Samsung LE22C450

[Hombre]

I got this tv.

The problem is that there's no backlight, with the flashlight i can see the menu is there.
Tested diodes for short, but they all seem ok.
Checked secondary windings, first is 1019, second is 1021 ohm, so that looks ok to.
There are 5V, and 13V so that looks ok too.
But, the voltage across primary cap legs is 315V when in stdby (which is ok), but after power button is pressed (red image appears for a second, and i can hear samsung sound) the voltage stays the same - 315V. It should be around 390-400V?
I measured with my DMM primary cap and it says 95uF, and on cap itself says it should be 120uF. Can that be the cause?
UI801 is a 16 pin IC but i can't read part number because it looks like someone erased markings altough the tv isn't opened before, mybe is because of heat, i really can't tell but it is a bit suspicious
PS numer is BN44-00370A and i can't find service manual for that one
UM801S is Q0765R

Sry for low quality pics, but my camera decided not to work anymore, so i had to take pictures with potato, i can probably have better res pictures tomorrow

[selldoor]

Re: Samsung LE22C450

Hi - Pic 2 to the left of the yellow transformer there is a green fuse - have you tested it?
Voltage at both sides?

[Hombre]

Re: Samsung LE22C450

Unbeliveable, i was sure i tested it, and that it showed continuity, and just wanted to check before replying positively to you, would you now, it is open. Can't believe it.
What a noob...

I'll replace it tomorrow and post results, hope it is just that, thx! Altough it blowed for some reason.

[Hombre]

Re: Samsung LE22C450

Ok, replaced fuse, same thing, no backlight

So, in stdby i have 5V and 13V on CNM801, after power button is pressed i have 2V on E_PWM pin so motherboard is sending signal, but still the voltage on primary cap is 315-320V
BLU_ON 0V in stdby, 5V with power button is pressed.

[selldoor]

Re: Samsung LE22C450

As you say - blew for some reason - please test it again- what is the voltage on each side with respect to a ground screw

[Hombre]

Re: Samsung LE22C450

13V, on each side, so probaly was dmm fooling around when i measured it last time , but now fuse is ok.
I assume as this cap is 450V that the voltage after tv powered on, should be around 400V? Am i right?

[selldoor]

Re: Samsung LE22C450

I am not sure - voltage on the cap on older sets would be mains VAC* 1.41 so you are not far away. It would only go higher if the set has PFC Circuit. If it has and its not working then that would stop the back lights coming on.
I have to go out today so perhaps others will chime in and help you with testing - or perhaps you already know - there are many threads - just type PFC in the search above.

[tom66]

Re: Samsung LE22C450

That TV does not have PFC circuit, so 315V is OK.
I would check bottom of board - inverter circuit probably uses the 13V supply.

[Hombre]

Re: Samsung LE22C450

OK, focused on the bottom of the board as you suggested.
I think i may have found something but need confirmation from someone smarter and more experienced than me
That 16 pin IC UI801 is bit suspicious to me, because i am measuring around 85-90 ohms between pin 3 and pin 6,7 which are GND. Marking on IC is damn hard to decode because it looks like it is sanded... After an hour or so of losing my eyes with magnifier and flashlight i am 70% sure that it is SEM2105, but can't find datasheet for that one
So i found somwhere info that is interchangeable with SEM2005. On sem2005 pin 3 is open lamp protection (pins 6 and 7 do match with my circuit as they are gnd). Should i try to change it, what do you think?
IC is unsoldered, it is out of cct.

[selldoor]

Re: Samsung LE22C450

So i found somwhere info that is interchangeable with SEM2005. On sem2005 pin 3 is open lamp protection (pins 6 and 7 do match with my circuit as they are gnd). Should i try to change it, what do you think?
IC is unsoldered, it is out of cct.

Was that a reliable source? clearly there is a SEM2105
http://www.aliexpress.com/store/prod...898714881.html

As yoiu say the datasheet is elusive perhaps it is a proprietary part for Samsung.

[tw2005]

Re: Samsung LE22C450

OK, focused on the bottom of the board as you suggested.
I think i may have found something but need confirmation from someone smarter and more experienced than me
That 16 pin IC UI801 is bit suspicious to me, because i am measuring around 85-90 ohms between pin 3 and pin 6,7 which are GND. Marking on IC is damn hard to decode because it looks like it is sanded... After an hour or so of losing my eyes with magnifier and flashlight i am 70% sure that it is SEM2105, but can't find datasheet for that one
So i found somwhere info that is interchangeable with SEM2005. On sem2005 pin 3 is open lamp protection (pins 6 and 7 do match with my circuit as they are gnd). Should i try to change it, what do you think?
IC is unsoldered, it is out of cct.

The only thing I can confirm for you is the pin outs are the same, labels and all. I just searched for another samsung board which has the same chip.

[Hombre]

Re: Samsung LE22C450

Update.
I found out that i have ~130Vac or ~150Vdc on heatsink where UM801S (Q0765R) is mounted. I assume that's not good, or at least not very usual?
Replaced Q0765R and leaky bridge rectifier but voltage on heatsink is still present. Heatsink is tied on DC -.
Any thoughts on that?

Thanks!

[tom66]

Re: Samsung LE22C450

That voltage is OK, many heatsinks are tied to -ve of cap. I would be focusing entirely on the secondary side (13V/5V side.)

[Hombre]

Re: Samsung LE22C450

I am losing it, i really don't know what to check next, i think i went through everything but obviously i am missing something
I forgot to mention that there is noise coming from primary transformer (13V 5V), but only when powered on, in stdby there isn't that squeaky noise. All electrolytics are changed, except the big one.

[tom66]

Re: Samsung LE22C450

If you have steady 13V and 5V, I would rule any fault out with that circuit for now. Instead, I'd focus on the inverter circuit.

[Hombre]

Re: Samsung LE22C450

OK, thx

[Hombre]

Re: Samsung LE22C450

I bought used PSU and seller says that is OK. But, when i press power button backlight powers up for a second or two, it's reddish not white btw, and shuts down.
Tried to drive lamps from this tv with a samsung 19" monitor PSU and they work OK. And what's interesting i also connected 19" lamps to this PSU from TV and that works OK to. But it won't work with lamps that is should
Any thoughts what's the problem, what to check?

thanks

[senndogg]

Re: Samsung LE22C450

Reddish/pink ccfl indicates failing ones. They are probably drawing much power, just a little bit more than this psu can handle.
Failing ccfl-s is a bit unusual for Samsung but maybe this one has exceeded its life span.

[Hombre]

Re: Samsung LE22C450

OK, thanks for a tip