I have had this problem before with a couple of machines and a bit of tape between coil and plate does in fact fix the problem until a new plate can be installed.
Heres my theory ( I emphasise theory )
After a certain period of time the plate becomes slightly magnetised.. you can prove this by putting a small lightweight object to it that contains iron.. it will have a certain amount of stick and youll feel the attraction etc of the magnet.. its only slight, but it is present.
When the coil fires it creates a high current pulling in the plate.. this high current is required to move the plate. When the coil deenergises it is not quite at zero potential.. most EMs use centre tap of the transformer as ground and its not true earth.. Edi currents and the such on AC create minor ripples in the voltages... the fine dust given off by any machine also contains very fine pieces of metal and it too can become conductive or slightly magnetic.
Because the coil never quite goes to zero potential (unless machine is turned off).. it is enough to just hold the plate in place causing the coil to latch on.. but it needs the high current through it to move the latch in the first place.
Result?.. machine is fine.. coil latches and wont turn off unless power is removed.
A new plate will sort out the issue and please do try holding a small screw ( must be the type that rusts) or similar to the plate to confirm a magnetic field.
Cheers!
Gav - enjoying AC theory
