Hi having the Samsung LN40A530P1F LCD TV that is taking 5 minutes to starts.
It seems to be worst with time.
All caps on the power supply were changed (even if the ESR and value were OK) .
I have the service manual but it doesn`t include the schematic.
5 volts standby power supply is 5.2V , so it`s OK.When powering up the TV , power LED is blinking and when pressing power button , takes 5 minutes to start.
Any idea ?
A little better desciption of what happens - or doesn't happen - might be helpful. Is this totally a case of nothing happens, or do you have sound, but a black screen for 5 minutes?
The slow startup screams 'bad caps'. Many (most) TVs have some sort of a DC-DC converter on the main board. In many designs these are LDO regulators; others use a bucking regulator. Have you checked the caps on the main board?
PlainBill
Perhaps you have a bad CFL in the display. I had a 21" samsung 940T that did not come on. There was no indication of bad caps, lack of oozing or bulging. I replaced them anyway with no results. I swapped out both power supply and video convertor board. I then opened up another display, parked it next to the dead unit and began swapping out the CFLs. I eventually found the bad CFL and had a display. When I opened up the bad unit, the suspect CFL had blackened ends. Replacement cured the problem. Aparently one cannot just disconnect the CFLs to diagnose as it may create an over voltage condition which shuts down the CFL inverters. The bad CFL may have drawn too much current again causing the inverters to shut down. Ya just can't win...
regards, al
When I had a laptop with a broken wire in the ribbon to the display panel which prevented power reaching the lamp, I found that what was meant to be displayed was visible when the panel was examined closely - the panel just wasn't illuminated. Considering the way LCDs work, I would expect this generally to be the case.
Sylvia.
This is a classic "bad power supply capacitors" problem.
Mark Z.
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Hi , doesn't seem to be the case this time. All off them were replaced even if the ESR or value were good.
The only caps I saw were on the power supply board.
What about the LDO regulator ?
Thanks.
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sPerhaps the power good signal is at fault. On the Samsung 904T displays there are several different voltage supply levels. All derrived from +5v. Ex; 2.5v and 3.3v using buck regulators. There is a lm393 comparator that compares two of these supplies and if they are at their required levels then the power good signal goes active enabling the CFL inverter supply. Google the chip numbers for the inverter supply and the regulators to get an idea how they operate. Measure voltages on the big decaps nearby. If you find a comparator see if it traces back to the local regulators (via dividers?) or gently bias its inputs one at a time to see if you can coax it into changing output levels. On the 904T display boards the power connectors were labeled. Look and see if there is a line labeled power good or display active line and determine if it is in the correct state. HTH regards...... Al
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OK , here are some readings:
On connector CN801 (main connector from PS to main board)
Pin 1(PS-ON) 4.15 volts Pin 2(SYNC) 3.28 volts Pin 3(STANDBY5.1) 5.23 volts Pin 7(13VS) 14.27 volts Pin 19(13VM) 13.87 volts
These readings are when the TV doesn`t start (LED blinking)
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After 15 minutes , TV is powered on and working. See readings :
Pin 1(PS-ON) 4.01 volts Pin 2(SYNC) 3.28 volts Pin 3(STANDBY5.1) 5.11 volts Pin 7(13VS) 12.80 volts Pin 19(13VM) 12.34 volts
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When TV is ON and working (after 15 minutes warm-up) , here are the readings:
When i power it off , PS-ON goes to 0V
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