701B Princess voltage issue?

[AL_as_needed]

Some time ago now I put a WE 701B together. Took a while but I got the correct ringer and wired in a 12v wall wort for the "night light" feature. All in all the phone works well, but I noticed something when its hooked up with others on the same line.

When the 701B is plugged in, I get an odd hum or low buzzing when I pick up the receiver of say my 500 or 554. Is this normal? Do these "bleed" some voltage into the line? When I put my 302 into the same system, the hum goes away... (good old 302 REN..?)

[Alex G. Bell]

Some time ago now I put a WE 701B together. Took a while but I got the correct ringer and wired in a 12v wall wort for the "night light" feature. All in all the phone works well, but I noticed something when its hooked up with others on the same line.

When the 701B is plugged in, I get an odd hum or low buzzing when I pick up the receiver of say my 500 or 554. Is this normal? Do these "bleed" some voltage into the line? When I put my 302 into the same system, the hum goes away... (good old 302 REN..?)

It's not normal.  It sounds like perhaps there is a connection between the light circuit and the telephone line inside the phone. 

Even though the lamp transformer secondary winding is normally and presumably isolated from the AC line, if there is a connection between the telephone line and the lamp circuit, capacitance between the transformer primary and secondary would unbalance the phone line causing a faint hum or buzz.  You need to make resistance measurements between the lamp transformer leads and the line leads.  This also assumes you are using at least a 4 conductor line cord with separate lead for the line and light circuits.

Also, if you are using a standard #46 miniature screw based lamp or #259 wedge based lamp, they're rated 6.3V 250mA.  They will have a short life and may cause discoloration of nearby dial parts due to excessive heat if operated at 12V.  The 27 ohm dimming resistor may also overheat.

[AL_as_needed]

This also assumes you are using at least a 4 conductor line cord with separate lead for the line and light circuits.

Also, if you are using a standard #46 miniature screw based lamp or #259 wedge based lamp, they're rated 6.3V 250mA.  They will have a short life and may cause discoloration of nearby dial parts due to excessive heat if operated at 12V.  The 27 ohm dimming resistor may also overheat.

I checked the line cord (original to the phone) and there was no issues there, all lines within the cord are isolated. Double checked my wall wort after you mentioned the voltage risks...lucky for me Its actually a 5v output....so one positive point there.

Doesnt the lamp circuit have capacitance built in for the hi/lo light function? I will need to take apart the phone and look for any issues in the hook switch. I have a suspicion the issue could be in there as rest of the wiring looks solid.

[Alex G. Bell]

I checked the line cord (original to the phone) and there was no issues there, all lines within the cord are isolated. Double checked my wall wort after you mentioned the voltage risks...lucky for me Its actually a 5v output....so one positive point there.

Doesnt the lamp circuit have capacitance built in for the hi/lo light function? I will need to take apart the phone and look for any issues in the hook switch. I have a suspicion the issue could be in there as rest of the wiring looks solid.

No, the lamp dimming function uses a 27 ohm resistor.

Taking the phone apart to inspect it may not locate the problem.  If you have a meter and can check resistance between the line and transformer terminals that's a much more certain way to determine whether that is the problem before looking visually for something which may not be there or may not be detectable visually.

Before doing anything inside the phone you should disconnect the lamp transformer from the AC wall outlet to see whether that makes the hum/buzz you hear in other phones when the Princess is connected to the line go away.

[AL_as_needed]

Before doing anything inside the phone you should disconnect the lamp transformer from the AC wall outlet to see whether that makes the hum/buzz you hear in other phones when the Princess is connected to the line go away.

This is actually what lead me to the 701 as the cause. For a short time I thought it was my yellow WE 554, as I noticed the hum/buzz testing that unit. Several phone swap outs latter, and I had my culprit. I'll go in-depth with the phone tomorrow. For now I'm leaving the transformer unplugged. Do not want the extra current messing up my XLink.

[Alex G. Bell]

This is actually what lead me to the 701 as the cause. For a short time I thought it was my yellow WE 554, as I noticed the hum/buzz testing that unit. Several phone swap outs latter, and I had my culprit. I'll go in-depth with the phone tomorrow. For now I'm leaving the transformer unplugged. Do not want the extra current messing up my XLink.

I thought you originally said you disconnected the Princess from the line rather than leaving it connected to the line and disconnecting the transformer from the wall.

[AL_as_needed]

Sorry for any confusion.

When I was narrowing down that the princess and its transformer were the issue, I did connect and disconnect the phone and the wall wort to help identify the princess as being the source of the issue. 

With the transformer disconnected from the wall outlet, the 701 is more or less like any other rotary phone in terms of how it is interacting with my phone line, at least I assume so....

I checked the line cord with the phone disconnected as well as the transformer, but for the night i'm leaving it on the line w/o the transformer (that way if my cell should ring for a work emergency, I can answer fairly close to the bed).

[Alex G. Bell]

Sorry for any confusion.

When I was narrowing down that the princess and its transformer were the issue, I did connect and disconnect the phone and the wall wort to help identify the princess as being the source of the issue. 

With the transformer disconnected from the wall outlet, the 701 is more or less like any other rotary phone in terms of how it is interacting with my phone line, at least I assume so....

Dunno what you mean by "interact" and "assume so". 

When any Princess is working properly it is like any other phone whether the transformer is plugged in to the wall or not.  The lamp circuit is isolated from and has no effect on the line.  However if there is an inadvertent connection between the lamp and line circuits then it can introduce noise on the line when the transformer is plugged in for the reason I stated in my first reply.

I checked the line cord with the phone disconnected as well as the transformer,

Checked by what method?  Visual inspection?  With a meter?

but for the night i'm leaving it on the line w/o the transformer (that way if my cell should ring for a work emergency, I can answer fairly close to the bed).

Sure.  Do whatever you need to do for the immediate moment to deal with everyday life.

Questions about the Xlink and lamp transformer:

Is the Xlink powered by a wall wart? 

If so does the wall wart have a 2-blade or 2-blade plus round ground pin ("3-pin" or "3-wire" plug?  If not does the AC power cord have 2 or 3 pins?

If it has 3 pins is it plugged into a 3-wire (grounded) outlet?

Same questions about the lamp transformer.

[AL_as_needed]

I totally agree with your initial response, however only having worked on and using one 701B, I was unsure of that was potentially a normal condition of these units, or it was a genuine issue.... as I now know it is, thanks to your input.

Xlink Answers:

Yes it is powered by a wall wort, non grounded (two blade plug) . princess is powered by similar, output voltage and amperage is different as per the needs of both.

I am assuming that the Xlink is not the source of the issue on the simple fact that this hum only arises when the 701 is on the line.

Line cord inspection:

Done at first visually, looking for any immediate signs of cuts/breaks etc, and then checked with a multi-meter. First by simply looking for any continuity between the four lines, then by applying 9volt DC current to on pair and looking for any "bleeding" on the other pair. (Process repeated between all pairs), and the line cord has been shown to be fine.

"Interact" as in how the phones and the system (phones on the line within the confines of my dwelling) affect one another when they are on the line. For example; I have a dutch PTT that likes to ring softly when I dial on another WE set on the same line.

"Assume so".....I'm making an educated guess based on what I know/see/understanding of how these phones work, personal turn of phrase. I am in no way an engineer, so this is all just advanced "redneck" thinkery with the help of CRPF and TCI   

[Alex G. Bell]

I totally agree with your initial response, however only having worked on and using one 701B, I was unsure of that was potentially a normal condition of these units, or it was a genuine issue.... as I now know it is, thanks to your input.

Xlink Answers:

Yes it is powered by a wall wort, non grounded (two blade plug) . princess is powered by similar, output voltage and amperage is different as per the needs of both.

I am assuming that the Xlink is not the source of the issue on the simple fact that this hum only arises when the 701 is on the line.

Line cord inspection:

Done at first visually, looking for any immediate signs of cuts/breaks etc, and then checked with a multi-meter. First by simply looking for any continuity between the four lines, then by applying 9volt DC current to on pair and looking for any "bleeding" on the other pair. (Process repeated between all pairs), and the line cord has been shown to be fine.

"Interact" as in how the phones and the system (phones on the line within the confines of my dwelling) affect one another when they are on the line. For example; I have a dutch PTT that likes to ring softly when I dial on another WE set on the same line.

"Assume so".....I'm making an educated guess based on what I know/see/understanding of how these phones work, personal turn of phrase. I am in no way an engineer, so this is all just advanced "redneck" thinkery with the help of CRPF and TCI   

Thanks for your clarifications. 

Regardless of the results of your tests and inspections, I don't think you've answered the question of whether the buzz/hum goes away if the Princess is connected to the telephone line (Xlink actually) with the lamp transformer/wall wart unplugged.  If you did, I missed it.

If it does that indicates there is some internal electrical leakage between the lamp circuit and the speech circuit inside the phone but the leakage is too small to detect with the meter you used or perhaps the way you performed the test.

To proceed you need to determine whether the hum/buzz goes away when the Princess is connected to the line with the transformer disconnected from the AC power wall outlet.

[AL_as_needed]

Thanks for your clarifications. 

Regardless of the results of your tests and inspections, I don't think you've answered the question of whether the buzz/hum goes away if the Princess is connected to the telephone line (Xlink actually) with the lamp transformer/wall wart unplugged.  If you did, I missed it.

If it does that indicates there is some internal electrical leakage between the lamp circuit and the speech circuit inside the phone but the leakage is too small to detect with the meter you used or perhaps the way you performed the test.

To proceed you need to determine whether the hum/buzz goes away when the Princess is connected to the line with the transformer disconnected from the AC power wall outlet.

I may/ may not have been direct but yes, the hum goes away when the wall wort is unplugged while the princess is left on the line. It is likely that the insulation on the phones internal wiring has deteriorated and making contact somewhere. I will perform a continuity test between the lamp and talk circuits within the phone and back-track anything that comes up.

[Alex G. Bell]

I may/ may not have been direct but yes, the hum goes away when the wall wort is unplugged while the princess is left on the line. It is likely that the insulation on the phones internal wiring has deteriorated and making contact somewhere. I will perform a continuity test between the lamp and talk circuits within the phone and back-track anything that comes up.

Good. 

There is another aspect of the connection of the Princess and wall wart I did not think to ask about.  What happens if you unplug the Princess from the phone line (Xlink) but leave the wall wart plugged into the AC outlet?  Is there hum in this case or not?

[AL_as_needed]

There is another aspect of the connection of the Princess and wall wart I did not think to ask about.  What happens if you unplug the Princess from the phone line (Xlink) but leave the wall wart plugged into the AC outlet?  Is there hum in this case or not?

Good question! I'll try that later and report back.

[AL_as_needed]

So the plot thickens....

The hum is only present when the wall wort AND the phone is connected to the line (plugged in). I did consider that maybe the xlink and the princess light wall wort were on the same electrical circuit and that one or the other was putting out "noise" into the circuit causing the other to have irregular voltage, but not the case. I tried other outlets and wall jacks and the hum was the same.

But...

Turns out after some poking around with my multi meter and finding nothing in the way of stray voltage....the hum is only there when the princess 1) has its light circuit plugged in 2) the handset is hung up/light is off.   

Lastly, not sure if i mentioned this earlier; the hum can only be heard on another set, and not on the princess. For example if the princess is on the hook (hung up)   and I pick up the handset on my 554, 302, etc (or any other in my collection as I swapped them around just to test) I hear it.

[poplar1]

Is the transformer output connected only to the one jack where the 701B is connected?

In other words, the transformer output should not back feed to other jacks. If your jacks are daisy chained, then you could disconnect the 2nd pair (black and yellow, or white-orange/orange-white) of the inside wire from the jack where the transformer is connected.