This is a similar symptom to my faulty 128K, with thick vertical lines and some video corruption (sort of like dead pixels) there abouts on the CRT. It did display a Sad Mac error, and I was happy to report that the two RAM modules replaced did repair the Mac to full working order.

viewtopic.php?f=7&t=14580

Before desoldering components, I'd look into cleaning the board with something like meth spirits, and double checking all components are properly seated etc.

JB