Subject: Re: Tech: Williams EM Flipper Hum/Buzz Date: Mon, 24 May 1999 04:06:02 -0800 From: cfh@provide.net Organization: http://www.remarq.com: The World's Usenet/Discussions Start Here Newsgroups: rec.games.pinball when you hold the flipper button, the flipper gives you lots of hum noise; a VERY common EM problem. here's how to fix it... FIRST. replace the coil stop. even though 1974 skylab has DC voltage for the bumpers, the flippers are still AC voltage. AC is a variable wave form; it moves between +30 to 0 to -30 to 0 to +30 volts, and so on. as the AC moves towards 0 volts, the flipper coil loses power for just a moment, they re-energizes. this happens 60 times a second. and this creates the hums. the way the makers fix this is to have a coil stop with a ferrite core (or some other magnetic core). when the voltage is at +30 or -30 volts, the core is "charged". as the AC voltage moves to 0 volts, the core keeps the flipper plunger in place until the voltage goes back to +/- 30 volts. over time, the coil stop's core doesn't hold the flipper plunger in place at 0 volts, and hence you get more hum (from the flipper plunger). SECOND. replace the coil sleeve with a nylon sleeve. brass or aluminum coil sleeves were VERY common in EM's. neither is a really good material for a coil sleeve. replace with a new nylon unit. THIRD. replace the flipper plunger and link. this doesn't cause a lot of hum, but it can contribute. and besides, it will make you game play MUCH better. 30 year old flipper links and plungers need replaced. also if the end of the plunger is mushroomed or damaged (from hitting the coil stop), this can cause hum. **** Posted from RemarQ - http://www.remarq.com - Discussions Start Here (tm) ****