555 Switchboard Trunk Circuit Issue

[trainman]

I have a CO Trunk circuit issue. My trunks units will not light up on an incoming call. I can answer them if i hear a call come in. I can plug in and place an outgoing call.

I have one individual trunk unit where the light will light on an incoming call, but when you plug in, it wont connect. and it wont connect if you try to place an outgoing call.

now, the weird part. when I brought the board home, there were two incoming lines wired directly up to the buzzer. I guess it wasnt working for who ever had this board before me.

Thoughts? do i need 48volts maybe to make it work correctly?

[Victor Laszlo]

Do not apply 48 volts. It will blow out your lamps.

Are you using a key system supply?

24 Volts?

Do you have the batt and ground reversed?

Is the BATT key turned to ON?

Do you have the supply grounded?

Are the incoming trunks conventional (from a real CO) or from a VoIP ATA, or from some other source (local PBX or key system, for instance?)

If you manually operate the R relays do they lock up?

[trainman]

Im using a key system power supply

mine has 48 volt lamps installed.

i have a POTS line, but I also have ATT Uverse internet on it.

i ve trie reversing battery polarity. doesnt make a differnece

yes, the R relay will lock up if i manually close it.

Ground the supply to what? The PBX frame?  Or something like a water pipe?

[trainman]

I dont know what i did, as it was working. But i still have two trunk circuits that act differently than the rest

[trainman]

i found one trunk that works. it has a different circuit arrangement than the rest. and the other one that sort of works has the same modification. probably a bad component on that one

[trainman]

I have two types of trunks with slighty different wiring,

one version has two 8a thermistors, and the other has only one 8a thermistor.

1 have two units with one thermistor, and only one of those works correctly.

the bulk of my trunks are the older version with two thermistors.

Right now, I can connect to every trunk. only the ones with one thermistor will have the lamp light on an incoming call.

Before, I couldnt connect at all to the trunk units that have two thermistors.

i think there is a short, or a loose wire that is common to all trunks.

[trainman]

Think I figured it out.


J59013F-2 trunk units look to be arranged for grounded ringing.

J59013F-3 trunk units are bridged ringing.

Which might explain why when I brought the board home, I had an incoming line attached to the buzzer

[trainman]

another weird thing. there are times when i cant connect to any trunk. Plug in, no dial tone.  Once I pull the switchboard dial off normal, a relay in the attendants telephone circuit clicks,, and i can connect to the trunks. weird

also i nothiced when i play with the switchboard, it makes my uverse modem go nuts. i get steady reds and flashing reds on the broadband and service lights. something about the 20 pps dial pulses seem to do it.

[trainman]

Odd behavior from that one trunk seems to be caused by a bad resistance lamp.