Samsung UN40EH5300F No Power

[meantomatoes]

it's the power board, i know that, but i'd rather not replace it. no backlight, no standby. none of the capacitors look bulgy, fuse is good i think. can yall help me figure out what's wrong? i barely know how to use a multimeter or how to troubleshoot a circuit board but i measured ac voltage and it's like 120-140 volts up until the bridge rectifier and it turns to about 340. voltage remains that up until the legs of the transformer that meets the hot and cold side where it goes to 0 on the output of the transformer. is that normal? sometimes if i plug it in with just CNL802 (backlight) and not CNM803 (main board) the backlight flickers on but then goes off and stays off and won't do it again. it was making a baby lightning bolt when i measured DC voltage on some of the components by CNL802 but now it doesn't do it anymore. pictures are from shopjimmy, board is BN44-00666A

[CapLeaker]

Re: Samsung UN40EH5300F No Power

check the connector that goes to the PSU for burnt contacts.
With the PSU turned off, there should be 170V DC on the main filter cap. You can unplug the main board from the PSU, plug the back lights in, then plug the PSU into mains circuit. The PSU should come on and the back lights should be on and stay on. The flickering could have been an back light led going bad. Pin 12 is A5V, so this pin should have 5V STBY all the time.

[meantomatoes]

Re: Samsung UN40EH5300F No Power

check the connector that goes to the PSU for burnt contacts.
With the PSU turned off, there should be 170V DC on the main filter cap. You can unplug the main board from the PSU, plug the back lights in, then plug the PSU into mains circuit. The PSU should come on and the back lights should be on and stay on. The flickering could have been an back light led going bad. Pin 12 is A5V, so this pin should have 5V STBY all the time.

not measuring any DC voltage at either leg of the main filter cap. that's the blue one correct? i put a probe on the leg and the other on the ground right? i don't know anything about this stuff.

so while the board is plugged in, disconnect the main board with the backlight not plugged in, then plug in the backlight and then the main board? this did nothing.

measured DC voltage of CNL802 and CNM803 using the method in 1st pg. i have a cheap multimeter so this might be why the readings fluctuate? can't afford a nice one, that's why i'm avoiding replacing the whole board.

• CNM803 is dead on all pins, 0 volts.

• on CNL802, pins 1-2 make a blue spark, jump to ~375 and slowly fall to ~295, repeating the cycle every 2-4 seconds.

• pins 3-4 do the same but jump to ~340 falling to ~260 with spark.

• pin 5 is dead.

• pins 6-7 jump to ~310 falling to ~240, no spark.

• pins 8-9 jump to ~280 and fall to ~220, no spark.

hope this helps

[budm]

Re: Samsung UN40EH5300F No Power

Put the DC Volt two meter's probes at each leg of the main filter cap CM804S, report then reading.

[meantomatoes]

Re: Samsung UN40EH5300F No Power

Put the DC Volt two meter's probes at each leg of the main filter cap CM804S, report then reading.

yup, 170 volts not fluctuating

[nomoresonys]

Re: Samsung UN40EH5300F No Power

yup, 170 volts not fluctuating

There's 2 parts to this test, the 170 seems about right, now hit the power button see if it goes up to about 380 or so, if so that part is ok, BE CAREFUL, this is the HOT/DEADLY side of the powersupply.

[budm]

Re: Samsung UN40EH5300F No Power

There is NO PFC Voltage booster so the Voltage on the cap will remain around 160V or so, the power supply is an always on power supply since it is the only power supply on that board, some of the outputs are switched (the one with 'B' marking).
I would like to see the pictures of YOUR board since there may be something that you did not see on your board.
DM851C is the rectifier diode for the A5V.
I would check all 7 diodes on the cold side.

[CapLeaker]

Re: Samsung UN40EH5300F No Power

I would start investigating why A5V isn't there. On the back side the A5V goes through 2 jumpers and goes to a surface mount diode. check it out.

[R_J]

Re: Samsung UN40EH5300F No Power

Can you provide the number on the ic on the HOT side (ic???1S) Is it a (SSC2S110) by chance? I suspect it should be operating in standby mode, which would produce the needed 5 volt standby, when the power on signal comes, opto (pc???1s) puts the ic into full on operation. and you should get the other voltages

[budm]

Re: Samsung UN40EH5300F No Power

There is NO PFC Voltage booster so the Voltage on the cap will remain around 160V or so, the power supply is an always on power supply since it is the only power supply on that board, some of the outputs are switched (the one with 'B' marking).
I would like to see the pictures of YOUR board since there may be something that you did not see on your board.
DM851C is the rectifier diode for the A5V.
I would check all 7 diodes on the cold side.

The two SMD MOSFETs on the bottom side of the board; One is for B5V and another one is for B13V; they are turned on when PS-ON is present.

[meantomatoes]

Re: Samsung UN40EH5300F No Power

There is NO PFC Voltage booster so the Voltage on the cap will remain around 160V or so, the power supply is an always on power supply since it is the only power supply on that board, some of the outputs are switched (the one with 'B' marking).
I would like to see the pictures of YOUR board since there may be something that you did not see on your board.
DM851C is the rectifier diode for the A5V.
I would check all 7 diodes on the cold side.

DM851C has no resistance in either direction, DM852C and DM853C have something wonky where they slowly increase slower and slower in the correct orientation to like 8k ohms (is that right? the dial is on 20k and it's showing ~8.00) and then slowly decrease with the opposite direction. DM855C-DM858C have ~16k ohms and then ~100k the opposite way.

Can you provide the number on the ic on the HOT side (ic???1S) Is it a (SSC2S110) by chance? I suspect it should be operating in standby mode, which would produce the needed 5 volt standby, when the power on signal comes, opto (pc???1s) puts the ic into full on operation. and you should get the other voltages

IC? where would that be?

[budm]

Re: Samsung UN40EH5300F No Power

OK the Diodes are not shorted.
Check DM851C in diode mode to see what you get.
The SMPS IC in question is ICM801S, it is the SMD 7-PIN IC.
BTW, when you tested the DC V on the cold side connector, is the board connected to the main board? If it is then try running the power supply board by itself to see what dc V you will get on the cold side connector.

[meantomatoes]

Re: Samsung UN40EH5300F No Power

OK the Diodes are not shorted.
Check DM851C in diode mode to see what you get.
The SMPS IC in question is ICM801S, it is the SMD 7-PIN IC.
BTW, when you tested the DC V on the cold side connector, is the board connected to the main board? If it is then try running the power supply board by itself to see what dc V you will get on the cold side connector.

DM851C shows 001, DM852C and DM853C show 328, and DM855C-DM858C show ~448.

for the IC, i assume you mean the number printed on it and not the voltage or anything? it's 3S111, SK391, 267(and maybe a 1 or I or L)

[budm]

Re: Samsung UN40EH5300F No Power

Hmm, I would remove DM851C and re-test again in Diode mode.
I found the picture of the IC but not the spec. sheet.
https://www.aliexpress.com/item/LCD-...469463424.html

[meantomatoes]

Re: Samsung UN40EH5300F No Power

Hmm, I would remove DM851C and re-test again in Diode mode.
I found the picture of the IC but not the spec. sheet.
https://www.aliexpress.com/item/LCD-...469463424.html

same reading

[R_J]

Re: Samsung UN40EH5300F No Power

The ic is similar to this SSC1S311, pin 1 is controlled by the opto to switch the ic out of standby condition. Check the voltage on pin 4 using the main cap's negative for meter ground
Sometimes one of those series resistors coming from the main cap's (+) goes open.

[neilc6]

Re: Samsung UN40EH5300F No Power

That board is $25 on ebay shipped. Not sure why you don't just buy another one. I had scrapped some 50" Samsung LED TVs and found out after that the boards were selling for $10 to $20 on ebay with shipping.

[meantomatoes]

Re: Samsung UN40EH5300F No Power

The ic is similar to this SSC1S311, pin 1 is controlled by the opto to switch the ic out of standby condition. Check the voltage on pin 4 using the main cap's negative for meter ground
Sometimes one of those series resistors coming from the main cap's (+) goes open.

should i put the diode back on before testing?

That board is $25 on ebay shipped. Not sure why you don't just buy another one. I had scrapped some 50" Samsung LED TVs and found out after that the boards were selling for $10 to $20 on ebay with shipping.

seems wasteful to me

[R_J]

Re: Samsung UN40EH5300F No Power

should i put the diode back on before testing?

??? what diode??
There are a series of 3 resistors that go from the main cap positive to supply the ic with its vcc voltage, If its not there the ic won't operate.

[budm]

Re: Samsung UN40EH5300F No Power

same reading

001 in both directions?