Mr. Pinball Tip:

Sticky solenoids are caused by one or more of the following causes:
1. Mechanical binding--This could be a loose screw that is allowing the assembly to be misaligned, or a worn linkage.
2. A worn coil--The coil may have overheated at one point and caused the coil to expand and bind. This usually can be checked by seeing if the coil sleeve can be easily removed from the coil. If not, the coil may need to be replaced. The exception to this is that some coils when new cannot easily have the coil sleeve removed. Another symptom of a worn coil is that the plunger cannot move freely within the coil sleeve.
3. A dirty plunger--The plunger should be removed and cleaned with a solvent such as alcohol. Never lubricate. Do not use graphite or oil. Plungers must be clean and dry to work properly.
4. Return spring problems--If the above items check out and the assembly will not return to rest when activated by hand with the machine off, the problem may be the spring. Check that the spring is not broken or too weak.
You may also have a problem with the return spring if it is too strong. If this is the case the coil will be fighting the spring instead of doing its job.
5. Missing or worn coil stop--The coil stop should be undamaged, clean, and firmly attached. If this is an AC coil it should have a copper ring visible in the stop.
6. Plunger friction--Check the end of the plunger where it strikes the coil stop. If it has mushroomed, you will need to file the end flat and put a small beveling around the edge so that the plunger will not bind on the sleeve. If you have filed the plunger end flat you will probably need to file the coil stop flat as well so the two will match.
7. Electrical problem--This is usually the least likely problem. Check the connections and verify circuits are all working and that no undue resistance is present.
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