It´s a Germanium diode like AA139 etc.
This diode has it´s function in the battery circuit and should be replaced, but it´s not what prevents the mainboard from starting correctly.

Have you checked all corroded and cleaned traces for continuity? You should also cover them with a thin layer of soldier (using good flux to avoid any shorts).

In the second picture there are some thin traces that are also corroded.
If one single of them is interrupted it can prevent the system from POSTing.

The motherboard it is full of apparent tracks corroded but I have tested several of them and they are in good condition.

I have two or three motherboards socket 7 that they need the CR2032 just to start to work. To check it in this motherboard my intention was to put a new socket for the CR2032 when I found the borken diode.

As you can see, before to clean the tracks under the battery socket, several of them looks corroded but all are OK as you can see in the previous pictures.

The diode D2 is connected throught the resistor R36 to the pin 97 of the IC VIA VT82C416. Maybe it has sense that the motherboard does not start.

But Germanium diodes usually has only one black strip but this has two. ????

Motherboard is working. Now, I have to protect the tracks with varnish (I am not sure if this is the name).
Thank you very much.

majestyk wrote on 2024-01-28, 17:32:

It´s a Germanium diode like AA139 etc.

Why germanium? These are usually standard silicon switching diodes like 1N4148. The current from the battery is very small, and even to the battery (if it's a rechargeable) is small enough, well below 100mA.
If you need low forward voltage drop then I'd suggest a modern Schottky diode, not germanium. There are quite a few problems with germanium diodes and in this particular case it would be the reverse bias leakage - it could result in some charging of the CR2032 cell and it eventually leaking out corrosive fluids.

Thank you for this information. I will replace the diode by the suggested 1N4148 (I have to buy it).
Regards.

Your question was:
"I am not able to identify this diode. Could you please help?"

That´s what I did.

You didn´t ask what diode to use for replacement or if there are better alternatives than the original component.

If you use a standard Si-diode like 1N4148 the lithium cell needs to be replaced earlier, because the voltage for storing data in the chipset and the RTC falls below the minimum value earlier (voltage drop).
With a Schottky you´re even better off than with a Germanium type.
The "backward leakage" of a Germanium diode didn´t harm the lithium cells in millions of mainboards for decades, so I wouldn´t bother too much here.

Thank you very much. Regards.