Sharpe LCD TV LC60E77UN

[brucetv]

Re: Sharpe LCD TV LC60E77UN

If all else fails Encompass in Atlanta GA USA has them at a rip off price of $138.58 if you have a wholesale discount...$173.95 if you don't have one plus shipping. Hope the component level repair goes well. Touch up all the solder joints especially around those transformers.

[BruceGilbert]

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. Any thoughts would be appreciated.

[dick_barton]

Re: Sharpe LCD TV LC60E77UN

With your meter leads connected to pin 1 and pin 2, what is the dc voltage reading.
With your meter leads connected to pin 3 and pin 4 , what is the dc voltage reading.
Repeat the tests when in standby and out of standby

[BruceGilbert]

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.

[dick_barton]

Re: Sharpe LCD TV LC60E77UN

From post #22 if pin 1 measured 5.93V and if S was pin 2 which measured 5.4V then the meter should have read the difference between them ie shown 0.53V

I have to admit without a diagram for this power supply it is difficult to know what is right or wrong with it other than the PFC circuit looks as though it's not boosting the supply.


With the set powered off what is the resistance from the 5v standby pin to ground?

At this point perhaps other forum members could offer you some advice.

[BruceGilbert]

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.

[dick_barton]

Re: Sharpe LCD TV LC60E77UN

The diode requires approximately 1.2V across it to switch on the transistor within the package.
What the IC does in your power supply I don't know without a diagram to reference against.

Basically the Opto's are switches and work by apply a voltage across the diode that then (shorts) turns on the transistor between pins 3 & 4. The diode and transistor are electrically isolated from each other so they can work between the HIGH / LOW section of the power supply. That is, if the diode is on the high voltage side of the circuit then the transistor can be on the low side or vice-versa.

[BruceGilbert]

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 is defective on the pin 1 and 2 side of the board correct?

[dick_barton]

Re: Sharpe LCD TV LC60E77UN

The voltage applied to the diode in the opto-isolator comes from other circuitry and again without the diagram it cannot be said that there is a fault with the diode. It could just be that the diode is not being turned on by the associated circuitry.
The quickest test is to replace it.

[budm]

Re: Sharpe LCD TV LC60E77UN

I am all confused about the Voltage readings of the IC's.
Can you give me the DCV readings of all the pins of the SMPS TNY IC U7905 with ref to the negative leg of the main filter cap?
Then remove the power and let the power supply board sit for 15 minutes then take the resistance readings of all the SMPS TNY IC U7905 pins against the negative leg of the main filter cap.
BTW, Check the resistance of the R7918, it should show <1 Ohms.

[BruceGilbert]

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.

[dick_barton]

Re: Sharpe LCD TV LC60E77UN

If i read the datasheet correctly EN/UV should be approximately 1V and if a current greater than 240uA flows then it disables the drive.

Pin 4 has a voltage of 0.002 volts but more puzzling a resistance of 3.3 ohms which is very low.

Can you trace where pin 4 goes? Perhaps if it goes back to one of the opto-isolators it may be that its internal transistor has gone short circuit.

[budm]

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.

The resistance reading is bad.
I need good clear hi res straight shots of the whole top and bottom side of YOUR board, and also close up of the bottom side of the board around IC7905. I suspect either Zener/opto/solder bridge connected to pin 4 is bad but I need your picture to verify.

[BruceGilbert]

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

[budm]

Re: Sharpe LCD TV LC60E77UN

https://www.badcaps.net/forum/attach...8&d=1608363227
Where did you get the replacement R7914 from? It looks like RED-RED- BLACK- SILVER which will be 22 Ohms instead of 2.2 Ohms, the body is also quite small.
Check the resistance of OPTO IC7900 PIN 3 and 4.

[BruceGilbert]

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.

[BruceGilbert]

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.

[BruceGilbert]

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.

[BruceGilbert]

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.

[budm]

Re: Sharpe LCD TV LC60E77UN

We need to find out first why Pin 4 of the standby SMPS IC show very low ohms reading, I try to trace out pin 4 of the IC using shopjimmy pictures but it is not clear enough to see where pin 4 goes to. Can you check pin 3 and pin 4 of other OPTO IC to see what they show?