HT 903 DVD player - surround sound service manual.

A friend of mine asked me to look at her surround sound system. It powers up and then a few seconds later displays Goodbye and powers down. The display is very dim so I suspect one of the power rails is out of spec. Inside there's a single sided power supply board and a heavily populated multi sided amp/dvd player board. The amp board is labelled HT503 HT903 so I suspect the 903 designation is a South African code as that was where it was purchased.

Anyone got any information on this device, especially the power board.

Thanks,

Mike.

What make is it?.

If you suspect PSU, I would run the scope round the supply rails (on the outputs of the rectifiers), to check for ripple caused by high ESR electrolytics.

The dim display 'may' be a red herring though, as (assuming it's a CCFL display) they tend to have a fairly short lifespan, and rapidly become too dull to see.

Very, very, occasionally you do find a duff PSU capacitor causing it though - I've changed dozens of high ESR capacitors for dim displays, and only improved things in a couple of cases (and not great then, but better than it was).

It 'could' be shutting down due to an output protection fault, due to a duff output IC, or (more commonly in surround systems) dry joints on the IC's or surrounding components.

Thanks Nigel, it's an LG made in 2009. Guess it's time to dig out my scope.

Mike.