What's wrong with this GPO 706?

[InterestedNewbie]

I'm completely new to phones and picked up a GPO 706 at a local auction hoping to convert it. Opening it up shows this is missing a screw head - with the head loose inside the case - and a lot of blue powder on top of it, with the silvery surface flaking off. What exactly could have happened to this and is it completely shot? I'm guess extreme heat at some point hence the flaking surface and possibly causing a head to be scorched off? I've cleaned it up a bit.

It's a wired 706, not the printed circuit board.

I've noticed the bell-ringing arm is off-balance too and only seems to hit one bell. I haven't rewired and connected it up as I don't want to waste any time on it until I know what I'm dealing with.

[Jim Stettler]

It looks like battery acid  corrosion to me . Those are the ringer coils not a transformer. the coils are electro- magnets that energize  alternately  to move the clapper back and forth between the gongs.

I think the clapper will probably hit both gongs  when ringing.
You should try hooking it up and testing it tosee what happens.

JMO,
Jim S.

[TelePlay]

Opening it up shows this is missing a screw head - with the head loose inside the case  . . .

I've never had a GPO 706 so are the screws on each side of that metal "block" the ringer mounting screws? If so, a lost head would not be a problem in taking out the ringer, removing what's left of the screw, cleaning everything and getting new mounting screws.

It looks like some sort of bi-metal corrosion. Is there any corrosion at the base of the screws, where the screw into the base?

[twocvbloke]

That's definitely corrosion from something like an acid of somesort, though how it got in there is anyone's guess, the 706 didn't have a battery in it as standard, but the corrosion does seem to have damaged the plate & screw that holds the magnet in place on the ringer assembly, might be worth getting another ringer to borrow parts from to repair it...

My only guess (just a guess, nothing more!) is the base of the phone possibly had previously been modified with a much later pushbutton dial that utilised a battery in its circuit and had the battery fail & burst, and the base later returned to being a rotary dial setup being made up with spares out of someone's collection of parts...

As for the bells not being struck properly, well, when you move the clapper side to side manually, it shouldn't hit the bells, there should be a 1 to 2mm gap, so the clapper arm bends slightly so the hammer strikes the bell when ringing, you can open or close this gap simply by rotating the bells as they're "eccentric" (I.E. the screw holes are off-centre), which also has the effect of increasing or decreasing the ringer's volume...

[InterestedNewbie]

Thanks for the replies everyone! After spending some time taking it all apart, the two screws either side secure a 'hood' underneath which has a counter-weight for the ringer and I'm guessing that one screw being now dead, is not securing the counter weight in place on one side so I will have to try and find a suitable screw to secure the remaining side. There seems to be a load of blue dust at the bottom of the phne, which will certainly need clearing out.

As for the bell screws being off-centre - interesting tip! Maybe that will serve as a temporary fix for moving one bell closer to the failing side?

Also, twocvbloke - that's an interesting idea regarding a later push button dial as the base has a date from gpo checks on it dating to late seventies and it's my understanding that the 706 was superceded by the 746 at this time.

[Stan S]

Hello Newbie
It appears that the metal wasn't properly cleaned before it was plated.
The green stuff is corrosion. Probably initially caused by contamination under the plating.
A little moisture over 50 years and you end up with lots of green stuff.
The ringer probably works fine.
A little baking soda and water applied with a stiff brush should clean it off.
You might want to cover the effected area with some type of paint.

Stan S.

[Ktownphoneco]

Here's a link to Sam Hallas' ( United Kingdom ) web site page which pertains to the GPO 706.    There's a fair amount of information on the page, and a picture of what the ringer should look like about 3/4's of the way down the page.

Link :   http://www.britishtelephones.com/t706dismantle.htm

Jeff Lamb

[twocvbloke]

That "weight" is actually a magnet, I'm sure others will know why they put them in there, but it's part of what makes an electromagnetic ringer operate, and it does indeed need to be kept secure in the frame...

Definitely clean out the dust as that will most likely be acidic and potentially corrosive to other parts of the phone, you can remove the entire PCB and ringer assembly by loosening (don't need to remove them) the two screws under the dial area (remove the dial first of course, being careful not to break the dial wires) and the two screws either side of the hookswitch frame, then lift out the board from the base, that makes cleaning a lot easier...

Rotating the bells is indeed useful for a slightly misaligned ringer, the 706 having its ringer integrated onto the PCB means the position of the assembly is difficult to realign (the 746 separated the PCB from the ringer, so it was easier to align), so the only adjustment is the bells themselves...

But the pushbutton idea is just pure speculation, I have seen 706-style phones retrofitted with pushbutton dials fitted, though these tended to be non-GPO phones supplied to private customers, but as with a lot of phones, we don't really know their history prior to our owning them, so can only make educated guesses...

[InterestedNewbie]

Thanks, removing the two screws underneath the phone allowed the ringer to come free and there's a pile of dust sitting at the bottom of the case so that will be sucked up.

If I strip off all the metal flakes - that are more like silver foil - what type of paint should I use? I assume this is to provide a layer of protection for the phone? But wouldn't that just flake off again over the years?

Thanks Jeff, that tear down was what I used to check the ringer looked fine! It's a great write-up! It appears that the damage is very localised to just this piece of metal, the rest of the ringer looking fine.

I assume the vibrations for the ringing caused the screw head to be sheared off.