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Old 10th Jun 2021, 2:46 pm   #1
Dave Moll
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Default "Duck" telephone

I have recently acquired the telephone shown below, which has a fault resulting in a very loud buzzing (attached as an MP3 in a ZIP file). As can be seen from an expanded waveform from Audacity (as used to record it) it is basically a triangular wave (with dial tone from my PABX superimposed, though at a much lower level than the buzz).

Microelectronics, as shown in the image of the duck's giblets, are not my forte, so any pointers as to what to check would be appreciated.
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Old 10th Jun 2021, 4:08 pm   #2
merlinmaxwell
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Default Re: "Duck" telephone

It looks to be the same frequency as your dial tone, is it. Does it go away on a silent line?
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Old 10th Jun 2021, 4:35 pm   #3
AndiiT
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Default Re: "Duck" telephone

Hi, it probably wouldn't hurt to change the electrolytic capacitors on the PCB and check the diodes which are connected across the incoming line (A and B legs) which are there to provide polarity reversal protection (they are basically a bridge rectifier with the A and B legs of the line connected to what would be the AC side of the bridge) one or more of these could have gone short circuit

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Old 10th Jun 2021, 5:44 pm   #4
Dave Moll
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Default Re: "Duck" telephone

Quote:
Originally Posted by merlinmaxwell View Post
It looks to be the same frequency as your dial tone, is it. Does it go away on a silent line?
No, it sounds a similar frequency to 50Hz mains hum, whereas the PABX uses the modern (350+440?) dial tone.

It certainly doesn't go away once the dial tone times out (after 20 seconds), though the dial tone is pretty much inaudible anyway over the buzz, so I can't hear when it has stopped.
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Old 10th Jun 2021, 6:15 pm   #5
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Default Re: "Duck" telephone

Is it worth trying swapping the line polarity?

A mate of mine bought a novelty phone back to the UK from the US and although fine in the US it buzzed on speech like mad over here.
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Old 10th Jun 2021, 6:39 pm   #6
merlinmaxwell
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Default Re: "Duck" telephone

Can we have a picture of it open? I love the look.
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Old 10th Jun 2021, 6:54 pm   #7
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Default Re: "Duck" telephone

Given that it's a one-piece instrument, there isn't really an inside (other than the "giblets" shown above), but here is the actual telephone side of it:
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Old 10th Jun 2021, 6:58 pm   #8
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Default Re: "Duck" telephone

Quote:
Originally Posted by McMurdo View Post
Is it worth trying swapping the line polarity?
I'll give that a try by lashing up a socket with reversed polarity.
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Old 11th Jun 2021, 12:03 am   #9
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Default Re: "Duck" telephone

Is it environmental? I'm thinking of a nearby light dimmer or similar.
Also, as this is a new acquisition, has the seller given the mouthpiece a squirt of (electrically conductive) sanitiser that is causing the hum pickup? It's something that generated more than one service call when I used to maintain office phone systems.
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Old 11th Jun 2021, 12:53 am   #10
hamid_1
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Default Re: "Duck" telephone

This brings back some memories for me.
These novelty phones date from the 1990s. From what I remember of the Duck phone, its eyes light up and it makes a "quack-quack" sound when it rings. I don't have one myself, but I do have a couple of different novelty phones, the Hamburger and the Stiletto Shoe. Both were faulty when I acquired them very cheaply from a car boot sale.

Some of my relatives in Canada have an electronics shop. Back in the 90s, they sold a whole range of novelty telephones. Their shop is still in business, though their website doesn't offer any novelty phones at the moment - I guess there's not much demand now. But I do remember they had a quite high rate of customer returns for the novelty and cheap one-piece phones on which they are based. They were all hastily assembled in Hong Kong or China. Some were faulty when taken out of the box brand-new. I remember visiting the shop and going through a boxful of faulty phones, testing them on a Radio Shack telephone line simulator and trying to fix some of them. Bad soldering and even wrong components fitted were some of the faults I came across, as well as faulty dialler ICs. Also, these phones sometimes get dropped on the floor, resulting in cracked print on the PCB or dry joints opening up. The hook switch was another thing that could go faulty.

I hope the above may give you some clues when fault-finding, but as I said, they weren't the most reliable things even when new; they were essentially throwaway novelties. If all else fails, keep it as a display piece. You may get another one with a different fault and be able to make one good one out of two.
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Old 11th Jun 2021, 8:09 am   #11
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Default Re: "Duck" telephone

Quote:
Originally Posted by hamid_1 View Post
From what I remember of the Duck phone, its eyes light up and it makes a "quack-quack" sound when it rings.
This is indeed the case. These functions are in working order. The eyes also glow when a loop is made (and therefore flash during loop-disconnect dialling). Both LD and DTMF dialling work correctly.

Quote:
Originally Posted by hamid_1 View Post
Bad soldering and even wrong components fitted were some of the faults I came across, as well as faulty dialler ICs. Also, these phones sometimes get dropped on the floor, resulting in cracked print on the PCB or dry joints opening up. The hook switch was another thing that could go faulty.
Having removed the single screw holding down the circuit board, a visual inspection of the soldering reveals nothing untoward, but something is clearly making a bad connection, as moving the circuit board around can cause intermittent increase of the buzz by several decibels. It appears that closer inspection of the wiring is needed.

Quote:
Originally Posted by hamid_1 View Post
They weren't the most reliable things even when new; they were essentially throwaway novelties. If all else fails, keep it as a display piece. You may get another one with a different fault and be able to make one good one out of two.
I do in fact already have the larger two-piece version (in full working order), but had not come across this one-piece type before, and felt it would make a nice companion. Apologies for the camera shake on the picture of the handset - even on the second take!
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Old 11th Jun 2021, 1:26 pm   #12
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Default Re: "Duck" telephone

Quote:
Originally Posted by Dave Moll View Post
Quote:
Originally Posted by McMurdo View Post
Is it worth trying swapping the line polarity?
I'll give that a try by lashing up a socket with reversed polarity.
Unfortunately, swapping polarity makes not a ha'peth of difference.
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Old 11th Jun 2021, 2:14 pm   #13
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Default Re: "Duck" telephone

Quote:
Originally Posted by rambo1152 View Post
has the seller given the mouthpiece a squirt of (electrically conductive) sanitiser that is causing the hum pickup?
I don't know whether sanitisation was the cause of a microphone problem, but while I was poking around checking component values, one lead from the microphone came adrift - and I found that with this now out of circuit I got a nice clear dial tone with no buzz. Once I soldered the lead back in place, the buzz returned. This at least narrows the problem down to the microphone circuit, even if not necessarily the microphone itself.

Whether I can source a replacement microphone is, of course, another matter.
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Old 11th Jun 2021, 3:02 pm   #14
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Default Re: "Duck" telephone

Good news and bad news.

The good news is that I have indeed found an identical microphone from the handset of a dead Duet 200 telephone - and the problem of the buzz is solved.

The bad news is that I now have a new problem to track down. I must have disturbed something else, as the duck has lost its "quack". There is neither sound nor flashing eyes on an incoming call. These were both working before.

Edit: ignore the above sentence. What I had disturbed was the "ringer on/off" switch. Unfortunately, in the "on" position I now get a continuous "quack, quack, quack ..." while the 'phone is on-hook - the equivalent of the continous ringing that can occur if A and B legs are transposed on a three-wire connection. Only this uses a two-wire connection.
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Old 11th Jun 2021, 7:40 pm   #15
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Default Re: "Duck" telephone

I've found a stray strand of wire that was shorting out two contacts of the "hook" switch. Having removed that short, everything now seems to be working as it should - no buzzing, and only quacks when rung.

I think, however, that I shall tidy up the wiring before reassembly, as it would be all too easy for adjacent wires to touch each other as it stands.
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Old 11th Jun 2021, 8:29 pm   #16
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Default Re: "Duck" telephone

I just read through the thread from beginning to end and by about half way through I was thinking 'I know what this is' because the electret microphone elements in some gear we make at work commonly fail in that way, producing a loud buzz instead of the expected audio output. Replacement of the microphone element always fixes it.

And then when I got to the end I discovered you had already found that out.
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Old 12th Jun 2021, 1:17 pm   #17
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Default Re: "Duck" telephone

I regret that my elation at getting this working has been short-lived. Having tidied up the wiring around the "hook" switch (removing the excess bare ends to the wires which were providing opportunity for them to short against each other and resoldering more neatly), with the 'phone now in full working order, I screwed the innards back into the body. The next time I rang it up and went off-hook, I was treated to a bust of buzzing even louder than the original followed by silence (no response to sound) from the transmitter insert. It would appear that the replacement has died. I have checked its wiring and everything appears to be solid.

I am setting this aside for the time being.
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Old 13th Jun 2021, 10:37 pm   #18
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Default Re: "Duck" telephone

Quote:
the problem of the buzz is solved
I bet that was the fault with my mate's phone from America. His house in the UK was a terraced house that suffered from damp. I wonder if it spoiled the mic capsule.
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Old 14th Jun 2021, 9:42 am   #19
Craig Sawyers
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Default Re: "Duck" telephone

This thread is quackers

I'll get my coat....

Mods delete as necessary
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Old 14th Jun 2021, 3:49 pm   #20
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Default Re: "Duck" telephone

Old Electret-capsules do seem somewhat fault-prone, I guess they're a bit like the crystal microphones/gramophone pick-ups of yesteryear that often don't age gracefully (I have had problems with electret capsules in two-way-radio mobile microphones - the temperature/humidity excursions inside a car can't help their longevity).

Good to hear you solved your duck's problem though! I've always had a bit of a weakness for 'gimmick phones'.
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