sundance-communications.com/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems Melco Intercom with Bell Systems 551C help needed

I hoping to get some help with some wiring on a installation I'm working on of a Bell Systems 551C and a Melco KT19. I've never worked on 1A2 and am stuck on wiring for the Melco Intercom. I've completed the 551C install and it's working fine. I installed the Melco today but couldn't get much working. When I was done I was only getting a single click on the buzzer (KS-20419 buzzer on 2564 phones)of a two of eight phones and I had a had hum on the talk path on all phones. I hooked up 110v from 551c (RG & RB) to AUD SUP and GRD on Melco, then 24vdc from 551c (GB and BB)to A BAT and A GRD, B BAT and B GRD, then T & R to each 2564 phone Line 5 T & R. The Melco instructions say filtered 24vdc to A BAT. Is filtered needed? Any ideas on clicking problem with buzzer or problems withhum on talk path?

Filtered DC will make the talk path clean and silent, otherwise it will have a hum on it. I do believe that filtered DC lives on your 551 power supply. I'll check, but I'm sure it's there.

The reason that the buzzer is clicking and not buzzing is that buzzers use 10VAC or 18VAC ( depending on whether they have blue or white wires). Also appearing on your power supply. 110VAC is for the ringers in the phone.

Sam

Thanks! Buzzers have blue wires so they are 10VAC right? Can lamps be used when buzzing phones from Melco?

Blue =10 Volts.

Lamps can be used, though depending on the number of lamps lit at the time, they may dim slightly.

I looked at a old power supply from a 551(may not be the same as yours) and it has two 24VDC supplies, one marked Signal and one marked Talk. Talk is filtered and Signal is unfiltered.

Sam

The buzzers won't cause any noticeable lamp dimming unless you buzz every buzzer at the same time. Watch your polarity on the 24VDC. Ground is positive. "A" Battery is -24 VDC Filtered Talk battery. "B" Battery is -24 VDC Unfiltered Signal battery. If you get your talk battery connected to "A" Battery on the Melco, the talk path will be silent.

You have 10V AC buzzers. There are 90 VAC (or ring current) buzzers available. They will have an "ingrown" lump on one of the leads which is a dropping resistor. Those would be connected to RB and RG.

Rcaman

Thanks for your help. OK. I see filtered and unfiltered on the schematic now.

Sam, I have a follow up question. My Melco has two battery supplies on the schematic A and B. They are hooked up to the shoebox correctly but there is some hum on the intercom line. Are you suggesting both be connected to the filtered supply? Anyone know why the intercom schematic wants filtered and unfiltered ? Just curious

Most subscriber (as opposed to Central Office) telephone equipment relays use unfiltered DC because it's cheap to make. Filtered DC is more expensive (requires a choke and a capacitor at every power supply) so it is generally reserved for talk paths.

You fastened wires from terminals in your shoebox that are labeled BB and GB to terminals on your intercom that are labeled A battery and Ground. That should be you first clue as to what you fouled up.

Use A battery where it calls for it and you will not have (much) hum. Is it required? Yes. Take a test set and listen to AC, unfiltered DC ("signal") and filtered DC ("talk'). You will hear the difference.

You can find A-ground / A-battery on the right side of the terminal strip in the shoebox, on terminals 43 and 44 (4th pair up from the bottom.) Pull the power plug when doing the terminations to avoid popping the fuses, or blowing out the full-wave bridge in the power supply. The geniuses who designed it put the power terminals at the least convenient spot, in a KSU that usually is mounted in the least convenient spot.

Do you have the BSP for the shoebox?

click

Yes I do have the schematic. Thank you.
When I hooked the Melco up I followed the instructions on the label. There were 3 power supplies listed. The signal supply which I have to the lamp supply for blue wire buzzers. And then two more inputs that are labeled A battery and B battery so that's what I hooked them to.

So basically what we are saying here is that both should be connected to the A battery supply correct?