atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems Can anyone tell me why...

Can anyone tell me why I would get an extreme amount of hum/noise on my non-1A2 telephones if I have one of the 2565's off hook when picking up a "standard" single line phone?

All the 1A2 keysets are 2565 desk models, with the exception of one cuckoo clock.

The "standard" phones consist of a wall mount rotary, a wall mount trimline, and a (I really don't know the model on the next one, but it's identical to the one that used to be on the Johnny Carson show, basically a phone in a wooden enclosure). Oh yeah, a payphone also, but unplugging it completely doesn't help either.

None of them (with the exception of the payphone)date past '75 - '76, and the hum is present regardless of which one I pick up - until I put the 2565 back on hook.

Also it happens regardless of which 2565 I first pick up.

All the standard phones are home run and connect to the CO line before the KSU.

My only guess is there is some sort of backfeed when a 1A2 is off hook, and the "standard" phones need to connect after the KSU instead of before it, but I think that's a bad guess.

Is this where a diode block would come in?

TIA for any tips -

Thanks
Matt

Sounds like you're putting battery from a lamp lead to tip and ring when going off hook. Are you using the SLTs switch hook leads for you A A1 control? If you are remove the second pair and see if the hum goes away, I'm sure it will. You will than have to figure what's wired wrong. Could be batt from the A lead control also.

Matt, it sounds like the violet/green, voilet/brown and violet/slate leads from your 2565 set(s) are not insulated from everything.

Hey all -

Got it. My alarm system is leaking voltage into the return T&R. Heard a small hum with the butt set, then measured across T&R and saw .75 to 1.25v.

Took the alarm panel out of the circuit, no more noise, no more volts.

I was having some other problems with it a month or two ago, this just confirms my suspision of a bad board in the alarm panel.

Thanks for the tips!

- Matt

Matt: Glad you found it. Now, let's get back to how you have your single line telephones ("SLT's") wired into your system.

There are two ways, the right way and, you guessed it! the Bell System Way.

The SLT's need to be converted to A-lead control, and they need to be wired into your system, AFTER the line cards, not BEFORE.

This method will ensure that if a key set is used first, then an slt is picked up, then, finally, the key set is put on hook, there will be no false hold condition.

Another advantage will be on an incoming call, if the call is answered by an slt, the system ringing will stop, and the line lamps will go from flashing to steady.

You will need to convert each slt for A-lead control, and then run their wires to the output of the KSU. More than one slt can be wired to the same pairs, by the way. They do not need to be home-runs, if that helps.

Hey, Arthur: I must respectfully disagree, or at least ask for clarification. You certainly have more experience than I do with this stuff.

If an RJ12C is T/R/A/A1 AHEAD of the line card (supposedly to keep ringer load on the line side of it) and an RJ13C is T/R/A/A1 BEHIND the line card for non-ringing devices, like credit card terminals, etc....Wouldn't what you said be contradictory?

Not to mention that a fully-protected line card (e.g: ITT K400-TPL) wouldn't even allow ring voltage to pass to the station side.

As long as anything sharing that line has properly-functioning A leads, I can't see false hold condition being possible.

THIS and THIS are about the only things left that truly address these conditions anymore. In doing a Google search, it is very disturbing to me how many "authorities" give grossly-incorrect RJ information.

Ed, it didn't mention RJ9! Someplace I read a reference that claimed that 4P4C is an RJ9. All I ever called it was handset cord plug/jack.
OOPS, after double checking, it does mention it as 'un-official' designation. I guess I'm semi-vindicated, based on the description.
I guess it's just another case of someone trying to be technical in a field where he should be plowing instead of thinking! John C.

Yeah, it did under the picture. Take a look:

"Left to right, RJ connectors: an eight-pin 8P8C plug (used for RJ49, RJ61 and others, but often called "RJ45" because of its outward semblance to the true RJ45), six-pin RJ25 plug, four-pin RJ14 plug (often also used instead of two-pin RJ11), and a four-pin handset plug (also popularly, though incorrectly, called "RJ22", "RJ10", or "RJ9"). The middle two can be plugged into the same standard six-pin jack, pictured."

PICTURE

It seems to me you can't wire a/a1 ahead of the equipment! t/r yes, but you must be behind the card to even get a/a1 no?

You can wire T/R ahead or behind the line card as long as the A/A1 leads are present and that the switch hook contacts make before and break after the ones controlling tip and ring (yellow/brown switch hook leads were used for the A lead closure in the set).

Because the tip and ring of the line passes through a sensitive reed relay on the line card, high ringing current draw on the station side can damage these windings. This would normally be due to a large number of bridged ringers. Also, later fully-protected line cards did not allow ringing voltage to pass through to the station side.

In general, an RJ12 was used ahead of the card for devices that required ringing, like phones, answering machines, etc. An RJ13 was used behind the card for devices that did not require ringing, like dialers, credit card terminals or modems. Regardless, the A/A1 leads were always the same. There are no separate line and station-side A leads.