Building entry telecom system - Sequal - ping Owain and cj

You may remember that I started a thread back in July about a problem I was having with the entry telecom on my holiday flat. [The problem was that the buzzer and door release worked ok, and I could hear what callers outside were saying but they couldn't hear me].

Having received some very helpful advice from the likes of Owain and cj, I decided that it was probably a problem with my handset, and replaced the handset. Problem solved - or so I thought!!

On returning to the flat recently, I found that the buzzer[*] on the NEW handset wasn't working - and that I couldn't hold a conversation in EITHER direction.

[* Or, more precisely, the warbler. The original Bell Systems 801 handset had a buzzer and springy wire hook switches, whereas the replacement had a warbler and a microswitch on the hook.]

On further investigation I found that when the handset was off-hook, it would warble very quietly when the outside button was pressed (or when I and Z in the handset were bridged to simulate the button press). But, if it was on-hook it would occasionally give a very short (fraction of a second) loud warble and then go dead - after which it wouldn't even warble quietly when off-hook. Pressing the door release button seemed to reset it in some way, and get it warbling quietly again - but still no speech.

It rather looks like the new (2 month old) handset has gone duff.

In order to verify that it was the handset and not a problem elsewhere in the system, I re-installed the old handset to see what that did. Sure enough, the buzzer on that works ok, but I still have only one way speech. EXCEPT that I've now discovered that if I fiddle with the hook switch - moving it up further than it moves under its own steam when the receiver is lifted - I can restore TWO way speech. So the problem with the original handset was not a duff microphone, but simply that one of the pairs of contacts in the hook switch wasn't making properly.

QUESTION TO THE EXPERTS . .

How do these springy wire hook switches work, and is there anything I can tweak to make them work more reliably. [If I can get the old handset working consistently, I think I'd rather have a buzzer than a warbler!

Another question . .

When investigating the latest problem I took the lid off the outside button/speech unit and measured a few voltages. The system appears to be fed with 15v AC from a transformer inside the building. The pushbuttons for all flats except mine had 15v AC across them - going to zero, of course, when they were pressed. But mine only had 6 or 7v. When I measured the voltage at pin I on the handset, this was the same. As far as I know, all the other flats have old-style buzzer-type handsets, which seem to output 15v on pin I. But my new warbler-type handset was only outputting about 7v. Does anyone know whether this is a 'feature' of the newer handsets, or does this indicate a fault?

Yet another question . .

Is it usual to power these systems with 15v? ISTR seeing some of the literature referring to a 12v supply. Inside the pushbutton/speech unit, I found what I at first thought was a fuse which had blown. But, on reflection, I think it is probably a festoon bulb to light up the panel at night. The markings on it say 12v, followed by a 3 but I can't see whether it's 3a or 0.3a or 3w or 0.3w or what. But assuming it's a 12v bulb, powering it with 15v is probably why it's blown. Any comments?

Sorry for going on a bit, but I wanted to give all the facts!

Reply to
Roger Mills
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Hi To try and answer your questions. The Bell 801 system has been arouns for many years in various guises and all were fed from a 12v mains transformer. This gives an AC output around 15v when measured with a standard meter as the reading is a peak voltage. The system is very simple with a 601 speech amp at the heart of the system . This has 5 terminals marked C H R O & T. Power goes to C (ac or +ve) and H (ac or -ve) The C terminal also goes to the Lock +ve(or ac1) & the flat call button common terminal with the button output connecting to the I terminal on the flat handset. R O & T connect to all phones on the system being R speech to handset ,O common (0V) ,T speech from handset. Finally all the handset Z terminals are connected to the lock -Ve (or ac2).

The earlier systems were dependant on AC to call the flat whilst newer systems have a 12v DC supply and the handsets have an oscilator cct to produce a warbling ring.

Lighting for front panels was usually 2 festoon type lamps 12v 3w wired in series across C and H giving a long lifespan to the lamps as they were running under voltage.

The early handsets had 2 brass springs slotted through the cradle arm inside the phone these were connected 1 each to the mic and earpiece return wires (feeds from each going to R & T repectively) when you lifted the handset the springs shorted to a steel bar connected to 0 making contact. They were prone to oxidation and often you would loose comunication eithe one way or both. The solution was easy carefully slide out the springs then vlean the wire on the pcb with emery cloth ,wire wool etc then cleam springs and reassemble.

Later handsets have encapsulated switches. On your last point if the new handset has a low warble when off hook and this is also heard at the front door it is a sign of a failing speech amp. This early warning is only aparent on newer phones as they are AC sensitive whilst the earlier phones had no electronics at all . If however the warble is just low check the jumper on the pcb of the phone (top left hand corner) move from LO to HI.

HTH CJ

Reply to
cj

Many thanks for your prompt and detailed reply.

There's definitely only *one* (failed!) festoon lamp in our unit.

Thanks for that - I'll have a go at cleaning the contacts tomorrow.

Yes, I guess my new one does. It says T-MEC on the top, but I can't see what's inside.

You can't hear it at the front door (although ISTR that you *could* hear the full volume warble at the front door when I first installed it - when it appeared to be working correctly. Should I not have been able to?

I'm sure I've read somewhere that it's designed to warble much more quietly when off hook - presumably so that you don't get deafened if someone presses the button again. The problem with mine is that it doesn't warble when it's *on*-hook - so I don't know when someone is at the door.

Mine is already set to HI, as supplied.

Reply to
Roger Mills

on mine I had to pull one of the springs a bit out of the cradle lever and glue it into position, so it made contact with enough force against the common bar.

The AC power supply will power a Friedland ding-dong chime (it's over- voltage, but only for a few seconds and didn't harm either the power supply or the chime)

Owain

Reply to
Owain

Well, I done what you said - cleaned up the springs and the back of the common bar with an emery board meant for finger nails - and it seems to be working fine, with 2-way speech without having to fiddle with the receiver rest.

Many thanks!

Now, I need to find out what went wrong with the new one - and get that repaired or replaced as a spare. I've emailed the supplier (Safelink) and am awaiting their reply.

Reply to
Roger Mills

Hi Sorry for misunderstanding,you are quite right you should hear the warble at the front door when you call the flat with a newer phone.(lets the caller know its ringing). IIR when the phone is off hook the tone generator is disabled so you should not hear the warble.(don't quote me never had it happen ears not wide enough apart to be at door and in flat at same time hehe). Must check next time installing one. You may indeed have a faulty handset and you could test it by wiring it across a known good phone. Just connect phones together wire to wire and (unless you got very long arms) get someone to call the phone. Both should ring (buzz or warble).

HTH CJ

Reply to
cj

I presume you mean two phones wired in parallel into the system - because two phones in isolation presumably wouldn't do anything without a power supply?

Anyway, it's a little academic because I'm now over 100 miles away from the system - which is at my other property. However, I *do* have the apparently faulty 2-month-old handset with me - ready to send back to the supplier.

I decided that it would be nice to do some further testing on that before sending it. I figured that I had ought to be able to test the warbler by applying a voltage between I and O. By using a bench power supply set at 12vdc, I got it warbling quietly off hook (like it did when connected to the system) and when I operated the hook switch it gave one loud warble and then stopped, just as before. However, whereas

- when connected to the system - I could reset it by pressing the door unlock switch (don't ask me why that worked!), nothing I have done to it here has reset it - so it doesn't even warble quietly off-hook any more.

Is it fair to assume that a 'good' phone should warble at proper volume when on hook if 12v is applied between I and C?

The supplier has said that if I send it back, they will return it to the manufacturer who will replace it if they find it to be faulty - so that is what I shall do!

Reply to
Roger Mills

Hi You presume correctly on the parallel connection. As for a bench test the C terminal (+) connects to the I terminal of the phone when the call button is pressed. The circuit is completed in the phone to the O (com -ve) terminal.So 12v across I (+) & O (-) should cause the phone to ring if on hook. Seems more & more like you got a faulty handset ,probably a fault component on the pcb. Send it back. If you have no luck and get to my neck of the woods (mcr) let me know I always have a few old handsets knocking about .

CJ

Reply to
cj

Thanks. It's on its way back to the supplier already. Assuming they send me a working replacement, I shall then have a spare - since the old one (buzzer-type, springy hook switch) now seems to be working ok since I cleaned up the contacts.

I'm rarely anywhere near Manchester, but I'll bear your offer in mind - thanks. Are you likely to have any of the old-type (non-electronic) handsets? All the phones in the system (including mine) are currently of that type, and whereas you're supposed to be able to mix and match with the new type, I can't help wondering if it's better if they're all the same.

Reply to
Roger Mills

Hi No old type as they get binned but next time I do a refurb will see if I can resue some from the skip. CJ

Reply to
cj

Ta!

Reply to
Roger Mills

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