Samsung UN55D6500VF won't power on

[jcamerox]

With AC power connected, power led glows steady red. When I push the power on the relay clicks and then after 5 seconds the relay clicks and then it goes into a cycle with the led flashing twice for 5 times and then repeating.

With the PS/Main cable disconnected and power applied the backlight Leds all turn on and voltage readings at the PS connector are; PWM DIM 1-4, 3.4v; B13, 12.8v; BLU ON, 3.5V; A5V, 5.3v; PS-ON, 3.4v; OD Level, 1.3V; OD ON, 1.5v; B13V, 12.8v; Vamp, 17v; B5V, 5.4v. These voltages are steady with the backlight on.

With the main board connected, all voltages start at 0 and try to rise to their proper values but fall back to 0 when the relay clicks.

I located the trouble shooting procedure in the service manual but it fails to take into account the power cycling on and off continuously.

With the Tconn cable disconnected from the main board there is no change.

Any thoughts would be appreciated.

[mmartell]

Re: Samsung UN55D6500VF won't power on

Sounds like mainboard. Pull the pson pin from the connector and reattatch everything and see if pson changes state when powered up. You can also try heating the main board with a hair dryer for 30 seconds and see if the set powers up normally.

[CapLeaker]

Re: Samsung UN55D6500VF won't power on

Measure 5V STBY, PSon and all the voltage rails during that spell with the TV.

[budm]

Re: Samsung UN55D6500VF won't power on

Main board problem.

[jcamerox]

Re: Samsung UN55D6500VF won't power on

Thanks for the replies Capleaker and BudM. When I tried mmartell's suggestion, the hair dryer had no effect. Great suggestion to remove the PS-ON pin from the connector, I didn't realize they are just held in with a spring clip so easy to remove individual pins.

With the PS-ON pin removed, the power supply comes on and stays up giving the same voltages I had when the backlights were on, but now the backlight is not on. I thought the main board was pulling down the power supply causing it to cycle on and off but I guess not. With steady power to the main board I did some checking on the obvious things, like the 3 local power regulators. The two 3.3v regulators were okay, but IC 704, is showing 0 volts in and out and from the part number 17-18Z, I assume it is a 1.8 volt regulator, the two 3.3 v regulators have part number 17-33z.

Thanks for the suggestions, will do some more checking. There has never been a time when I had a video or audio signal.

[CapLeaker]

Re: Samsung UN55D6500VF won't power on

I guess you do have a short or bad regulator etc. somewhere on the main board, if you never had audio/video and it's doing things like that it is doing now.

[jetadm123]

Re: Samsung UN55D6500VF won't power on

hard to tell from your photo, but there appears to be 4 voltage regulators:
smaller one between the two 3.3v? regulators and a regulator in the lower right corner.

[jcamerox]

Re: Samsung UN55D6500VF won't power on

Yes, jetadm123, you are correct, that is another regulator, a fixed 1.2v between the two 3.3v regulators. The problem is with the 1.8v regulator in the corner, showing no voltage input. Need more light to do some more voltage measurements, have to wait till morning.

[agapes]

Re: Samsung UN55D6500VF won't power on

i have same problem with my un55d7900 samsung
when i put the power cord to wall tv just clicking and does not power on
when i detached cables from main-board and just the power supply connected tv power on and backlight on with white screen but when mainboard connected just clicking
after 15 min clicking tv power on and working for long time without any problem???!!!!
do you know whats the exact problem??
mainboard should be replace or power board?

[budm]

Re: Samsung UN55D6500VF won't power on

"when i detached cables from main-board and just the power supply connected tv power on and backlight on with white screen" That means the power supply board and the Backlights circuits are OK, you have problem on the main board.

[agapes]

Re: Samsung UN55D6500VF won't power on

But why after a while tv power on and working for long time without any problem and never power off

[budm]

Re: Samsung UN55D6500VF won't power on

Because you have problem on the main board that may be temperature sensitive. That is why you need to troubleshoot the problem, the hard part is that how much time you are willing top spend to locate the problem down to component level, Hours?, Days? Weeks? Months?
Schematic diagram will be really big help. It can be as simple as bad connection.
And may be someone out there that spent lots times that he/she works on this particular model with this particular board for the first time will post something to share with us, someone has to do the dirty works first. I share lots of my repair experience that some one may have never work on before or never see the problem before so they do not have to spend hours trying to repair the units.
Right now we have narrow it down to the main board, so there are more steps to go.
Removing the cables between the main board and the power supply for this model (and many SAMSUNG newer model) is one of the troubleshooting method to find out at least which board is not working. In the older model you will have to use resistors to force on the power supply and inverter to find out if they are good or bad.
You can try heating the board with hair dryer or cool it down with freeze spray to see how it will react.
BTW, I would not let the power relay keeps clicking like that (due to the PS-ON signal from the main board comes and goes) for a long time, not good for the relay contacts and components on the power supply board due to in rush current.

[tibimakai]

Re: Samsung UN55D6500VF won't power on

Jcamerox, measure the removed PS_ON wire. See if it changes states.

[jcamerox]

Re: Samsung UN55D6500VF won't power on

Good point, tibimaki. With the PS_ON pin disconnected, the pin itself has 3.4v and the connector on the main board has 0v, and there is no cycling on and off.
If I jumper the pin to the connector and press the power button, the cycling starts.
I put the pin back into the connector and reattached the main/ps cable and turned power on to start the cycling. In the photo, the PS_on signal comes from BD202 (a 2 ohm resistor) and then from Q202 which is being driven on and off between 3.3v and .3v. Without a schematic it is difficult to go much further.

[tech2014]

Re: Samsung UN55D6500VF won't power on

I have this tv in my shop today. Tv comes on then turns off and on. When I removed the PS_ON pin from the connector to the main board, the power supply still clicks, so in my case its a power supply issue. The removed pin stays at 0 the whole time.

[tech2014]

Re: Samsung UN55D6500VF won't power on

I found the problem with my tv. I noticed when I tapped on the power supply, the tv would turn off and on by itself. I found a bad solder joint on a transformer. I reflowed the solder on all of the pins of the transformer and now the tv is working again.

[dick_barton]

Re: Samsung UN55D6500VF won't power on

Good work. Another success story.

[thoma]

Re: Samsung UN55D6500VF won't power on

link

[JeffJ]

Re: Samsung UN55D6500VF won't power on

I found the problem with my tv. I noticed when I tapped on the power supply, the tv would turn off and on by itself. I found a bad solder joint on a transformer. I reflowed the solder on all of the pins of the transformer and now the tv is working again.

TY for this, I had a similar problem but bank 4 of the edge lit leds didn't light and it would turn on and off indefinitely. I touched up the joints on the transformer and it still dd it. so i tore it down and tested every led in all 4 banks of the edge lighting. All were fine. So i decided to re-solder the transformer again just in case. and it works now.

Fruity loops... but thanks for the tip.