This power supply is dead is there any common failures on these power supplies that would help me get started. Without a schematic I am really fumbling around.
I do know that it is supposed to have two outputs and I don't have either. The power supply doesn't have that "expensive electrical" smell and I am not able to see anything obvious that is wrong. Any help or suggestions would be appreciated.
Thankyou
Bruce
BruceGilbert
Member
Last Activity: 02-23-2021, 01:56 PM
Joined: 04-05-2020
Location: Currys Cornor
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Re: Sharpe LCD TV LC60E77UN
Here is the latest update. I finally received the Zener Diodes that I suspected had failed and I replaced D7905. I then powered the TV up and it came to life. That was the good news. Attached is what is now displayed on the screen. I believe that I still have a power problem but also a video fault. I feel now that this is beyond my capability so I am going to throw in the towel unless the fault is obvious to anyone. Thank you very much to everyone who helped me along the way.... -
Re: Samsung LN40B5ooP3FXZA Cycling on/Off
Wow thank you so much for all your help. I believe I found the problem. Hopefully optimistic. I found that on assembly of the TV a screw that holds the back cover on the TV in the center went through the cable between the power supply module and the main board. I split the ribbon cable and repaired the wires and the TV has worked for a few hours now. If I get an opportunity I will take the recommended pictures for everyones reference perhaps on another TV or possibly this one if it fails again.Last edited by BruceGilbert; 01-17-2021, 06:03 AM.Leave a comment:
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Re: Samsung LN40B5ooP3FXZA Cycling on/Off
Thank you everyone for your input. I was leaning towards a bad main board. Just to be clear if I disconnect the connector to the main board the backlights should remain on? As previously stated I get about 10 seconds when connected but only about three seconds if I disconnect the cable to the main board as soon as the backlights are on. This is why I suspected the main board possibly not sending a return signal to the power board to remain on. Just my thoughts.Leave a comment:
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Samsung LN40B5ooP3FXZA Cycling on/Off
Have a Samsung given to me. When power is applied backlights will come on and stay on for approximately 10 seconds then power off and then on once again. When looking at the back lights from the rear they appear to be flickering. Tried disconnecting the cable from the power supply to the main board when it powers up and there appears to be no flicker however display will only remain on for 3 seconds with the cable disconnected.. Tried disconnecting the TCONN board with no change. I suspect the main board BN94-02746Y.
I am unable to purchase a repair kit for this board and replacement boards... -
Re: Sharpe LCD TV LC60E77UN
Update I have ordered the Zener diode D7905 and will install it once it arrives and update my findings. Is the above readings inline with what is expected? IC7906 between pins 3 and 4 17 meg ohms.Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
I have measured between the resistance between pins 3 and 4 of IC7906 and it reads 17 meg ohms. Now to order a replacement Zener diode. I spoke to my local Jentronics dealer and he seems confident that he will be able to identify a replacement diode.Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
For you information I removed D7905 and measured 2.4 Ohms either way. I measured 117 Meg ohms one way and 3.41 Meg ohms the other way. I am sorry I am going by memory for the exact values. I did not measure between pins 3 and 4 of IC7906 but I will today. I believe that the Zener diode D7905 needs to be replaced Correct? It will take a few days but I will replace it and report the out come. Thank you everyone. budm I am not sure what you were asking by typing +1 are you looking for some additional information? Thank youLeave a comment:
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Re: Sharpe LCD TV LC60E77UN
Thank you for getting back to me. If you look at the above pictures the second one of the back of the board you will see the opto isolators at the top The bottom one is IC7900 and the resistance between pin 3 and 4 is 3.41 meg ohms however the IC above this one IC7906 the resistance between pins 3 and 4 is 2.8 ohms and there is a Zener diode D7905 that has a resistance of 2.8 ohms either way I test it. This diode is connected between pin 4 of IC7900 and pin 4 of IC7903. Hope this helps.Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
Does anyone have any ideas as to which direction I should go based on the above readings. Your thoughts would be appreciated.Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
The P/N of the resistor is FRN50J2R2/>A40 TE conn Fuseable Metal Film resistor
I measured the spare resistor I ordered and it was 2.2 Ohms.Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
Attached are pictures of my power board. Hope this helps if you require any additional pics I will get them to you....Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
I bought the resistor with the IC7905. When I measure across the resistor I read 2.4 Ohms.
The resistance of IC7900 pins 3 and 4 is 4.37 Meg Ohms.
Hope this helps and thank you for your patience with my problem.
I will also start to up load some pictures of the board.Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
I am working on pictures but have some readings for you to think about.
With respect to IC7905 pin 4 and D7905 (Zener) 3.4 ohms and 1.2 ohms
With respect to IC7905 pin 4 and IC7906 (PC123) I think pin 3 Identified as X8 1.2 ohms
As I said I will get pictures...Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
Thank you for taking an interest in my problem.
IC7905 with power on
Pin1 5.97 DCV Pin8 .015 DCV
Pin2 .01 DCV Pin7 .01.6 DCV
Pin3 .016 DCV
Pin4 .002 DCV Pin5 167.5 DCV
After 15 minutes Resistance on IC 7905 between neg of C7830
Piin1 75 K ohms Pin 8 1.1 ohms
Pin 2 1.1 ohms Pin 7 1.1 ohms
Pin3 1.1 ohms
Pin 4 3.3 ohms Pin5 2.6 Mohms
Resistance of R7918 2.9 ohms
I am using a digital meter and my readings are changing slightly hope this helps.Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
Thank you for the explanation. I will reread this slowly and try to apply your explanation to my circuit
I have taken some additional readings for you to review and taken additional pictures of the surrounding circuit to see if this might help.
C7830 167.5 VDC across the capacitor.
IC7905 between the neg of C7830 and pin 1 5.94 VDC
IC7902 between pin one and two as mounted on the board .790 VDC
IC7902 between pin 3 and 4 as mounted on the board .726 VDC
Therefore by your explanation I believe I have a diode that...Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
I did read a less than one volt but disregarded this as noise I did not think that it was critical. I will record the exact values and post them. Can you explain what IC7902 is supposed do? I thought that if I see 5.93 on pin one and 5.4 on pin 2 this IC would then repeat this on the low side between pins 3 and 4.
Thank you.Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
Measured the voltage as you asked.
Between 1 and 2 I read 0 volts
Between 3 and 4 I read 0 volts
Hope this helps.Last edited by BruceGilbert; 12-23-2020, 05:01 AM.Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
Here is an update. I was able to take some readings.
1ST of all previously I was referring to IC7905 and I should have said IC7902.
When I measure between pin 1 as indicated on the board and the negative side of C7830 I read 5.93 volts and between C7830 negative and S of IC7902 I read 5.4 volts. On the low side of IC7902 I do not see and voltage. With the power off of the board I measure 120Kohms between X8 and pin 4 of IC7902. Does this mean that IC7902 is not working and therefore I am not getting my standby voltage at BU5V of the connector....Leave a comment:
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Re: Sharpe LCD TV LC60E77UN
Today I hope I will be able to do some voltage measurements.Leave a comment:
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