527/528 encountered APS fault during PM. ~~~~~ 527/528 encountered APS fault during PM.     EMU528 unable to Aux O -Brake ON local indication,status and a/c control panel light remain on,emergency lights remain on.Checked and found B106 line with battery voltage when BCB,DPCB1 and DPCB2 tripped on individual cars on EMU528.Further checked and confirmed #3528 lines 6621 at BCB and B106 at DPCB1 having continuity when BCB,DPCB1 and DPCB2 tripped.Suspect diode between B106 to 6606 shorted.To follow up OPS-20 Checked by Lim J.H. 05/7/21 To check and find B106 to 6606 diode.     Checked and confirmed B106 to 6606 (pin D to U) when measured from CN12.Electrical uncoupled #3528 from #1528,normalised #1528 and #2528 BCB emergency light did not light up.Isolated 6606 from junction box 1 & 2,measured CN12 pin D to U,not shorted,satis.Further checks found blocking diode between B106 and 6606 to be at s/w panel B.Confirmed diode is shorted.To raise 0030 to replace diode and carry out function test. Done by Jack/Koh. 07/7/21 To follow up Replace Blocking Diode and function test.     #527/528 Blocking diode replaced and function test satis. Done by Lin Zhesheng. 08/7/21