While there are plenty of websites and forums discussing the do’s and don’ts of EM machines, I figured I would summarize some of the key points here on our site.  Most of these are actually first-hand knowledge.

• Check your fuse blocks.  Most of these are going to be cracked and brittle by now (and barely hold fuses).  If you’re handy with a soldering iron (or just a beginner), this is an easy fix.  Buy some new fuse holders anywhere (Radio Shack, Home Depot) for cheap.
• Resist contact cleaner spray!  I repeat – do not use contact cleaner on any items below the playfield or in the backbox.  I too have ignored the advice of many forums as I thought – hey these look pretty dirty and this stuff works really well.   One, it leaves a residue that still needs to be filed off.  I’ve made a perfectly working (but dirty) EM machine go from working – to completely dead by using a cleaner.  I ended up having to remove each contact and hand cleaning with alcohol and filing.  Also, many contact cleaner sprays are flammable.   We have one report recently of a machine igniting the fumes trapped inside the cabinet.  That must have been scary.
• Use business cards as a low abrasive contact cleaner.  Cut a business card in 3 strips – lengthwise.  Dip them in alcohol (if your contacts are really dirty) and pinch the card between each contact and pull out.  It’s like flossing – and you’ll see a huge dirt/rust trail.  Repeat until clean on each contact.  Your machine will love you and you’ll probably notice a bunch more life and functionality out of your EM.
• Get a contact adjustment tool.   It is a simple item with a slit on each end used to properly bend/adjust contacts.   Contacts should always be straight (not wiggly looking) and aimed by bending at the base.  Adjustment for relays is a little trial and error.  You can also use a dry business card as a guide for normally-open contact gaps.
• Find the schematic for your machine.  Buy it if you have to.  It is imperative in understanding the wiring and diagnosing logic issues.
• Many issues come from poor wiring harness connections.  These long connectors are used in mating the wiring harness between backbox and cabinet, and with the fuse blocks.  These contacts often get loose or the spring metal loses it’s tension.
• Some machines use DC for pop bumpers and slingshots (and some other coils).  If yours are not working, check your fuse and replace the bridge rectifier.
• If you have a coil that is stuck on (buzzing, getting hot) – do not leave your machine running.  Power it off and find which relay or switch that is causing the problem.   IE:  I’ve seen chime relays burn out because of stuck rollover switches and for poorly adjusted  (10’s) &  (100’s) count up relays.