atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems 1A2 Shoebox KSU "Relay" function help

I've done it before with one of these old 4-line shoebox KSU's where you can rewire it in a way so that when a call comes in and triggers the KSU to ring the phones (flash the lamp, buzz the buzzers etc) that it opens a circuit as long as it's ringing (and closes again when the line is answered or calling party hangs up from no answer) that can be used as a low voltage relay. I used this function to control a light in a radio studio that would come on while the phone was ringing using the KSU to open and close the 24v circuit to the light. (I'm not 100% sure as it was almost 10 years ago since I did that wiring job but it may have also involved moving jumpers around on the line card.) I need to replicate this function on a different system to hold a circuit open to control an external system while the line is ringing.

Does anyone have an idea of what I'm talking about and how I can do it again as I forgot the steps.

Thanks in advance!

The "ST" lead on the lower-right side of the 551's 66 block provides a steady ground whenever a call of any type causes the interrupter to run. This would apply to incoming calls AND calls on hold to cause a ground to be present on the ST lead.

I recall seeing a "continuous ring" option on some KTU's (line cards).

Here's the option table for a 400E that shows a "T" option will get you "steady ringing", which is probably what I'm thinking of, and I take to mean continuous ringing without the ring cadence from the interrupter, not sure.



From what I can guess, the "T" option taps the RB (Ring Battery) directly through the ring relay on the card, passing ring voltage to the RC output of the KTU (to the Y-S pair in the phones) for the entire duration of ringing, as opposed to the "W" option which is the normal interrupted ringing option which I imagine taps to the RN (Ring sequence from the interrupter) which gets you interrupted ringing (typically 1 sec on, 3 sec off ring cadence, IIRC).

Looks like the 400D card has option "T" as well ("Steady Ringing), as an alternative to option "W" (factory default "interrupted ringing").
Also, in my above reply where I mentioned "RB" (Ring Battery), I believe RB and 105V± are different names for the same signal; RB being what usually appears on the KSU's punch block, and 105V± being the label for the KTU edge connector on schematics. But I think they end up being wired together in the KSU's internal wiring.

To be sure I'd have to check to see if there's a bell system schematic for that shows the backplane wiring of 551's punch block and KTU edge connectors. Not sure if I've seen one.. I haven't ever had to rewire a shoebox before, or I'd have such a thing handy.

Are you thinking of 518-215-407?

Should be available here.

Years(!) ago I had a copy of Key Systems Service Manual Vol. II.

I'm using the Canadian version of the 551B (called QUJ8A here) with ITT 400E-1 line cards. I know if I bridge pins 2 and 3 on jumper 8 on the line card it will trigger the line card to ring (lamp flash + buzzer) continuously until you unbridge the pins.

I use this function on my line 2 card (white/brown pair wire visible running to the line card) to ring the telephones via a relay closure on the intercom system connected through the line 2 card when a call comes in on the intercom. (The intercom operates on 24v and does not generate ring voltage to ring the line card normally).

What I'm trying to do is generate a contact closure from the KSU for when a call rings on the line 1 card to activate a GPIO input on the same intercom system (GPIO can be programmed to activate intercom system functions). The last time I did this with the same KSU and line cards there was some jumper settings on the line card itself that were changed and the contact closure was connected off the 66-block somewhere but I just can't remember how it was done or where connections were made.