Re: Samsung LE26B455C4W backlight problem
I finally found the fault. It was CP810 0.22nF 1KV capacitor. It was cracked but I didn't see that earlier. Now the TV works. Thanks for the help.
thth
Member
Last Activity: 12-20-2016, 12:45 PM
Joined: 06-20-2016
Location: Western Finland
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Re: Samsung LE26B455C4W backlight problem
I wasn't until now that I undestood how this circuit works. Sorry for being so thick.
It was mentioned here before but I didn't understand it then and I only got the schematic recently. The backlight is now working because it is getting rectified mains voltage but the voltage is not boosted as it should be by FAN7530 IC. So the backlight is not getting the full power. Presumably there is some circuit in the FAN7530 that cuts the backlight if the boost is not working. By removing the jumper I disabled that circuit.
...Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
Would it be safe to do a longer test with the jumper left open? I haven't kept the tv on longer than a minute or so.Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
I left the TV overnight and when I tested it today the backlight wouldn't come on but putting it on standby and on again made it work. The jumper was still open. I tried to reconnct it but the backlight wouldn't turn on. Opening the jumper resumed the operation of the backlight.
What is the function of the FAN7530? I'm guessing that it is not wise to leave the jumper open permanently?Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
I opened the jumper and was measuring the VCC of U801S (actually UM801S) when the backlight suddenly came on. What could have happened? And why would the light be on when the supply for FAN7530 is cut?
EDIT: I just wanted to add that the light came on when I was actually doing the measurement (I saw the light from the back through some holes in the metal back plate). Also it _might_ be that I accidentally poked the probe between the Vcc and ground shorting them momentarily (but I'm not 100% sure about that).Last edited by thth; 12-17-2016, 05:41 PM.Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
Thanks for the manual link! I checked CP809. It was OK (ESR was 0.2 ohms). Can you suggest what I should do next?Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
I changed the FAN7530 chip but it didn't help. What can I do next, please help?Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
Hello again. It's been a while since I worked on the TV but now I'm trying again.
I removed a jumper that gets the Vcc for the FAN7530 (pin 8). The voltage is 14 volts but it goes low when I connect the jumper. Also I heard a click from somewhere.
So the FAN7530 is drawing too much current? Could the fault be after the output of the IC or would the built-in over-current protection handle that?Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
I have tried to trace the Vcc for the FAN7530 but I'm not sure where it is supposed to come from. Does anyone have a schematic?Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
OK. I got confused when you said earlier U801S, sorry. I found the correct IC (FAN7530) and the VCC is about half a volt so it is not getting power.Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
There is 18 volts in the VCC pin of U801S (= ICE3BR0665J)Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
OK. Thanks for the clarification. I tested Q802S (FET) with a cheap Chinese component analyzer and it checked OK. Should I change it anyway? The original is K8A60DA. I have IRF840 and 2SK3562, would one of these work?
The diodes checked OK with the multimeter diode check function.Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
There is a pin marked inv_on/off on the connector between boards. The voltage on that is 5 volts.
The voltage on the electrolytic cap is 320 volts. I thought it was supposed to be rectified mains voltage (or line voltage) ie. 230 Vac x 1.41 = 324 Vdc ?Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
Thanks for the excellent pictures!
It was around 320 volts if I remember correctly. I'll re-measure that too....Leave a comment:
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Re: Samsung LE26B455C4W backlight problem
Here are a couple of pictures. They are not clear or focused, unfortunately. Sorry about that. I'll try to get a better camera next time.
I'll measure the BL-ON voltage and report it here later....Last edited by thth; 06-21-2016, 02:39 PM.Leave a comment:
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Samsung LE26B455C4W backlight problem
I'm repairing a Samsung LE26B455C4W TV for a friend. The fault is no backlight. Sound and everything else is OK, the picture is there (looked with a flashlight). The power supply board is BN44-00259A.
I searched the net and this forum and I found some info where to look but so far I haven't found the problem.
What I have tried so far:
I found a Samsung service note for this model about a diode causing backlight problems. The diode has to be changed to a more realiable type but that part is already the correct type.
[url]http://www.docfoc.com/samsung-lcd-tv-repair-power[/url]... -
Re: New Members - please post your introductions here
Hello. I am new here and looking forward to getting a Samsung TV fixed.Leave a comment:
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