atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems 400D cards on 1A2 system

Hi, I just solved a big mystery with a 620A panel and 79B2 power supply which would not light the lamps on 565 sets with inbound ringing.

The 400D cards were pre-issue-15, and I found they *must* have a good ground through the power supply to work properly. The 79B2 p/s I was using did not have a ground connected to LOC GRN.

Someone on my antique telephone collecting list clued me in on this issue.

I earth grounded the terminal at LOC GRN on the p/s, then called in on the CO line. The interrupter powered up, and the lamp began winking.

I also re-tested it by disconnecting the ground and then replacing the older 400D card with an issue 15 400D card, which I found will ring on bridged ringing. I called in on the CO line, and the interrupter powered up, and the lamp began winking.

This solved a big mystery for me, and perhaps it will also help someone else.

Yes we discussed that very problem in another post where someone couldn't make a 551 (I think) ring. You are right you have to have an external ground.

Yes all those 1A2 power supplys needed to be earth grounded . That is why they had a screw lug for it . Another big problem was installers using to small of gauge wire between power supplys and 1A2 equipment . That caused all sorts of system havoc .