Hey all -
Looking for a little troubleshooting advice. I wasn't sure if I should post it here or in the alarm forum, but since (I think) I've narrowed it down to the KSU, I chose here.
OK, first off, the components:
ITT 601A KSU, 4 K400 line cards, 1 K403 MOH card, 1 SAN/BAR FM card, interrupter, ring generator, Melco intercom unit, 24V Valcom filtered talk battery transformer.
1 DSC Power 832 alarm panel
1 DSC Escort 5580 voice module/w X10
3 1A2 desksets connected
2 incoming CO lines (7303, 3942), one of which (7303) goes to the DSC alarm, and from there feeds the KSU/all other house phones. The 7303 run between the demarc and the alarm panel does not have the 3942 line in the cable, i.e. it's a dedicated seperate run.
1 Power 832 DSC alarm
1 5580 DSC voice module/w X10
I use the DSC/5580 to control alarm functions, various X10 controls and my HVAC via any deskset in the house (or away).
The problem: If CO line 2 (3942) is connected to the KSU, either tip, ting, or both, there is a very noticable hum when "chatting with" the 5580 voice module on 7303. If I disconnect the KSU from that line (3942), the hum goes away.
Things I've tried to isolate the problem:
1. Disconnected all house phones, except the KSU feeds, from the incoming CO lines.
2. Running the KSU CO feeds from the demarc on completely seperate feed cables.
3. Unplugged all 1A2 deskets, leaving the 1A2 powered up, and used a non 1A2 phone to check for hum.
4. Swapped out the 2 active line cards.
5. Powered down the KSU, and everything else 1A2 related, removed all line cards and used a "normal" phone to test.
6. Ran the supply from the demarc to the alarm panel, and then back to the KSU, on physically seperate cables.
7. Powered down the entire house by shutting off all individual breakers as well as the main breaker.
8. Swapped my alarm over to 3942 from 7303. Same hum, but now on 3942.
9. Just for a laugh, swapped T&R on 3942.
No matter what I try, the hum between any house phone (1A2 or not) and the alarm panel remains until I disconnect the 3942 line from the KSU, and then it's clean and clear between 7303 and the alarm panel. Normal voice calls are always crystal clear on 7303 and 3942, no hum at all.
The only thing that is definate is that if I disconnect 3942 from the KSU, the hum goes away.
I'm at a loss as to what to try next. I'm guessing there has to be some sort of induction going on in the KSU, but given that I've taken out all the line cards and powered it down completely, with the hum remaining... I don't see how this is possible. There are no AC lines near the incoming CO feeds, the alarm feed/return, nor any of the outgoing 25 pair cables.
Maybe the problem lies with the DSC escort card.
One other thing: the 601A is EXTREMELY well grounded. Ken made sure of that.
And another: If I access the escort from an outside phone line (in this case, my cell phone) - the hum does not "seem" to be there. But the voice quality of my cell is pretty poor, so I can't say for sure if the hum is there or not when accessing it this way.
I'm not looking for a fix with ths post, just maybe some other brainstorm type things to try.
The only next step I can think of is to replace the escort card, but my gut tells me it's not the problem, and at $175, I'd prefer that to be the absolute last thing I try.
Thanks much for any and all thoughts on this....
- Matt
