RCA 20F420T Shuts Off and On
in [Repair]
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From: Chris F. on 3 Dec 2009 12:04 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?
From: Allodoxaphobia on 3 Dec 2009 20:59 On Thu, 3 Dec 2009 09:04:01 -0800, Chris F. wrote: > 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? :-)
From: Mark Zacharias on 4 Dec 2009 06:57 "Chris F." <zappyman(a)hotmail.com> wrote in message news:4b17ef83$0$5357$9a566e8b(a)news.aliant.net... > 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.
From: Chris F. on 4 Dec 2009 11:07 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. "Mark Zacharias" <mark_zacharias(a)sbclobal.net> wrote in message news:0005e438$0$2114$c3e8da3(a)news.astraweb.com... > "Chris F." <zappyman(a)hotmail.com> wrote in message > news:4b17ef83$0$5357$9a566e8b(a)news.aliant.net... >> 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.
From: Dave on 4 Dec 2009 16:40
"Chris F." <zappyman(a)hotmail.com> wrote in message news:4b17ef83$0$5357$9a566e8b(a)news.aliant.net... > 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 something like this twice, and both times it was due to faulty power delivery. The first time it was a fuse that was the wrong type, which had burned through but not blown "wide open." It arced across the burned out portion until the wire inside the fuse heated up, causing it to curl, which widened the gap, and the machine shut down. Then the wire inside the fuse cooled and uncurled, until it started arcing across the burned gap again. Machine powered up. And down. And up. That was on a 1/4 million $ high speed printer in an mainframe environment. The original fuse had blown and someone had but the wrong type in as a replacement. And... Second time it was with a portable boom-box. AC plug did not securely fit into the power socket on the back of the box, and because the contacts were slightly loose they heated up as it operated. This made them a little looser, and the box turned off, until the contacts cooled down and contracted around their respective "male" pins again. Box came back on for a little while, then went off again, and back on... Check the power delivery to the unit very carefully, and try not to make any assumptions. May the wind be at your back... Dave |