Chosen Solution
Hello. I have a Sharp Roku LC-55LBU591U TV that has no picture but seems to have all other functions. When using the remote I can hear the normal sounds as I’m making selections but the screen is simply black with a back light. I unplugged the ribbon cable to the t-con and half of the screen went white. I tried to test voltages at the t-con board but I’m not really sure what most of the test points should be reading. I get a decreasing range of voltages at the various ribbon test points. I will post pictures momentarily. Any help is appreciated. Update (07/14/2020) Pictures:
Update (07/15/2020) Main board:
Update (07/24/2020) I am proud to report that the replacement main board solves the problem. Full functionality and picture has been restored to the tv. thanks so much for the help
At the very top, the grey wire Ribbon that connects your PCB to your Main Control Board should have a pin out diagram on one of the boards by the connector. by the looks of the picture, this pinout diagram is located on the power board side of the connection (right above the connector). Throw your meter on DC and Test your 5v Standby, 12v and 24v rails (if there are any) BE CAREFUL NOT TO SHORT ANY PINS THIS CAN KILL THE PCB IN SOME CASES If the voltages don’t line up with the Pinout Diagram, unplug the main control side and see if the voltages jump up where they are supposed to be. (remember nothing will kick on until the 5v standby is pulled low) if the voltages aren’t there at all, you have a bad PCB. if the voltages are there only when the Main control board is unplugged, you have a drain somewhere in your main control board that’s creating a voltage drop from the Power Board causing it not to run the GPU or other components properly. at this point unless you are good at component level repair, its time for a new Main control board. Here is where to get parts for your Model SHARP tv If going for a main board MAKE SURE it lines up with the model code as there are multiple versions of this board for this model. https://www.shopjimmy.com/sharp/lc-55lbu…
with your testing…. your power supply is fine, as well as your backlights. based upon the readings of your tcon board, it is receiving the proper voltage to operate, but its not getting the proper signal from the main boards processor. In your case, the main board is the cause of the signal error. this can be caused by old, cracked solder connection under the processor itself or a failed chip. you could try heating the processor with a hair dryer to see if you can get a signal (essentially reflowing the solder balls) if it comes back, it wont last but will confirm the issue. if it doesnt, you can try to heat for a longer period of time…( with a hair dryer, anywhere from 5 to 10 mins..careful not to move the chip.) of course you can find a reputable vendor that can take your order, help with symptom vs solution and accept any parts back with no fee if it doesnt correct. i recommend electropartsonline for this, shop jimmy is another good source. i checked for an exact match for your tv, both vendors do not have in stock. i have one other vendor i use, but they have a restocking fee if board is sent back. your troubleshooting confirms the main board, but there are always chances. here is a link to your exact board needed for the repair: https://www.tvpartstoday.com/216995-Best… if you have any other questions, please post back here for assistance. please also update the post with success for others to use as reference.
