SHARP LC-80LE633U has open resistor r7133 on PSU

[budm]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

OK, I will look at the board layout of the standby power supply section and will get back to you with the test points for you to test.

[ki4mqz]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

Can't thank you enough. I'll be around to tonight and on standby if you come up with something. Thanks!!!

[ki4mqz]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

See attached photo for IC7102 Pinout with measured voltages. Using HOT ground. All DC.

Pin 1 - 0.56v
Pin 2 - 5.89V
Pin 4 - 170V
Pins 5-8 - 0v. After tracing, it looks like pins 5-8 are on the HOT ground bus.

Also, the "burn" marks on this board is flux from where I installed the new IC. No obvious burns or anything anywhere.

[ki4mqz]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

After reading the PDF for the TNY274 attached earlier in this thread, I may have a direction to chase. Pin 1 of the IC controls the oscillation of the chip. Pin 1 signal is fed from the optocoupler, and the optocoupler is referencing the secondary voltage. If the secondary voltage goes high, the optocoupler begins to close the emitter and collector side of the OC, forcing the voltage of pin 1 to drop, thus controlling the secondary voltage. According to the IC PDF, Pin1 (EN/UV) switches the IC off when voltage drops below 1v. No IC on equals no oscillation which would thus keep the transformer from working.

Looking at my diagram above, pin 1 is at 0.56v. This tells me that I might possibly have an issue with that optocoupler. One possible way to test it is to uncouple the OC from the circuit on the Collector/Emitter side and see if it powers up. Any harm in that? I will continue to dig into this tonight once I get off work.

[ki4mqz]

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.

[budm]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

That Zener diode on pin 1 (EN) is for protection to clamp down the Voltage to protect that input pin, as you can see in the application circuit, they do not even install the Zener on that pin.
Since EN typ Voltage is about 2V per spec, you can use 6.2V or 5.1V Zener.
BTW, did you check the resistance in both direction of that Zener?

[ki4mqz]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

I did check resistance. It shows resistance both ways (170 ohm forward, 350 ohm reverse) which makes me think its bad?

[budm]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

It is bad, that is why EN pin is only getting 0.56V, it should be around 2V on EN pin to enable the TNY to run.
I am glad you found the cause of the problem on your own.
When TNY blows up, it will usually take the opto and zener (if it is implemented) with it.

[R_J]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

On a similar power supply using a TNY274PN, pin 1 has a MTZJ8.2B zener

[ki4mqz]

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 help!

[R_J]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

The standby controller ic usually supplies the vcc for the main ic's also, so check that voltage. Did you replace the small elec. caps in the standby circuit? C7114, C7107.
It looks like Q7101 is the vcc regulator/switch, so check the voltage on it's emitter & collector

[ki4mqz]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

I have not replaced anything other than R7133 and IC7102. Would powering the board up with D7110 missing possibly have something to do with it? It has never done this before.

Collector is 18.8vdc, emitter is 15.7vdc.

[R_J]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

I don't think having the diode out of the circuit would effect the operation as it is the standby circuit, but it is possible. The Q7101 voltages look correct.

[ki4mqz]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

What is your thoughts on the noise? What is it? Loudest right on top of the transformer highlighted below using a stethoscope.

[R_J]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

Those two inductors L7203, L7204 are part of the pfc circuit, I'm not sure why they are making noise, although it might be normal as the pfc circuit turns on, or it could be as the main supply and led drive circuit comes on and starts drawing more current.

[ki4mqz]

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.

[R_J]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

Check the pfc voltage across one of the main primary caps, C7220 for example, the voltage should be around 160vdc in standby, then come up to around 385vdc when the tv is turned on.

[ki4mqz]

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.

[budm]

Re: SHARP LC-80LE633U has open resistor r7133 on PSU

Does the noise change if you increase or decrease the backlights level (not Brightness)?

[ki4mqz]

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.