Telecom 8100R (Ambassador) dial phone help wanted

[andy1702]

So I just bought three phones from E-Bay. All separately but from the same seller. There's a Canadian 500 already fitted with a UK plug, a 706 which I haven't tried yet and a UK 8100R with a dial, which is the one that's giving problems. Basically it works ok except for the fact it doesn't ring. I've taken the top off and found the phone contains a blue coloured PCB with quite a few c0onnector pins sticking up all over the board. Many of these are marked T1 - T16 etc. I've read that the wiring is the same as a 700 series, but I don't see how it can be as nothing seems to be strapped together. The terminals are all over the place, not in a nice neat row like on the 700 series. I've checked the bell coil and associated switch, both of which seem to be ok. Also checked back along some of the tracks on the circuit board to make sure there are no breaks. Again everything appears to be ok. The only thing left that I can think of is that some of the jumper wires on the board (which I assume are similar in operation to the more traditional metal links in 746s) are either missing or bridging the wrong things.

Does anyone have any info on these phones that might be able to help me? It's the Mk1 version with the dial that I have. Manufacturer code on the back is 8100R GNA 81/1

[twocvbloke]

If you could post a picture of the inside of the phone, that may be helpful, don't think anyone's turned up with an Ambassador on this forum so far, so it's probably "New territory"...

One thing that comes to mind though to try first is not inside the phone itself, but with the telephone line, if you're in the UK (I'm guessing you are) and have ADSL or the VDSL "fibre optic" stuff (referred to by BT as Infinity), then the bell wire, which the phone in default wiring requires, may have been cut out by the faceplate filter on your master socket, and one simple solution to that is to use an ADSL filter on your slave sockets, this will add in a bell wire that'll help the phone to ring, assuming that is the issue of course...

[andy1702]

Thanks for the tip about the bell wire. I don't think that's the problem though because other phones work ok when plugged into the same socket. I'll take a few photos and try to upload them (never had much luck iploading images to this site). You're right, I am in the UK.

While I'm here and we're discussing bell wires maybe I'd better explain a bit more about my setup. Basically there is one PSTN line coming in which feeds into a BT Revelation PBX. From there all the extensions, except the one the system phone sits on, are run two wire only to standard master sockets. So there is already a capacitor in each socket.

Also coming into the Revalation are two C*net lines which are remotely hosted via a Grandstream ATA. Independent of this is a second ATA which runs two phones off my own AstLinux server for C*net, this time connected via a PAP2 ATA.

Photos to follow...

Andy

[twocvbloke]

Ah, hit the ground running then, most people come here with a couple of phones and end up buying a phone system!! 

As an aside, I used to have a Revelation system about 10 years back, never got it to work properly but that was due to a lack of suitable master sockets, ended up selling it on ebay I think...

Anyway, assuming the phone is wired up correctly (I've never seen inside an Ambassador so can't say for sure) and has a mechanical ringer (later ones I believe had a tone ringer) it could be worth probing the ringer coil with a multimeter to see if it's gone open-circuit, or if a wire's broken a solder joint or the like, same with the line cable, might have an internally damaged wire in the cable or the plug through rust or clumsy previous owners tripping over the cable...

[andy1702]

Hopefully I've now managed to attach a couple of images of the inside of the 8100. If you look close you'll see various pins scattered about the board marked T1, T2 etc. This is what makes me think it may electrically be the same at a 746. However if that is the case then things are connected to the wrong terminals and some are also not strapped together the way they should be. Also I've not spotted T18 or T19.

I've had an electrical tester across the single 400 ohm coil of the mechanical bell and that checks out ok. The line cord checks out too. I've also checked the tracks on the other side of the circuit board that end up at the connections to the bell coils and none appear to be broken. So the only thing I can think of is either the terminals are not wired up correctly or there is something strange going on with the hook switch. The hook switch seems to have two pairs of terminals which connect and disconnect. However there is also another single terminal that goes in there somewhere which never seems to connect to anything. This seems a bit suspicious. The problem is, with the hook switch being the big black plastic thing mounted straight onto the board, it's impossible to see where any of the connections go and it appears to be impossible to take apart.

UPDATE: I tried attaching the photos and I get told my images have failed security checks, even though I've gone to a lot of trouble to resize them! Can anyone help? I've never yet been able to upload a single image to this forum no matter what I try. /b]

[twocvbloke]

The photo problem's a known one, sometimes just renaming the files can help, but it seems to be a bit hit & miss as to what triggers the security check failure and what doesn't...

[andy1702]

I'm trying again to post the photos of the 8100, this time in .PNG format. Hpopefully they'll be tagged onto the end of this message.

[twocvbloke]

Definitely is quite different inside, could you get a picture of the other side of the PCB? I'm trying to map out where everything goes compared to the 746 diagram but not having much luck with the rather haphazardly positioned terminals (most seem "right", others are rather oddly wired)...

It seems odd with all the "miniaturisation" that took place in the 80s, that BT went the other way with these phones and made a huge PCB compared to that of the 746, which itself was a marvel of miniaturisation for its time...

[andy1702]

I think you're thinking along roughly the same lines that I am. Some things look reasonable in terms of connections, but others just don't look right if we're using the 746 wiring as a basis.

Attached are three more photos which I hope will help. First is another view of the top of the board, showing the resistors etc, then I turned it over top to bottom to show the tracks on the back. The third image is a composite I did in GIMP. I optically flipped the tracks to be a top to bottom mirror image then overlaid them on the photo of the other side (top) so hopefully you can get a bit of an idea of which component is connected to which track. I think it's fairly accurate, but I did the overlay by eye, so some places might be a little bit out.

I'll be very interested to hear what you or anyone else here thinks. It's got me baffled.

Andy.

[twocvbloke]

They actually released that as a design? I can think of a few electronics engineers who design PCBs who'd frown upon what BT did there... 

The composite is pretty much what I was thinking of doing, so saves me some graphical editing (aside from going through and labelling things)...

[twocvbloke]

Actually, I think I may have spotted it, the blue wire going to T3, looking on the 746 diagram, that should (in theory) be going to T17, going to T3 sends it the wrong way for a ringing circuit...

[andy1702]

Thanks, I'll give that a try. Although to be honest, that might be me sticking it back on the wrong terminal because I had to take that one off to flip the board over. Oops! 

The thing I can't quite get my head around is why there don't seem to be the same terminals strapped together that there are on a 746?

Andy.

[twocvbloke]

I have a feeling that the strapping is probably done by the traces on the underside of the PCB, that and the general wiring adapted so that it can cut out the need to use strapping like that used in the 746 layout (E.G. the ringer wire going straight to T17 rather than via T16 with a strap to T17)...

One other thing I noticed, that grey microswitch, is that a part of the bell assembly? And is it across the wires that go through the coil assembly (presumably used as a ringer mute)? Seems an odd place to put such a thing with no visible way to actuate it...

[andy1702]

Yes, the little microswitch is to adjust the bell volume. There is a plastic wheel under the phone a bit like on a trimphone which has a plastic peg on it. When you turn the wheel the peg moves along the switch and throws it in the process. I've not moved the switch but tested it in it's current position for continuity which checks out ok. The resistance of both the microswitch and bell coil together is just under 4000 ohms, which seems about right. What I haven't done and am now wondering about is to check if the switch is powered from elsewhere so the close position actually turns the bells off somehow. I do know it's in series with the bell though, just not sure what the voltage is supposed to be at either side.

Andy.

[andy1702]

Actually, I think I may have spotted it, the blue wire going to T3, looking on the 746 diagram, that should (in theory) be going to T17, going to T3 sends it the wrong way for a ringing circuit...

Ok, so I tried moving this wire and it does very strange things. When off hook it gives a dial tone (until the dial tone coming from my PBX times out. But when on hook it also gives a faint dial tone. It's only very faint when on hook, but it's there. The result of this is any other phone calling it gets the engaged tone all the time. Put it back on T3 and the whole phone seems to work ok except for the bell. You can make and even receive calls as long as you know the phone should be ringing.

I'm now wondering if the hook switch (big black plastic box on the photos) is suspect. There appear to be two pairs of terminals which make and break depending in the state of the switch. However there is one solder terminal on it's own under the switch that I don't seem to be able to trace through the switch at all.

Andy.