TM  55-4920-401-13&P (5) Turn RESISTANCE & A/C INDICATOR CHECK  switch  successively  to  8  ,  15  ,  and  22 positions. In each of the above positions, multimeter shall  read  higher  than  when  switch  is  in  NULL BAL  position. 4-7. Trouble Analysis. a. General Troubleshooting Information. (1)  Initial  Check.  Before   troubleshooting   a tester using tables 4-4 through 4-11 and paragraphs 4-7 b through 4-7  e, determine  (1)  that  power  of  the proper voltage and frequency, as specified at the POWER  INPUT  receptacle,  is  applied  to  the  tester, and (2) that the MASTER POWER switch is on. (2)  Gaining  Access  to  Circuit  Boards. CAUTION Always remove power from the tester when removing or installing a circuit board, (a) Probe Controller Boards. 1. Disconnect  BH15184A  power  inter- connect  cable  from  INTERCONNECT  connectors. 2. Support tester lid and remove lid stop arm screw (12, fig. 4-29). 3. Remove  screws  (3)  around  edge  of probe  controller  deck. 4. Lift controller asssembly high enough to slip support (fig. 1-43) under back edge of deck. 5. To operate tester after opening probe controller,  connect  BH15184A-1  power  interconnect cable  (table  1-15)  to  INTERCONNECT  connectors. (b)  Trimmer  Card  Cage  Boards CAUTION For   proper   terminal   identification and  to  prevent  damage  to  a  circuit card  in  the  card  cage,  install  an  ex- tender   board   assembly   (table   1-15) such   that   the   lettered   terminals   are toward  the  deck  and  the  circuit  board such  that  its  components  are  toward the  deck. 1. Disconnect  BH15184A  power  inter- connect  cable  from  INTERCONNECT  connectors. 2. Remove  screws  (1,  fig,  FO-7)  around edge of trimmer deck and lift deck assembly from case. 3. Remove circuit card retainers, (8) to gain access to circuit cards. 4. Place   an   extender   board   assembly (table 1-15) between the card cage receptacle and the circuit board being tested, observing the caution above. 5. To power the tester after removing the trimmer  assembly,  connect  the  BH15184A-1  power interconnect  cable  (table  1-15)  between  the  INTER- CONNECT  connectors. (3)  Test  Points.  Test   points,   star-encircled Arabic  numerals,  e.g. ,  are  identified  on  the schematic diagrams and board assembly drawings for  the  purpose  of  troubleshooting. (4)  Integrated  Circuits.   Note  from  the  part lists in Section V of Chapter 4 that one board assem- bly may contain several integrated circuits having the same manufacturer’s part number. Swapping locations of identical integrated circuits may pro- vide a clue to a malfunction. Care should be exer- cised when swapping gates to note which circuits are affected by the gates. CAUTION Integrated circuit leads are fragile. Exercise care when removing or in- stalling integrated circuits. Always  remove  power  from  the  tester  when  re- moving  or  installing  a  circuit  component.  The  num- bering  of  integrated  circuit  pins  is  explained  in paragraph 1-4 b (11) (b). b.  Troubleshooting  the  DC  Power  Supplies. Table 4-12 lists voltages and voltage test points of the dc power supplies in the tester. Voltages shall be within voltage ranges when line voltage is 115 ± 15  percent.  There  are  no  adjustments  to  these  volt- ages. c .    T r o u b l e s h o o t i n g    t h e    A /D Converters.   Before   troubleshooting   an   A/D converter,   open   the   trimmer   assembly   per paragraph   4-7a.   (2)  (b).  Make   the   testsetup   of figure  4-1  when  troubleshooting  the  TEMP  °C indicator  and  of  figure  4-2  when  troubleshooting the  %  RPM  indicator.  When  troubleshooting  either indicator,  apply  a  full-scale  signal  and  use  an oscilloscope to check the waveforms of figure 4-7. Indicator data is listed in table 4-13. Test points are identified  in  figures  4-8  and  4-9  and  on  the  A/D converter schematics (figs. FO-4 and FO-5). 4-6