Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!sdd.hp.com!zaphod.mps.ohio-state.edu!casbah.acns.nwu.edu!nucsrl!telecom-request From: dave@westmark.westmark.com (Dave Levenson) Newsgroups: comp.dcom.telecom Subject: Re: An Old Instrument Develops Bell-Tap Message-ID: Date: 9 Mar 91 08:11:26 GMT Sender: news@casbah.acns.nwu.edu (Mr. News) Organization: Westmark, Inc., Warren, NJ, USA Lines: 26 Approved: Telecom@eecs.nwu.edu X-Telecom-Digest: Volume 11, Issue 188, Message 4 of 10 Originator: telecom@delta.eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu Nntp-Posting-Host: hub.eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu In article , tots!tots.Logicon.COM!tep@ ucsd.edu (Tom Perrine) writes: > Is this "bell-tap"? Is it a matter of reversing the polarity on the > pair, or is it due to wear in the electro-mechanical ringer? After > thirty years, I would assume that it could be a *little* out of > adjustment :-). The most likely culprit here is the blocking capacitor. This is probably a 1 or 2 mFd capacitor mounted inside the 'network' (the potted module in the right rear corner of the instrument with a bunch of screw-terminals on top) and connected between terminals A and K. It is normally wired in series with the ringer, so that only the AC component of the signal passes through the ringer. It has probably become shorted, allowing the DC to bias the ringer. The dial pulses look like 48 volt DC pulses, and will tap the bell if the capacitor is shorted. If AT&T still owns the telephone, they should replace it. Dave Levenson Internet: dave@westmark.com Westmark, Inc. UUCP: {uunet | rutgers | att}!westmark!dave Warren, NJ, USA AT&T Mail: !westmark!dave Voice: 908 647 0900 Fax: 908 647 6857