... I'm losing my time trying to understand how VCOM is distribuited
within the panel matrix.
As you can see in this picture, VCOM is generated by SM4041 in this case ...
between the chip and VCOM test point there is a 10 ohm resistor (R65) ...
and there is also what looks like a resistor partition (R64-R63) connecting
back to the chip (probably some sort of feedback).
Now, the first thing I didn't understand is why R63 is not connected to GND
but instead is connected to a capacitor (C226) follewed by a 0 ohm resistor (R60). So I checked where R60 is connected ... and I found out that it's
connected directly to the matrix itself.
So, it's a sort of feedback but it doesn't check only VCOM but some sort
of balance between VCOM and a VCOM-FEEDBACK.
The point is that this panel has a problem ...even rows are OK,
but odd rows have probably a low VCOM on the left of the panel (and
it go down gradually getting worse and worse moving to the left).
As you can imagine, this cause a persistance image in part of the screen.
I'm just trying to understand if there is a way to hack the TCON
and manipulate the VCOM.
I am also very interested in how VCOM is distribuited within the matrix
because I want to understand why the problem regards only the odd rows
This is more something I want to understand than a repair.
Do you have any idea how it works in the details?
Thanks in advance.
PS: For the records, VCOM is just 4.1V with a VDD of about 12V and
if you test R65 R64 R63 R60 C226 .... they are at the same voltage (4.1V).
So there is no current in their path. And none of the is shorted, they are all good.
within the panel matrix.
As you can see in this picture, VCOM is generated by SM4041 in this case ...
between the chip and VCOM test point there is a 10 ohm resistor (R65) ...
and there is also what looks like a resistor partition (R64-R63) connecting
back to the chip (probably some sort of feedback).
Now, the first thing I didn't understand is why R63 is not connected to GND
but instead is connected to a capacitor (C226) follewed by a 0 ohm resistor (R60). So I checked where R60 is connected ... and I found out that it's
connected directly to the matrix itself.
So, it's a sort of feedback but it doesn't check only VCOM but some sort
of balance between VCOM and a VCOM-FEEDBACK.
The point is that this panel has a problem ...even rows are OK,
but odd rows have probably a low VCOM on the left of the panel (and
it go down gradually getting worse and worse moving to the left).
As you can imagine, this cause a persistance image in part of the screen.
I'm just trying to understand if there is a way to hack the TCON
and manipulate the VCOM.
I am also very interested in how VCOM is distribuited within the matrix
because I want to understand why the problem regards only the odd rows
This is more something I want to understand than a repair.
Do you have any idea how it works in the details?
Thanks in advance.
PS: For the records, VCOM is just 4.1V with a VDD of about 12V and
if you test R65 R64 R63 R60 C226 .... they are at the same voltage (4.1V).
So there is no current in their path. And none of the is shorted, they are all good.