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Old 28 December 2020, 18:10   #1
Retrogradient
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Amiga 2000 Floppy209 rebuild - Unusual Green output on RGB

Hey English Amiga board users,
Happy Holidays!

A while back I purchased a 2000, with a very damaged main board.
Diagnostic tests failed and it took less time to get a replica board mailed to me then a Diagrom chip.

I rebuilt the motherboard, diagnosing problems as they arrived.
I now am faced with a green screen on RGB out...
This may not sound unusual, as you may suspect Agnus... however I do get video out on composite, and the system does indeed boot to workbench.
Further - Agnus has been replaced with a known good Agnus....

Diagrom yields no errors on anything either. Ram all checks good (and this is new old stock ram being used on the motherboard at this point)

I have reflowed all joints on the board, and I am still scratching my head.

Any input on where to look or what to put my multimeter on would be great.
Thank you Amiga community,
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Old 28 December 2020, 18:50   #2
Jope
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How about your Denise or video hybrid?

What does green screen mean here? Solid green with no graphics visible?
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Old 28 December 2020, 20:30   #3
Retrogradient
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Yep Solid green on the RGB out... usually indicating a ram or Agnus error/issue.

I’ve tried with a different vidiot circuit and replaced Denise... same issue
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Old 28 December 2020, 20:42   #4
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So you're getting solid green on RGB, but you get a legible picture from mono out?
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Old 28 December 2020, 22:14   #5
Retrogradient
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Quote:
Originally Posted by Jope View Post
So you're getting solid green on RGB, but you get a legible picture from mono out?
Yep!! Pretty strange right?
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Old 28 December 2020, 22:34   #6
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Very strange indeed. Anything in your video slot?

Basically there is "nothing" but some ferrite beads between the video hybrid and the 23pin RGB port. Maybe the ferrite for green is shorted.
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Old 30 December 2020, 04:47   #7
Retrogradient
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Thanks Jope,
Tomorrow when I have some time I will test for continuity between the farrites and the pins.
I’ll let you know how it goes!
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Old 11 January 2021, 00:53   #8
Retrogradient
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Quote:
Originally Posted by Jope View Post
Very strange indeed. Anything in your video slot?

Basically there is "nothing" but some ferrite beads between the video hybrid and the 23pin RGB port. Maybe the ferrite for green is shorted.
So I have checked all traces between the RGB Video, Vidiot HY200 circuit, U205 and U206... Denise, and the hsync/vsync coming off Agnus...
all apparently good... checking out okay... really confusing.
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Old 11 January 2021, 09:49   #9
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Make your Amiga come up with a black screen and measure the voltages along the r + g + b signal paths to see where it starts going high?
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Old 12 January 2021, 02:24   #10
Retrogradient
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Quote:
Originally Posted by Jope View Post
Make your Amiga come up with a black screen and measure the voltages along the r + g + b signal paths to see where it starts going high?
Hey Jope,

So I can get the system to halt on a white screen on boot if I pull the floppy ribbon out...
to be clear though, I mean white on composite RCA out, and the rolling green screen output on RGB, that continues to periodically go out of sync to black screen.
The voltage outputs are as follows:
White screen gives:
R:1.525v
G:1.515v
B:1.524v

Csync 3.75v
Hsync 4.41v
Vsync 4.77v

If I let it boot to workbench however:
R:0.917v
G:1.106v
B:1.355v

Csync 3.73v
Hsync 4.41v
Vsync 4.77v

The high blue signal would make sense I would imagine as WB 1.3 screen is mostly blue...

Is it at all possible my cheap scan doubler is defective?
I’m using an amivga adaptor to this GBS-8200 V4 scandoubler...

Just throwing an idea out there... it’s probably fine though.
Attached a picture of my workbench screen working through composite:


I guess my testing is somewhat limited with out an oscilloscope... lol
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Old 12 January 2021, 04:21   #11
dalek
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For the GBS - you know that you need to use the white connector for RGB in from the Amiga, not the VGA connector right?

Google some GBS-8200 Amiga specific connection images.

Also, the quality will be bad unless you use something like https://github.com/ramapcsx2/gbs-control
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Old 12 January 2021, 21:50   #12
Retrogradient
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Quote:
Originally Posted by dalek View Post
For the GBS - you know that you need to use the white connector for RGB in from the Amiga, not the VGA connector right?

Google some GBS-8200 Amiga specific connection images.

Also, the quality will be bad unless you use something like https://github.com/ramapcsx2/gbs-control
I have been using the white connector to pinout initially on the GBS-8200, as well as having tried it with vga cable in to the GBS-8200.
Same result in either case.

Thanks for the info on the GBS firmware though!
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Old 18 January 2021, 02:45   #13
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In hopes of shedding some more light on what this problem actually looks like,
I have posted a couple videos on YouTube.

First video shows the RGB output when I power on the system.
Additionally it doesn’t actually boot. I can tell because if I switch to composite video, it just shows a frozen white screen on composite.
[ Show youtube player ]

Second video shows composite video output successfully booting.
I have to disconnect the RGB video for this to be successful....
[ Show youtube player ]

Anyone seen anything like this?
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