2500 phone sidetone question

Recently bought a Western Electric 2500MM phone. Volume of dial tone is very quiet, and there is not much sidetone. Tried another handset, with same results, so I believe the problem is in the phone and not with the handset. I also called a friend, which confirmed that the talk volume was okay. The listen volume is the issue.

I understand there are resistors and capicators on the underside of the speech network box inside the phone. Unfortunately, I can't get the network box out from under the three retaining straps which are riveted to the phone base. I do not wish to break anything by prying.

So two questions: (1) how do I remove the network box from the phone base, and (2) after I've removed the network box, what steps might I take to test the components and improve the perceived volume of the phone?



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You shouldn't need to. In 30 years of dealing with Western Electric phones, I've yet to find one that had a bad network assembly. I would be utterly stunned if it's the cause of your problem.

I have, however, troubleshot this problem with other 2500 series TouchTone sets. I would wager 3,642 Quatloos that your problem is dirty or oxidized muting contacts on the backside of the dial assembly.

What you want to do is hit up whatever local electronic supply place (preferably NOT Radio Shack, but they'll do if you have no one else in your area) for some electrical contact cleaner. CRC Chemicals makes one called 'CO Contact Cleaner' that will work beautifully. If you can't find this at an electronic supply store, any branch of Graybar Electric, Platt Electric Supply, or Grainger should stock it.

DO NOT, under ANY conditions, use WD-40! It will leave an oily residue behind that may damage the paper/phenolic circuit board on the backside of the dial, and that will also attract lots of dirt and other nastiness after the fact.

Once you get the right cleaner, remove the dial from its brackets, separate the plastic halves of its protective cover, press and hold any of the buttons on its front, and hose down the gold leaf-spring contacts and posts in the dial's upper corner with the cleaner. Then release all buttons and repeat the process.

What happens with the TouchTone dials is that, in the idle position, one of those contacts shorts out a muting resistor that would otherwise be in series with the receiver end of the circuit. If the contacts get dirty, the resistor is never shorted out. The result: Low receive volume.

Good luck.

Reply to
Dr. Anton T. Squeegee

I agree. However I'd suspect that you might have used a defective handset to test the phone. It's possible, but the chances are a lot less, that you could have two low volume handsets. It is extremely uncommon for the network to have a problem.

Also, he assumes, below, that you have a type 35 dial pad. There are a lot of 2500 sets that have the type 72 dial pad, and it may be different than the type 35. The type 72 uses the IC chip instead of the transistor and big pot core inductors.

Still, cleaning the contacts, if there are any accessible, is a good idea.

Reply to
Watson A.Name - "Watt Sun, the Dark Remover

Thanks Dr. Squeegee! Your solution was completely correct. A triumph for this venue.

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You are entirely welcome. Donations may be made to the Dutch Surrealist Plumbers Retirement Fund. ;-)

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Dr. Anton T. Squeegee

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