Mulja tv repair portal
Equipment Repairs => LCD TV forum => Topic started by: jkb242 on March 09, 2012,19:33:07
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The problem I am having is there seems to be no 4-5 VDC latching at the microprocessor to provide bias to the transistor that drives the relay coil on the power board. This relay applies line voltage to the remainder of the power supply that is not connected when the TV is in standby or off mode.
I have Bus 5 VDC and Bus 6.0 VDC in standby. When pressing the power switch (momentary contact) the Key circuit applies ~4.5 vdc to the STBY-POW line connected to the microprocessor IC 2004 pin 54. The current level inside the controller should increase due to the lower resistance of the key input.
Pin 15 of the processor is labeled SMPOW and eventually (on the main board makes a direct connection to a lead labeled PS_ON that is connected to the power board via connector CN705. This connection in turn connects to the base of the transistor on the power board, the collector is connected to the relay coil.
The only issue is that the trigger feed PS_ON does not latch high to supply this bias and there is no latching circuit that I see on the power board. I guess I don't understand why the microprocessor SMPOW pin does not latch high.
It would also be helpful to understand the definition of SMPOW, TV_POW and TV_POW2. I do have the service manual containing all schematics for this set LC-37D5U.
Thanks and really appreciate any input that can be provided.
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When pressing the power switch you should have at least 2vdc on PS_ON to start the PSU.
If not then you could have a corrupt memory.
I have never seen a LC-37D5U becourse they was not sold in my country,
but I have seen other model with no led, no startup
and it was the NWM memory. Some of those
I could repair with I2C bus update method, one I had to change
to a preprogrammed memory.