I have a PI 4 and accidentally broke the red led. I don know how to identify it in order to get a replace piece and soldering Any idea or help, please?
I assume you are referring to the PWR led on the board. Just a heads-up, the full BOM isn't provided for the Raspberry Pi, so this is just my best guess based on what is available. Looking at the schematic here, the LED in in series with a DSS13UTR protection diode, and a 1kOhm resistor. The protection diode from its datasheet will drop 0.5V when in forward conduction mode (during normal LED operation) so the resistor/LED pair will be dropping about 4.5V.
I measured the pads on the board, and it's clear that it's designed for an 0603 package, side-view diode. Here is a photo below with an 0603 resistor next to it for scale:
Looking on Mouser at 0603 package side-view LEDs, there are several options, at a variety of forward voltages, however the most common available is 2V. Looking at a few of these options, it looks like most of them should work just fine for an indicator light use.
Using the nominal forward voltage of 2.2V, that means the current in the LED when on would be (4.5-2.2)/1000 = 2.3mA. Of course, at that current the forward voltage for that model ends up being closer to 1.9V, which gives a current of (4.5-1.9V)/1000 = 2.6mA so that gives an approximate range of where it will end up operating. Looking at the luminous intensity graph, that is within the "on" range, and gives a relative intensity of about 15%, which seems about right for an indicator light. So SML-A12V8TT86 seems like it would work as a replacement.
Example 2: LTST-S270EKT Using similar analysis on this, we get a relative intensity of around 10%. The graph doesn't have good resolution on the lower end, so this may or may not work.
Hopefully that helps point you in the right direction.
Note that you don't have to rework the PCB for this if you don't want to. You can get a LED+resistor assembly which can be soldered to either GND/5V pads some place convenient, or even fitted with jumper cable ends and connected to 5V and GND pins on the GPIO connector:
The GPIO solution has the benefit of flexibility: if your Pi works, you can just disconnect the LED which has little purpose. If you experience power issues, you can connect the LED and let it tell you whether 5V is present or not. Or you can wire the LED to a USB plug and use it to check the presence of USB power.
A broken red LED (the "Power LED") need not be a concern. Some people (incl. myself) consider the "Power LED" a nuisance, and prefer that it be disabled. The subject of the "Power LED", and in particular how to disable it has generated a huge amount of discussion over the years. 1, 2, 3
Instead of taking on the time, effort & expense of replacing the red LED, you may want to consider this alternative: Disable the "Power LED", and use the green LED ("Activity LED") to indicate both power and activity. It's a simple change; you'll be finished in 2 minutes, and if you don't like it, simply remove it. Here's how:
Open the file
/boot/config.txt in your editor; e.g.:
sudo nano /boot/config.txt
Add the following lines near the end of the file:
# ACT LED off during disk activity, on all other times dtparam=act_led_activelow=on # PWR LED off at all times dtparam=pwr_led_trigger=none dtparam=pwr_led_activelow=off
After the edits, save the file, close it & reboot. If you want to revert, simply "comment out" the 3
You could replace with practically any LED, but frankly is difficult unless you have the right equipment.
There is also little point. The LED indicates the presence of 5V but is hardly essential and attempting to restore it risks damaging your Pi.
Incidentally "accidentally broke" usually means ripped a component off and almost invariably this also means ripped the board traces off leaving nothing to solder to. Any such attempt usually causes further damage.