Samsung LN40A630 won't turn on

[Drametta]

The TV kept takinglonger and longer to turn on. Eventually, it didn't turn on at all and the front LED just keeps blinking. I inspected the power supply caps and they didn't appear to be damaged. I replaced six of them with no change. I measured the PS output voltages and they are close. The TV attempts to turn on when plugged in without hitting the front button or using the remote. The ON/OFF signal to the PS was measured at 3.8V. Any ideas? Thanks in advance for your help.

[selldoor]

Re: Samsung LN40A630 won't turn on

You need to locate the startup capacitor {if it has one} on the power supply in the primary section and befor switching the set on try pre heating it gently with a hairdryer. It is a small cap often 50v 47uf

[tibimakai]

Re: Samsung LN40A630 won't turn on

You should replace all the capacitors, they are most likely 12-14 of them.

[Drametta]

Re: Samsung LN40A630 won't turn on

Ok...I will replace them all today.

[Drametta]

Re: Samsung LN40A630 won't turn on

I replaced all 11 caps that I bought from shopjimmy. They came as a 'caps replacement kit' for this power supply, bn44-0098a. This change made no difference. One cap was a 0.47 uf, 50v cap that may be in the startup circuit selldoor mentioned. I have the schematic for this ps.

Why would the on/off signal from the main board turn on without me touching the remote or the front switch? If I disconnected the cable from the front switch/ir board from the main board, would anything get damaged? Maybe there is a problem with this front switch board.

I am tempted to just buy a new ps board from eBay for $60. What do you think?
Thanks.

[multimeter]

Re: Samsung LN40A630 won't turn on

disconnect power buttons and retest,is it buttons on side or touchpanel?

on/off signal should show 0v

[Drametta]

Re: Samsung LN40A630 won't turn on

The buttons are on the touch panel. The touch panel board connects to another smaller board (IR?) board that connects to the main board.

Should i unplug the cable from the touch panel to ir board?

Maybe there is a fault on the ps board that is pulling up the on/off signal to 3.8v. That is an odd voltage.

[multimeter]

Re: Samsung LN40A630 won't turn on

The buttons are on the touch panel. The touch panel board connects to another smaller board (IR?) board that connects to the main board.

Should i unplug the cable from the touch panel to ir board?

Maybe there is a fault on the ps board that is pulling up the on/off signal to 3.8v. That is an odd voltage.

3.3v is around right

yes,unplug from the touch panel to ir board

[Drametta]

Re: Samsung LN40A630 won't turn on

I unplugged the ir and touch panel boards from the main board. The on/off signal still goes to 3.8v when I plug in the TV. I then tried unplugging the Main board from the ps board. Now the on/off signal stays at 0v. That tells me that the ps isn't pulling this signal high through some ps fault.
Does anyone know where I could find a main board schematic (Bn41-00975c)?

[tom66]

Re: Samsung LN40A630 won't turn on

Samsung sometimes include main board schematics in their service manuals. You can try the link in my signature and Elektrotanya.com for service manuals.

[Drametta]

Re: Samsung LN40A630 won't turn on

I didn't find this (or many) main board schematics online. How close are these main board circuits to one another?

When I push the off button on the remote, sometimes the on/off signal drops to 0 volts (the fan stops running) but then jumps back to 3.8v. If i could isolate the failure to one board or the other, I would decide on buying a replacement board.
Any ideas? Thanks

[selldoor]

Re: Samsung LN40A630 won't turn on

I dont know if this is one of them but I have read that on some power supplies the
on/off pin is high and to switch on it has to be pulled low. I am not sure how to do that
perhaps ground it - Tom/ Multimeter might know?

[multimeter]

Re: Samsung LN40A630 won't turn on

some do pull the standby to ground,not in many though.that i have seen

it sounds like it could be capacitor issues,because of the time it takes to power up.

things to try...

disconnect mainboard ,does that pin stay high?

does the pin that is showing that voltage at the mainboard have low resistance to ground?

what brand and series caps where they replaced with?

heat the psu board for thermal issues,

what voltage is at the startup cap?,though this would give the symptom of ,chirping,fluctuating standby voltages,or dead.

id be heating the startup cap,and output caps,and looking for a change of symptoms.

it could also be EEPROM related,as this chip will use a booting sequence for the tv powering up,maybe worth a check also.using a datasheet for that eeprom,you can check vcc to ground for low resistance,and other problems

[Drametta]

Re: Samsung LN40A630 won't turn on

I decided to start replacing boards since my family was asking me to buy a new tv. I bought a power supply from eBay for $60. Replaced it and no change...I then bought a main board from Encompass Distributors for $100. That fixed the problem and everybody is happy. I would rather spend $160 and get my tv back than pay someone a few hundred to repair or buy a new one for $600. Shame on samsung for building such an unreliable product! A TV should last more than 5 years. While this was broken, we were watching my old tube tv that has lasted more than 15 years.