Xtech
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Dec 30, 2010, 8:25 PM
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Hitachi big screen cycles in protection.
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I am working with an Hitachi big screen model 53SBX59B.
When plugging in the power cord the unit immediately
starts cycling in and out of protection. It does this
continuously without pressing the power button.
All 8 of the green leds on the main board
that indicate voltage except for D939 5 volt and D946 9 volt come on.
Both are monitoring the voltage of a 5 pin regulator,
but I'm not sure if either of those are supposed
to be lit in standby anyway.
They all then go out as soon as it goes
into protection. It only takes a couple of seconds for
this to all happen.
Just as the 6 Leds come on it immediately then
goes into protection, then they all go off and
the cycle repeats. It does this for as long as its
left plugged in. While its doing this I can tell
it generating high voltage at the anode of the
CRTs.
Here's some of what Ive done so far.
1 I have checked all fuses (all ok)
2 Checked all electrolytic caps in the power supply
for high ESR and value, all check ok.
3 Checked all transistors and diodes in the
protection circuit and power supply. The
HOT also checked ok.
4 resoldered joints throughout the supply
including any ICs.
Any help appreciated, thanks.
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