LCD TV Samsung LN40A530 - long to startup

[benitos]

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 ?

[Plai...@yawhoo.com]

On Fri, 29 Jul 2011 15:07:06 -0700 (PDT), benitos <pot...@cae.ca>
wrote:

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

[mickgeyver]

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

[Sylvia Else]

On 10/08/2011 8:54 AM, mickgeyver wrote:
> On Jul 29, 6:07 pm, benitos<poth...@cae.ca> 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.

[Mark Zacharias]

"Sylvia Else" <syl...@not.here.invalid> wrote in message
news:9ae1bo...@mid.individual.net...

This is a classic "bad power supply capacitors" problem.

Mark Z.

[benitos]

On Aug 10, 7:36 am, "Mark Zacharias" <mark_zachar...@labolgcbs.net>
wrote:

> 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.

[mickgeyver]

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

[benitos]

> regards......  Al- Masquer le texte des messages précédents -
>
> - Afficher le texte des messages précédents -

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)

[benitos]

> These readings are when the TV doesn`t start (LED blinking)- Masquer le texte des messages précédents -

>
> - Afficher le texte des messages précédents -

When TV is ON and working (after 15 minutes warm-up) , here are the
readings:

> Pin 1(PS-ON) 4.05 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

When i power it off , PS-ON goes to 0V