The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com Unpotting a Neon Transformer, Disassembling A Neon Transformer! After unpotting  9kV 60mA, 7.5kV 60mA, and 5kV 120mA neon transformers, I discovered that some of the problems were cracked tar and two of the transformers had shorts in one half of the windings. This can tested by carefully arcing each individual secondary coil to the mid-point grounded core.  If one fails to arc, there is an internal short.  Lets see why... The finished coil as I unpotted it... First step is to remove the shunts with a screw driver and hammer Next step is to take an angle grinder and remove the weld bead along the middle of the case that holds the core together.  A gentle tapping with the hammer afterward will release the two sections... ...like this! To disassemble the coils from the cores can be hard if the tar is still hardened around them.  I am using an arbor press to help matters. One finished secondary coil This one came off of the core fairly easy.  The other with the primary was more difficult to pry off! One side looks okay, but look at the large voids...tar everywhere in the case, except where needed! The other side had a large arc over portion.  I carefully scrapped away the burned paper insulation and tried not to disturb the windings. Progress so far! "That looks easier said that done!"