This LCD set was dead when I received it, but after obtaining the schematic and service manual, I have determined the power supply seems to be OK after a repair to replace a shorted MOSFET in the switching stage that produces the high voltage DC. But still the set will not turn on nor are there any LED's lit or blinking when I attempt to do a force start for service mode using the input and and combination of vol +/- and channel buttons to to enter this mode. I would be happy to attach any part of the service manual showing the relevant suspect circuits described below.
In a normal power on sequence, the power switch (momentary contact) places a momentary ~ 5vdc at the pin of the microprocessor where all key (ch+/-,vol+/-, input and power-on off) signals are presented the microprocessor on the LCD controller board. Those change of bias levels do appear from the key connector on the LCD board and I have to assume they are provided to the microprocessor. One pin of this micro-controller, labeled SMPOW, has to supply a positive going voltage to the system board where there is another controller that receives this signal then appears to provide a latched high for POW_on, D_Power and EU-P_power. All three of these leads which are fed back to the power supply board must go and remain high to cause all of the operating voltages to be produced. I have confirmed that the supply board do that all operating or running voltages are produced. I have applied this bias from the standby 5vdc to verify that the power supply does indeed produce all required operating voltages for the set to run--but even with the bias applied, the set will not start. The power supply also produces the high voltage (`400vdc) necessary on the primary side of the transformer where the power MOSFETS are located but there is no high voltage present on the secondary, or so it appears. The low power oscillator which is transformer coupled to the Power MOSFETS cause the MOSFETS to begin switching the high voltage on and off at the transformer which connects to the lamps.
I have replaced the power board in spite of the fact that my gut tells me that the trouble lies on the LCD controller board or lies on the system board that should provided the latched high (5.0vdc) to drive the relay that connects AC to the run part of the power supply. The replacement supply acted exactly like the original one that I repaired--no LEDs, no start up and because there is no latching of the Ps_on or the other two bias feeds that are necessary to make the set run. I don't know if the second power board is good, it is suppose to be, supplied by TVPartsNow, located just outside of Chicago. I think they have a good reputation.
The dilemma is that the power board contains parts on both sides making it impossible to meter voltages on the reverse side and the same is true for the system board. The LCD Controller board is rarely available except from Sharp and it over $250.00. Same with the system/main board.
This is a great set which just suddenly would not turn on one day. Got this when they first came out, paid over $3K!! Yea, makes me sick but at the time, that was the best price available.
After establishing where I am in attempting to repair this set, I would so much appreciate any input or suggestion from others more familiar with this set than I.
In a normal power on sequence, the power switch (momentary contact) places a momentary ~ 5vdc at the pin of the microprocessor where all key (ch+/-,vol+/-, input and power-on off) signals are presented the microprocessor on the LCD controller board. Those change of bias levels do appear from the key connector on the LCD board and I have to assume they are provided to the microprocessor. One pin of this micro-controller, labeled SMPOW, has to supply a positive going voltage to the system board where there is another controller that receives this signal then appears to provide a latched high for POW_on, D_Power and EU-P_power. All three of these leads which are fed back to the power supply board must go and remain high to cause all of the operating voltages to be produced. I have confirmed that the supply board do that all operating or running voltages are produced. I have applied this bias from the standby 5vdc to verify that the power supply does indeed produce all required operating voltages for the set to run--but even with the bias applied, the set will not start. The power supply also produces the high voltage (`400vdc) necessary on the primary side of the transformer where the power MOSFETS are located but there is no high voltage present on the secondary, or so it appears. The low power oscillator which is transformer coupled to the Power MOSFETS cause the MOSFETS to begin switching the high voltage on and off at the transformer which connects to the lamps.
I have replaced the power board in spite of the fact that my gut tells me that the trouble lies on the LCD controller board or lies on the system board that should provided the latched high (5.0vdc) to drive the relay that connects AC to the run part of the power supply. The replacement supply acted exactly like the original one that I repaired--no LEDs, no start up and because there is no latching of the Ps_on or the other two bias feeds that are necessary to make the set run. I don't know if the second power board is good, it is suppose to be, supplied by TVPartsNow, located just outside of Chicago. I think they have a good reputation.
The dilemma is that the power board contains parts on both sides making it impossible to meter voltages on the reverse side and the same is true for the system board. The LCD Controller board is rarely available except from Sharp and it over $250.00. Same with the system/main board.
This is a great set which just suddenly would not turn on one day. Got this when they first came out, paid over $3K!! Yea, makes me sick but at the time, that was the best price available.
After establishing where I am in attempting to repair this set, I would so much appreciate any input or suggestion from others more familiar with this set than I.
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