I had the same stripy pixelated thing on a fixer upper. Also suspected the logic board or graphic card. But I was wrong: When I booted it holding D to do the hard ware test, my monitor was showing no lines. I aborted the test, and booted from another external HDD, and it came up without the pixelated stripes. So I used that boot up to erase the build in HDD, which by the way had been maxed out, restored that HDD with a fresh OSX, and voila....no more stripes. My conclusion: Always fix the most likely component to fail: the HDD.
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=== Update (02/06/2019) ===
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@imacpain1 rich, I would say that the fix I found is still working: I did send in the GPU and had it repaired in California, by http://stores.ebay.ca/brickfence.
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Not just a reflow, but had a new chip installed on the GPU, came to about US$ 140.
Hi YpeH,
I had the same stripy pixelated thing on a fixer upper. Also suspected the logic board or graphic card. But I was wrong: When I booted it holding D to do the hard ware test, my monitor was showing no lines. I aborted the test, and booted from another external HDD, and it came up without the pixelated stripes. So I used that boot up to erase the build in HDD, which by the way had been maxed out, restored that HDD with a fresh OSX, and voila....no more stripes. My conclusion: Always fix the most likely component to fail: the HDD.