Hey guys, recently I repaired a Hitachi 55HDX99 Plasma TV with help from you guys on this thread. https://www.badcaps.net/forum/showthread.php?t=75627
The problem ended up being a shorted buffer IC on the upper buffer board.
After the repair, the TV was working fine and we used it on and off for about 20hrs. However, the last time we were using it, the TV just turned off in the middle of watching a show. There was no power at all and the power button did nothing.
Unplugging the TV and plugging it back in makes all the relays click and the power light starts flashing blue. After a couple flashes, a relay on the power board clicks and all power is cut. I tried disconnecting the upper and lower buffer boards one at a time to see if another chip had failed but this made no difference. The symptom is also different from the bad buffer chip.
Unplugging the main power connector coming out of the power supply board causes the TV to stay on and I can use the soft power switch normally but obviously there is no display. There is also no power on any of the output pins on the power supply. I suspect this is some sort of fault protection on the power supply board kicking in due to there being no load.
One thing that I found interesting is that there are 3 heatsinks on the power supply board that each have a voltage labelled on them. There is 5V, 11V and 90V. When the TV is powered up with the output connector disconnected, the 5V and 11V heatsinks both have the listed voltages present on them when measuring between the heatsink and the chassis. However, the 90V heatsink does not have any voltage on it. I don't know if this is significant or not.
If anyone has any ideas on what to look at first I would appreciate it.
The problem ended up being a shorted buffer IC on the upper buffer board.
After the repair, the TV was working fine and we used it on and off for about 20hrs. However, the last time we were using it, the TV just turned off in the middle of watching a show. There was no power at all and the power button did nothing.
Unplugging the TV and plugging it back in makes all the relays click and the power light starts flashing blue. After a couple flashes, a relay on the power board clicks and all power is cut. I tried disconnecting the upper and lower buffer boards one at a time to see if another chip had failed but this made no difference. The symptom is also different from the bad buffer chip.
Unplugging the main power connector coming out of the power supply board causes the TV to stay on and I can use the soft power switch normally but obviously there is no display. There is also no power on any of the output pins on the power supply. I suspect this is some sort of fault protection on the power supply board kicking in due to there being no load.
One thing that I found interesting is that there are 3 heatsinks on the power supply board that each have a voltage labelled on them. There is 5V, 11V and 90V. When the TV is powered up with the output connector disconnected, the 5V and 11V heatsinks both have the listed voltages present on them when measuring between the heatsink and the chassis. However, the 90V heatsink does not have any voltage on it. I don't know if this is significant or not.
If anyone has any ideas on what to look at first I would appreciate it.
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