SharpLC 52D64U Signal kills backlight

[G Nicholls]

I am servicing a Sharp LC 52D64U. It is similar to the 42, 46, 52, & 65" models in the D64 series. The board views and service manuals are in existing posts.

This unit had a typical backlight failure: a pair of shorted MOSFETs on the slave inverter board. {J655 and K3706} I ordered up IRF539N and IRF9530 from Jameco that are 100V 17A rated N & P channel replacements. The repair seems fine, BUT ONLY WHEN THE UNIT IS IN "MENU" MODE OR WITHOUT A SIGNAL INPUT IN THE OTHER MODES.

So, the unit is fine when processing it's own generated "video" {menu selections} but not with the tuner or VGA inputs (the only modes I verified) are selected.

Has anyone experianced this? I suspect:

1) The replacement MOSFETs have too different a technical spec issue to work reliably under all conditions. {Unlikely as the unit will disply happily for hours with only the self-generated menu screens displayed.}

2) The TCON is dropping the backlight on command {Seems unlikely as the video drive signals in menu mode are fine enough to keep the set happy.)

3) the problem is a "fault" that is still stored in the memory and will kill the backlight and cause the frontpanel "green light blink" upon a normal input like the tuner or VGA input.

4) There is a fault with the IC8001 AV Decode & Main CPU (or similar) due to a voltage regulator unable to supply the circuit when in operation (under load) of signal processing.

This set is a frustration as the original defect, no power-up, was traced to a shorted inverter pair of MOSFETs and likely repaired.

Just my favorite emoticon!

Any other folks have this issue and find a component level solution? This unit is a bit marginal for a $100 replacement video board that might not be the issue and the inverter board repair.

I do enjoy the challenge or these repairs and the helpvided by the forum users. Beer for all of you, and your horses!

[audiofreak19]

Re: SharpLC 52D64U Signal kills backlight

I would think it might be a fault in the main board not processing the video signal correctly and seeing a fault causing the tv to shut down. Just guessing though. Are you getting correct voltages at all boards when the problem occurs.

[G Nicholls]

Re: SharpLC 52D64U Signal kills backlight

Thanx for the reply. The power supply voltages seem fine when the set has no input from the tuner or VGA inputs (did not have equipment to feed HDMI inputs in the field). Did not check them when it shuts down the backlight. Good thought though. If the 60volt feed shuts down, that would explain alot.

I doubt this is the case. I think the control signal to the inverters (like from the TCON as is typical in many sets) is turning them off.

I downloaded the service info online. I will check to see if there is any fault info stored in the EEPROM. It sure had a hard short in the inverters, and perhaps a fault bit is being stored. I have had little success repairing Sharp units in the past, so my experience base with these units is very limited.

Any Sharp techs out there?