Hello, I've got this TV which contains the Y-Main and Buffers reputed to short each other out. [LJ92-01200A, LJ92-01202, and LJ92-01203].
I've read the Coppell TV blogs and several threads here regarding how to diagnose these three.
I know the lower buffer is shorted power to common. Too many SMD pins to repair myself. I installed the Y-Main with just the good buffer. The TV still shuts itself off, so I know the Y-Main also has a failure.
I will attach photos of the Y-Main and the area I'm troubleshooting.
I understand from reading Coppell's blog that the shorted fet would read a lower resistance Gate to Drain than good FETs, but only lower by 100 or so ohms.
I put black probe on Common and red probe on each of the low-value resistors in the gate curcuit. Gate to Drain resistance readings on the Y-Main with Y-Buffers disconnected:
Resistors near the Upper Y- Buffer which appears good:
R5085 98.4 Kohms
R5091 98.5
R5092 98.6
R5029 99.3 Kohms
Resistors near the bottom Y-Buffer which is shorted:
R5100 98.5 Kohms
R5101 97.6
R5103 99.7
R5102 97.1 Kohms
Coppell writes that the shorted fets will just read 10-100 ohms below the others. So it looks like R5101 and R5102 are connected to the gates of bad fets. I read elsewhere that the 1" by 3" heatsink is a bear to remove.
I also found two power diodes on heatsinks, D5012 and D5013 read a short between the outer two of three legs. Other diode check readings look like a diode or OL.
Any concurrence of opinion or suggestions?
I've read the Coppell TV blogs and several threads here regarding how to diagnose these three.
I know the lower buffer is shorted power to common. Too many SMD pins to repair myself. I installed the Y-Main with just the good buffer. The TV still shuts itself off, so I know the Y-Main also has a failure.
I will attach photos of the Y-Main and the area I'm troubleshooting.
I understand from reading Coppell's blog that the shorted fet would read a lower resistance Gate to Drain than good FETs, but only lower by 100 or so ohms.
I put black probe on Common and red probe on each of the low-value resistors in the gate curcuit. Gate to Drain resistance readings on the Y-Main with Y-Buffers disconnected:
Resistors near the Upper Y- Buffer which appears good:
R5085 98.4 Kohms
R5091 98.5
R5092 98.6
R5029 99.3 Kohms
Resistors near the bottom Y-Buffer which is shorted:
R5100 98.5 Kohms
R5101 97.6
R5103 99.7
R5102 97.1 Kohms
Coppell writes that the shorted fets will just read 10-100 ohms below the others. So it looks like R5101 and R5102 are connected to the gates of bad fets. I read elsewhere that the 1" by 3" heatsink is a bear to remove.
I also found two power diodes on heatsinks, D5012 and D5013 read a short between the outer two of three legs. Other diode check readings look like a diode or OL.
Any concurrence of opinion or suggestions?
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