Samsung LA26C450 does not turn on

[Markus1]

I have got this small LCD TV. Red LED on the front is on but the set does not respond to either remote control or touch buttons on the bottom edge, and the red light stays steady on.
Inside no components look burnt or swollen. No back light. STB 5V is OK as shown by the red LED.
I took some measurements on the power supply board:
* with Main Board connected both 24V and 13V lines fluctuate from about 3 to 15V and 0.6 to 4.2V respectively.
* with Main Board disconnected the 24V line reads around 16.7V while 13V line reads around 8.6V
* also voltage on LVcc pin of ICM801 (FSFR1700) is unstable.
I am not sure where to look next. Is it a faulty switching IC (ICM801) or is it a protection circuit acting? Your guidance for further troubleshooting steps would be very much appreciated.
Attached below are the pictures of the Power Supply Board and also its schematic diagram.

[budm]

Re: Samsung LA26C450 does not turn on

Check the DC Voltage right at the TWO LEGS of the main filter cap to see if it has large fluctuation when TV is on.
Try heating the board with hair dryer for 2~3 minutes and then apply the power to see if the voltage will be steady.
Check the capacitance of the white rectangular cap that has '2J 183J' ptinting on top.

[Markus1]

Re: Samsung LA26C450 does not turn on

Budm, your instructions were spot on. Thank you. It really amazes me how quickly and correctly you (and others on this forum) can recognize the issue and indicate direction to pin-point the problem.
Yes, the capacitor (white rectangular with '2J 183J' printing) was creating the problem. Schematic indicates this cap as CM808 18nF, 630V. When measured off the board it showed only about 1nF. I could not find the exact replacement but substituted it with 22nF, same voltage range. The TV is alive.
I hope that this slightly higher capacitance is not too critical in the long term. It seems to be doing well now.

BTW - What is the role for this cap? It sits directly in the DC supply line to primary winding of the switching transformer. Why wouldn't the transformer operate without that cap? I would really like some theory on this point, if possible.

As a reference to other readers I include again the schematic diagram with an arrow marking pointing to the location of the replaced capacitor in the circuit. It is on page 2. Please disregard two red oval markings, they are irrelevant to this case, came originally on the download.

Thank you again, fantastic platform for exchange of knowledge. I am learning a lot from it.

[budm]

Re: Samsung LA26C450 does not turn on

It is the coupling/dc blocking cap for the primary winding of the transformer, you will need to get the correct type and value otherwise it will have problem. It has to be made for high switching circuits:
http://www.digikey.com/product-detai...2122-ND/585189

[Hyper]

Re: Samsung LA26C450 does not turn on

Hi Markus, Is your TV still working with 22nF 630v cap?

I think I have same problem and very hard to get 18nF caps in Oz.

Thanks

[Markus1]

Re: Samsung LA26C450 does not turn on

Hi Markus, Is your TV still working with 22nF 630v cap?

Hyper, yes it still works. It seems that the 22nF cap instead of the original 18nF is acceptable. Obviously its voltage can not be lower than 630V.

[Hyper]

Re: Samsung LA26C450 does not turn on

Hyper, yes it still works. It seems that the 22nF cap instead of the original 18nF is acceptable. Obviously its voltage can not be lower than 630V.

Thanks Markus

Put in a new 22nF 630v but no difference. The voltage to inverter board measures 25v only when if inverter board disconnected. When inverter connected voltage fluctuates between ~5 to 25vdc

Wondering if the if ICM801 could be at fault?

[Markus1]

Re: Samsung LA26C450 does not turn on

In this case I would think the inverter could be the problem causing the voltage to fluctuate.
Perhaps others can shine more light on it.

[budm]

Re: Samsung LA26C450 does not turn on

Thanks Markus

Put in a new 22nF 630v but no difference. The voltage to inverter board measures 25v only when if inverter board disconnected. When inverter connected voltage fluctuates between ~5 to 25vdc

Wondering if the if ICM801 could be at fault?

Is the PFC Boosted Voltage steady?

[Hyper]

Re: Samsung LA26C450 does not turn on

Hi Bud

The PFC voltage fluctuates between 150 & 220 volts DC measured between Diode DP801 Cathode to chassis

Thanks

[shackwish1]

Re: Samsung LA26C450 does not turn on

I have just picked one of these tvs up from the tip it's doing the same as mentioned above constant steady stand light .I removed cap 2j183j and I can see a slight bulge at one end .I'm having problems locating this cap ecept for in China and US .

[dick_barton]

Re: Samsung LA26C450 does not turn on

I have just picked one of these tvs up from the tip it's doing the same as mentioned above constant steady stand light .I removed cap 2j183j and I can see a slight bulge at one end .I'm having problems locating this cap ecept for in China and US .

A 22nF as indicated above seems to be a reasonable replacement for it.

You could try Mouser UK