C, 107 bytes
#define p(x) printf("%c",x);
f(char*s){for(;*s>64;s++)p(*s)p(10)for(;*s<58;s++)p(*s)p(10)for(;*s;s++)p(*s)}
Call with:
int main()
{
f("UK7898S14");
return 0;
}
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