atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems A question that makes you go "hum"

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

And now you see the difference between installation and repair.

Unless I missed it, I did not see the phrase "...and then I took out my meter and checked for metallic problems..."

A doctor will first check temperature, pulse rate, and blood pressure, regardless of the complaint, because experience shows that those three parameters can quickly be indicative of a patient's general condition.

The analogous readings by a professional telephone repairman are the results of testing with the KS meter. He will open the line(s) at the NID and look back towards the CO, and inward to the building, for metallic problems such as opens, shorts, escapes, grounds, crosses, and unbalances.

Eliminate those suspected problems, and then the real testing can take place. A parts replacer is not a repairman. In my career, I have followed around a herd of parts replacers.

As my old boss would say about his least favorite of them: "He couldn't find a cross in a church."

Arthur what is an "escape"?

Arthur -

As it happens, I'd had a hum on 7303 last week, for voice, nothing to do with the alarm panel.

Last week I finally got around to asking AT&T to come out to investigate noise on 7303. He found a number of problems, some of which you mention above. Now the voice quality is crystal.

I'm not a pro at this, I am a parts changer with very limited 1A2 troubleshooting experience, and it's a hobby. I learn as I go. I wouldn't even know how to begin to check for crosses, unbalances, or escapes, even if I knew what they were. I try this or that, trying to follow a process of elimation as best I can.

The problem lies somewhere between/within the KSU and/or within the alarm panel, and I'm suspecting a bad escort board in the alarm. Yes, parts changing again, but it's been acting up from time to time anyway, losing it's programming, etc.

So I'll keep doing as best I can, trying various things to at least narrow it down. As for your analogy... I'm not a Dr. at this.... a better one would be that more or less I'm a janitor with an interest in heart surgery, and that's the best I can do.

Thanks for the help though,

- Matt

Matt -

If you disconnect 7303 from the alarm panel and leave both lines working on the KSU - do you still have a hum when you call line to line?

Sam

OPEN = broken wire
Symptom = no dial tone, hum on adjacent pairs, hum on bridged appearance (see unbalance, below)
Measurement = no continuity to ground or battery references

CORRODED OPEN = a splice point that has gone bad, or a spot in a wire that has been nicked, then corroded, so that it acts as a high resistance.
Symptom = static (station beyond the fault) / hum (station before the fault) ...see also unbalance.
Measurement = a slight unbalance.

SHORT = a low impedance cross of tip and ring sides
Symptom = NDT, NINC, CBC, BDR.
Measurement = 15 points or more continuity across tip and ring

HIGH RESISTANCE SHORT CIRCUIT = a high impedance cross between tip and ring
Symptom = noise, static, hum, pre-trip, BDR.
Measurement = less than 15 points across tip and ring

GROUND = low impedance continuity from a conductor to earth
Symptom = loud hum (tip side) NDT or permanent signal ("PS") (ring side)
Measurement = continuity to ground, over 15 points.

CROSS BATTERY = low impedance continuity between a conductor and a foeriegn battery potential (usually the ring side of another circuit) Symptom = cross-talk, hum, false ring-up, and in severe cases, NDT or PS
Measurement = 15 volts, or more, DC to ground.

ESCAPE = a high impedance cross from a conductor to either ground or battery.
Symptom = noise, static, hum.
Measurement = Generally any reading less than 15 points will not affect service.

UNBALANCE = an imbalance of the earth-referenced capacity of the two sides of the circuit.
Symptom = hum or static
Measurement = a differential of even one point, comparing the tip and the ring sides, will indicate an unbalance.

SPLIT = two halves of two pairs make one pair
Symptom = hum
Measurement = correct kick from earth to each side. Lower than expected mutual capacitance between sides

TRANSPOSITION = pair numbers do not correlate at each end
Symptom = repairman confusion
Measurement = good pair

REVERSAL = Tip and ring swapped somewhere
Symptom = CBDT on TT sets without polarity guards, NDT and false ring-up on ground start trunks, and a few others
Measurement = good pair, battery and ground reversed at NID

One point of measurement from earth to tip or ring, represents, roughly, a length of copper wire 500 feet in length.

BDR Bell Doesn't ring
NDT No dial tone
SDT Slow dial tone
CBC Can't be called
CH Can't hear
CBH Can't be heard
CBDT Can't break dial tone
CCO Can't call out
CXTRF Can't transfer
DTRAD Dial tone returns after dialing
BRCM Bell rings, can't meet
HOOL Hears others on line
NSY Noisy
STC Static
OHOP Only has one phone
ETIR Every time it rains
WIM Where is man?
GWN gets wrong numbers
GCIE Gets called in error
HICAP high capacitance
BT bell tap
NCR No coins return
CTC Cut to clear
DIY Dog in yard
KWS Key with super
KWD Key with doorman
KWN Key with neighbor
SDD Sleeps during the day
NA No access
O/D out of order
FDR Feeder
BP Binding post
UG Underground
MH Manhole
P Pole
PS Permanent signal
PG Permanent glow (British)
ROH Receiver off hook
XTALK Cross talk
ESC Escape
ESCT/S Escape on the tip side
ESCR/S Escape on the ring side
GRD Ground fault
GRDT/S
GRDR/S
OBS Open both sides
OTS
ORS
XBAT Cross battery
XBAT T/S
XBAT R/S

This is only a minuscule look into what a repairman needs to know. Obviously, actually knowing how to fix the above faults is a much more complicated endeavor, which would take me a few years to explain. Telephone repair, even though it "only uses low voltage" is a craft that takes years to learn and to decades to perfect.

Sam -

In between 2 get togethers right now, have to bolt again.... but will try this when I get back and let ya know -

Thanks!
Matt

Arthur -

That's about as complete a list as I've seen in years. Thanks for posting it.

Just to stick my $0.02 in -

Why is "out of order" abbreviated O/D?

In my youth, I once used OOO for "Out of Order".

I was corrected by an old timer who told me it stood for "Over & Drop" - An action used by repairmen on the old cord boards (We or SC 555 or similar). If the line was Out of Order they would pull the associated cords out and hang them OVER the back of the board and DROP them down to keep the operator from using them till the circuit was fixed.

I don't know if it's true or not, but it sounded good.

But getting back on track.....Arthur - Why are you beating up on Matt? He asked a question about a complex repair problem. He's trying to do the right thing. I don't think he has a KS meter.

Is this a long seated grievance of Installer vs. Repairman?

I think that war is over. At least for us.

Sam

It's easier to say "oh-dee" than it is to say "oh-oh-oh" (and believe me, I love to hear people say the latter.)

We just took a rubber band and tied the defective cords together. An operator would never put up with something draped over "her" switchboard. When the board gets busy, the cords would definitely get in the way of operations.

I guess that did sound a bit harsh, sorry.

I am not beating him up. I sometimes, however, wonder how people can expect to solve a "complex" problem that might not be so complex if only the correct initial tests are performed. I was actually trying to help him by showing him that his trouble-shooting methods were probably giving him skewed results, and complicating his interpretation, rather than eliminating the basic faults.

If one's hobby is, say, old cars, would you not expect the hobbyist at least to own a timing light and a dwell meter, and to know how to use them? The simplest tools are the buttset and the KS meter. They are available and a telephone hobbyist of Matt's interest and capabilities (I've spoken with him, and he's a smart cookie) really needs to get acquainted with the use of them.

I repeat: For humans it's blood pressure and temperature. In telephony "It's all battery and ground."

Matt is to be commended for diving into the problem, but we don't want him to drown in a sea of confusion, do we?

All,

I wish to close this thread down, I think I threw too much out there at once. I can completely eliminate the KSU from the circuit, and the problem remains. Why having 2 incoming lines would cause hum when communicating from 7303 to my escort voice module would induce hum is beyond me... but there it is. Not a big deal, everything works fine, I can live with the hum. It's just one of those things that sticks in my side.

Thanks -
Matt