Sharp LC-42SB48UT-a no standby voltage

[jts1957]

Re: Sharp LC-42SB48UT-a no standby voltage

Service manual attached with power supply schematic, hopefully

Be sure to look at 42", there is also a 32".

AcGeorgiegirl: 1st attachment wrong PS.

[AcGeorgiegirl]

Re: Sharp LC-42SB48UT-a no standby voltage

Here are the PFC & Key Diagram, too.

[budm]

Re: Sharp LC-42SB48UT-a no standby voltage

I got it from ELEKTROTANYA and it does not match the OP diagram. See post 57

[AcGeorgiegirl]

Re: Sharp LC-42SB48UT-a no standby voltage

You have the schematic?
OK, I download the service manual from ELEKTROTANYA.
My manual show TNY277, your manual shows something else.
Please look at what is actually printed on top of the IC903.
Where did you get the manual from?

Yes, it is printed on the ic as TNY277. My manual, pretty sure, came from ELEKTROTANYA. I'll post the manual here, too, if that helps.

[budm]

Re: Sharp LC-42SB48UT-a no standby voltage

OK, your manual does not match your TV version.
The one I download is the 'A' version and seem to match your power supply board picture.
But any way, it uses TNY277 none the less, so I still suspect the parts in the feedback regulation circuit.
Try having the main board connected to the power supply board to see if it will go up to 5V in case the circuit does not like to work without the load.

[AcGeorgiegirl]

Re: Sharp LC-42SB48UT-a no standby voltage

Yes, that's it, then, BUDM! Mine didn't have the "a" after model code, but I just looked again, and it's the one that I get from my search on ELEKTROTANYA.

[budm]

Re: Sharp LC-42SB48UT-a no standby voltage

This is weird. ELEKTROTANYA is the only site that I've found that has the manual free, and I'm pretty sure mine came from there. Don't know if it matters, but my model has "A" after the name, and the manuals don't.

There are two manuals at ELEKTROTANYA, the one I downloaded is for the 'A'.

[AcGeorgiegirl]

Re: Sharp LC-42SB48UT-a no standby voltage

I am so sorry for causing all this confusion, while you guys are trying to help me. My translation app for Elektro- apparently mussed up my search, without me noticing. The "a" was left out.

[AcGeorgiegirl]

Re: Sharp LC-42SB48UT-a no standby voltage

OK, your manual does not match your TV version.
The one I download is the 'A' version and seem to match your power supply board picture.
But any way, it uses TNY277 none the less, so I still suspect the parts in the feedback regulation circuit.
Try having the main board connected to the power supply board to see if it will go up to 5V in case the circuit does not like to work without the load.

I tested with psb connected to the main, and got a fluctuating voltage from around 2.8 to 3.8 or so.

[budm]

Re: Sharp LC-42SB48UT-a no standby voltage

OK, so it cannot even maintain the regulated 5V output.
I would try replacing C969 in the primary side and the 4 cap in the cold side by the connector that goes to the main board.

[AcGeorgiegirl]

Re: Sharp LC-42SB48UT-a no standby voltage

So it lookds like you meter is OK.
There are parts that are used for regulating the output of the 5VSTBY:
IC913 (Vref diode xx431??, IC911 (OPTO), Voltage divider for the IC913.

OK, your manual does not match your TV version.
The one I download is the 'A' version and seem to match your power supply board picture.
But any way, it uses TNY277 none the less, so I still suspect the parts in the feedback regulation circuit.
Try having the main board connected to the power supply board to see if it will go up to 5V in case the circuit does not like to work without the load.

The IC's you suggest I test...can you give me some guidance on how to do this, if other than removing them completely from the board?

[budm]

Re: Sharp LC-42SB48UT-a no standby voltage

The IC is kind of working because you do have output Voltage, just not the right level as needed, there really no 100% test to verify that it is good or bad. You can try replacing it but I would try replacing the cap first.
This IC when it failed, it usually blew up badly due to shorted out internal Power MOSFET.

[AcGeorgiegirl]

Re: Sharp LC-42SB48UT-a no standby voltage

The IC is kind of working because you do have output Voltage, just not the right level as needed, there really no 100% test to verify that it is good or bad. You can try replacing it but I would try replacing the cap first.
This IC when it failed, it usually blew up badly due to shorted out internal Power MOSFET.

Ok. You mention one IC....are you referring to the IC913? What about the IC911? And by "voltage divider" for the IC913, are you meaning a voltage regulator that I should find to check?

[budm]

Re: Sharp LC-42SB48UT-a no standby voltage

I am referring to the TNY277 IC.

[CapLeaker]

Re: Sharp LC-42SB48UT-a no standby voltage

He means IC903 (TNY277)

[AcGeorgiegirl]

Re: Sharp LC-42SB48UT-a no standby voltage

Ok. I mistook your previous post(I quoted it above) as the area you are now referring to. So, which cap to replace? Is it c969(one closest to TNY277), or do you mean the filter cap?

[CapLeaker]

Re: Sharp LC-42SB48UT-a no standby voltage

change c969 first.

[AcGeorgiegirl]

Re: Sharp LC-42SB48UT-a no standby voltage

Replaced C969. No change.

[CapLeaker]

Re: Sharp LC-42SB48UT-a no standby voltage

Did you check the ESR of C955 and C934? What DC voltages do you get on all the pins of IC903?

[AcGeorgiegirl]

Re: Sharp LC-42SB48UT-a no standby voltage

I don't have an esr meter, so I can't test the caps. The IC reads .06 on pin #4(the Mosfet drain connection). All others are between .04 and .05 BUT these are a negative(-) number. My DMM is set on 20 dc volts.