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Old 26 October 2014, 00:40   #41
Stedy
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Hi,

I've ordered a GBS-8220, along with some Arduino goodies, will be here in 2-3 weeks

@djkoelkast

What value resistors did you use?

Measure the resistance from the sync input of the card to ground please?

@RizThomas

In your situation, the GBS8220 has not detected a vertical sync signal. Can you set your A1200 to interlaced mode and see if the issue is still present?

Amiga 240/288p video mode causes issues, when the adaptor expects 480i/576i, there are some clever kludges to try.

@thread

I checked the VESA video standards for sync signals, they state compatibility with 5V TTL signals but I know for a fact that some modern monitors/adaptors, running off 3.3V will not like 5V logic. I may be wrong but until I have some hardware to play with I won't know for sure.

The main issue with Amiga SCART cables was driving a 4.8V signal into a 1V input, attenuating the level fixed 90% of issues.

Back to coding.

Ian
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Old 26 October 2014, 00:54   #42
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I used 240R, because I didn't have 150 + 330 (and 2x 240 is 480 as well, or maybe I shouldn't have thouhgt this way).

You want the resistance between the GBS Sync in and GND on what side?
And should it be turned on and functioning (if it matters)? Should I measure the end of the cable or the connector on the board itself?
I assume I should test in the original config: so no resistor coming from the sync out of the sync stripper.
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Old 26 October 2014, 01:29   #43
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Quote:
Originally Posted by RizThomas View Post
Hello,
I have been watching how this thread goes (also scanned other messages) and can't seem to find a solution to my problem (too) with the GBS-8220. When used with A1200, the screen is split in 2 with the top part of the window (Amiga menu..etc) showing in the lower part of the screen (about 1/4 of it) and the other bottom part of the window showing on top of the screen. However, i am using the the direct wiring from DB23 to the RGB/C pins.

I have almost given up but I will probably try the one using the component inputs as stated by the OP.

Has anyone experienced or read about my problem. Thanks
If you have a picture of it I could confirm same problem I had when using PAL resolutions.
I fixed it with GBS picture adjustments, I think mostly CLAMP and PIXEL settings. Also, PAL works better at 800x600 GBS resolution.
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Old 26 October 2014, 17:53   #44
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I will pull out my whole GBS-8220 setup again (I put it back on the closet) and give your recommendations a try.

Thanks
RizThomas
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Old 27 October 2014, 12:52   #45
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Originally Posted by Stedy View Post
Hi,

I've ordered a GBS-8220, along with some Arduino goodies, will be here in 2-3 weeks
Oh yes, now I can buy a GBS-8200 without any second thoughts knowing that you'll whip up one of your 110% technically correct schematics

Can't wait for it
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Old 28 October 2014, 02:00   #46
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Hi,

@djkoelkast,

On the P3 connector, measure the resistance between the B and GND pins with the unit powered off and no cables connected. I expect 75 ohms.

@jbenam

My solution may not be simple, depends how much fiddling I have to do.

@thread

Can someone try AC coupling the RGB video into this device?

Based on my updated SCART cable, http://www.ianstedman.co.uk/Amiga/am...cable_V1.1.png, replace the 220uF capacitors with smaller 100nF capacitors. This removes the DC offset on the Amiga video before the adjustment potentiometers.

I have a list of tests to try on the GBS-8200 when it arrives. It was posted today but will take upto 2 weeks to get here. I don't remember the flight from Singapore being that long!!

Ian
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Old 29 October 2014, 09:51   #47
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Purple hue... there's something funny with A1200 and purple color... I have one that has purple hue screen while it's connected directly to the monitor (monitor supports 15 kHz), but it's fine when connected via RGB to SCART + that "famous" SCART to HDMI adapter, or directly to CRT TV.

Monitor or cable aren't the culprits either, other A1200, A600 and few A500 work fine with them, only this one A1200. I should try it over GBS8200 and see what happens . I got one few months ago and it worked fine, although I never connected this one to it.
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Old 29 October 2014, 11:09   #48
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My test was done on an A2000 though.
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Old 30 October 2014, 00:34   #49
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Quote:
Originally Posted by Stedy View Post
Hi,

@djkoelkast,

On the P3 connector, measure the resistance between the B and GND pins with the unit powered off and no cables connected. I expect 75 ohms.
I've measured it, it's 72 ohms on my meter, measured it a few times to be sure.
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Old 31 October 2014, 22:23   #50
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RGB & YPbPr are different colour space representation. So of course the colour is messed up. You cannot convert it simply by scaling the individual RBG components with voltage dividers.

Scart uses RGB, so you can connect the Amiga to it.

for people who want to understand the math:
http://en.wikipedia.org/wiki/YPbPr
Y = 0.2126 R + 0.7152 G + 0.0722 B
Y carries luma (brightness or luminance) and synchronization (sync) information.
PB carries the difference between blue and luma (B − Y)
PR carries the difference between red and luma (R − Y)

See RGB to YPBPR Component-Video Conversion here:
the circuit does the conversion math of equations below the schematic.

http://www.linear.com/solutions/1311
FYI: those are video amplifier not your regular opamp as their phase delay changes over frequency (i.e. picture get distorted).

Voltage dividers on their own cannot do subtraction. You need active circuits for that.
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Old 04 November 2014, 01:12   #51
Stedy
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@djkoelkast

A reading of 72 ohms is acceptable, assuming 5% resistor tolerance and maybe 1% DMM tolerance. Thanks for measuring it.

Will wait until I get my board before posting again.

@K.C.Lee

For SDTV, you should use the colour space in ITU-R Recommendation BT.601, which is,
Y' = 0.299 R' + 0.587 G' + 0.114 B'

Colourspace conversions are fun!

I plan to add a RGBS to YUV/YPbPr circuit and see how it performs. I agree, the crude resistor approximations are no good but they were only tried as the GBS-8220 did not accept RGB on the other connectors.
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Old 07 November 2014, 01:38   #52
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Hi,

My GBS-8200 V4 board arrived today. Hope to start experimenting this weekend. I have 18 tests planned for it. It is smaller than I expected and the build quality looks good, see how it performs.

Ian
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Old 07 November 2014, 11:24   #53
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Hi,

My GBS-8200 V4 board arrived today. Hope to start experimenting this weekend. I have 18 tests planned for it. It is smaller than I expected and the build quality looks good, see how it performs.

Ian
Exciting! Waiting for updates on this
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Old 07 November 2014, 12:15   #54
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Great news!
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Old 07 November 2014, 12:54   #55
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I'll have to connect mine. I don't remember if it it shows version anywhere in the software. Mine is also V4, but sellers say it's only because PCBs were printed when V4 was up to date and they should have V5 firmware regardless.

They're also sold under HD9800 name, the board is the same, only silkscreening is a bit different, these usually have v5.0 written on them. I don't know if there's any difference in quality.
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Old 08 November 2014, 12:21   #56
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I have a V3 mounted on the VESA points on my LCD monitor.
I replaced the capacitors with good quality ones and have a quality PSU powering it.
I wired a female SCART connector to the GBS flying leads and then have a 'Retro Computer Shack v2.3' AMIGA-SCART lead (with some added components from Ian's diagram).

The colours are a bit off. Difficult to get a nice white. But is it ok. I don't really have the space for a CRT but I would like higher resolutions.
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Old 08 November 2014, 13:40   #57
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Hi,

I'm still playing with this board but with a quick RGB to YUV to YPbPr conversion then fed into the GBS8200 I had a reasonably good picture.

The white speckles are caused by a black level clamping issue, I had to adjust the options a little to remove them. When I changed video source, the speckles and some breakup came back. I have a few ideas why, need to run the tests over the weekend.

The occasional ghosting/distortion you see around the mouse pointer, particularly on Workbench, is due to the de-interlacing method used. The grid effect points to de-interlacing, it looks like bob and weave but I think the scaling factor also contributes to this.

I have my system running off a bench power supply hooked up to my current monitor circuit. It uses 0.4A at 5V. The power does not vary with video activity. My board has switchmode converters which are more efficient than linear ones, seen elsewhere. But using a 5V to 3.3V linear converter and allowing for losses, a 1A supply would be sufficient.

My final observation is that the board is somewhat susceptible to external noise. I switched on my soldering iron and the video image jumped and then recovered. The PC and 2 monitors I had running were not affected by this. I have a few ideas of where to look.

Off to the workshop
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Old 08 November 2014, 16:50   #58
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@Stedy good luck with this converter, yep i said before RGB> YUV > VGA (8200) is reasonably good picture, is not very good.
Sometime im thinking svideo to vga looks better.
The thing is how to work this converter to as RGB to VGA with clear and stable signal,like this should working..
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Old 09 November 2014, 23:28   #59
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@Anemos

I have a clear, speckle free RGB to GBS-8200 image. I used a tweaked V1.1A SCART cable design.

There is a small band of 3-6 pixels of stale data caused by a sync artifact at the bottom of the screen, which can be removed with position offsets.

Still have more tests to try.

Ian
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Old 10 November 2014, 14:23   #60
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Originally Posted by Stedy View Post
The occasional ghosting/distortion you see around the mouse pointer, particularly on Workbench, is due to the de-interlacing method used. The grid effect points to de-interlacing, it looks like bob and weave but I think the scaling factor also contributes to this.
Any hope for a way to mitigate this? It bothers me quite a bit on my LCD with an homemade SCART cable using your schematics.

Quote:
Originally Posted by Stedy View Post
My board has switchmode converters which are more efficient than linear ones, seen elsewhere.
Which revision and model it is? I'm going to buy one shortly and I'd like to get a board with switchmode converters.

One more question: could you do some tests on smooth scrolling? I've heard that the GBS-8200 doesn't allow for it, but I would like a true expert like you to express his own opinion on that.

Thanks a lot!
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