Repairing Garrett ACE 250

[Ruben2000]

So that you have an idea of what happens since I turn it on, here I explain it to you.
First I connect the 6V power supply to the Board, I also connect the sensor, then when I press the power button I hear a small clicking sound in the speaker that tells me that the audio is active. But the screen does not turn on and it takes about 1 minute or more for it to turn on, before the screen turns on I take a measurement at PIN5 of U13 where there should be around 4V, it turns out that there is 2.77V.
After time the screen turns on and you hear the detector turning on sound and then you can no longer hear it even if you bring some metal close to the sensor.
Something curious is that while it is on at that moment, I disconnect the sensor and it makes a sound as if it were a sensor disconnection sound.
When the sensor is disconnected, I touch C53 with my finger on the side that is connected to pin 4 of Xt1 (or also by touching KT22) and it happens that the screen is erased and then appears making a power-on sound.

[Aleks85]

СХЕМА МЕТАЛЛОИСКАТЕЛЯ GARRETT ACE 250.pdf

[Ruben2000]

So that you have an idea of what happens since I turn it on, here I explain it to you.
First I connect the 6V power supply to the Board, I also connect the sensor, then when I press the power button I hear a small clicking sound in the speaker that tells me that the audio is active. But the screen does not turn on and it takes about 1 minute or more for it to turn on, before the screen turns on I take a measurement at PIN5 of U13 where there should be around 4V, it turns out that there is 2.77V.
After time the screen turns on and you hear the detector turning on sound and then you can no longer hear it even if you bring some metal close to the sensor.
Something curious is that while it is on at that moment, I disconnect the sensor and it makes a sound as if it were a sensor disconnection sound.
When the sensor is disconnected, I touch C53 with my finger on the side that is connected to pin 4 of Xt1 (or also by touching KT22) and it happens that the screen is erased and then appears making a power-on sound.

Here I add an outline of the MCU and surroundings.

[Ruben2000]

[ATTACH]n433824[/ATTACH]

Thank you very much friend, I already have that scheme and I have compared it with mine and it has several differences. My Garret Ace 250 is PCB Rev. L
Surely your diagram is from another revision or the person who drew it did not draw it well. But anyway, thank you very much because the description is useful for me to be able to find the fault.

[GeoMax]

I only drew it in PAINT that the same PC comes with, I only used a KT315 scheme and I only had to modify it according to my hand-drawn scheme; It was easier for me that way. I was drawing it in EasyEDA but it took me a long time and I'm just learning how to use it.

I use Diptrace for drawing schematics & PCB's. It took me only about 2..3 days learning how to draw a schematic and to make a PCB from the schematic. The learning was quite fast. For small projects there is also a free version with all program features enabled. The restriction is only on the number of pins (300) & layer numbers (2 + ground planes).
Compare to the free program KiCad, which is also a good program, I feel to work with Diptrace is much easier to work with.

[ivconic]

...But the screen does not turn on and it takes about 1 minute or more for it to turn on...

It looks like leaking capacitor.
Although... I once happened to come across a Fisher F70 that behaved similarly.
It turned out to be a bad crystal in the end!??
By simply replacing the crystal; the detector worked fine.
But at you there, it first looks like one or more capacitors that are "leaking" and close to making a short circuit.

[Skippy]

Has there been any water damage, especially salt-water? The conductive residue can cause problems with the very-low current power-on circuitry, by leaking the charge on capacitors.