Hi all!
I've been scouring the corners of the internet for some time now trying to find a group of technical know-hows to run some questions by. Looks like I finally found the place!
Anyways, here is my story. I have a Sharp Aquos LC-42D69U that does not power up. It has no standby LED, but the PSU does output +5VSB. If I manually short PS_ON and BL_ON to +3.3v I can see the backlight illuminate the display, however, the motherboard still has no logic. I've soldered wires to the TTL (serial) output to see if I can see anything from the processor. I used 9600 and 115200, 8, N, 1, but I didn't get any output. I purchased another identical motherboard (PN# 795951300500R from eBay, but I still have the same results. I'm stumped! I've been referencing the service manual for repairs (sharp_lc-32d59u_lc-42d69u.pdf). Here is what I've done so far.
So after all this I am still unable to get it going. I could use some expert advice and appreciate anything you can provide!
One thing I forgot to mention is that I noticed the original motherboard CPU gets hot to the touch after a few minutes and the new one doesn't seem to get above room temperature.
I've been scouring the corners of the internet for some time now trying to find a group of technical know-hows to run some questions by. Looks like I finally found the place!
Anyways, here is my story. I have a Sharp Aquos LC-42D69U that does not power up. It has no standby LED, but the PSU does output +5VSB. If I manually short PS_ON and BL_ON to +3.3v I can see the backlight illuminate the display, however, the motherboard still has no logic. I've soldered wires to the TTL (serial) output to see if I can see anything from the processor. I used 9600 and 115200, 8, N, 1, but I didn't get any output. I purchased another identical motherboard (PN# 795951300500R from eBay, but I still have the same results. I'm stumped! I've been referencing the service manual for repairs (sharp_lc-32d59u_lc-42d69u.pdf). Here is what I've done so far.
- Visual Inspection of PSU, Motherboard, Inverter. All looks good, no burn spots on the PSU, no blown caps.
- Tested all fuses in PSU and original motherboard.
- Confirmed +161V at D801 (Diode feeds +5VSB).
- Confirmed +5VSB from PSU to motherboard, +3.3V and +1.85V on motherboard.
- Shorted PS_ON, BL_ON to +3.3V and confirmed +12V and +24V rails on PSU are outputting. Backlight will turn on. Still no logic from Motherboard.
- Desoldered the major caps from the PSU and tested each one for a short and confirmed they are slightly charging using my multimeter.
- Confirmed power switch is working by seeing ~600 Ohms when pressed. May need to investigate further. Unfortunately I don't have the remote to try turning on.
- Accidentally burnt up Q1403 (NPN Transistor, PMBT3904, see attached picture) on the original board while attempting to short BL_ON with too much voltage. May order replacement part from Digikey if main mobo is not dead.
- Confirmed standby LED is not burned out and in the process I did burn it out :P. I soldered another LED in place, but decided to use my multimeter instead to watch for input voltage because I wasn't sure if my LED would light up.
- Replaced motherboard from eBay with exact same item model #795951300500R. Tested new motherboard and reached the same results. No standby LED, no power. Tried holding power button 30+ seconds, etc.
So after all this I am still unable to get it going. I could use some expert advice and appreciate anything you can provide!
One thing I forgot to mention is that I noticed the original motherboard CPU gets hot to the touch after a few minutes and the new one doesn't seem to get above room temperature.
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