Re: Best Buy / Sharp LC-32LB261U backlight failure

Yes, I have the schematic. I have removed the strips and the LED lenses and will remove the LED chips and measure the package outline and look at the pin-out (pads). I'm sure I can find suitable replacements at Mouser or DigiKey or via EBay from China. Yes, this is a very poor design with the LED strips driven in parallel. You are right about one failing which increases the current in the remaining strips or strip until they all fail. Too bad designers and manufactures don't take a conservative approach to the design, but a limited...

Hi, I picked up a free Best Buy / Sharp LC-32LB261U LED TV from Craigslist. The LED back light had failed. I found that the set uses 3 LED strips which have 7 LEDs per strip, and the 3 strips are driven in parallel by the Power Forest PF7903B boost converter. During troubleshooting, I found that the boost converter would startup but be shut down by its over voltage protection circuit as the output voltage spiked to around 42V.

From the schematics and product brief, the feedback voltage on the PF7903B is 240mV and the 0.192489 ohm current sense resistance in the LED return path...

Re: Insignia NS-50LC240A13 questions

Since it appeared that the main TV signal processor IC was damaged, I found a replacement main board on EBay from Electroparts Warehouse. Before installing the replacement board, I applied power on 5VST and found that it pulled around 100mA, not the 650mA that the original (bad) board pulled. Also, there was no detectable temperature rise on the 5VST to 3.3V LM1117 regulator or on the main IC. I installed the replacement board into the TV and it worked well and the TV is functioning again. Afterwards, I again powered up the original bad board...

My Insignia NS-50LC240A13 quit the morning after a night time electrical storm in our area. At first, it randomly popped up menus and changed options as if someone was changing settings with the remote. After a bit, the menu popping up would cease and it would operate normally for while, from 5 to as much as 30 minutes at time. After a few power on reset cycles, it would no longer turn on at all.

I took it down, got the the back off and found no visible problems. The power supply was working (5VST at 5V, 12V rails OK) and the PON pin was at 2.95V - the main board was signally for...

Re: New Members - please post your introductions here

Thanks for adding me. I found this site while searching for information on an Insignia NS-50LC240A13 LCD TV. I am an electrical engineer by trade and as an applications engineer for a US based analog semiconductor manufacturer. My electronics career started back in the early 1970's by building lots of Heathkits, working in a TV repair shop and working in broadcast stations, initial AM & FM radio stations and later in a TV station. I am an amateur radio operator and enjoy fixing things and restoring older electronic equipment....