Re: SHARP LC-80LE633U has open resistor r7133 on PSU
Alright R_J and Budm, I need help. I have found the culprit for the 5vsb shutting off, but do not know what the circuit I have isolated does. See the attached tracing picture I borrowed and edited from this thread.
I got the PSU to act up pretty consistently today. I began probing voltages and found the BP/M pin was going to ground on shutdown and the IC was getting hot. So, I looked at the tracings and checked all zeners between that tracing and ground. All test good. So I decided to unsolder and lift J7109 at the...
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
Parts ordered. I believe I may have caught it. I moved around some of the optos and after letting it sit a while, i got a new error blink light for AC_DET. Moved that opto (PC7101) back to the BP/M spot (PC7104), and viola, the power board came back up. So I ordered new optos and got the caps while I'm at it.
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
After troubleshooting more last night, I got the feeling that something could be going to ground around the BP/M pin circuit between the IC and the bias winding of T7101. See the attached photo below, but after doing some reading, I realized there is a diode (D7111) connected to the BP/M pin trace. According to the writeup, this is for overvoltage feedback protection for the IC. I am going to pull it tonight and test it. Being I found one diode already in this circuit bad from when IC7102 failed, I do not find it far fetched there...
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
It began the problem again. Whatever it is, it is isolated to the primary side. When the TV shuts off, the BP pin goes to 0v and the EN pin goes to 0.35v. The IC also gets very hot while off. Intermittently it will come back on, but immediately go back off.
There are 3 like optocouplers in the area, so I moved them around and it seems to have no effect. Ideas?
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
Also see that the BP/M pin of IC7102 is connected to one leg of PC7104 with the other leg tracing back to the bias winding of the transformer. Looking in the datasheet for IC7102, this appears to be an overvoltage protection circuit.
With this knowledge, am I wrong to assume either I have a problem with voltages on the secondary side or I am dealing with an optocoupler issue?
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
Reopening this thread.....again. TV worked for a while but has begin to exhibit a problem again. After probing around on the bench with everything connected, something is shutting off the 5V standby circuit causing the tv to power cycle randomly. Further probing shows that the PFC voltage is there, and when the TV does power on, PFC goes to proper ranges and TV function. For grins, I changed the 5VSB IC7102 as I ordered spares previously, but no change. New Zener diode I installed is also still ok. So, I am beginning to suspect...
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
I have some findings on this noise. When I power the TV on, randomly, as the backlight comes on, this noise begins. I did some probing and found the following. See the photo attached.
[ATTACH]223279[/ATTACH]
What seems to be at least a symptom is the higher voltage when the noise is being made. As the noise subsides, the voltage falls to 110v at the locations in the photo. Does this shed any light on this for anyone?
Another interesting find is at the leg of the capacitor I have marked with...Last edited by ki4mqz; 11-07-2020, 02:19 PM.
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
Also, any alternatives on the diode? Mouser and Digikey are backordered. Thoughts on running without it?
At Budm suggestion, I found a 6.2 volt that will do the job. Should be good.Last edited by ki4mqz; 11-05-2020, 09:05 PM.
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
I have the TV laying face down on a bench. So changing that is going to be quite difficult. If I feed it a signal, as the input/display changes, it changes with it. But after a 30 seconds or so, it completely disappears.
I said brightness, what I meant was backlight level. Sorry for the confusion.
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
It is right at 388VDC and does not fluctuate when the backlight comes up.
With it making noise. The noise starts as soon as the backlight starts to come on and ramps up as the brightness comes up. It is very clearly related directly to backlight brightness.Last edited by ki4mqz; 11-05-2020, 08:05 PM.
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
It is very interesting. As it warms up, it disappears. I will get the diode you spoke of ordered and installed and see if it changes anything, but I don't expect it to.
Edit: It does not sound normal. It is very audible and would not qualify as acceptable.
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
Thanks for all the replys. Feels good to find it. Only remaining problem I am concerned about is randomly, when you power the unit up, as the backlight comes on, there is an audible rapid "clicking" coming from the primary transformer area of the board. The clicking changes speed with the brightness of the backlight. Any insight on that?
Edit: the backlight and all comes up and does function normally. TV performance doesn't seem to be affected by it.
Thanks a ton R J on the part number. Huge...Last edited by ki4mqz; 11-05-2020, 06:36 PM.
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Re: SHARP LC-80LE633U has open resistor r7133 on PSU
Update! As mentioned, I began probing around IC7102 Pin 1. First I unsoldered pin 1 from PC7103 and had no affect on the voltage. Next, I unsoldered diode D7110 and viola! Pin 1 came up to 1 volt! 5v bus on and TV powers up! So it appears D7110 is bad. It appears to be a zener. Any ideas on the spec for it?
Diode is marked either B62, 2B6, or 62B. Hard to say as the numbers go all the way around....Last edited by ki4mqz; 11-05-2020, 05:37 PM.
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