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Old 26th Mar 2024, 11:56 pm   #1
mpaxton
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Default 746 Phone wiring - doesn't ring connected to VOIP router

Hello everyone,

I'm looking for a little help with my classic 746 phone that I'm trying to hook up to my internet router-based phone line.

I can listen/talk on the phone perfectly, but it just doesn't ring when.. "rung" I didn't want to mess up the original cable, so butchered a spare RJ11 lead to wire in the "modem" to the phone to start with (you can see this on top on the pic).

I can meter out the terminals when ringing, and detect the 50v AC ring signal.

From looking at the board inside, it looks like the C1/2 capacitor is missing, which I understand is a common issue... I'm in The Netherlands, and don't have a microfilter handy to test with (of course I threw out 3 of them 2 months ago before I started this project..), instead I hooked up a couple of 490uF caps in parallel across the terminals and didn't get anything.

Can anyone take a look at the wiring and suggest what to try? Perhaps an experienced eye will spot it in seconds or you can at least help with some fault finding steps.

I've attached a picture of the board but can always do some more if anything isn't clear.

Thanks in advance!
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Old 27th Mar 2024, 8:27 am   #2
Station X
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Default Re: 746 Phone wiring - doesn't ring connected to VOIP router

My first thought is that two 490uF capacitors in parallel (980uF) is way too high! The originals were two 0.9uF capacitors in parallel totalling 1.8uF.

http://www.samhallas.co.uk/repositor.../0000/N846.pdf
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Old 27th Mar 2024, 9:23 am   #3
Dave Moll
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Default Re: 746 Phone wiring - doesn't ring connected to VOIP router

Looking at your image, a 1.8µF (as Graham says, or thereabouts) capacitor needs to go between T6 and T8 (given that you say there is no capacitor between T7 and T9) and the line connection between T8 (B leg) and T16/17/18/19 (A leg). Although the A & B legs are traditionally connected this way round, it would also work with them reversed.

Am I right in thinking the black lead with red and green wires is what you are using to connect to the VoIP router?
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Old 27th Mar 2024, 9:37 am   #4
mpaxton
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Default Re: 746 Phone wiring - doesn't ring connected to VOIP router

Thanks for the quick reply!

I was referring to this diagram for reference BTW, I think it was posted in a thread elsewhere on the forum. http://www.stevegs.com/projects/tele746/tele746cct.png

But now you point it out, that's many silly mistakes on my part. I was aiming for approximately 900nF (reading C1/2 as needing to be 900nF), I must have thought I was using 2 470nF caps at the time to get 940, but now I look at them again the code is u47K63. So not only did I aim for 1000 x too much, but in reality I didn't even do that and got more like 100 x too much.


I'll head back to the parts drawer and look for the correct ones!! Seems funny the space for C1/2 is massive on the PCB, but I'm pretty sure the real component is going to be even smaller than the 47u ones.
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Old 27th Mar 2024, 9:42 am   #5
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Default Re: 746 Phone wiring - doesn't ring connected to VOIP router

Quote:
Originally Posted by Dave Moll View Post
Looking at your image, a 1.8µF (as Graham says, or thereabouts) capacitor needs to go between T6 and T8 (given that you say there is no capacitor between T7 and T9) and the line connection between T8 (B leg) and T16/17/18/19 (A leg). Although the A & B legs are traditionally connected this way round, it would also work with them reversed.

Am I right in thinking the black lead with red and green wires is what you are using to connect to the VoIP router?
Yes, those go to the RJ11 plugged into the router, an "ExperiaBox 10" which is a standard wifi router, with telephone socket outputs. https://nl.hardware.info/routers.9/z...box-v10.280129

As mentioned silly errors on my part so far.
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Old 28th Mar 2024, 6:43 pm   #6
AndiiT
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Default Re: 746 Phone wiring - doesn't ring connected to VOIP router

Hi, as has already been mentioned, you need a "ringing capacitor" in your phone, either soldered in the C1/2 position or across terminals T7 and T9.
The capacitor needs to be non-polarised either 1.8uF or 2uF and have a working voltage of around 250 Volts AC.

Once you have the capacitor fitted suitably, you need to wire your phone to "two-wire" working as follows -

Strap T4-T5-T6-T7
Strap T8-T9
Strap T16-T17-T18-T19

The red of your RJ11 cord connects to T8
The Green of your RJ11 cord to T18

Regards

Andrew
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Old 30th Mar 2024, 1:19 pm   #7
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Default Re: 746 Phone wiring - doesn't ring connected to VOIP router

Can I just clarify whether your VoIP port on the modem works with pulse dialing directly? From my research it seems these devices are generally quite rare.
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