GBS-C causes A1200 boot failure?

teh · 27 July 2023, 03:46

I purchased a Mcbazel ODV GBS-C Converter and plugged it into my Amiga.

Tried to boot and I get the flashing LED of guru meditation and then it resets and so on.

Take it off, boot the Amiga with my CRT and we get the Workbench. At which point I can then swap it into the GBS-C and it works just fine.

Reboot to try and play a game... back to constant reboots.

What gives?

teh · 04 August 2023, 04:27

Little update.

Originally I was using the RGB to VGA (15-Pin D-sub), and this was causing the Amiga to boot when connected to the GBS-C via a VGA can;e

I then found an RGB to scart lead in my box that I acquired when I acquired all my stuff way back. This seems to work with all 15Khz modes, and multiscan (though the top bar is a bit wonky as shown)

I then started playing with some of the other modes like DblPal no flicker and DblNTSC no flicker and that's when it went a big haywire.

Do I need a resistor on any of these cables or something (I've seen that posted).

Sorry for my vague knowledge on these things! My expertise is in modern computing nowadays!

bluewizard · 21 August 2023, 05:02

While I have never used SCART at all I have been using a modified GBS8220 that has a GBS-C modded into it some.

I find it works great for 640x200 NTSC. When I using 640x400 Interlaced NTSC it is less than enjoyable. I get some flickering and things don't feel as sharp.

If I try DblNTSC the GBS-C just well does not handle that well and I get garbage or the screen or my monitor just goes to sleep. I am unsure why it does not handle that and just pass it through but that has been my experiences anyway.

Snoopy1234 · 21 August 2023, 06:33

Ironically the scandoublers are set up for a CGA (15khz) vertical sync input which is the usual output of Workbench through the RGB port. Despite the RGB port being a DB23 type, DblPAL, DbLNTSC and Multiscan Productivity all produce a 31khz vertical sync similar to DB9 VGA not CGA. GBS doesn't like the input - it wants to convert to 31khz itself.

Snoopy1234 · 21 August 2023, 06:38

Quote:

Originally Posted by teh

Little update.

Do I need a resistor on any of these cables or something (I've seen that posted).

Sorry for my vague knowledge on these things! My expertise is in modern computing nowadays!

The GBS-8200 is setup for a 3.xV input from the composite sync input. The Amiga puts out 5v so an appropriate resistor modulates it to 3v.
It is said to promote longevity of the device. I put a resistor in mine and couldn't tell the difference so I guess that's up to you.
I'm not aware of what the later GBS devices such as yours are set up for though.

LordCrass · 21 August 2023, 18:33

The GBS-8000 series have a framebuffer and a motion adaptive de-interlacer, so there shouldn't be any flicker in this mode. There will be some warping around moving objects such as the mouse cursor as a side effect though. Look in the settings and make sure you don't have the de-interlace method set to "bob", as that will indeed flicker.

One of the improvements the GBS-C firmware offers is fixing the behaviour of the original to not try to de-interlace non-interlaced signals.

As a scan doubler designed to convert 15kHz sources to 31kHz output, it makes sense that it doesn't deal with already 31kHz input. I don't believe there is any pass-through option.

Daedalus · 22 August 2023, 10:49

To answer the original question, the difference with using SCART instead of VGA is that it uses composite sync instead of separate horizontal and vertical sync. If the H- and V-sync lines of the Amiga are excessively loaded, it expects there to be a genlock attached and tries to sync with it. When that doesn't happen, you get a guru. Using the C-sync line instead leaves the H- and V-sync signals alone so the Amiga can boot normally.

In general, modern displays and devices tend not to load the sync lines enough to upset the Amiga, but that GBS-8200 must be borderline. One solution (aside from using SCART) is to use a buffered VGA adaptor. These buffer the sync lines so that any loading doesn't affect the Amiga itself.

As for resistors, SCART cables need a couple of them to provide signals fully within the SCART specification. Depending on the display/device you can get away with some or none of these. Some 3.3V chips are happy to accept 5V inputs, others only put up with it for so long before they give up. I don't know which type the GBS chip that handles C-sync is... I would hope that it's fully 5V-compatible given the job it needs to so, but it's safest to assume it's not and add a resistor to drop the signal down.

xc8 · 21 February 2024, 16:09

does this crap work with Amiga ? just got one - not for the Amiga, but for a Wii, issue is when I ve tried with my A600 (scart input) the (output) signal 'resets' every some seconds, thanks.

27 July 2023, 03:46	#1
teh aka Superfrog Join Date: Nov 2003 Location: Vancouver, Canada Age: 33 Posts: 153	GBS-C Issues I purchased a Mcbazel ODV GBS-C Converter and plugged it into my Amiga. Tried to boot and I get the flashing LED of guru meditation and then it resets and so on. Take it off, boot the Amiga with my CRT and we get the Workbench. At which point I can then swap it into the GBS-C and it works just fine. Reboot to try and play a game... back to constant reboots. What gives? Last edited by teh; 04 August 2023 at 04:16. Reason: Change of title

04 August 2023, 04:27	#2
teh aka Superfrog Join Date: Nov 2003 Location: Vancouver, Canada Age: 33 Posts: 153	Little update. Originally I was using the RGB to VGA (15-Pin D-sub), and this was causing the Amiga to boot when connected to the GBS-C via a VGA can;e I then found an RGB to scart lead in my box that I acquired when I acquired all my stuff way back. This seems to work with all 15Khz modes, and multiscan (though the top bar is a bit wonky as shown) I then started playing with some of the other modes like DblPal no flicker and DblNTSC no flicker and that's when it went a big haywire. Do I need a resistor on any of these cables or something (I've seen that posted). Sorry for my vague knowledge on these things! My expertise is in modern computing nowadays! Attached Thumbnails

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21 August 2023, 05:02	#3
bluewizard Registered User Join Date: Sep 2022 Location: Washington, DC - USA Posts: 10	While I have never used SCART at all I have been using a modified GBS8220 that has a GBS-C modded into it some. I find it works great for 640x200 NTSC. When I using 640x400 Interlaced NTSC it is less than enjoyable. I get some flickering and things don't feel as sharp. If I try DblNTSC the GBS-C just well does not handle that well and I get garbage or the screen or my monitor just goes to sleep. I am unsure why it does not handle that and just pass it through but that has been my experiences anyway.

21 August 2023, 06:33	#4
Snoopy1234 Registered User Join Date: Apr 2022 Location: Australia Age: 52 Posts: 894	Ironically the scandoublers are set up for a CGA (15khz) vertical sync input which is the usual output of Workbench through the RGB port. Despite the RGB port being a DB23 type, DblPAL, DbLNTSC and Multiscan Productivity all produce a 31khz vertical sync similar to DB9 VGA not CGA. GBS doesn't like the input - it wants to convert to 31khz itself.

21 August 2023, 18:33	#6
LordCrass Registered User Join Date: Feb 2021 Location: Undisclosed Posts: 50	The GBS-8000 series have a framebuffer and a motion adaptive de-interlacer, so there shouldn't be any flicker in this mode. There will be some warping around moving objects such as the mouse cursor as a side effect though. Look in the settings and make sure you don't have the de-interlace method set to "bob", as that will indeed flicker. One of the improvements the GBS-C firmware offers is fixing the behaviour of the original to not try to de-interlace non-interlaced signals. As a scan doubler designed to convert 15kHz sources to 31kHz output, it makes sense that it doesn't deal with already 31kHz input. I don't believe there is any pass-through option.

22 August 2023, 10:49	#7
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,379	To answer the original question, the difference with using SCART instead of VGA is that it uses composite sync instead of separate horizontal and vertical sync. If the H- and V-sync lines of the Amiga are excessively loaded, it expects there to be a genlock attached and tries to sync with it. When that doesn't happen, you get a guru. Using the C-sync line instead leaves the H- and V-sync signals alone so the Amiga can boot normally. In general, modern displays and devices tend not to load the sync lines enough to upset the Amiga, but that GBS-8200 must be borderline. One solution (aside from using SCART) is to use a buffered VGA adaptor. These buffer the sync lines so that any loading doesn't affect the Amiga itself. As for resistors, SCART cables need a couple of them to provide signals fully within the SCART specification. Depending on the display/device you can get away with some or none of these. Some 3.3V chips are happy to accept 5V inputs, others only put up with it for so long before they give up. I don't know which type the GBS chip that handles C-sync is... I would hope that it's fully 5V-compatible given the job it needs to so, but it's safest to assume it's not and add a resistor to drop the signal down.

21 February 2024, 16:09	#8
xc8 no c= no fun Join Date: Jun 2008 Location: Birmingham Posts: 320	does this crap work with Amiga ? just got one - not for the Amiga, but for a Wii, issue is when I ve tried with my A600 (scart input) the (output) signal 'resets' every some seconds, thanks.

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