Wharfedale L32TA6A lcd tv - trips to standby after a few minutes.

[Contrast John]

Hi All
Guess this could be a stock fault on this model. A customer arrived with two identical sets both with the same problem. They`d run fine for the first half hour or so then trip to standby. Both sets would start again ok but would now run only 10-15 minutes before tripping back to standby. The next start would only give a 5 minute run before reverting to standby.
The problem was traced to thermal runaway in U30 (AP1501-50) a 12Volt in / 5Volt out Buck Regulator on the signals board. Its operating frequency appeared to fall as the temperature rose. Presumably this caused the temperature to rise further, creating a runaway effect until a thermal trip inside the IC was fired. Nearby capacitor CA100 470mF 25v looked stressed but was not in fact the cause of the problem as replacing it first didn`t provide a cure.
A permanent solution was provided by soldering a strip of copper heatsink (taken from an old Salora tv chassis) to the mounting tab of the regulator and bending it into a safe position. A similar strip of copper was soldered to the reverse side of the board underneath the body of the regulator. This made a dramatic difference to the operating temperature of the IC. Where it had been 'burn your finger' hot, it was now quite bearable to touch. Both sets were ran on test for several days with no problems before being returned to their owner.

John.