Screen not powering up(immediately)

The screen does not power up after plugin it in. The led flickers and there is a chirping sound. After some time it turns on.

I concluded it might be an broken capacitor. I found a broken one on the board and replaced it.

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The other capacitors seemed to be ok(checked using Multimeter measured capacity). The replacing of the broken capacitor did not fix the issue.

Afterwards I started checking the voltage regulators. I measured the voltages after plugging in the power supply until the board switched on.

There are three Voltage regulators on the board:

  • Power supply: 19.5V
  • MP1484: 5V
  • G1084(LT1084 replica?): 3.3V
  • 912T45: 1.2V

The 5V regulator provides only ~4.5V after connecting the power supply. The voltage jumps a little in intervals and after some time it provides steady 5V. Before that the 3.3V regulator cant provide its voltage as well.

Video of the power up - Measuring 5V and then 3.3V

I think next step should be replacing the 5V regulator or are there any other suggestions?

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Which cap did you replace? I desoldered & measured the 220uF/16V directly above MP1484EN, and found the capacitance has dropped to 185uF at room temp. If you aim a hair dryer at it, the board stops blinking and powers up immediately.

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Hey, thanks for the response.

I replaced the 470uF capacitor, it was well below 200uF and the cap bulged a bit outwards.

I just remeasured the 220uF capacitor you suggested and maybe i measured it wrong (still warm from unsoldering?) last time. It shows about 190uF. It does not seem much of a variance but I have a spare to replace it with and it's way easier than replacing the regulator.

I will do that tomorrow and check back here with the results.

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In my case, if you flip the board over, you can easily see severe discoloration under both MP1484 and G1084, that means they must have been running very hot for an extended period of time. Your 470uF/25V popped? Mine still looks alright, but my multimeter only goes up to 200uF and shows 1/infinite, so it should still be above that, by how much I don't know though. Actually I replaced that one at first too, but like you said it didn't make the difference.

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I just replaced the 220µF/16V with 220µF/25V I had and it seems it solved the problem completely. No noises, no wait, it just powers up as it should. I still have to reassemble the complete screen to check if it actually works again.

Yes I noticed the discoloration as well the first time I disassembled the device. I figured it literally must have fried those caps.

Yes my 470µF capacitor was not flat on the top anymore, it bulged outwards. You can see it in the picture I posted with the question if you look closely.

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Replacing the following two capacitors I fixed already three screens of this type.

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X-)

Thank you for your help again lonnie.chang!

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Marschos will be eternally grateful.
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