TM5-6115-593-34 NAVFAC P-8-631-34 TO-35C2-3-463-2 resistance one way and low resistance    the    other    way.        A shorted  diode  will  read  full  scale both   ways.      An   open   diode   will read infinity (no reading) in either direction.   Check   all   diodes   and replace disconnected leads. (7) Check zener diodes CR1 and CR4 by connecting   a   voltmeter   across   each zener and its associated resistor. CR1 must show reading of 6.8 volts across input  range-of  20  to  40V  DC.    CR4 must show reading of 15 volts across input range of 20 to 40V DC. b. Test of TD1. (1) Connect  time  delay  module  TD1  as shown in figure 4-13. (2) Close  switch  S1.    Time  the  period  it takes  before  lamp  DS1  lights.    The lamp  must  light  in  25  to  35  seconds, or    TD1    is    defective    and    must    be replaced. c.Test of TD3 (1) Connect  time  delay  module  TD3  as shown in figure 4-14. (2) Close switch S1 and time the period it takes  before  lamp  DS1  lights.    The lamp must light in 4.5 to 6 seconds, or TD3 is defective and must be replaced. NOTE Wait at least 15 seconds before proceeding. d. Repair. If any of the replaceable components tested in a (above) are defective,  TD1  and  TD3  are  repairable  by replacing  the  defective  component.    If  the printed circuit wiring or a terminal board, or a non-replaceable component, proves defective   (test   b   or   c,   above),   the   entire assembly must be replaced. e. Replacement. (1) Tag  and  disconnect  wires  to  TD1  or TD3 (12 or 15, figure 4-10). (2) Remove  screws  (13)  to  remove  time delay    assemblies    (12    or    15)    with brackets (14). (3) Components are replaced by carefully unsoldering    them    from    the    printed circuit board. CAUTION Do not apply excessive heat when soldering or unsoldering components.  It may damage the printed circuit wiring. (4) If    either    TD1    or    TD3    are    to    be replaced    as    an    assembly,    remove screws  (10)  and  nuts  (11)  to  release time  delay  assembly  (12  or  15)  from brackets (14). (5) Prepare  time  delay  assembly  (12  or 15) for installation by attaching brackets  (14)  using  screws  (10)  and nuts (11). (6) If   components   are   to   be   replaced, carefully  solder  new  component  into place. CAUTION Do not apply excessive heat when soldering or unsoldering components.  It may damage the printed circuit wiring. (7) Install time delay assembly (12 or 15) by securing brackets (14) to shelf (21) using screws (13). (8) Connect    wires    to    terminal    boards, then remove wire tags. 4-26.      MOTOR-OPERATED   POTENTIOMETERS   P4 AND P5. a. Replacement.        The    two    motor    operated potentiometers  P4  and  P5  (2  and  4,  figure 4-10), are mounted on the component panel assembly  (shelf)  (43,  figure  4-1)  in  the  AC- DC control box assembly enclosure. Removal for either unit (P4 or P5) (figure 4- 15), is as follows: 4-23