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!