According to the analysis of fault phenomenon of the failure for the STBY power supply circuit, the P board PR501 multimeter test on both ends of the voltage found no voltage output (normal 15 v) as the judge IC407STBY circuit does not work, use multimeter measuring IC407DC Q432 foot - starting voltage DC circuit found the only 1 v low voltage should be normal (12 v) (D) feet normal should be 175 v voltage of only 10 v. (at the STBY circuit normal removed Q432 Q431 test (S) feet 10 v, 60 v (D) feet or so), thus judging voltage start-up circuit is short circuit or leakage, the multimeter resistance measured their resistance to only 100 euro, circuit has the short circuit, starting circuit measuring each element separately with the table, found D406 breakdown. Replace D406 (MA4200 - M), the machine back to normal.T4iservice manual download site