RGB to GBS Control, do I need to use the luma pin?

[Amagni]

The museum at which I volunteer has just got hold of a CPC 464, which I cleaned up and checked today.
One cool thing is it says "Awa" on the startup message, which I've never
seen before!

The monitor isn't working, so I soldered up a cable from the RGB output to a GBS Control so it will work on a VGA monitor.
It looked good at first, but there's an odd issue where the colours are all full brightness. E.g. grey 13 looks the same as white 26, dark red looks the same as bright red, etc

Is this due to not using the centre pin? I thought that was only for a monochrome screen. If not, does it mean I need to put resistors on the colour lines?

We're hoping to run an Amstrad day for the 40th anniversary next year, so I'm keen to get this machine working and start coding on it!

[McArti0]

A CRT RGB monitor does not use Pin6
A CRT BW monitor does not use RGB Pin1,2,3

Are you using the D-SUB input on the monitor?
Maybe you need to change the input level voltage?

[pelrun]

Ah, an early aussie model, from before Amstrad established a local sales office! My original 6128 was the same until I fried the AY in the late '80s; the replacement pcb was an "Amstrad" version. I eventually added the link to change it back to "Awa"

No, you don't need the luma pin or resistors. You probably need to modify the adc gain in the gbs-control settings, though.

[Amagni]

Thanks! I figured it was just an issue with the levels but I wanted to make sure it wasn't something like CGA with an extra brightness signal.
The last thing I had on this screen was an Oric and they only have 8 colours so it wasn't an issue I guess!

[eto]

What is a GBS Control? A GBS 8200? 

If yes, you could check if there is a 100 Ohms resistor between sync and GND: https://ramapcsx2.github.io/gbs-control/Wiki/Hardware-Mod-Library.html

If the GBS 8200 is already equipped with the GBS Control mod, everything should be fine then. If this mod is not equipped it should be applied on the GBS8200 for best results with the CPC. While it works without, you will have some issues like screen lag or weird scrolling behaviour in some games. You can perfectly align the screen with it and even add stuff like (simple) scan lines, which (imho) improves the look and feel a lot. 

[Amagni]

What is a GBS Control? A GBS 8200?

It's a pre-built unit with the control mod built in, along with some other features like HDMI out and nicer buttons.

I've used it with a Megadrive and an Oric, and now the CPC, and it's been great at getting a nice steady picture out of whatever I've plugged into it!

We do have the Amstrad monitor, so with any luck our CRT guy can make it work, but until then I'm using an LCD to test the computer separately.
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[Animalgril987]

@Amagni  Hi.
I take it the CPC video output goes to the Sync, R, G and B phono connectors of the GBSC?
Are you connecting the CPC stereo output to the audio inputs as well?
AliExpress are selling these for about 48GBP, so I might get one

Another question, sorry:
There are several switches on this unit, how do you have them set?

Thanks

Alan.

[Amagni]

@Amagni  Hi.
I take it the CPC video output goes to the Sync, R, G and B phono connectors of the GBSC?
Are you connecting the CPC stereo output to the audio inputs as well?
AliExpress are selling these for about 48GBP, so I might get one

Another question, sorry:
There are several switches on this unit, how do you have them set?

Thanks

Alan.

Yep, R,G,B and Sync are broken out to separate phono plugs.  I put Ground on all of them, just twisted all the ground wires together and soldered them.

The audio input isn't used with VGA output, so I haven't done that, but if you have a HDMI TV it will pass the audio through on HDMI, which is how I did the Sega.

I can't remember what I did with the switches, I just toggled them until the picture stopped rolling!

A nice feature of the GBS Control is that you can access the options menu via wifi on your phone or PC, so I used that to set it to 1280x960 (320 x 240 at 4x scale) and have left it there ever since.

It's a slightly hacky device from a no-name Chinese supplier, so the usual caveats apply, but my one at least has worked perfectly every time!

[Animalgril987]

Thanks @Amagni !
I was going to ask about the grounds, but you beat me to it!

Alan.

[Amagni]

Well, I tried playing with the colour settings on the GBS and the monitor last week, but at best I could barely see the difference between white and grey.

I saw something on the wiki about adding resistors to the colour lines ( https://www.cpcwiki.eu/index.php/TV_SCART_cable#Additional_Resistors ) so I went and added some 330ohm resistors to my cable.  The colours are much more distinct now, although the dark ones are still a bit bright so I'll try a higher resistance next.

Still, you can see how vivid the colours are in these images I converted on my PC, saved to "tape" on an emulator, then played back into the tape drive of the CPC:
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We still haven't got the original CRT working, but the LCD has been good so far.  It shows the "rollies" when loading games so I feel like it's getting the correct sync.

[darkhalf]

I recently got the GBS8200 / HD9800  barebones board from ebay (whilst I wait for my flybacks to arrive for the dead CTM monitors). These are only about $30AUD and you just need to wire in the CPC DIN connector to it and provide 5V-12V power input

[eto]

and you just need to wire in the CPC DIN connector to it and provide 5V-12V power input

You also should apply the GBS control mod. 

Otherwise you have much more screen lag and some games (Ghosts'n Goblins e.g.) don't sync properly.

If I am not mistaken, it also translates the 50Hz screen to 60Hz VGA. With GBS Control mod, there is a 50Hz output option. 

Plus some other features, like administration via WLAN or Scanline filters. 

[darkhalf]

@eto thankyou. Good to know. I've not used these cards much on the CPC (originally got one the Amiga) but did notice it would just 'hold' the screen. Have to look into it