Sharp 80” backlight error - LED circuit troubleshooting help needed.
crwdns2934249:0crwdne2934249:0:
Hello Sharp TV experts[br]
Our Sharp LC-80LE642U displays one short one long flash error code which is a backlight error. I went into service mode and there were 8 lamp error counts recorded. I reset the count to 0 and did a reset. The last monitor error cause was 16 B00014639:12. 16 is the code for backlight error. I tried to power the tv up but went back into error mode.[br]
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> I checked voltages on the power supply board and they all check out .. including 3.28 volts at the error pin.[br]
> There is power to the cpu and T-CONN and no faults found there. The cpu has a flashing green led.[br]
> I have 110 volts DC at the LED driver MOSFET and 192 DC volts at the L1 LED string input connection. I found a spec for the LED input voltage of 215 volts. Backlight lights up in Service Mode.[br]
> I removed the front panel and checked the LED strips with an LED backlight tester. I recorded 283 volts at each light strip in automatic mode and all LEDs light up bright. There are 15 rows with 21 to 24 LEDs per row.[br]
> I checked voltages at the FETS on the return circuit. The voltages at the collector pin were 36 volts DC (+ or - 1/2 volt) at every FET. There are 15 FETS, one for each light string.[br]
> This is where I found a peculiarity. I checked the voltage at the emitter of each FET and I also got 36 volts which I would expect … except for 4 FETS all beside each other had double or triple voltages. Three were 70 volts and one had 93 volts. I checked the gate voltages and they all are 5.5 volts except these 3 have 1.5 volts and is one has 18.4 volts. I removed the FETS from the board. There are 4 per heat sink so I removed 8.[br]
> I checked the FETS with a multi meter following an online transistor test procedure. They all checked the same … okay.[br]
Any ideas as to what is going on here and or what my next steps should be????[br]
Thank you in advance. All expert opinions are immensely appreciated.
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