Author Topic: Got a "new" STK (=STC) exchange, need help  (Read 498 times)

Offline dsk

  • **
  • Posts: 4391
Got a "new" STK (=STC) exchange, need help
« on: April 11, 2021, 08:09:34 AM »
Thinking about some modernizing so I got a "new" exchange Marked STK  (Norwegian STC)  but I have not a clue how to get it working.   I just guess on 48V and this need help to learn how to wire it up. I'll probably need a ring voltage source, and a dial tone source, but where to connect it?  The back board is wood painted slate as the exchange.  :-)

Offline RB

  • **
  • Posts: 1770
  • Love old phones
Re: Got a "new" STK (=STC) exchange, need help
« Reply #1 on: April 12, 2021, 05:54:26 AM »
Hi DSK!
Wow, you don't pick the easy stuff for a project. :)
That's quite the board!
Well, lets start by saying, I don't know much about multi line exchanges.
Only that once you find the first connection, the rest work the same.
My guess would be...
Extensions,Incoming lines, Lites...Fairly certain about these.
 Ring, Tone, ?, power... The order, not sure about. can't read that language.
And the power connections at the end.
Once you get the extensions, incoming lines, lites, and power wired, you can take the audio from a radio, and connect it to one of the unknown inputs, and be able to hear it when off hook. "low volume".
That will be the "TONE" input.
The ringer I am not sure of???
Start there, and I bet you will have about 70% of it wired.
You can try it with a 24 volt power supply.
If it is too low, once you start selecting lines, etc... you will notice that the relays get slower to react.
And then will fail to lock.
That will be an indicator that you need to go to 48 volts power. "Which is probably what it needs".
The lites in the phones may also lead you to the correct input power needed.
Well, that's about all the initial help I can be.
Good luck with the project, and keep us updated  :)

Offline dsk

  • **
  • Posts: 4391
Re: Got a "new" STK (=STC) exchange, need help
« Reply #2 on: April 12, 2021, 03:12:38 PM »
Seems like 24V is OK but it may be a capacitor or something making a problem of holding the line. 
When I press one relay I can hear a buzzer making a sort of dial tone, and generating an AV ringing current

Enclosed 2 bad 5 sec mp4 films. (not easy to film with 1 hand and press on the relay with the other hand.  :P

I actually do not know what the next step will be.
dsk

Offline RB

  • **
  • Posts: 1770
  • Love old phones
Re: Got a "new" STK (=STC) exchange, need help
« Reply #3 on: April 12, 2021, 07:38:02 PM »
Thanks for the vids.
The tone seems almost ok.
The off hook, bothers me.
IMHO, The set is experiencing a voltage starvation.
Going off hook, closes the line.
Included in the line is the OFF HOOK relay.
That's not what it is called, just my version.
There are at least 2 relays assoc with that off hook sample.
When you close relay 1, it powers relays 2 and 3.
As soon as that happens, you have 3 relays fighting for power.
If it is not supplied, the relays will collapse and release, only to see OFF HOOK, and lock on again
That is why it is "Buzzing", or chattering.
Bump it up to 48 volts, and give it a "QUICK" check.
Before that tho, check the CAPS for operating voltage.
That may tell you more.  :)

Offline Key2871

  • **
  • Posts: 2852
Re: Got a "new" STK (=STC) exchange, need help
« Reply #4 on: April 12, 2021, 09:02:41 PM »
Yes I think it's going to want 48 volts to run right.
It seems things are acting voltage starved.
I saw a you tube vid of a British switch the guy got and didn't start of with enough voltage so it too didn't work right.
KEN

Offline dsk

  • **
  • Posts: 4391
Re: Got a "new" STK (=STC) exchange, need help
« Reply #5 on: April 12, 2021, 11:50:29 PM »
I have problems reading the size of the cap's, but it seems like max 2 uF. It is one of the grey sealed boxes with a lots of wires in to that I do not know what is, but it may be that who makes the low frequency ringing.

I have carefully tested with 48V and the that makes the relay sound much quicker.

When I force one of the relays going on/off to keep on (holding by finger) the voltage disappears from the phone-line.

Offline RB

  • **
  • Posts: 1770
  • Love old phones
Re: Got a "new" STK (=STC) exchange, need help
« Reply #6 on: April 13, 2021, 05:40:06 AM »
Hmm...
Now you have me hung up. lol. ???
That could be a hold circuit missing a switch ???
Are you able to translate the wording?
That may tell us more.
Do you have a multi line phone attached to it?
We need to have "line one" switched on, and a lite to monitor with.
That may help us "See" what the phone sees???
I am wondering if the relays "clicking", was from the flash circuit?
If anyone who knows these large relay based systems has a schematic they could share,
That would help bunches!!!
We need to know the general operating flow.

Offline RB

  • **
  • Posts: 1770
  • Love old phones
Re: Got a "new" STK (=STC) exchange, need help
« Reply #7 on: April 13, 2021, 07:51:11 AM »
I was wrong on my pic...
retjenningsboard means control board, not lites.
not sure how that is wired?

Offline Key2871

  • **
  • Posts: 2852
Re: Got a "new" STK (=STC) exchange, need help
« Reply #8 on: April 13, 2021, 09:53:43 AM »
When they were removing the #5 xbar in town, there were NOS relays they threw out. I took a few home and tried them with various voltages. None acted really well until I connected them to the CO line. They jumped to life. Those relays look exactly like those that were in the racks and stuff I took home.

Good luck on getting that figured out.
KEN

Offline dsk

  • **
  • Posts: 4391
Re: Got a "new" STK (=STC) exchange, need help
« Reply #9 on: May 14, 2021, 03:16:56 PM »
Got it working except trunk no 2  :)

Offline RB

  • **
  • Posts: 1770
  • Love old phones
Re: Got a "new" STK (=STC) exchange, need help
« Reply #10 on: May 14, 2021, 07:10:43 PM »
Go through the relay contacts for that trunk again...
Betcha get it working ;)