feeling what was supposed to be a symptom of arc damage, when arc damage was absent and/or  impossible? And why did these detents feel much weaker than those on S/N's 1035 and 1041? This new  problem had me stumped until the shafts were rotated to the detent positions and the pots were placed  back in the FeinFocus X-ray machine.  Close examination of the X-ray images showed that at the -190 degree shaft position on S/N 1027, the  wiper bracket on the shaft passed very close to the flat ribbon wire connecting the "CW" terminal to the  resistance element. On most pots, the flat ribbon wires were bent towards the case immediately upon  exiting the hole in the conductive plastic disk. However, on SIN 1027, the "CW" flat ribbon wire was not  bent towards the case, leaving it closer to the rotating parts than usual. Careful examination of X-ray  images of S/N 1027 show that the wiper bracket rubbed the insulating Teflon sleeve on this flat ribbon  wire. This rubbing interference was consistent with all observations listed above, represented a new  discovery, and was declared to be the cause of the detent.  The flat ribbon wires were welded to the ends of the terminals inside the pot case. However, from one pot  to another there was no uniformity to the angle or direction that each flat ribbon wire pointed as it left its  terminal (Figure 3). On S/N 1027, the "CW" flat ribbon wire left the "CW" terminal in a direction pointing  away from its termination in the conductive plastic disk. Therefore, the flat ribbon wire had to be bent back  upon itself in order to be inserted in its hole. Doubling the flat ribbon wire back on itself used up some of  its finite length, and was likely why the "CW" flat ribbon wire wasn't bent towards the case when it exited  its hole; there simply wasn't enough length available.  r I L-i  b  Figure 7. X-ray images of pots show cause of detent: interfering Teflon sleeve on flat ribbon wire  X-ray images of SIN'S 1021 and 1036 (Figure 7) also showed that their wiper brackets rubbed the  insulating Teflon sleeves on their flat ribbon wires. This rubbing interference was consistent with all  observations listed above, and was declared to be the source of their detents as well.  Note that these three pots were never disassembled for direct visual verification because:  a) the cover (lid) was glued on and prying open this lid would create debris which could contaminate  the bearings and resistance element, and  b) removing the lid with its integral bearing allows the shaft to tilt in the single bearing in the cup,  preventing accurate checks of the clearances between the wiper bracket and Teflon sleeving, and  c) since the detent-causing interference could be clearly seen from the X-ray images, it was not  necessary to de-lid the pots.  The three pots had been subjected to 5400 revs during testing by the manufacturer and then received  another 300 revs at JPL during testing on the gang fixture. The Teflon sleeve had been rubbed by the  metal wiper bracket 5700 times, deflecting the flat ribbon wire each time. The number of rubs that cause  failure of the flat ribbon wire was unknown, so no prediction could be made as to how much life remained.  31 0