Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

[nomoresonys]

Have this sammy LN40C650L1FXZA, all the readings at power supply connectors appear correct, have ol on the 450v filter caps, with tv plugged in and on or off, checked bridge rectifier, read good in circuit. Not sure what to check, tv will make the power on sound/music, backlight will maybe flash, very brief if at all, when turn tv on get solid red light, when turn it off red light blinks 5 times then goes out, can see no menu with flashlight, no obvious signs of damage to anything, sorry for no pics. my camera crapped out. THANKS for any help.

[maxvalutech]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

Your title and post conflict somewhat. Basically it seems PSU is OK and set is normal until backlights due so I would be checking if they can be forced on. If so mainboard suspect for blon/dim signals or firmware problem.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

Your title and post conflict somewhat. Basically it seems PSU is OK and set is normal until backlights due so I would be checking if they can be forced on. If so mainboard suspect for blon/dim signals or firmware problem.

Not sure about the backlight force on for this one, I tried unplug powersupply and main board connector, backlight only flashes for a split second then goes off.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

Not sure about the backlight force on for this one, I tried unplug powersupply and main board connector, backlight only flashes for a split second then goes off.

Just tried again, first power on have bacllight for about a second, unplug powersupply to mainboard connector, backlight comes back on for about 2 seconds then goes off.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

I think having no voltage at the 450v filter caps is bad but don't know what the cause is.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

Your title and post conflict somewhat. Basically it seems PSU is OK and set is normal until backlights due so I would be checking if they can be forced on. If so mainboard suspect for blon/dim signals or firmware problem.

I don't think I can do much with the firmware, can't get a menu.

[budm]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

No way you can have 0VDC between the two legs of the main filter cap and still able to have backlights and standby power supply running.
You should have about 160VDC between the two legs of the main filter when TV is plugged in and NOT turned on, do you have that?
Can we at least see the pictures of your power supply board?

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

No both on and off while plugged in, read ol.

[budm]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

OL on the DCV scale that means it is higher than the meter can display.
What scale on the meter did you set it to?
You should know how to read your meter by now.
As I indicated, now way you can have 0VDC on the main filter cap, operator error.

[budm]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

What is the power supply board P/N?
BN44- ??????
If I remember correctly, this power supply is know for having low PFC Voltage due to bad feedback resistor network.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

Think I got some low readings on a few of the transformers on the inverter board.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

OL on the DCV scale that means it is higher than the meter can display.
What scale on the meter did you set it to?
You should know how to read your meter by now.
As I indicated, now way you can have 0VDC on the main filter cap, operator error.

Lol, I forget things faster than I learn them, meter was at 20 will try higher setting. board is bn44-00340b.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

on 200, I get 15.8 on both caps. my bad have about 170 and 385, ok theyre good.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

Ok I'm suspecting the inverter board.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

What is the power supply board P/N?
BN44- ??????
If I remember correctly, this power supply is know for having low PFC Voltage due to bad feedback resistor network.

Is the feedback resistor network on the power supply?, I tested all the diodes and there only looks like one resistor but I'm probably missing seeing them.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

You think maybe I could have one bad cfl, making the tv shut down? Thanks for the help.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

What is the power supply board P/N?
BN44- ??????
If I remember correctly, this power supply is know for having low PFC Voltage due to bad feedback resistor network.

Is there a fix for this or do you think it will just keep failing?, might not be worth fixing.

[maxvalutech]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

What voltage is going to inverter and is it constant. I would also check that board screen connection is good just a few taps with a pencil end or some such to see if any flash. More likely what budm says though.

[maxvalutech]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

Is this your PSU ? There is also a circuit diagram on elektrotanya but comes up in images when board number googled.

[nomoresonys]

Re: Samsung LN40C650L1FXZA Backlight flash no voltage on 450 v. filter caps.

Is this your PSU ? There is also a circuit diagram on elektrotanya but comes up in images when board number googled.

Yes, that's the board.