The pics are off the other really long thread as they are much clearer than my phone will do.
The fault:
In standby there is no buzzing.
After signal input and turn on, a loud buzzing is emitted from the main transformer, no backlight.
It is because the 24v line is at 21v irrespective of whether the inverter is plugged in. There is a picture on the screen.
If you wait long enough the buzzing stops and the 24v line changes to 24v and the inverter comes on.
I have checked every single cap on the psu and logic board by un-soldering and using an esr meter and another meter that tells you capacitance. I have replaced the C603, C605 and c707 as they are usually suspect on this board. C606 which people say is suspect I do not have a replacement but it measured at 3 ohms ESR which according to all the charts I could find is well in spec. And had correct capacitance. I also tried one off an identical board I have.
I replaced the output cap on the 24v line also.
I have another psu board for this monitor from one with a broken lcd, I swapped from that one the 2 transformers from the middle of the board and U601 chip to no avail. This PSU can not be used for testing as I cannibalised it ages ago as it had faults anyway.
The buzzing is coming from the big transformer.
If I heat the board with my hot air station around U601 the backlight comes up quicker. How can this be if it is not the caps? Can U606 be out of spec at 3ohms, I can order some from RS for tuesday. But can it cause the loud buzzing etc.
What can cause lower voltage on an output please?
Once it is working if I turn off to standby and turn back on it usually buzzes again....
Any ideas please?
Voltages on C603 -> 22.5v
C606 -> 71.1v
C605 -> 12.9v
(No change after buzzing stops).
Many thanks.
The fault:
In standby there is no buzzing.
After signal input and turn on, a loud buzzing is emitted from the main transformer, no backlight.
It is because the 24v line is at 21v irrespective of whether the inverter is plugged in. There is a picture on the screen.
If you wait long enough the buzzing stops and the 24v line changes to 24v and the inverter comes on.
I have checked every single cap on the psu and logic board by un-soldering and using an esr meter and another meter that tells you capacitance. I have replaced the C603, C605 and c707 as they are usually suspect on this board. C606 which people say is suspect I do not have a replacement but it measured at 3 ohms ESR which according to all the charts I could find is well in spec. And had correct capacitance. I also tried one off an identical board I have.
I replaced the output cap on the 24v line also.
I have another psu board for this monitor from one with a broken lcd, I swapped from that one the 2 transformers from the middle of the board and U601 chip to no avail. This PSU can not be used for testing as I cannibalised it ages ago as it had faults anyway.
The buzzing is coming from the big transformer.
If I heat the board with my hot air station around U601 the backlight comes up quicker. How can this be if it is not the caps? Can U606 be out of spec at 3ohms, I can order some from RS for tuesday. But can it cause the loud buzzing etc.
What can cause lower voltage on an output please?
Once it is working if I turn off to standby and turn back on it usually buzzes again....
Any ideas please?
Voltages on C603 -> 22.5v
C606 -> 71.1v
C605 -> 12.9v
(No change after buzzing stops).
Many thanks.
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