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3-wire Phone on a 4-wire network

Started by Craterranch, September 16, 2015, 07:39:24 PM

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Craterranch

Quote from: unbeldi on September 17, 2015, 09:15:13 AM

This board doesn't seem to have any kind of energy storage capacitor to provide a boost during DTMF generation.


There are four capacitors under the board.

Craterranch

Thanks everyone for your responses so far. To answer one of the questions, I don't currently have another rotary phone I can test with.

I will take some pictures of an office phone and post them this afternoon. Tomorrow (Friday) I'll bring the rotary back to the office for some more tests and let you know exactly what happens when I start dialing.

Craterranch

The phones at my office are Cortelco 250000-VBA-20M single-line phones.

G-Man

Quote from: Craterranch on September 17, 2015, 12:48:25 PM
The phones at my office are Cortelco 250000-VBA-20M single-line phones.
Good, they are standard single-line telephones.

Is it a large office with a lot of telephones; enough to require a pbx?

As previously stated, the "specs" call for a line voltage of between 32 to 48-volts @ 20-40ma. Most pbx's provide approximately 24-volts.

G-Man

Also, have you tried connecting your 302 directly without the converter to see if you can dial out?
If not, move the telephone line cord's green wire from P1 to L1 and leave the red on L2 and try to place a call.

Craterranch

I took the phone into the office today and here are the results of different tests:

1) Connected directly to the line (no converter): Dial tone. Incoming calls work correctly. Can't dial out (when I start dialing I can hear a click when the rotation stops, but the dial tone remains).

2) With converter, green on P1, red on L2: Dial tone. Incoming calls work correctly. Can't dial out (when I start dialing I can hear a tone and a click when the rotation stops, but the dial tone remains). Interestingly, dialing 0 gets our company operator, but that's the only outgoing I can do.

3) With converter, green on L1, red on L2: Dial tone. Incoming calls work correctly. Can't dial out (when I start dialing I can hear a click when the rotation stops, but the dial tone remains).

4) With converter, green on L2, red on L1: Dial tone. Incoming calls work correctly. Can't dial out (when I start dialing I can hear a click when the rotation stops, but the dial tone remains).

5) With converter, green on L2, red on P1: Dial tone. Incoming calls work correctly. Can't dial out (when I start dialing I can hear a tone and a click when the rotation stops, but the dial tone remains).

6) Green P1, red L1: No dial tone.

G-Man

Most likely you already knew this but It has now been established that your office telephone system does not support rotary dialing.

Once more, is it a large workplace with many telephones; one that needs a pbx? If so, then, if the manufacturer's specifications are to be believed, a pbx may not be supplying the required voltage. 

Another possibility is that they may be using Centrex, though it may be branded with another marketing name. Do you know who provides their telephone service?  If it is conventional Centrex service then standard +/-48-volts is being used.

If it is being supplied via a VoIP modem from the local cable company, Verizon's FiOS or AT&T's U-verse, then other voltages may be involved.

Craterranch

It is a very large workplace with many telephones; 10,000 at least, spread across several facilities. I do not know whether or not we have a PBX but is sounds reasonable that we do. We can call any phone in the company with a 4-digit extension; do not need to dial area or prefix codes. We have both Verizon and AT&T phone services.

At this point I'm inclined to think that it's a voltage issue as others have suggested. Is this a case of the phone not applying enough voltage? Could I up the phone's capacitor?

I'm also suspicious of the converter. If you see the red-circled part in the image, things don't look exactly right, and not like the manufacturer's image. I'm going to try using it at someone's home (I don't have a land line) and see if it works there. If it does, then I can at least confirm that the converter works.

NorthernElectric

Quote from: Craterranch on September 18, 2015, 11:46:53 AMI'm going to try using it at someone's home (I don't have a land line) and see if it works there. If it does, then I can at least confirm that the converter works.

Try and test it at someone's home that has service that supports pulse dialing so you can test the phone with and without the converter.
Cliff

twocvbloke

Quote from: Craterranch on September 18, 2015, 11:46:53 AMI'm also suspicious of the converter. If you see the red-circled part in the image, things don't look exactly right, and not like the manufacturer's image.

Looking at those badly displaced components, I'd recommend not using it, they seem to have slipped in the solder bath process and could be shorting out other sections of the board, declare it faulty and get a replacement or refund, unless you're handy with repairing electronics on such a small scale it'd be a PITA to re-do (assuming damage hasn't already been done)...

Craterranch

Quote from: twocvbloke on September 18, 2015, 01:44:47 PM
Looking at those badly displaced components, I'd recommend not using it, they seem to have slipped in the solder bath process and could be shorting out other sections of the board, declare it faulty and get a replacement or refund, unless you're handy with repairing electronics on such a small scale it'd be a PITA to re-do (assuming damage hasn't already been done)...

I agree and have already started that process with the seller. They are in China, so fun times ahead. If anyone can recommend a good converter I'm all ears (must have #-key capability).

twocvbloke

Quote from: Craterranch on September 18, 2015, 01:47:39 PMThey are in China, so fun times ahead. If anyone can recommend a good converter I'm all ears (must have #-key capability).

Sometimes you can get lucky with chinese sellers with instant refunds (after all, it costs them virtually nothing to make!!), other times they procrastinate long enough that they escape claimbacks...

As for recommended pulse-to-tone adaptors, there's the Rotatone (fits inside the phone) and the Dialgizmo, plenty of info on those on this forum... :)

Craterranch

I just took this over to a friend's house that has a VOIP line. I got a dial tone, and when I started dialing the tone fell silent and I could hear the tones being sent at the end of the rotation. But, no call was ever placed. Eventually I got a message saying that the number was unrecognized or something like that. When I tried dialing in, you could hear the ringing on the source phone, but not on the 302 or any of the house phones.

19and41

If voltage is the issue, the Dialgizmo unit is able to operate on lower voltages.
"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke

Phonesrfun

Quote from: 19and41 on September 18, 2015, 03:25:59 PM
If voltage is the issue, the Dialgizmo unit is able to operate on lower voltages.

Yeah, but I don't think this thing is a Dialgizmo, and all anyone can do at this point is guess. One thing I have heard about the Dialgizmo is that the capacitors need time to charge up, and so supposedly you can't just plug it in and have it work.  How long it takes to charge, I don't know.  Whether this thing works like that is anyone's guess.
-Bill G