A diode should normally let current flow in only one direction through it (indicated by the orientation of the triangular symbol).
In your radio the diode normally sits reverse biased across the supply - that is non conducting.
If the diode had broken down - and was
conducting a lot of current backwards through it then the PCB track supplying it (and the rest of the radio) - the little frayed red thing - could get too hot and melt. This would prevent current flowing further into the rest of the radio.
Removing / cutting the diode (that is the short across the supply) and fixing the melted track would therefore restore power to the electronics.
...anyway - make sure the set is fused (5A might be more sensible than 10A) when you test it out in case the duff diode theory is wrong and something else in the 'rest of the radio' is lunching on all that current.
If your repair to the track is beefier than it was originally - and there is still a fault, somewhere else will heat up instead and you want it to be a fuse - not something important!.