atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems 1A2 key system A-Lead issue.

I’ve had an old 551 style 1A2 key system in my home for some time but it started acting up and I tracked the issue to the female amphenol connector on the 25-pair cable coming from the KSU itself (that connects to the male amphenol terminated 25 pair cable that came from the BIX).

The BIX was initially wired in parallel from the single cable and I’m rewiring the BIX block using the 7A multipliers that were supplied with the system (but never used when it was installed) with fresh wires from the KSU’s 66-block and from the 7A’s to the 1A’s the lines from the phones are terminated on.

The issue I’m facing is that the line 2 key on the 564 or 2564 telephone sets is triggering the a-lead on the line one key (causing the line one key to light up when its line two that pressed.) The hold key is also not working on this line key.

I have some 20 button ITT call directors what when I plug in and press like 2 - both line one and two light up but the actual telephone lines don’t come through - and I have one 564 set that the keys for both lines 1 and 2 are triggering both lines to light.

Any ideas where this issue is arising from in the system? The BIX is wired as it should be so I don’t get what is causing the issue as it all worked fine before.

Not sure what a 7a multiplier is, but if you're using a CPC connector, one feed to two phones seems like you had to isolate the v/br and v/sl pairs. It's been a long time but I remember these pairs had something to do with a speaker phone. Anyway, if it worked prior to your rewire, just backtrack to see where the issue started. Once you start throwing 10 and 20 button sets into the mix it's a whole new ball game.

Hi,

I'm guessing that you know 10 and 20 button keysets are wired completely different then a 6 button set. The pairs used for the A Lead control are reassigned to get the extra pickup buttons, and the Speakerphone, if used, had to be wired into the set with a separate cable. Also, if you multiplied the sets with the CPC adapters, you had to disconnect the pairs inside the phones that 'justbill' mentioned, otherwise if set B went off hook, it would interfere with Set A (assuming it had the speakerphone). The only pairs in common between a 6 button set and a 10 button set are the first 3 pairs (Blue/Orange/Green). The false pickup lights you mentioned are a symptom of not following the exact color coding for the remaining 9 button pickups. Also, you cannot mix 6 and 10 button sets on the same CPC adapter (you knew that). Hope this helps!

7A is a type of BIX strip similar to 5A but was designed to feed one whole line of 1A2 key system circuits to 7 telephone sets. They are the bottom 4 BIX strips in my system and have the orange labels.





It’s funny because I installed that key system many years ago when I was 13 and first got into phone collecting. Because I didn’t understand the concept of how the multiplier strips worked I took a 25-pair pair with a male connector already attached (the KSU came with a 25 pair with female connector already terminated to the internal 66 block). The way I set up the system was to take the 25 pair and spread the wires out and run them up the back of the BIX block and punched them down to every BIX strip that the cables running to the phones were connected to in parallel (essentially mirroring the 66-block on each 1A BIX) (see the below ‘before’ image where if you look closely you can see the parallel wires running up the back).

The interesting thing is when it was wired the old, and technically incorrect way I could plug any key set into any of the cables throughout the house and it worked without issue. Didn’t matter if it was a 6 button set or 20 button set.

What I don’t get is how with the wiring being done the correct way why the line 2 A-leads aren’t working properly. Even though I’m using the 7A strips, the 6 wires for each of the two lines I have connected are still terminated to the same spots on the 66-Block and on the BIX strips the telephone sets are connected to. If I’m not mistaken, to make a standard key set work all that needs to be terminated is the 3 pairs for each line, right?

You need the first three full pairs for the first line. Each additional line only requires 2-1/2 pairs (no A1 lead). For five lines or fewer, there's no harm in connecting the full three pairs. The A1 leads don't start getting "stolen" until the sixth line. Oh, and yes: If you are bridging two X565 sets together, the violet/green through violet/slate pairs must be insulated and stored inside of at least one of the sets to prevent switch hook interference.

Somewhere, in a phone, connector, frame or KSU it sounds like there's a connection of the A leads of line 1 and 2. The A lead voltage (+) seems like it's constant on the line 2 from somewhere, and that would explain why hold doesn't work since pressing the hold key would normally open the A lead signal from the phone into the A lead. But, in this case the A lead voltage is constantly there from elsewhere.

I recall 40 years ago a 1A2 key system had similar issues, as well as hum on the lines. But that was a different situation - after the floor was mopped with no consideration for the Amphenol connectors.

The A lead for a line is seeking a ground (BG) from the system via the first A1 lead. The A1 passes through the switch hook first, then through the NC (normally closed) contacts on the hold button. There is no "voltage" to speak of other than what is feeding through the line card's circuitry. A foreign ground of any kind that is placed upon an A lead will cause that line to appear in use. Always remember to insulate/store the violet/green through violet/slate pairs on any X565 sets when bridging adapters (CPC) are in use or you'll forever be plagued with phantom hold/in-use indications, not to mention cross talk.