How near is "near"? Ohm's Law says that at 5 VDC, 10 mA will flow through a resistance of 500 Ohms. If  the resistance between the "CCW" and "W" terminals varies from 0 Ohms to the full 6250 Ohms over the  320 degree electrical range, then a current in excess of the wiper circuit's 10 mA rating would flow if the  wiper was within 320 * (500 / 6250) = 25 degrees of the "CCW" end of the resistance element. If the shafts  were in purely random orientations when connected, one would expect 25 / 360 = 7% of the pots to be  damaged. Of the 31 MIL-PRF-39023-style pots connected, two (or 6.5%) were damaged.  Based on the preceding failure analysis, this problem was attributed to test error due to a procedure fault.  Pot S/N's 1035 and 1041 were scrapped. The pot specification and drawings were revised to include the  10 mA rating for the wiper circuit. The following lessons were learned:  LESSON 1. Be aware of low resistance circuits which exist between the "CCW" and "W" terminals  when the wiper is positioned near the "CCW" end of the resistance element, as well as between the  "CW" and "W" terminals when the wiper is positioned near the "CW" end of the resistance element.  Warn of these cofiditions in the test procedure.  LESSON 2. In the pot specification and on the pot drawing, clearly state the current rating for the  wiper circuit.  LESSON 3. Based on a fraction of this rating, set current limits on all power supplies used in pot  testing.  LESSON 4. Provide an electrical schematic for connecting wires, and write detailed procedure steps.  LESSON 5. Use insulated test clips to connect to terminals that are in close proximity to each other.  Alternately, solder hook-up wires to the terminals and connect leads to the wires.  LESSON 6. Turn off the power supply outputs when connecting test leads - do not hook live  (powered) test leads to flight hardware.  LESSON 7. Before they are allowed to play with electricity on the job, make sure all mechanical  engineers and technicians can pass the "flashlight test" (hand them a 0-cell, a single piece of wire  and a flashlight bulb and ask them to enlighten you).  The RiDDk? Effect  It would have been great to end the investigation there. However, every flight pot that underwent functional  testing per the quoted procedure was potentially damaged and had to-be proven flightworthy all over  again. It was not possible to tell from the X-ray images if the conductive plastic disk was damaged,  therefore the only sure way to prove that a pot was undamaged was to remove its lid and conduct a visual  inspection using magnification. Each lid was retained by three equally spaced radial set screws threaded  into the wall of the cup which were tightened against the bottom of a circumferential groove machined in  the lid. Loosening these setscrews should have allowed the lid to be removed. But disassembly of S/N's  1035 and 1041 showed that it wasn't quite so easy:  a) one of the shaft bearings was mounted in the lid. Removing the lid thus represented major  disassembly, unloading the preloaded wipers and possibly invalidating all the qualification testing  performed to date, and  b) the set screws used to retain the lid had no secondary locking feature, so the original cognizant  engineer required that the manufacturer apply Solithane to the set screws to bond them in. The  Solithane used by the manufacturer had wicked into the circumferential groove and effectively  bonded the lids to the cups. Removing the lids would contaminate the wipers, tracks and bearings  with Solithane debris, requiring complete disassembly for cleaning and re-lubricating.  Time constraints necessitated an alternative though admittedly less rigorous approach. It was decided that  the remaining flight pots would all be screened for any of the characteristics observed in the failed S/N's  1035 and 1041 , namely:  a) out-of-spec electrical performance by electrical functional testing at room temperature, at the  operating temperature extremes of -75" C and +70" C, and again at room temperature, and  b) any "scratchy, detent" feel as each shaft was rotated.  308