Lowcostrepairs
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Jun 24, 2005, 8:42 AM
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Philips plasma goes off.. comes on.. goes off
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My last plasma TV repair?
This Philips 32FD9944 gives a beautiful picture but this goes off after about 10 minutes. It goes off because a pair of relays in the PSU turn off, removing power to the main chopper circuit. After about 4 minutes the picture reappears by itself for 2 minutes before going off again... the cycle then repeats ad nauseam.
The power relays may have thermistors in their coil circuits which get hot and prevent the coils energising afresh until they've cooled down... hence the delay to come back on. What's happening? Presumably a problem is being detected which is serious enough to shut down the set? Maybe it's a faulty detection circuit?
There are no fans fitted so it could be a temperature problem. This must be due to ageing though as the set was working for 2 years. Could it be a display panel problem. ie too much current being drawn somewhere ie. a write-off?
Could it be a simple psu problem? The voltages at the two big connectors on the psu board are 53.1, 5.2 and 80.6. The two regulators at the lower edge of the psu board have 5 and 3.3 volts on them. There are no distressed components... everything looks pristine.
What if was to hold the relays on or fit resistors intead of thermistors to eliminate switch on delay?
Any chance it could be a common or garden 2p electrolytic in the PSU or do I tell the customer to ditch it?
I have a feeling it is more serious than a 2p capacitor. Any advice??
(This post was edited by Lowcostrepairs on Jun 24, 2005, 8:54 AM)
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