Samsung PN43D450A2D No Standby Voltage

[neilc6]

Full model number PN43D450A2DXZC

Lots of threads with this model mainly with a shorted X-main board whose symptoms are a clicking relay and/or flashing LED.

Mine has no voltages at all on the connectors, no LED, and no clicking relay. No bulged caps and fuse is ok. Measured 120VAC on it plugged in on both sides. No 5V standby which is the first step in the fast track troubleshooting guide.

Checked transistors on heat sink for cold solder joints and they look ok.

PS board part number is BN44-00442A. Can't find a schematic. Would prefer to not give in and buy a new PS board but may end up doing that.

[neilc6]

Re: Samsung PN43D450A2D No Standby Voltage

I checked my board inventory and I had a power supply board from a Samsung PN51D450 TV with part number BN44-00443A. The pcb board itself was identical so I decided to plug it in and the TV powered up. Not sure how safe it is to do this. I'll also see if the VS and VA voltages match the panel.

[maxvalutech]

Re: Samsung PN43D450A2D No Standby Voltage

Good idea plus the others as well. For the dead board of course should check the voltages of the two main caps hot side and if OK track the standby from there.

[neilc6]

Re: Samsung PN43D450A2D No Standby Voltage

Voltage on the big caps is 0V as well so nothing out of the PFC. Would assume the PS board for a 51" TV would be OK for a 43" since it probably has more power for the larger TV. Even a schematic for a similar board would help.

[tom66]

Re: Samsung PN43D450A2D No Standby Voltage

Will probably work but I have a feeling the Y-main connector is different

[maxvalutech]

Re: Samsung PN43D450A2D No Standby Voltage

Yes there is a lot I just searched for PN43D450 and a few service manual sites though some dicky. Apparently the X board can cause power board problem on this model and there is a firmware update to fix. Month and Year important being Jan Feb production ninth letter indicates in serial either 1 or 2. How is the bridge rectifier on bad board?

[maxvalutech]

Re: Samsung PN43D450A2D No Standby Voltage

Attachment

[neilc6]

Re: Samsung PN43D450A2D No Standby Voltage

Manufacturing date is Nov 2011 so past the firmware bulletin date.

Bridge rectifier diodes test ok but I don't measure any voltage at the input with the power plugged in and 120VAC carefully measured at both sides of the fuse and gnd.

[neilc6]

Re: Samsung PN43D450A2D No Standby Voltage

Ohming out the AC input path, I am losing connectivity by the relay and thermistors. The area is a little brown from possible heat damage. One measures 3.0 ohm and the other 2.8 ohm at room temp in circuit. Thermistors are marked SCK 2R58 (2.5 ohm, 8A). Relay is OJT-SS-105LM

Not sure how the circuit is supposed to work since the relay is in the AC path but would need voltage to close it???? Datasheet says the relay is normally open and has a 5V coil voltage.

I would compare with my other working board but I have buttoned it up.

[tom66]

Re: Samsung PN43D450A2D No Standby Voltage

The power passes thru the thermistor which charges the caps on the board slowly. The controller chip on the power supply bypasses the thermistors when the caps are charged, this reduces inrush current when the TV is first turned on but also allows the TV to work relatively efficiently

[neilc6]

Re: Samsung PN43D450A2D No Standby Voltage

Found a non-readable schematic for a samsung plasma supply which should give me some hints of where to probe. The relay click that is heard when the power is first plugged in is the main AC relay closing to provide main power so without the relay closing, there will be no AC on the bridge rectifier.

[tom66]

Re: Samsung PN43D450A2D No Standby Voltage

Depends which relay you are referring to. Lowest relay is the thermistor bypass - power always available to stby circuit without its activation. Main power to high power side only active after second relay clicks.