[Elecraft] K2 PA and 232 problem

[Bob G3PJT]

Hi

My CAT just stopped working and I have found that there appears to be a 
low resistance on the 5v rail which supplies the PIC / 232 interface 
chips. This pulls the 5V rail down to 1 v with the result that the PIC 
and 232 interface chips are not operating and the 78L05 at U3 is rather 
hot and bothered.
Before I get the PA board off the heatsink and start desoldering chips 
has anyone any idea of checks I could do to localise the problem

73 and thanks for any info

Bob G3PJT