Samsung UN46EH5000

[tonyh88]

Hi,

I've been trying to repair a UN46EH5000 for some time now and I think I need some help.

The inital fault was that there was no backlight on the TV. This TV uses LED for backlight. The LED PSU  is integrated in the main SMPS and it is a constant current driver based on the SLC1012C IC.

The SLC1012C was blown and about half of the LED on the strips were OPEN.

I replaced all the LED and ordered a New PSU unit (BN4400667A).

OK so now we reach the part were I need help. With the replaced LED and the new PSU unit there is something weird going on. If I only connect the LED strip to the PSU they light up and draw 470mA at 142V as expected from the markings on the PSU so the new PSU constant current driver is doing it's job.

If I only connect the main board of the TV to the PSU without connecting the LED strip the TV turns on just fine and I can see everything on the display using a flashlight.

The problem is If I connect the LED strip and the main board at the same time the TV PSU keeps power cycling.

Since it is a new PSU i'm a bit puzzled. I bought the PSU from an online tv repair parts store. Did they sell me a bad PSU with crappy capacitors causing this power cycling?

Should I be checking for anything special? Let me know if you have any ideas. I will post some pictures soon.

Thanks

[tonyh88]

Schematic of a similar model can be found here : https://www.electronica-pt.com/esquema/lcd/bn44-00497a-psu-35975/

and attached are some pictures

[keymaster]

470mA is not what is expected . i thing 350mA is the max of the tv leds  . in the schematic you provide , its say that the led should drown 250mA.
Are you sure that you put the correct leds ?

[tonyh88]

Yes as I said the shematic is not for the same PSU I have. It is just using some of the same parts and is only a reference.

For my PSU 470mA is the correct value. This current is controlled By a pair of resistor in parallel on the sense pin of the SLC1012C. I tried increasing the Resistance value to lower the current since 470mA is pretty high for these LED. Under normal operation 470mA is when the backlight is at 100% and is way too bright.

It is a bit of a design flaw on these TV all the LEDS are driven way to hard and the heatsinking is pretty bad.

I think I need to investigate the Fault signal on the FAN7340 this might be causing the PSU to power cycle.