Samsung UE46EH5000 - Flashing red light but not turning on

[Phil289]

Hi
I aquired a Samsung UE46EH5000 from a lady that said it was turning on and off so she just purchased a new one.
On plugging into the mains and turning on i get a solid red light.
On using the on/off button or remote i just get a flashing red light in a pattern of flash/flash gap flash/flash gap flash/flash etc.
Opened it up and disconnected the main board from the power board by removing the connecting ribbon cable with the hope of getting either a 'no backlight' or a 'working backlight' but got neither,i just got a blinking backlight that turned on and off randomly at about 1 second or so intervals.
So i disconnected the led connector from the power board so that there was nothing connected except the power lead and started to check the voltages.
At CNM803 which is the connector to the main board it said there should be 13v at pins 1,3 & 4 but all i got was a fluctuating voltage of 0v to 8v and at pins 11,12 & 13 i should have got 5v but at 11 & 13 i got a fluctuating voltage of 0v to 4v but at pin 12 i got a solid 5.2v which seemed as it should be.
Next i checked the led backlight voltage at CNL802 (the connector that connects to the backlights) and at the 2 pins 1&2 (D1+ and D1+) i got a fluctuating voltage of between 288v and 318v (this is obviously with no load on)
I would appretiate some info of where to go from here.
I suspect that something is not quite right with the power board but need someone with more experiance to advise what to check next.
The power board is a BN44-00497a - rev 1.2, it all looks very clean with nothing visually obviously bad (no bulging caps or anything leaking or burnt)
I have an lcr-t4 esr meter that i can use to test the caps but maybe somebody else may have a better idea of what to try.
Thanks
Have attached a picture of the power board

[dskall]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

Are pins 11, 12, and 13 all connected to each other? What is the voltage across your main capacitor??

[nomoresonys]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

easy things first, check the diodes and resistors, also check the underside for bad solder joints, examples of bad joints: https://www.google.com/search?q=bad+...ih=607&dpr=1.5

[nomoresonys]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

if no joy, maybe check those 5 electrolytic caps by the connectors.

[neilc6]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

Bad backlights can cause them to flash in Samsungs. First suspect with any backlight issue.

[Phil289]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

Are pins 11, 12, and 13 all connected to each other? What is the voltage across your main capacitor??

Thanks for the reply

Pins 11 and 13 are connected but pin 12 (the one with good voltage ) is not connected to pins 11 & 13.
Voltage across the big 400v cap on the hot side is 390v.

[Phil289]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

easy things first, check the diodes and resistors, also check the underside for bad solder joints, examples of bad joints: https://www.google.com/search?q=bad+...ih=607&dpr=1.5

Thanks for the reply
Will check these out today and report back

[Phil289]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

Bad backlights can cause them to flash in Samsungs. First suspect with any backlight issue.

Thanks for the reply
I will bear that in mind
I was more concerned about the poor voltages on the rest of the power board when the backlights were disconnected and was wondering if the lack of voltage was causing the non start up and unstable voltage to the led's?
Will carefully work my way through all your suggestions 🙂

[Phil289]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

Thanks for the reply

Pins 11 and 13 are connected but pin 12 (the one with good voltage ) is not connected to pins 11 & 13.
Voltage across the big 400v cap on the hot side is 390v.

Sorry this should read that the big cap is rated at 450v not 400v but I couldn't see how to edit my post 🙂

[nomoresonys]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

steady 390 on the big cap/s is good, no problem there.

[nomoresonys]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

being about 10 years old, wouldn't be surprised if it was bad backlight/s as mentioned, but the fluctuating voltages when stand alone (unhooked from everything) is strange.

[Phil289]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

Well I'm making some progress and learning on the way.
I decided to check all the diodes on the board - so set multimeter to diode mode and tested everyone I could find - nearly all the diodes would only give a value when the test leads were placed one way round - if i reversed the probes then they just read 1 but on the 3 larger diodes near the CNM803 connector I'm getting a value for both directions so can i take it these are probably faulty and allowing voltage to flow both ways instead of just one?
If so is there a way to find what values they are so i can order some and also would there be anything else that would need to be checked that would have caused them to blow or are they just a failable part like caps?
Thanks

[nomoresonys]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

maybe take one of the 2 that are together out of circuit, then recheck it, see if it still reads bad, if reads bad it is bad, recheck the others while still in circuit see what they read, depending on configuration sometimes only one is bad and making the other read bad. Adding a little fresh solder to the joints make the component come out a lot easier.

[nomoresonys]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

value should be written on the diode, just need to match it up with replacement or suitable substitute.

[nomoresonys]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

they don't cost much, a rule for myself is, if I think I need 3, I get 5 or 6, it's the shipping that cost in these cases, meaning if you have to reorder the shipping is there again, unless you get free shipping of course.

[dskall]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

I think this is your schematic. What voltage do you get at your ps_on terminal in standby and power on?

[Phil289]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

I think this is your schematic. What voltage do you get at your ps_on terminal in standby and power on?

Thanks very much for that should come in handy - i will check the ps_on voltage once i get the board back together (see my next post ) 🙂

[Phil289]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

Getting a bit strange now.
Pulled out the 3 ‘faulty' diodes and guess what - they all read good once they are disconnected.
So while i had the iron out i pulled out the 5 caps near the ribbon connectors and the values look good-

25v 470uf reads 485uf
10v 1200 uf reads 1275uf
25v 470uf reads 509uf
200v 47uf reads 45.7uf
350v 22uf reads 20.56 uf

So with the caps still out I replaced just one of the diodes as in the attached picture and it went back to being ‘faulty ‘ so when it was tested with the probes either one way or the other way it gave a value.
What could cause this - it seems to be picking up a reading from something that the diode connects to ?
Thanks

[nomoresonys]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

probably had a resistor across them or something, do an ohm reading of the holes they go in, see what you get.

[nomoresonys]

Re: Samsung UE46EH5000 - Flashing red light but not turning on

also check the components on the heatsinks, are any of them labeled D for diode? if so you can check those in diode mode too.