Samsung UH50EH5300FXZA, help with a transformer?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

How many wires are there on the LED connector?

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

When I unhook the main board from the PSU the backlights are on.

OK self test is fine then if it stays as long as the AC is applied to the TV.
But the 264V on the Anode of the first string is quite high unless the Voltage chart is wrong.

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

'12 A5V.......5.25 constant'
Since standby is contstant but the control signals are not then you have problem some where on the main board, exactly what I do not know.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

OK self test is fine then if it stays as long as the AC is applied to the TV.
But the 264V on the Anode of the first string is quite high unless the Voltage chart is wrong.

229V backlight voltage spec is confirmed written on my board. In this case I agree the reading is high. I don't see any current limiting resistors on the top of the board so they must be SMD on the back. Seems like I ought to check them if so equipped?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

'12 A5V.......5.25 constant'
Since standby is contstant but the control signals are not then you have problem some where on the main board, exactly what I do not know.

I do believe the main board is the problem as well.

The problem started while smart hub was updating. Seemed OK until then save for an extended turn-on time.

Reminds me of what this TV is doing, another one of mine.

https://www.badcaps.net/forum/showth...un46eh6030fxza

It also had a flashing standby light when TV is turned on but no backlights or display. I heated up one of the RAM chips and it would turn on. I also applied heat to the same RAM chip on this 50" and it seemed to help it turn on.

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

229V backlight voltage spec is confirmed written on my board. In this case I agree the reading is high. I don't see any current limiting resistors on the top of the board so they must be SMD on the back. Seems like I ought to check them if so equipped?

It uses constant current driving circuit, not just simple current limiting resistor.
The D- is the Cathode return of the LED string that goes to ground via PWM control MOSFET Q9151C and current sensing resistors.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

It uses constant current driving circuit, not just simple current limiting resistor.
The D- is the Cathode return of the LED string that goes to ground via PWM control MOSFET Q9151C and current sensing resistors.

Just for the heck of it I checked for voltage at the EEPROM test points and found they all have 3.29v. Does this mean the EEPROM isn't working or shorted maybe?

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Well the replacement main board arrived. I installed it in to the TV and so far we're back in business!

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

This will be my final update on this TV. It continued to work fine with no other problems so it is approved and now gone. I donated it to an animal rescue organization for their waiting room, so they can put up slide shows and show people what they do!

Thank you to everyone who participated in this thread and I do appreciate it!

[budm]

Re: Samsung UH50EH5300FXZA, help with a transformer?

This will be my final update on this TV. It continued to work fine with no other problems so it is approved and now gone. I donated it to an animal rescue organization for their waiting room, so they can put up slide shows and show people what they do!

Thank you to everyone who participated in this thread and I do appreciate it!

Thank you for supporting animal rescue organization.

[DXseekerMO]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Thank you budm for all of your help, I appreciate it!

[howardc64]

Re: Samsung UH50EH5300FXZA, help with a transformer?

Repaired the PSU and saved one of these from the dumps. PSU PN BN44-00668A. Got it for free after power outage took it out.

CP805 (221pf 1kv) blew up with all the smoke exiting towards bridge rectifier and under the heat sink. Tested all MOSFETs and big diodes per budm in post #2. QP801CS was shorted. Fuse was blown of course. TV came up after replacing these 3 components.

Pic attached, you can still see the smoked debris field near the bridge rectifier haha. Thanks for badcaps again on this one, no exact schematics online but many similar BN PSU schematic does exist.

Avoiding software update per OP's post in #77. Had a similar experience with a 32" Samsung that screwed its firmware (was able to reload when cold and recover in that case)