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50al can't break dial tone with 295a subset

Started by Argee, July 25, 2012, 10:12:48 PM

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Argee

I've got a 50al candlestick that works fine with my 434a subset.  But the same phone will not break dial tone when hooked up to my 295a subset.  Everything else works with the 295, it rings and I can hear and talk fine.  So what has failed in the subset to prevent only dialing out?  I've traced all the wires and everything looks to be wired correctly. 

G-Man

Some of the early 295A side-tone subsets did not contain the optional condenser for the ringer.  Or if it does have a ringer condenser it may be faulty. 

Try to eliminate it by temporarily disconnecting one of the ringer leads and see if  that allows you to dial out.

Phonesrfun

I had a similar problem with the 295 and the 334 subsets.  Both subsets have the single, "dual purpose" capacitor.  These subsets were designed mostly for sidetone phones, and maybe even more importantly, non-dial phones.

My belief is that with the single cap, the waveform of the dial pulsing is pushed way out of whack compared to the ideal square wave.  This whacked-out wave form was no issue when using a POTS line in the past, but when using anything electronic, I.E. an Internet, cable, DSL, etc service, those services just cannot deal with the fact that the capacitor is charging and discharging back through the circuit.

You can probably solve the problem in either of two ways.  The first is the easiest, and that is to just disconnect the ringer and do without ringing.  The second way is to go to Radio Shack and get a 1.0 mF 250-volt metal film capacitor and divide the ringing up and have two capacitors.  That's what I did.

One 1-mF capacitor might not be enough for the old style ringer.  You may need to get two caps and put them in parallel to achieve 2 mF in total capacity.

-Bill G

poplar1

G-man: If the condenser is shorted then it would keep the line off-hook (if the ringer is connected) or at least trip ringing, and if it is open the ringer won't ring....
"C'est pas une restauration, c'est une rénovation."--François Martin.

G-Man

Quote from: poplar1 on July 25, 2012, 11:09:51 PM
G-man: If the condenser is shorted then it would keep the line off-hook (if the ringer is connected) or at least trip ringing, and if it is open the ringer won't ring....

If a condenser is of marginal performance/out of tolerance, it can exhibit the symptoms  that were described. 

In any event, it does not hurt anything to quickly eliminate it by disconnecting one lead of the ringer.

If it is not the problem, we can move forward and troubleshoot it further.         

Argee

Phonesrfun, you were right on the money.  dialing out worked after disconnecting the ringer.  Then I added a .47mf cap I harvested from a GTE styleline between the red ringer wire and L2.  I can dial out and the phone rings, if a bit weakly.  I'll probably upgrade to a bigger cap later, but at least I have proof of concept.  Thanks so much.

G-Man

Quote from: G-Man on July 25, 2012, 10:45:08 PM
Some of the early 295A side-tone subsets did not contain the optional condenser for the ringer.  Or if it does have a ringer condenser it may be faulty. 

Try to eliminate it by temporarily disconnecting one of the ringer leads and see if  that allows you to dial out.

I'm glad that my suggestion of temporarily disconnecting the ringer pin-pointed the problem. You may be able to use a new capacitor having the same value as the old condenser/capacitor. Generally old condensers start getting "leaky," causing problems.  As Phonesrfun stated, they can affect the waveforms of the pulses and the newer (poorly designed) technologies are particularly sensitive to out-of-tolerance components.

poplar1

Argee, are you using this on a POTS line (landline) or VOIP (MagicJack, Comcast digital voice, etc.)?

Bill, are you saying that the problem of one cap. is only on non-POTS lines?

G-man, thanks for the info; I didn't realize a failing condenser would cause this problem.
"C'est pas une restauration, c'est une rénovation."--François Martin.

Argee

thanks for  the advice G-man. 

poplar1: I'm on Cox Digital Telephone, same basic tech as VOIP (though since they use a private network it's not actually true voip).

like I said, adding the 2nd capacitor fixed the problem.  As far as I can tell the original condenser is fine.  It has a very strong ring as wired originally.  Can't be 100% sure without measuring it's actual capacitance. 

Phonesrfun

Quote from: poplar1 on July 26, 2012, 05:04:45 AM
Bill, are you saying that the problem of one cap. is only on non-POTS lines?

David:

Well,.... kind of.

When I first noticed the problem I was on Vonage and I was using their ATA.  I was getting bad numbers when dialing out.  I was so perplexed, that I tried other phones and other subsets.  It boiled down to the older sidetone subsets with the single capacitor.  Those always caused the problem.  I then took one to my work and tried it on an outside POTS line, and it worked OK.  I then concluded that it was the electronic ATA that was intolerant, but that was based on a very limited number of situations.  Later, I think it was Dennis Markham who was restoring a 295A subset for someone who was having the same issue.  Again, splitting it into two sections solved the problem.

I have since had some discussions with some other people who have the opinion that the design of the newer electronic ATA's is too rigid and needs to be able to handle the inconsistencies of analog switching that involves the irregularities from switching pulsing LC networks.

So it boils down to my two cents, coupled with experiences.

-Bill G