1A2 key system A-lead issue and hum

[rturner]

Hey guys! I'm looking for some help with my old key system. I apologize for the long post but the back story helps explain the situation I need help with.

I have a 551a style KSU that worked fine for the past 20 or so years since I put it in when I was a teenager. My skills in installing them back then was rather limited and I installed the key sets by punching the 25-pair cables down to a BIX block of 1A strips which I then took a male terminated 25 pair cable and ran the individual wires up the back of the BIX, punching them down to each 1A strip in a daisy chain (I know, not the right way to do it, but I was young).

The BIX rack came with four 7A strips to terminate the KSU lines to the 1A strips properly but at the time I didn't understand how to wire them and left them. I've taken over the house that had that system and have gone to start using it again but the telephone sets weren't working and I traced the problem to the female connector on the cable coming out of the KSU that was connected to the cable I had attached to the BIX block. I guess with age the connections in the cable wore out. I decided it would be a good chance to wire the system correctly using the 7A strips but since doing so I've had nothing but problems! With the old cheated wiring I could plug in any key set (6 button or even the 20 button ITT call director sets I have) and they all worked 100% just by plugging them in.

There are two lines with dial tone connected to the KSU. Line 1 works without issue as it should but Line 2 is giving me hell. There is a hum on the line on all the sets that's not there if you test the source line with a regular phone outside the KSU, and the darn A-Lead for Line 2 is triggering the lead of Line 1 (line 1 key is lighting up when you pick up on line 2 and the hold function does not work).

If I plug a set into the old 25-pair coming out of the KSU it works (with a bit of wiggling the connector around) just fine. The A-leads trigger as they should (although it's hit or miss whether the line 2 key will hold). However, any key set plugged in to a line from the BIX block will not work properly with the line 2 A-lead.

I don't get what's going on as I never removed the 25 pairs going to the sets from the 1A strips they were punched to - only changing the wiring on the opposite side in regards to the connections to the KSU via the 7A strips. The wiring is correct from the KSU 66-block through the 7A's to the 1A and out to the sets. It's the same wires connected to the same spots on the 66-Block they would have been in the old wiring so they should work. Can anyone who knows these systems well tell me where to look to fix this A-lead issue and tell me why the line is humming?

If it helps I've attached a side-by-side of the same block before and where it's at now. With the image on the left you can see in the back of the block how I had the old wiring coming straight up to all the strips vs using the 7A's on the right.

[poplar1]

If the A lead works only on the first line, this is usually caused by the A lead for the first line and A1 lead being reversed. (There is only one A1 lead for the entire set, whether 4-, 6-, 10-, 18-, 20- or 30 keys (line buttons)).

I believe that your top 25-pair cable  (left photo) is punched down starting with the blue-white conductor, and the second cable is punched correctly starting with white-blue. So if you don't want to repunch the whole cable, you will have to reverse each one of the single-pair jumpers (on one end) going to the top block. Or, at least reverse the one jumper pair going to the second pair of the cable, so that the white conductor of the jumper goes to white-orange (A lead of first line) of the 25-pair cable, and the blue conductor of the jumper goes to orange-white of the cable (A1 for the entire set).

Table is for a WE 564HK or HL. L1 and L2 are the line/busy lamps for the first two lines. (From TCI Library)

[rturner]

If the A lead works only on the first line, this is usually caused by the A lead for the first line and A1 lead being reversed. (There is only one A1 lead for the entire set, whether 4-, 6-, 10-, 18-, 20- or 30 keys (line buttons)).

I believe that your top 25-pair cable  (left photo) is punched down starting with the blue-white conductor, and the second cable is punched correctly starting with white-blue. So if you don't want to repunch the whole cable, you will have to reverse each one of the single-pair jumpers (on one end) going to the top block. Or, at least reverse the one jumper pair going to the second pair of the cable, so that the white conductor of the jumper goes to white-orange (A lead of first line) of the 25-pair cable, and the blue conductor of the jumper goes to orange-white of the cable (A1 for the entire set).

Table is for a WE 564HK or HL. L1 and L2 are the line/busy lamps for the first two lines. (From TCI Library)

How did I not notice that the pairs were reversed. Then again those 25-pairs were punched when I was 13 before the days of being able to have the chart to follow on a tablet... I must've punched the straight up daisy chain the same way as the 25 pairs which is why the system worked right the first time.

The leads are working now for the correct lines. Now that the lead control is fixed the only issue with Line 2 is that it won't hold anymore but I think that's more a problem with the line card as when I swap the cards in the KSU the "won't hold" issue of the hold button just breaking the A-Lead is following the card regardless of what slot it's plugged into. I'm going to guess the card is probably also the issue of the faint hum/buzz I'm hearing on that line as well.

[rturner]

This is the 400 type line cards my system has, although none of the 400 series line cards I find online look the same as this one. Similar, but not the same.

[poplar1]

You can use other manufacturer's cards, such as Western Electric 400G or 400H. Do you have a ground wire connected to the Key System? If so, you can also use any W.E. 400D card.

Older issues of W.E. 400D cards will not detect incoming ring without a ground connection to the key System.

What kind of lines do you have?

[rturner]

You can use other manufacturer's cards, such as Western Electric 400G or 400H. Do you have a ground wire connected to the Key System? If so, you can also use any W.E. 400D card.

Older issues of W.E. 400D cards will not detect incoming ring without a ground connection to the key System.

What kind of lines do you have?

Line 1 is a standard POTS telephone line and Line 2 is the phone line generated by the MCS350 system I have installed alongside it.

I've swapped the cards back and forth to see if it was a line issue (which it shouldn't have been as they worked fine with the system before) and the problem with the hold seems to follow the card.

[rturner]

This is the current state of my communications systems. The key system on the right I just finished redoing the wiring for. The system on the left is new to the setup but is installed there on a temporary basis which is why for the moment I can live with the mess of wires coming off it. The core of the system is supposed to be installed in a system enclosure which I don't have yet but plan on building a custom one.

Eventually that system will move to a room upstairs and be connected to the lower of the double BIX blocks by a single 50-pair (if I can find one that long) cable.

[5415551212]

Whats the system on the left?

[rturner]

Whats the system on the left?

It's an MCS350 intercom system integrated with the key system. The MCS has its own consoles to control the system but can generate a telephone line via an interface card which allows any DTMF telephone to use the system by using * shortcuts. I have it connected to line 2 on the key system so in places where there are no consoles (since the system maxes at 3 when the interface card is installed) I can use the intercom from a phone.

Came out originally in around 1983 as the Petcom MCS250, was acquired by Dukane in 1989 and upgraded and renamed the MCS350 before being sold off a couple more times and ultimately discontinued in the late 2000's.

Here's the basic specs and system components:

https://static1.squarespace.com/static/53a0d6dde4b0a181d652968b/t/540e801ae4b03cae57f0ef35/1410236442961/Dukane+MCS350+Intercom+Systems.pdf