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TV set won't stay on one channel

Hi Folks,

My TV works fine except that it won't stay on the channel it's set to. It keeps cycling through the channels as if the channel-up button is being pressed. The problem is not in the remote, since it happens when the batteries are removed from the remote and the remote is put in a different room.

The model is Panasonic CT-20G21, a 21" box from 1996.

I have little test equipment beyond a multimeter. I am able to solder, and I have some understanding of electronics, but no experience working on TVs.

Please advise.

Reply to
Matt
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Cover the IR window on the tv with black tape and advise.

Reply to
Meat Plow

Just a wild guess: Check the channel-up and channel-down buttons on your TV. They should "click" when pressed. If the button is stuck down, or the switch below the button is damaged, you probably won't feel that "click", or it might have a "mushy" feel.

Reply to
none

Okay, tried that. No difference.

Reply to
Matt

The buttons are okay. I suspect an electronic defect in the tuner.

Reply to
Matt

Does the set have an OSD and do the channel numbers change when it changes channels on its own?

If they do not change it /could/ be a problem with the tuner but no guaranty.

I'd look more into the device(s) that decode the IR and or those that interface the buttons to the sets logic control if the OSD changes channels. Without a schematic/service literature this may not be something that you can perform due to your limited knowledge.

Reply to
Meat Plow

As I recall, years back we had a KV25XBR with a shorted channel switch that felt just fine mechanically.

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One meter, to within 0.0125% accuracy (off by just under .005 inches):
        Three feet
        Three inches
        Three eights of an inch
Reply to
clifto

This could be caused by what I call "MOSFET lockup". (I've seen things like this in other products.)

With the set turned on, pull out the power plug and let the set sit for several minutes. Then see what happens.

Reply to
William Sommerwerck

Check the channel up and down switches on the front panel in case one of them is making contact. It can also be a fault in the uPC.

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JANA _____

Okay, tried that. No difference.

Reply to
JANA

Such things do occasionally happen. And that is why I used the term: "Probably"...

Reply to
none

let's start eliminating the easy stuff. if the IR sensor is covered and the set keeps changing, remove the back, slide out the pcb a few inches, stay away and power up.Observe. sometimes the plastic keys on the set deform and press the microswitches. if this does not cure it, desolder the microswitch for ch+ and see what happens.

-B

Reply to
b

If someone sprayed something on the screen to clean it , or kids with something .. it could run down inside and drip on those buttons . Take the board out and inspect . Take care not to get shocked .

Reply to
Ken G.

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