On Aug 17, 8:33*am, benitos wrote:
On Aug 10, 7:36*am, "Mark Zacharias"
wrote:



"Sylvia Else" wrote in message

...

On 10/08/2011 8:54 AM, mickgeyver wrote:
On Jul 29, 6:07 pm, *wrote:
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 ?

Perhaps you have a bad CFL in the display.

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.- Hide quoted text -

- Show quoted text -

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.

Perhaps 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