RCA 20F420T Shuts Off and On

[Chris F.]

This is a strange one... the set comes on and works normally for a few
minutes, then starts turning off and on at random. It goes through it's
screen wipe effect each time, which suggests that something is signaling the
normal power off/on function, not as if it's shutting down from an overload
condition etc. I've never seen anything quite like it... any ideas?

 

[Allodoxaphobia]

This is a strange one... the set comes on and works normally for a few
minutes, then starts turning off and on at random. It goes through it's
screen wipe effect each time, which suggests that something is signaling the
normal power off/on function, not as if it's shutting down from an overload
condition etc. I've never seen anything quite like it... any ideas?

Does the set face a window that in turn faces the street?

 

[Mark Zacharias]

This is a strange one... the set comes on and works normally for a few
minutes, then starts turning off and on at random. It goes through it's
screen wipe effect each time, which suggests that something is signaling
the normal power off/on function, not as if it's shutting down from an
overload condition etc. I've never seen anything quite like it... any
ideas?

I've seen defective tact-switches on Sony's do similar things. One or more
tact-switches on the front panel could be causing a leakage path through,
for example a resistive ladder arrangement. I've also seen window cleaner
leak down the front edge of the picture tube and cause similar problems.

Mark Z.

 

[Chris F.]

I tried removing the power switch from the board but it made no change.
There's also no evidence of glass cleaner on the board. Looking on the net I
see that this is a very common fault, but nobody seems to know exactly what
the cause is.

 

[Chris F.]

Just a quick follow-up: I replaced all six tact switches and the set now
works fine. Another case history to add to my mental database.....
Thanks for the suggestion.... I should have thought of it myself but it
seemed too obvious.