permanent use, series resistors would be the best fix, I suppose.

Edit:
Passthrough modes don't electrically connect source to display. All signals get either sampled (RGB) or mirrored (Sync).
The difference is that passthrough modes don't do anything significant to the raw data, ie: no digital processing on it.
Even the memory bus is disabled now. You could desolder the memory chip and it'll work! ( I think! :p)

Just to be clear on this, you recommend a 100ohm resistor at HS and VS, in series with the existing termination resistors?

^^manuelink64, there isn't necessarily a one-for-all schematic. Like with my wemos board, I had to figure out which pins would go to SDA and SCL. The info on the wiki gets you going in the right direction, it may be exactly correct for the arduino board you use to drive your GBS, or may require a little bit of inventiveness..but not too much. :)

In addition to the wiki, replacing the resistors at C33 and C35 with 1nF SMD resistors is recommended to clean up the stock sync circuit and avoid having to use an external LM1881-based circuit.


Last edited by NoAffinity on Sat Oct 20, 2018 4:37 am, edited 2 times in total.

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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Mon Oct 15, 2018 8:12 pm 



Joined: 08 Mar 2017
Posts: 569
If you're planning to use standard PC VGA as well as TV level sources, then you need a switchable resistor Sync-In to ground of 100 Ohms.
The resistor goes on when using TV level sources and goes off for VGA.

The VSync input is only connected to the VGA port VSync pin, so only VGA mode is relevant for it.
The stock GBS setup is 100 Ohms series, 1kOhm to ground. This allows 4Vpp to the chip pin. I don't know why they made it that way.
Some analog frontends claim to be 5V compatible, but the Datasheet for the GBS doesn't mention any of that.
So my recommendation has to be to increase the series resistor for VSync in.

The HSync path is slightly different, and the HSync input pin on the chip sees a 3.6Vpp signal for a 5V source.
This is barely safe, so another series resistor should be added if you plan to use VGA a lot.

I realize that adding series resistors is difficult.
Either those traces need to be broken and re-routed, or the existing 100 Ohm series resistors (R21, R22) replaced.
Again, this is only relevant for VGA modes.
All RGBS (TV level) sources are fine with just the extra 100 Ohm Sync-In to ground resistor.


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Tue Oct 16, 2018 10:01 pm 



Joined: 16 Oct 2018
Posts: 4
Hi


Last edited by jicko777 on Sun Nov 11, 2018 9:54 am, edited 1 time in total.

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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Tue Oct 16, 2018 10:32 pm 



Joined: 16 Oct 2018
Posts: 4
https://oldbrowser.files.fm/u/hr5gee9u


Last edited by jicko777 on Sun Nov 11, 2018 9:59 am, edited 1 time in total.

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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Wed Oct 17, 2018 8:23 pm 



Joined: 08 Mar 2017
Posts: 569
By the way, if anyone wants to mod their first generation PSX (SCPH 1000, 1001, 1002), this is an easy and fully buffered CSync modification.
CSync will be transistor buffered and ~ 0.7Vpp when terminated with 75 Ohms. Perfect for TV or gbscontrol ;)

Image

Image

Image

The AV Multi Out will now carry CSync on the old CV pin, so regular RGB SCART cables will work with it.
CV is still available on the yellow RCA jack, if necessary.


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Fri Oct 19, 2018 2:13 pm 



Joined: 11 Aug 2018
Posts: 17
Location: Stockholm
rama wrote:
The 100 Ohms are necessary still, yes. And yea, just replacing the 2 SOG capacitors removes the need for a sync stripper.
Doing this, the internal stripper works great!

Great findings rama :) The other day I made a 3d sketch of a case design I had in mind for gbs-control...just wanted to get a feeling for how it would/could look like...
Spoiler: show
Image

Spoiler: show
Image


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Fri Oct 19, 2018 3:09 pm 


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Hey rama, I got the 1nF caps, going to replace C33 and C35 tomorrow. My buddy's having a get toghether/BBQ tomorrow, and I've been called upon to bring my SNES and N64. His 60" Aquos TV has a VGA input, and my intent is for GBS-Control to be at the core of the gaming. :)

:edit: @rama - I'm starting to plan this out further before I jump into the final mods on the GBS-8200, before tomorrow's get together. I will be making a SCART female-to-RGBS adapter, in order to use my existing SCART cables and plug them into the 5-pin header. Using the SNES csync cable and N64 sync on luma cable, both of which work great on OSSC (cables are high quality from RGC, properly terminated/attenuated), is there anything else needed on my homemade SCART female-to-RGBS adapter - any additional resistors, caps, etc.?


Last edited by NoAffinity on Sat Oct 20, 2018 4:37 am, edited 2 times in total.

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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Fri Oct 19, 2018 10:20 pm 



Joined: 08 Mar 2017
Posts: 569
jbilander:
Do you have a 3D printer for trials?

NoAffinity:
Without changing to the 1nF caps first, I can only guarantee that the CSync source will work.
Luma will most likely work, but may have those white to black sync dropouts.
You can put the 100 Ohm resistor on the GBS itself, so nothing special is required for the SCART adapter.
But test this first! SCART pinouts are confusing ;p


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Fri Oct 19, 2018 11:42 pm 


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Replaced the caps at c34 and c35 (I was mis-stating the locations, and have gone back and fixed that on my posts). The image looks great, no more dropout on bright screens! :D

Now to hack together a SCART connector. Thankfully, I have the 8-pin connector for the alternate RGBS input, and pinouts are not hard to find for these boards. 8)

Spoiler: show
Image
Image


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Sat Oct 20, 2018 12:13 am 



Joined: 08 Mar 2017
Posts: 569
Wow, these are the most tiny caps they could possibly find :p

But yeah, I'm afraid you've got a wrong one with that C34 :p
I've done 3 boards so far, and it's always C33 and C35 that go to the SOGx pins.
You can check this: There is a 102 (1kOhm) resistor right next to the C33 SOG cap.
If the cap and the resistor are connected on one side, then your cap is the SOG cap (and the resistor is one of the 2 that make up the ~560 Ohm default termination).

That C34 should be switched back to roughly 100nF.
(Though the datasheet says 47nF, I think going 100nF won't affect the picture.)


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 Post subject: Re: GBS 8200/8220 CFW Project
PostPosted: Sat Oct 20, 2018 4:23 am 


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Dammit...I looked at the picture you marked up, but should've read through a few more posts to see the actual mod you did. Of course the caps I removed have disappeared. Is the stock cap at c33 suitable to place at c34?

Sent from my SM-G955U using Tapatalk


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