Possible contenders?
http://personalpages.tds.net/~rcarlsen/ ... /vic20.txt
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UB7 6560-101 VIC VIDEO/AUDIO
White or blank screen, garbled or no video, screen full of (or few
random) "garbage" characters. "Blind" disk commands may still work.
Partial failure: Dark or smeary image, loss of color, garbled or no
sound, game paddles or light pen doesn't work.
UB9 7402 (M53202P) OSC MASTER CLOCK OSC
White screen... no RF interference in AM radio (see text). Partial
failure can produce missing color or incorrect colors, slight or severe
tearing of picture or diagonal lines, sounds play at incorrect pitch.
Symptoms may only appear after warmup.
UC2 74LS04 LOGIC
Screen character colors incorrect (scrambled). If very bad, entire
screen becomes garbled with flashing characters, vertical bars and
random colors.
UD1 CD4066 QUAD SWITCH (LOGIC GATES)
(UC2 in very early version) Screen characters have incorrect colors.
UD2-UD6
UE1-UE6 2114 or TMM314A SRAM MEMORY
Blank screen. Partial failure: less than normal "3583 BYTES FREE" at
startup, sometimes will produce "garbage" screen or screen freeze after
warmup. Shorted chips may get very hot. NOTE: UE1 is used to generate
character color.