TM 55-4920-412-13&P will   indicate   between   21   and   27   vac.      If   not,   perform Troubleshooting Table 4-6. (5) Disconnect lead from loop 2 and connect to loop 4.    Digital  multimeter  will  indicate  between  21  and  27 vac.  If not, perform Troubleshooting Table 4-6. (6) Disconnect lead from loop 4 and connect to loop 29    and    disconnect    negative    lead    from    loop    8    and connect   to   loop   43.      Digital   multimeter   will   indicate between  7  and  9  vac.    If  not,  perform  Troubleshooting Table 4-6. (7) Disconnect   lead   from   loop   29   and   connect   to loop   53   and   disconnect   negative   lead   from   43   and connect   to   loop   49.      Digital   multimeter   will   indicate between  7  and  9  vac.    If  not,  perform  Troubleshooting Table 4-6. (8) Disconnect   lead   from   loop   53   and   connect   to loop  7  and  disconnect  negative  lead  from  loop  49  and connect   to   loop   11.      Digital   multimeter0   will   indicate between  23  and  29  vac.    If  not,  perform  Troubleshooting Table 4-6. c.  Power Supply Circuit (Voltage Output A1 Board). (1) Connect  Digital  multimeter  positive  lead  to  loop 47  and  negative  lead  to  loop  63.    Digital  multimeter  will indicate   between   4.9   and   5.1   vdc.      If   not,   perform Troubleshooting Table 4-6. (2) Disconnect     leads     from     loops     47     and     63. Connect  Digital  multimeter  positive  lead  to  loop  23  and negative lead to loop 27. Digital  multimeter  will  indicate  between  4.9  and  5.1  vdc. If not, perform Troubleshooting Table 4-6. (3) Disconnect     leads     from     loops     23     and     27. Connect  Digital  multimeter  positive  lead  to  loop  5  and negative lead to loop 14.  Digital multimeter will indicate between  14  and  16  vdc.    If  not,  perform  Troubleshooting Table 4-6. (4) Disconnect    positive    lead    from    loop    5    and connect    to    loop    3.        Digital    multimeter    will    indicate between -14 and -15 vdc. If not, perform Troubleshooting Table 4-6. (5) Disconnect    positive    lead    from    loop    3    and connect    to    loop    1,    Digital    multimeter    will    indicate between  33  and  41  vdc.    If  not,  perform  Troubleshooting Table 4-6. (6) Disconnect    positive    lead    from    loop    1    and connect   to   loop   19.      Digital   multimeter   will   indicate between -33 and -41 vdc. If not, perform Troubleshooting Table 4-6. (7) Disconnect    positive    lead    from    loop    19    and connect   to   loop   18.      Digital   multimeter   will   indicate between     1     1.5     and     12.5     vdc.          If     not,     perform Troubleshooting Table 4-6. (8) Disconnect    positive    lead    from    loop    18    and connect   to   loop   46.      Digital   multimeter   will   indicate between     11.5     and     12.5          vdc.          If     not,     perform Troubleshooting Table 4-6. (9) positive  lead  from  loop  46  and  connect  to  loop 13.    Digital  multimeter  will  indicate  between  -11.5  and -125 vdc.  If not, perform Troubleshooting Table 4-6. Table 4-6.  Troubleshooting Power Supply Circuit (AVIM) NOTE Before performing troubleshooting, remove power supply A1 board and reconnect using extender board. Trouble Probable Cause Remedy No AC inputs to A1 board Fuse F1,S1,T1 Transformer Replace defective components, Figures 4-4, 4-5, FO-1, FO-5 or re- place A1 board. 5VFL NO 1 and NO 2 vdc reading NO 1-(R3) (R3) or (R6) are Fixed Resistors, use out of tolerance NO 2-(R6) decade Resistor Box and check or replace, Figures 4-4, 4-5, FO-1, FO-5 or replace A1 board. 5 VFL NO 1 and NO 2 no vdc or NO 1 - CR1, C7, U Replace defective components, shows excessive reading after trim NO 2 - CR2,C8,U2 Figures 4-4, 4-5, FO-1, FO-5 or resistors (R3) or (R6) checked or replace A1 board. replaced 15 vdc reading out of tolerance CR4,R8,CR6,C6,C13 Replace defective components, Figures 4-4, 4-5, FO-1, FO-5 or re- place A1 board. 4-8  Change 2