Powering up a 557A Cord Board

[RB]

I found an AUX signal circuit, it may be what is used to provide RING for incoming trunk calls.
I have not messed with this circuit, so...guessing here.
so, generally speaking, we got two different animals in the same box.

[simonwolfe]

WOW! that is just too cool! 

Yes, I believe the 555 is a standard PBX board that is used in an office to transfer calls around to station lines.  the 557 was for a call center so customers cold call in and have the operator  answer the call as a "secretary" for the subscribing customer.  this is what most of the board is set up for. In addition the 557 could ace like an office PBX with a small number of station lines.  DFrom what I can tell the 555 and 557 are almost identical at that point.  Does that sound correct to you?

I did find a BSP on the 555. 

[poplar1]

557A has station lines.The more common 557B does not.

[simonwolfe]

Ah, OK.  I wasn't overly sure about that.  Thanks!

[poplar1]

Also, the 555 and the 557A have cord pairs. The 557B uses single cords since there are no stations that need to be connected to a trunk.

At the answering bureau where I worked, there were three 557Bs. There was also a 1A2 Key System with several 830 sets (9-line) with appearances of the same trunks that appeared on the 557Bs. Of course, you couldn't access the secretarial lines from the 830 sets.

[RB]

WOW! that is just too cool! 

Yes, I believe the 555 is a standard PBX board that is used in an office to transfer calls around to station lines.  the 557 was for a call center so customers cold call in and have the operator  answer the call as a "secretary" for the subscribing customer.  this is what most of the board is set up for. In addition the 557 could ace like an office PBX with a small number of station lines.  DFrom what I can tell the 555 and 557 are almost identical at that point.  Does that sound correct to you?

I did find a BSP on the 555.

Simon, from what I can tell, the 555 and 557A are almost identical in the basic construction.
The options, of course, varied with each installation. But the pages of the schematics from both look the same.
You will need at some point, to determine what supervisory options are in place on that board.
That will help with understanding how the lights work.
Or, you may be lucky, and they just work...