Samsung LN40D550K1FXZA Backlight Problem

[budm]

Re: Samsung LN40D550K1FXZA Backlight Problem

I removed CI818 and tested it and was getting ~.47-.5. It should be a .47uf capacitor right? I'm attaching a picture for reference.

That cap is Polypropylene type.

[nomoresonys]

Re: Samsung LN40D550K1FXZA Backlight Problem

This one LD-4088 is also one of the ones on shopjimmy list. https://www.ebay.com/itm/APEX-LD-408...MAAOSw4GVZ4OPf

[nomoresonys]

Re: Samsung LN40D550K1FXZA Backlight Problem

Not sure, maybe the info. shopjimmy has there in post #18 is wrong?

[nomoresonys]

Re: Samsung LN40D550K1FXZA Backlight Problem

Your inverter board probably looks like this. https://www.ebay.com/itm/Samsung-40-...UAAOSwMgdXxdUd

[nomoresonys]

Re: Samsung LN40D550K1FXZA Backlight Problem

Would it be easier for him to verify the PFC circuit if the inverter board was not connected to the powersupply?

[nomoresonys]

Re: Samsung LN40D550K1FXZA Backlight Problem

I'm a little new to this. Is there something specific I should test on the inverter board?

Inverter board testing, couldn't find your exact model so might not be very useful.
https://www.youtube.com/watch?v=oE6K4xBVweA

[classicmac]

Re: Samsung LN40D550K1FXZA Backlight Problem

Thanks everyone for your suggestions. I measured voltage at the capacitors again and it doesn't look like it goes over 360-380v. Is that an acceptable voltage? They only reach that voltage for a split second then the voltage drops down again.

I'm attaching a picture of the inverter board. Any suggestions on what to check next?

[dick_barton]

Re: Samsung LN40D550K1FXZA Backlight Problem

I tried disconnected the main board to test the backlight as suggested in the troubleshooting manual attached to post https://www.badcaps.net/forum/showthread.php?p=792496. I get the same behavior when I connect power where the backlight just flickers on then turns off again. I'm attaching a picture of the power supply board. I don't see any visibly failed components or bulging/leaking capacitors.

If you carry out this check again can you measure the voltage across the large capacitor using your meter probes between the two legs of the capacitor and is is steady?

[budm]

Re: Samsung LN40D550K1FXZA Backlight Problem

Remove the white fuse with purple stripe right next to the main filter cap and then turn the TV on and see if the Voltage on the main cap stays on 380V or so without dropping back down to 160VDC.

[classicmac]

Re: Samsung LN40D550K1FXZA Backlight Problem

I removed the fuse and powered the television on and the voltage is still at 160V. It is steady at that voltage. Anything else I should check?

[budm]

Re: Samsung LN40D550K1FXZA Backlight Problem

OK, I see why will get only 160VDC on the main caps after tracing out the fuse connection, that fuse is for the the STBY power supply and the Inverter Transformer driver circuit, I was trying to isolate the Inverter transformer driver circuits from the rest of the power supply to see if the PFC Voltage will stay up at 380vdc or not.
Right now we may have PFC circuit problem, or Inverter circuit is drawing too much current and cause the PFC to shutdown, or the Inverter circuit detect error so it sends the error signal to shutdown the circuit..
So have all the boards connected back in place then put red probe of DC V meter on Pin 12 (LD = Lamp Detect)) of connector CNI801, Black probe on Pin 8 (GND) then Turn on the TV to see what you GET. Do the same on pin 9 (OVP = Over Voltage Protection).

[classicmac]

Re: Samsung LN40D550K1FXZA Backlight Problem

I am getting 11.83VDC on pin 12 and 0VDC on pin 9.

[budm]

Re: Samsung LN40D550K1FXZA Backlight Problem

LD is OK, I not sure the pin 9 OVP <1V = bad OR = good

[classicmac]

Re: Samsung LN40D550K1FXZA Backlight Problem

I just did another test. When I plug the television in I see pin 9 briefly jump to .4VDC before dropping to 0.

[classicmac]

Re: Samsung LN40D550K1FXZA Backlight Problem

Does anyone have any ideas on how to isolate the problem to a component or board? Should I try replacing ICP801 as suggested in the other thread?

[classicmac]

Re: Samsung LN40D550K1FXZA Backlight Problem

Thanks so much for the link to your other thread neilc6! I replaced ICP801 and the TV is back to life. Thanks everyone for your help and suggestions.