I have two Q840AV logic boards that I have recapped. Both machines passed all tests on TechTool Pro 3. Everything seems to work on BOTH of them except…. The lower portion of the display when it requires more VRAM than the onboard 1M. See pics below. The VRAM simms are 80mhz and work well in my Quadra 800. The issue happens both with my 16” Apple Display and when using a DB15 to VGA adapter to LCD. Screen capture software captures the corrupted screens. Booting from different System 7.5 hard drives and using different system RAM does NOT change the problem. Neither machine was known to be working before the recap. I have been looking at Bomarc schematics and Apple‘s Developer notes to find the likely location of the problem.
I wonder: if the machine passes component tests in TechTool and the problem is present in screen captures, then does that suggest the problem is the lines between VRAM and DAC or in one of the millions of resistor packs, etc.? I am hoping that y’all have seen something like this before.
Resolution 832x624, Thousands of colors (only requires on board VRAM)
Resolution 832x624, Millions of colors requires 2mb VRAM
The pattern was visible during power off:
Additonally, Corruption was only the bottom 1/8th of the screen at 640x480.
I welcome your suggestions and questions.
Thanks,
Sam
AKA “Bama”
I wonder: if the machine passes component tests in TechTool and the problem is present in screen captures, then does that suggest the problem is the lines between VRAM and DAC or in one of the millions of resistor packs, etc.? I am hoping that y’all have seen something like this before.
Resolution 832x624, Thousands of colors (only requires on board VRAM)
Resolution 832x624, Millions of colors requires 2mb VRAM
The pattern was visible during power off:
Additonally, Corruption was only the bottom 1/8th of the screen at 640x480.
I welcome your suggestions and questions.
Thanks,
Sam
AKA “Bama”
