Hello, i'am new at yours forum. I have burned out element on my cosmopolit 3f, could someone help me to recognize it? This is SMD sot-23 part. Name starts with 31. I'am adding pictures.

 

It is switching diode MMBD1402

 

The silkscreen labels it as Q708 and the leftmost pad appears connected to a trace running under the R703 label. That diode wouldn't have a connection there.

 

Looks like a transistor or mosfet. The ones I use have 3 character codes. They’re hard to identify unless you know what they are to begin with. It looks like it still works. You should try to take some readings to see if the gate works or whether it’s a transistor.

You may want to contact the manufacturer if all else fails. Nevermind Grundig is gone.

 

Well this picture is from german forum but marker coupe not help me to recognize. Radio is 6v powered and it is giving noise all the volume range not when muted. Mine looks like that.

 

The only sot23 component I found online with 31X marking is a regulator. http://www.s-manuals.com/smd/31 might explain the 6V... not sure if that's supposed to correct. If the voltage is out it could ruin your biasing for your amplifiers, so can a transistor...

The SMD codebook references a diode: MMBD1402 but it doesn't make sense due to being a single diode with only 2 pin connection:

Seems like the same issue here: https://www.elektroda.pl/rtvforum/topic3602228.html
use google translate