12 August 2024, 17:30 | #1 |
Retro Tech Restoration
Join Date: Aug 2024
Location: Tallahassee, FL
Posts: 2
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Amiga 1200 Video Problem (rolling/flicking bars on left side of screen)
I'm currently working on an Amiga 1200 with the video issue shown in the attached photo. If anyone here is familiar with the problem and can point me at a specific chip, bus or signal path to look at that would save me a ton of time. Otherwise I'll just plug along and trace the power, clock circuit and make my way down the video path.
Here some additional info to answer some of your questions... - Amiga A1200 Chan Z., Rev 1D.4 bare board with a Budgie Rev 0 - The bars are only on exactly the left side of the screen, rolling or flickering constantly rapidly and are consistent across all video outputs regardless of what the machine is doing or what peripherals are plugged in. - Using a RetroPower US 110v/60hz PSU - This board was recapped by the previous owner, but all the solder joints and caps test good - The previous owner removed and shorted E127R, but I also removed E123C and E125C as per the proper way to do that mod. E121C and E122C were already not installed from the factory - 1.2. ref voltage was confirmed on the D215A VP101-3BA DAC circuit with the D215D zener diode present. LM385 not present. - The board is super clean and I see no obvious board or component damage - My thermal camera sees no overheating components - U32 74F139 tested okay Thanks! |
12 August 2024, 20:05 | #2 |
Registered User
Join Date: Jul 2018
Location: Stockholm / Sweden
Posts: 260
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Tested on only one or other monitors as well?
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13 August 2024, 02:11 | #3 |
Retro Tech Restoration
Join Date: Aug 2024
Location: Tallahassee, FL
Posts: 2
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Atm, I only have an Amiga RGB to SCART cable and two different SCART to HDMI adapters (SCART being uncommon here in the US). So I've tested this machine on both SCART to HDMI adapters on two different HDMI displays, and of course I've looked at the composite output. I do have a broadcast monitor that takes composite and supports PAL, but oddly it's having trouble syncing and does not show color, even when explicitly set to PAL mode. I have an Amiga RGB to VGA adapter on order and when it arrives I'll test the machine with my good Trinitron multisync monitor. |
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