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I have an HP 1740 monitor that, when I turn it on, just remains 2-3 seconds to display and turns off completely (even the pilot). It seems to me that the problem is not in the backlight. I opened the monitor and on the power supply board, I didn't find anything visually damaged.

I measured all the capacitors with a multimeter (on the PCB, I did not desolder them) and yet only the two large green capacitors rated 150 with the multimeter in Diode mode.

I also tested the MOSFETs (without desoldering) between the drain as positive and source as negative. In all, the value of Diode mode went up.

I suspect the 1200AP60 integrated circuit, but I don't know how to test it. Could it be the problem?

I am an enthusiast, trying to learn more about electronics and how to solve.

power supply board of HP 1740

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    \$\begingroup\$ You can't measure capacitors in-circuit. If it powers up for 2-3 seconds the main SPMS chip is not dead, but there can be overvoltage or overcurrent so it shuts down to protect from further damage. Some capacitor may have dried up and lost original capacitance value. Did you download the service manual with schematics and troubleshooting guide? \$\endgroup\$ – Justme Feb 23 at 20:04
  • \$\begingroup\$ It might be worth replacing the big electrolytics in the PSU. I've known some to be bad, even when not bulged at the top. If any are bulged (difficult to see in the piccy) definitely replace those. \$\endgroup\$ – Neil_UK Feb 23 at 20:15
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I found the issue. The problem are in the board of controller buttons of the screen. I didn't understand what is wrong. I disconnected and now it works normally.

Thank you all for the reply.

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There are a few possibilities come to my mind:

  1. Latched OLP (over load protection): Unlike the hiccup mode, the PSU shuts itself down on an overload or short circuit. And it requires a power cycle after removing the cause of the extreme situation. You may want to check the load side against any ahort circuit.

  2. The microcontroller (or microprocessor or microcomputer, whatever it is) shuts the entire system down: If the controller senses an extraordinary situation then it can turn the entire system off to protect the whole product. You can check if the output voltages of the PSU and especially the MCU's supply voltage(s) (1.8V, 3.3V or even 5V) still exist.

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