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Old 24 September 2015, 08:15   #1
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Amiga 1200 washed out video and flicker problem


I was testing out my new ACA1221 today and got it fully licensed and wanted to see if it was going to be stable at 28Mhz. (From my trial tests it seemed to be doing fine), so I decided to copy a bunch of files to RAM: to fill it up and task the CPU and see how it would do. Came back later and machine was locked up, with LED flashing and screen looked washed out! I turned it off and then back on and now it boots up with the screen all washed out and colors look a little off, lot of PINK, and the screen also flickers/flips every every once in a while. Does it with Composite and RGB, see pics. The Car pic is RGB. Seems to work fine otherwise. So is this a big coincidence with the lockup or bad luck? Did I fry something? What can I check?
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Last edited by TjLaZer; 24 September 2015 at 09:19.
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Old 25 September 2015, 05:54   #2
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Ran into a thread and saw this quote

Originally Posted by Zetr0 View Post

Sadly my friend the fault you are having is a Bad (dying) DAC (Digital.Analog.Converter) its very common on the 1D1 board I have 3 of them that have suffered this fate in a box awaiting the day I can find the right revision of DAC.

There are 3 different DAC revisions used in the A1200, each with a subtle modification specific to the motherboard revision - I have a repaired one, but it has tearing on one side of the screen - as its not the right version for the board.

btw, U30 is the DAC =)

Sorry I wasn't here sooner to help.

Interestingly enough - any clip-on SCAN Doubler has its own DAC and by-passes this problem.
My DAC BT101 chip gets hot to the touch, and the screen flickers when I press on it. Does it sound like this might be the problem?

How can I make sure this is the problem and where can I get this chip? The chip I have is VP101 3BA.
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Last edited by TjLaZer; 25 September 2015 at 06:15.
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Old 25 September 2015, 12:14   #3
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If something happens when you press on it, that would indicate a broken connection in that area. Maybe a pin on the IC has come loose from the PCB, or a track or via was damaged (usually due to leaking caps).
Your problem looks like you are missing the green channel and since it also happens on composite, the problem is located before the RGB signal splits to the RGB port and the CXA encoder.
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Old 02 October 2015, 02:14   #4
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The cap that is right above that looks like it leaked a bit, maybe it damaged some traces near the DAC... Yes when I press on the DAC, the screen jumps a little, but the color problem does go away, I do see it improve in that split second when the screen flips. So I am thinking it is a bad trace to the DAC!
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Old 02 October 2015, 04:22   #5
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(Edited) So then try to resolder all of the pins of the DAC. Watch some video first to see how to make that if you've got a good soldering iron and you think you can do it.

Of course change all of the caps if just one has leaked.
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