TM  55-4920-401-13&P Table   4-4.   General   Troubleshooting   Table. Malfunction P O W ER light when is on. O N    l a m p    d o e s    n ot MASTER POWER switch POWER   ON   lamp   lights   when MASTER  POWER  switch  is  on  but displays do not light when DISPLAY control  is  turned  clockwise. Display  digit  shows  wrong  numeral sequence  or  digit  has  missing segments but checks OK on press-to- test. Probable  Cause — a.  Open  circuit  breaker, CB1,  in  probe  controller b.  Open  circuit  breaker, CB1, in trimmer. c.   Defective   MASTER POWER switch d .    D e f e c t i v e    p o w er transformer a.   Defective   DISPLAY control b. Trimmer PCB retainer left  off  card  cage  and boards  loose  in  connectors. c. Defective 15 vdc supply d.  Defective  lamp  voltage voltage e. Defective logic voltage supply. a.  One  of  decade  counters DC1-DC3, DC6, DC7 or one of    counter-latch-decoders CLD1-CLD4, or CLD9- CLD12  defective Corrective   Action a. Replace circuit breaker (30,  figure  FO-8). b. Replace circuit breaker (25,  figure  FO-7). c. Replace switch (41). d.  Replace  transformer  (39). a. Replace control (63, figure FO-7). b.  Install retainer (8). c. Repair 15 vdc supply. d.  Repair  lamp  voltage  supply. e.  Repair  logic  voltage  supply. a.  Replace  defective circuit. Table   4-5.   TEMP   °C   Indicator   Troubleshooting   Table. Malfunction TEMP  °C  indicator  drifts  upscale to  1400°C  then  flashes  on  and  off. TEMP   °C   indicator   cannot   be calibrated  with  CAL  ADJ  pot. Probable  Cause a. Open input circuit a. Temperature indicator out of calibration. b.   Temperature   signal generator   out   of   cali- bration. c.  Defective  CAL  ADJ  pot or connecting wires d.  Defective  A/D  con- verter Corrective Action a.  Provide  an  input signal and check for open in appropriate  temperature  signal circuit. See figures 1-16 and 1-17. a. Calibrate. b. Calibrate. c. Replace pot (69, figure FO-7) or  repair  wire. d.  Troubleshoot  per  para.  4-7c. 4-8