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Mend Panasonic TX-W28R4DP TV Picture Problem

My Panasonic TV keeps going into standby mode?

when i try to put my Panasonic 28 inch widescreen TV model TX-W28R4DP on it just goes into standby with the red light on ....when i try to put it back on again with my remote control it powers back up again and it sounds like its coming back on again but just as the picture is about to come up it drops back into standby mode again can anyone help?????

I have general electrial knoledge and some soldering experience i feel this problem may be caused by dry solders but i need some advise!!!!

Ive been having problems with the picture on it for a couple of weeks now where the picture drops to the bottom half of the screen sometimes lower but when it mess wih the scart leads at the back of the TV (weather using AV channels of normal channels) it used to come back on this was a intermitent problem and may be on for days then other daysit would happen a couple of times

Lonenickel
February 2007

Panasonic Panasonic TX-W28R4DP Video, Televisions Panasonic TV Picture Problem

thanks again cobweb ill get it sorted by a pro because i dont want to damage anything else...........nothing is simple is it ...thanks again for your asvise

lonenikel
February 2007

IC451 is the small 7-pin vertically mounted IC, clipped to the heatsink which runs down the centre of the main pcb.
From the underside of the pcb the pins run parallel to a strip of the plastic chassis moulding.

The original is best desoldered with a fine desoldering braid as solder pumps may be to aggressive against the soldering points and the weakened print could easily be damaged.

After removal of the old IC the soldered pads should be cleaned. The replacement IC requires a film of non-silicone based heat-sink compound. I would also brush the pcb pads with liquid solder flux to ensure a good soldered joint to the replacement IC.

Although, this is a simple repair, I recommend the job is carried out by a suitably qualified person. Very high voltages remain inside the TV after the power is switched off.

Cobweb
February 2007

Thanks cobweb for your prompt reply.... as i thought a dry solder....... is there any other info you can help me with please....... ie i need to know where the IC 451 is on my tv is it on the main board or is ot on the back of the CRT ......if you could give me some more indepth information it would be of great assissstance to me as i can repair / replace this item myself
thanks again

lonenickel
February 2007

thanks cobweb for your prompt rely as i thought a dry solder is there any other info you can help me with please ie i need to know where the IC 451 is on my tv is it on the main board or is ot on the back of the CRT if you could give me some more indepth information it would be of great assissstance to me as i can repair and replace this item myself
thanks again

lonenickel
February 2007

This is usually due to IC451 (LA7845N) frame output IC failing.
The soldering of the 7-pins will have crystallized.

Re-soldering may provide a temporary repair but the IC should be replaced. Also checking C561, C567 and C456.

There are several other possible causes for the protection circuit to activate but this is currently the most common.

Engineer est. repair cost £65-£80

Cobweb
February 2007