lagasse@biomed.UUCP (Robert C. Lagasse) (05/17/85)
I'm sure everyone who reads this group has opened up a telephone to see what's going on inside. No, I'm not writing about the new high-tech single-piece electonic pulse phones, I mean the good old all-American Western Electric black rotary dial desk phone. The kind that hard-wired to a wall junction block (called a 42A) with three or four wires (third was ground and fourth was lamp supply for lighted sets which used an accessory transformer hiding somewhere in your cellar). I believe it is called a "model 500" set or something. The guts of this phone are still used in 5-line with hold systems and also with DTMF dialing desk sets from W-E. The large coil block riveted in the base which I believe is called the "network" has about fifty screw terminals and has got to be one of the most confusing pieces ever invented. In the first place, this thing is labelled with numbers and letters most of which are meaningless unless you are an installer. Half of the terminals are jumpered to others underneath where you can't see and the others connect to coil windings and .......caps?? Anyway, this network thing is filled with thick sticky goop either to keep people like myself out of it or to seal it from moisture. The other strangeness in this phone is the number of contacts used in the "hook switch". This switch must be a million-pole double-throw. It seems that the only things that would be needed to be switched are the network (completely out of circuit) and the bell with it's series cap (in circuit) when the phone is "on-hook" and vice-versa for "off-hook". Sounds as if a SPDT switch would do just fine or maybe a DPDT if you need contacts for a dial lamp. Now that all of the phone stuff is deregulated, none of this must be top-secret anymore. Does anyone know where I can get the training manuals that they teach the installers from? Those guys amaze me when they open up these phones and actually figure out how do anything they want to with them. Also, where do all of these new modular jack numbers come from (RJ-11, RJ-35, etc.) ? Is there a committee somewhere dreaming these up and do they relate to ANYTHING? Comments appreciated. Bob Lagasse biomed. eng. MGH
W8SDZ@SIMTEL20.ARPA (Keith Petersen) (05/17/85)
The following was recently posted to the Telecom mailing list. It
explains some of the things you asked about.
--Keith
Arpa: W8SDZ@SIMTEL20.ARPA
uucp: ...{decvax,unc,hao,cbosgd,seismo,aplvax,uci}!brl-bmd!w8sdz
uucp: ...{ihnp4!cbosgd,cmcl2!esquire}!brl-bmd!w8sdz
--cut here--
Date: Tuesday, 14 May 1985 14:04-MDT
From: *Hobbit* <AWalker at RUTGERS.ARPA>
To: Telecom at RUTGERS.ARPA
Re: Wiring
It's rather difficult to send out schematic diagrams to a network of people
using regular old ascii terminals, but since wiring inside most fones is
pretty standard, a description should do the trick. This applies to *all*
WE phones and ITT phones that use the standard dial/ringer/network block/
handset configuration. I've rebuilt lots of these suckers, and can
confidently say that they're all the same.
Everything basically talks to the network block. The network block contains
the ringer capacitor, the induction coil that handles the handset, and very
little else save some spare screw terminals. Left to itself, the network
block can function as a standard line load [it looks electrically like a
phone] when a line is connected across RR and C. These are the inputs to
the coil. The ringing capacitor is indeed across A and K as someone mentioned.
In addition, older blocks have a smaller capacitor across F and RR, to
decrease sparking across rotary dial contacts.
Handset:
Green and White: Earpiece leads. These connect to net R and GN respectively.
Black and Red: Mike leads. Connect to net B and R respectively.
Ringer [two-winding]:
Black and Red: To line. Connect to L1 and L2 [or whever your line comes in].
Grey and Grey/red [these may vary; they are the ''other two'' wires, anyway]:
Connect to net A and K. The circuit thus formed runs from one side
of the line to one ringer winding, thru the A-K cap, thru the other
ringer winding, to the other side of the line. This configuration
has infinite DC resistance, but picks up the AC ring voltage.
Ringer [one-winding, rare]: Connect the single winding [two wired] in
series with the A-K capacitor somehow, and this whole thing across
the line as above.
Rotary dial:
Blue and Green: Interruptor. Connect to net F and RR.
White [2]: Earpiece suppress. Connect to net B and GN if desired.
Touch-tone dial:
Green: + Line in. Connect to net F.
Black: + Line out. Connect to net RR.
Org/Blk: - Line in. Connect to net C.
Red/Grn: output common. Connect to net R.
Blue: output. Connect to net B.
*Note: the above 5 connections will give you a ''bare-bones'' dial
configuration without features. Features are mike disconnect, earpiece
suppress, etc which are done simply by routing leads to these through the
extra contacts on the dial instead of directly. If you want the features,
modify the wiring as follows. If your network block doesn't have the S and
T terminals, you have an old one designed for rotary dials, and you'll have to
do kludges.
Earpiece mute:
Move Handset lead at White to net S. Also connect Dial White-Blue to net S.
Connect Dial White to net GN. This routes the earpiece through
the dial switching mechanism which resistifies the circuit on button press.
Mike disable:
Move Handset Red to T. Also connect Dial Red to T. This completely disables
the mike on button press. Make sure Dial Red-Green is connected to R if you
do this mod!
Hookswitch:
You'll find many variants of this in different units; some configurations
switch both sides of the line, some only one, some switch out the ringer
when off-hook [which isn't necessary, really]. The following should work:
Yellow: Connect to net L2. This is where the line enters.
Brown: Connect to net C.
Green: Connect to net L1. This is the other side of the line.
White: Connect to F. This is switched line power to the dial and the rest.
Red: Connect to R. This, with Black, is shorting earpiece mute.
Black: Connect to GN.
Line in:
Green and Red connect to L1 and L2. Try one polarity; if the touchtone dial
doesn't work, then flip them. Rotary dials, of course, don't matter.
If someone sees errors in this, please notify the list with the correction...
_H*jbn@FORD-WDL1 (05/26/85)
One of the less-known capabilities of the old WE 600 series telephone
instruments is that automatic compensation is provided for losses in the
local loop; a varisistor driven by the DC level as seen at the instrument is
used to adjust the signal level. This is not an audio compression circuit;
it's the long-term DC voltage (``battery'' in telco terminology) as
seen at the instrument that does it.
Since a varisistor is a non-linear component, this makes a telephone
an RF detector in theory and sometimes in fact, and there was a fix kit for
RFI available for the model 600 at one time; later models had it built-in.
This gives a little more insight into what's inside that potted network.
John Nagle