Over the past few months I've received a few cheapo LCD TVs with blown
power supplies that could not be repaired, the reason being that replacement
parts (or whole boards) were simply not available. Another one just came in
with the same problem, and this time an idea occurred to me.
The power supplies in these sets are pretty simple, at least in terms of
outputs and connections. They usually consist of a 5VDC standby supply and
switchable 12 and 24VDV supplies. The standby voltage is always derived from
a separate switching transformer, and it's usually the 12/24 volt circuit
that goes bad. The connections are usually GND,5V,12v,24v, and power on
signal.
So the obvious question is - can an external power supply be added to the
set? I once tried this but my homemade power supply wasn't filtered or
regulated well enough to provide satisfactory operation. Looking on Ebay, I
see that low-cost switching power supplies are readily available, in a wide
assortment of voltages and amperages. I thought I might buy some and try
creating external power supplies for these TVs, but first I'd like to know
just how much current is required for a 27 to 32" TV. The 24 and 12V power
supplies are available in current ratings of 2,3,5,10 amps and higher. A
relay circuit would have to be added so that the backlights etc. wouldn't
stay on when in power off mode.
Adding an external power supply might not be as practical as replacing the
internal one, but it's far cheaper and in some cases may be the only way to
save the set from the landfill.