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Old 20th Mar 2015, 6:21 pm   #1
PaulR
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Default 150 Telephone dialling fault

I have a 150 series phone that works perfectly except that it "mistakes" a 9 for a 0. If I dial my mobile number which starts 07799 I get 07700 unless I keep my finger in the dial hole which makes it dial the correct number. The points open and close the correct number of times.

It seems as though it may be dialling too fast, but I would think that would cause it to miss a pulse rather than adding one. The fault happens every time I use it.

Can anyone help?

Thanks

Paul
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Old 20th Mar 2015, 7:41 pm   #2
ThePillenwerfer
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Default Re: 150 Telephone dialling fault

Dialling a 0 should take a second.

Have you got a dial 'phone that you know works? If so dial 0 on both and release the dials at the same time and see which one finishes first.

- Joe
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Old 20th Mar 2015, 9:34 pm   #3
dagskarlsen
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Default Re: 150 Telephone dialling fault

It may be measured pretty well without the signal generator too.

http://tinyurl.com/ppb2j7t

dsk
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Old 21st Mar 2015, 9:55 am   #4
PaulR
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Default Re: 150 Telephone dialling fault

I have checked it against a correctly operating 300 series phone and it actually takes slightly longer on the 150 to dial 0.

Paul
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Old 21st Mar 2015, 10:33 am   #5
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Default Re: 150 Telephone dialling fault

I've been following this thread, and am interested in the use of Audacity to view the performance of a dial. I've just started to play around with Audacity (complete novice with this), and would be interested to know how to go about linking a phone to the PC in order to view the characteristics of a dial. Seems that this is potentially a very useful program.
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Old 21st Mar 2015, 12:40 pm   #6
PaulR
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Default Re: 150 Telephone dialling fault

On further investigation, it doesn't matter whether I use my finger in the 9 hole to slow the dial return down or to speed it up, it still dials the correct number. It only displays the fault if I leave it to return naturally.
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Old 22nd Mar 2015, 10:40 am   #7
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Default Re: 150 Telephone dialling fault

I wonder if it isn't overtravelling and sending an extra pulse?

There were two kinds of dial mechanisms. Early ones relied on metal-to-metal friction to prevent pulsing during the "wind-up". Later ones work by having a pawl which catches in a slot in a plate as the dial reaches the finger stop, and is pushed out as it returns to its rest. It's much easier to understand from looking at, than to describe.

Whichever kind of dial you have, look for worn parts that may be causing an extra pulse to be emitted.
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Old 22nd Mar 2015, 5:04 pm   #8
PaulR
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Default Re: 150 Telephone dialling fault

It is a No 10 dial. On playing with it further it seems that the dialling is simply unreliable, not just on the 9. It doesn't really seem to be worn as far as I can tell. I have tried cleaning the contacts as best I can with switch cleaner but it hasn't helped. Keeping my finger in the dial hole does still help.

I have come across this http://www.samhallas.co.uk/repository/po_docs/B5126.pdf which is a GPO instruction sheet for the dial. It seems to be adjusted according to that but I wonder whether the best way forward would be to take it apart, clean it all and reassemble it.
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Old 22nd Mar 2015, 5:21 pm   #9
julie_m
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Default Re: 150 Telephone dialling fault

Well, a good field-strip and relube never hurt anything mechanical. You've little to lose by following the GPO instructions, anyway.
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Old 23rd Mar 2015, 12:30 am   #10
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Default Re: 150 Telephone dialling fault

Paul

I've no experience whatsoever with the Series 150 telephones, but are these two GPO Engineering Instructions detailing two telephone dial variants relevant to what you have.......

http://www.britishtelephones.com/tel%20auto%20b5126.htm

http://www.britishtelephones.com/tel%20auto%20b5125.htm


Chris
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Old 23rd Mar 2015, 12:58 am   #11
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Default Re: 150 Telephone dialling fault

I had a problem with a Number 10 mis-dialling which turned out to be due to having not put the "Forked Stop" back properly after changing the Governor Gear.

- Joe
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Old 23rd Mar 2015, 7:05 pm   #12
PaulR
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Default Re: 150 Telephone dialling fault

Thanks all. Rather than dismantle it all I think I will borrow my son's oscilloscope and see whether I can get a trace of what is happening. Audacity as suggested earlier in the thread is also a possibility.

Thinking about it, if it dials properly if I put pressure on the dial as it returns might suggest that the spring is at fault. The actual return time is pretty good compared with a working phone.

I have tried the "Forked Stop" in its other position and it would not send any pulses at all.

Very odd

Paul
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Old 24th Mar 2015, 4:00 pm   #13
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Default Re: 150 Telephone dialling fault

When the dial returns, it starts sending breaks 9=9 breakes, 0=10. When the dial comes close to rest position, it should engage 1 of 2 depending of construction:
1 a mechanical "finger" stopping the unit making the breakes. or
2 engaging a contact shorting the circuit making the breakes.
This mechanical thing may be slightly out of position, and when you touches the dial during return, it works OK.

The most typical are something like on this picture.

Adjustment in the upper right area may solve it. The ideal speed and rate are 10 pulses pr second, and 66% break.

By my experience it may not be very accurate to work OK.

dsk
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