Identify and fix a (perhaps) GPO 746

[Antonio]

I am trying to revive my old rotary phone. I used it in the past until the early 2000's as far as I can remember.

I believe the phone to be a GPO 746, but that is one of the reasons of this post, to help identify it.

The "flywheel" has stamped on: "TVR 12" and "468A".





Besides identifying it I have issues with its working, or lack of it. I can receive calls, the incoming part is ok.

But when I dial numbers I'm not connecting with the correct number.
Example: I dial my own cellphone number and an old lady picked up, I tried to ask what her number as so I could try and debug the issue but she didn't know her own number and I didn't want to bother her more, let alone try and explain why I, a random man, should be calling her.
 
If I call other numbers that I know and whose owners are standing beside me, I get the calling tone on the handset but none of my friends phones ring, so I'm calling someone else.
Other times I end up getting the "unconnected phone number" and sometimes it hangs as if there is 1 missing number to dial.

I Guess that some of the numbers aren't being dialed correctly. I know that the numbers 9 and 2 are ok because we start all of our phone numbers with either a 9 or a 2.

I've open the phone and tried to clean it with WD contact cleaner but I just spray it randomly because I don't really know how phones work.





I was hoping anyone could help with identifying my phone, point me how to clean it and help me use it!

thank you and sorry if my english is not perfect. I have more photos of the dial mechanism.

[HarrySmith]

I am not familiar with European phones. There are some very smart European members here that I am sure will chime in. First, WD-40 is not a good thing for phones. I would recommend using some type of spray cleaner to remove all that. I am not sure what you have over there but I use automotive brake cleaner, there is aslo electronic contact spray cleaners available. Then use compressed air to dry it out. As far as calling out do you know if your service provider supports pulse dialing?

[countryman]

I'll second Harry's advice. I had good results from auto brake cleaner. It normally does not harm most plastic materials, but better keep it away from the phone shell, fingerwheel etc. and use it sparingly on the metal parts and the contact side of the dial. It is a very efficient degreaser, the pivoting points might require a very slight lubrication after cleaning. Quality sewing machine oil normally can be used in very small amounts.
Classic switching equipment is no longer used on the network operator side. Modern computerized interfaces have taken over, often right at the subscriber's premises in form of voice over internet protocol (VOIP) analog adapters. Your line apparently supports pulse dialing, as you could make a connection at all. Typically the VOIP equipment is not tolerant with sticky dials and oxidized contacts. Try cleaning, chances are good this will make the phone fully usable.
In fact the design and the schematic of your phone is very similar to a GPO 746:
https://www.britishtelephones.com/diagrams/n846.pdf
However, it might be a AEP 7: https://museu-telecom.pt/telefones/page/2/
https://museu-telecom.pt/fabricante-ou-marca/aep/

[tubaman]

That looks like a Portuguese version of a GPO phone and as long as it's wired as per the diagram it should work ok. Before attacking the dial with any chemicals I'd gently run some clean paper though the contacts to clean them. If it's running obviously slow then a tiny spot of oil on the bearings at each end of the governor can often sort it.

[TelePlay]

Before attacking the dial with any chemicals I'd gently run some clean paper through the contacts to clean them. If it's running obviously slow then a tiny spot of oil on the bearings at each end of the governor can often sort it.

I'd agree.

That dial looks pretty clean and that type of dial doesn't have complex places for crud to build up. A bit of good oil on bearing points may help but it would be good to know the dial speed before oiling.

If you search the forum for the word "audacity" you will find a lot of topics on how to determine the dial speed.

Also, can you flatten out that wiring diagram and post a picture with the whole diagram in focus. If so, we can add it to the fitting diagram board.

[HarrySmith]

I only recommended cleaning due to the fact he already used WD-40 on it. I thought it would be a good idea to get all that off before it gums things up

[LarryInMichigan]

The shell of the phone looks like a GPO 706.

Larry

[tubaman]

The shell of the phone looks like a GPO 706.

Larry

Agree, but the circuit board is neither 706 nor 746, and the base, with its ringer volume control and very small sound holes is not GPO type either.

[Antonio]

thank you all for your help, I'll try to address all of it!

First, WD-40 is not a good thing for phones. I would recommend using some type of spray cleaner to remove all that. As far as calling out do you know if your service provider supports pulse dialing?

I Used WD40 Contact Cleaner, not regular WD40. Did I still messed it up?
I'm assuming my service provider supports the dialing because I got to speak with an unknown old lady from a "mistake" dial. And many other calls I try to make I get the "calling sound".

Quality sewing machine oil normally can be used in very small amounts.
Try cleaning, chances are good this will make the phone fully usable.
In fact the design and the schematic of your phone is very similar to a GPO 746:
https://www.britishtelephones.com/diagrams/n846.pdf
However, it might be a AEP 7: https://museu-telecom.pt/telefones/page/2/
https://museu-telecom.pt/fabricante-ou-marca/aep/

I have WD40 Silicone Lubrificant, will this work for oiling or big no no?

I'm now fully convinced it's an AEP 7!!

Before attacking the dial with any chemicals I'd gently run some clean paper though the contacts to clean them. If it's running obviously slow then a tiny spot of oil on the bearings at each end of the governor can often sort it.

The contacts are the small black dots that "open" or "close" when we engage the flywheel?

I only recommended cleaning due to the fact he already used WD-40 on it. I thought it would be a good idea to get all that off before it gums things up

I think I will clean it all allover again in the next couples of days!

That dial looks pretty clean and that type of dial doesn't have complex places for crud to build up. A bit of good oil on bearing points may help but it would be good to know the dial speed before oiling.

If you search the forum for the word "audacity" you will find a lot of topics on how to determine the dial speed.

Also, can you flatten out that wiring diagram and post a picture with the whole diagram in focus. If so, we can add it to the fitting diagram board.

To my untrained eyes I would say everything was clean... But I took a piece of paper with that contact cleaner fluid and I bits of dark "trash" did come out, but very small amounts really.

What are the bearing points?

I will provide a better image of the diagram! I dont want to unstick it from it's shell But I'll take better photos and flatten it in photoshop.
I will look into audacity here in the forum, thank you!

Yesterday I noticed that when I "dial the dial" tiny sparks are seen in the black dots that actuate when the "numbers cog" opens and closes those 2 black dots, this is normal?

Again, thank you all!

[HarrySmith]

Contact cleaner is fine, that's what I recommended to clean it. Silicone is not a good idea for the dial. As previously stated light sewing machine or clock oil is fine. I bought a small tube with a needle point many years ago and still use it. Only a very small amount is needed, a drop or two in certain spots. There is a great topic on here about cleaning & lubricating dials.

[TelePlay]

https://www.classicrotaryphones.com/forum/index.php?topic=7899.0

The caution of using solvents to clean a dial with plastic is having the solvent eat away at the plastic parts. There are different types of materials used to make the plastic parts, some of which are more resistant to solvents, others may not be.

[dsk]

I,m a little late in this thread, so it looks like the cleaning and oiling is don already. I have been told about problems coming long time after using silicone oil, but I have not tried it out. I have used regular WD40 a lot of times. Thespeed adjusting system are not happy eith oil, but may be cleaned with alcohol.  The speed of the dial should be slightly more than 1 second from you release the 0.  The systems will usually accept it with +/- 20%.

[TelePlay]

1)  I Used WD40 Contact Cleaner, not regular WD40. Did I still messed it up?

2)  I have WD40 Silicone Lubricant, will this work for oiling or big no no?

3)  The contacts are the small black dots that "open" or "close" when we engage the flywheel?

4)  I think I will clean it all allover again in the next couples of days!

5)  To my untrained eyes I would say everything was clean... But I took a piece of paper with that contact cleaner fluid and I bits of dark "trash" did come out, but very small amounts really.

6)  What are the bearing points?

1)  I looked up the MSDS for WD-40 Specialist® Contact Cleaner and it appears to be a good spray cleaner/degreaser that is free of a lubricant component. It contains 70-80% Heptane, 10-20% Isoparaffinic Hydrocarbon and <20% 2,2,4-Trimethylpentane. All components seem to completely evaporate after use. As such, this would be a good vehicle to remove grease and crud from a dial - spray on the dial mechanism and after a few seconds, clear the solvent with compressed air (note: this will also remove much of the oil/lubricant need for proper dial operation - the dial bearing points and gear faces will need to be lubricated with a proper lubricant after cleaning or the dial will run slow.

2) WD-40 is not recommended as a dial lubricant in that it dries out after a short period of time causing the dial to run slow and if silicone is present in the lubricant, it will contaminate all mechanism surfaces (sprayed on) including the inside of the governor raceway which will cause the dial to run fast - only dial disassembly and cleaning of surfaces with lacquer thinner will remove the sprayed on contaminant. WD-40 was developed as a spray to replace water, displace water on metal surfaces, not lubricate the items.

3)  The contacts are the points on the end of the leaf spring switches. In the attached image, the pulse contacts are in the red box, the mute circuit contacts in the blue box. These contacts, when made, were coated in a rare earth metallic coating that would keep the contacts from corroding over time. This was a very thin layer and using anything other than a strip of heavy (cardstock) paper to clean them will remove the thin coating and ruin the dial contacts. While the rare earth contacts will not corrode, they can accumulate a build up of crud (oil mixed with dust) over time and running a strip of paper through the contacts (when closed) 2 or 3 times will remove the crud.

4)  Every time you clean the dial with a solvent, liquid or spray, you MUST re-lubricate the bearing points and gear teeth (green circles in the attached image). Lubricant must be applied with a pointed object (a 20 gauge bare copper wire or similar object) to insure the lubricant is applied to the bearing points and gear teeth only, to avoid getting any oil in the governor raceway (yellow arrow in the attached image). Repeated cleaning with new lubrication will cause the dial to run slow.

5)  Unless you take a dial apart and clean each piece in a good liquid solvent (I use lacquer thinner), there will always be some residue on the dial mechanism. As long as the governor shaft teeth and worm gear are clean, other oily residue on non-working surfaces doesn't affect anything. The bearing points and worm drive must be clean and lubricated and the governor raceway  (and the half rubber brakes on the ends of the governor fly wings must be free of any/all lubricants).

6)  Bearing points are where the gear/drive axels rest and turn (green circles in the attached image). AE type dials have fewer axle bearing points that WE dials in that WE used gear trains to drive their governor and dial mechanisms. Whenever two metal points are in contact with each other and one of the metal parts moves during dialing, that point must have lubrication to keep the dial from slowing or not working properly.

All of the above and more, for different dials, can be found in this Forum Board:

      https://www.classicrotaryphones.com/forum/index.php?board=25.0

[Antonio]

Thank you very much for your explanations! I haven't been able to be around the mechanism again but I plan to take it apart and clean everything up and then get some sewing machine oil as advised and use it very gently in the parts indicated by you.

There is a yellow wire that is unconnected on the board, is this normal?

[TelePlay]

. . . I plan to take it apart and clean everything up and then get some sewing machine oil as advised and use it very gently in the parts indicated by you.

There is a yellow wire that is unconnected on the board, is this normal?

I would not try to take that dial apart. Plastic gears and the other plastic parts can become brittle over time and some may be press fit together. Breaking a plastic part is an unrecoverable event, the dial becomes junk.

You said it misdials numbers. The first thing you need to do is analyze your dis dial, determine your dial speed and check its Break/Make ratio. The Western Electric dial specs are 8-11 PPS with a 60 +/- 5 Break/Make ratio. Other parts of the world have slightly different but similar specs.

There are a lot of topics on the Forum discussing dial speed measurement. If you use the Forum search function for "Audacity," you'll find many of them. This is a link to one of my posts which kind of summarizes dial speed measurement.

Dial speed measurement using Audacity

That will tell you everything about your dial. Once you "see" what your dial is doing when pulsing, you will know how to proceed.

========

As for the unconnected yellow wire, the right side of your wiring diagram shows 2 line cord conductors coming into your phone (L1 and L2). These are usually the red and green conductors of the line cord. The typical line cord has 4 conductors, red/green/black/yellow. The yellow and black conductors can/may be used for a second line on a mult-line phone or grounded ringing (the yellow conductor usually). If your phone service at the wall only uses red and green (2 conductors), the yellow and black are not used.