Paired a 51AL to a 584-A subset - troubleshooting help please

[Nortonics]

Hello everybody - new member in the ranks.  Great forum - thanks for having me.

Need some help! Purchased a 51AL candelstick some time back, and now recently purchased a refurbed 584-A subset. Straightforward connections - three wires - yellow, green and red.

Plug it in and lift the receiver and get dial tone. Can hear my voice back into the receiver (sidetone unit). Hang it up and call it with the cell phone, it rings, I pick it up, audio is good both directions. Hang up. Lift receiver, get dial tone, dial a phone number, it clicks away and dial tone goes away, but it never connects the call - just dead air as if it didn't recognize the dial pulses. I connect a different dial phone to the line and that works correctly. My telephone service connection terminates into a Cisco cable/telephone modem (DPC3208) with services supplied by Charter Communications.

I've verified with an ohm meter that all contacts are in fact working correctly on the dial. As well, disconnected from wall, attaching an ohm meter across the red and green wires I get:

- on hook: open
- off hook: about 200 ohms. I presume this is the resistance of the receiver and mouthpiece while in-circuit?
- holding dial on-return to close dial contacts: about 20 ohms. Seems odd to me. I was thinking maybe it should be zero ohms/shorted?

It does pulse the line during the full dial return. Return action is good although a little bit labored - not a perfectly timed/stable return, but not real bad either.

Here's the 51AL schematic along with a similar subset attached:

http://telephonecollectors.info/index.php/component/docman/doc_details/2124-desk-stands-51al-tl?Itemid=11

And a couple pics of my actual items:





I can get even closer shots if needed.

I'm at a standstill here. Thoughts, anybody? Anything glaring?

Thanks for your thoughts!


Tom

[poplar1]

Tom, it appears to be wired correctly. 

Since the dial tone goes away after dialing the first digit, the modem is apparently registering the first pulse of that dial pull, but not the rest. My guess is that the dial speed is not precise enough (i.e. close enough to 10 pulses per second) for the modem. You can get a rough idea of the speed by simultaneously releasing the 4H dial and the working dial.

If you know someone with a traditional POTS line (landline), you may find that the 51AL will work there without any modification. If so, you will need to clean the dial and perhaps adjust the speed.

You are reading 20 ohms rather than 0 because the primary of the induction coil (L1 and R) is still in the circuit while the dial is held. In a 302, the dial completely shorts the line because R of the dial is jumpered to L1, rather than to R, on the induction coil. Either method produces a square wave (0 and infinity, or 20 and infinity, not counting the loop resistance) to the dial central office while the dial is pulsing.

[Phonesrfun]

I agree that dial speed is probably the issue here. You might also consider sending the dial to Steve Hilsz for cleaning and alignment. 

[unbeldi]

One aspect you have to consider though is that your telephone appears to have a No. 4H dial, while most or all diagrams show a 2A dial for that desk stand, including the diagram you are quoting.

The 4H has an additional terminal R which splits the W/BB/BK switch into two separate switches, W/BB and R/BK.  To make them equivalent, a short jumper wire needs to be installed on the 4H that connects the R and BB terminals.  This does appear to be installed on your dial, I think I see some kind of brass bridge.

The primary winding of the induction coil remains in the switching path.  The resistance of that coil in the No. 46 induction coil is about 14 Ω, so that is your lower bound for measurements.  If you're measuring 200 Ω when the dial is pulled, then I am suspicious. Perhaps the dial pulses are actually flowing through the transmitter, resulting in very unreliable dialing, especially when the loop current comes from an ATA on voip.   What is the line voltage on the DPC3208 ? How much current flows when the loop is shorted directly with an ammeter?

Perhaps you can measure the loop current when the dial is pulled. It may be too low for the proper signaling on the ATA.

This could indicate a poorly working transmitter shunt by switch BB/BK on the 2A or BK/R on the 4H dial.  This is exactly the problem area of the difference between those dials. So please check this out in detail, we can't really see the details of wiring on the pictures.


PS: I misread your earlier description of your measurement.  You are measuring 20 Ω, so that is ok.