I am hoping to tap into the vast knowledge of this forum. I recently acquired a 551 KSU that was installed in a house. I have a power supply and the key unit. Not really sure if I am on track with the power supply wiring or not.

Also, I would like the phone to ring and I recall there is a jumper I need to connect to make that happen.

I am not sure if the masking taped wires originally went to the power supply or not, this system was in my parents house and it all got ripped off the wall when it was replaced with a different shoebox ksu.

Thanks in advance for the help.

Your A Battery (24v DC Talk) is wired around the fuse. (Probably a blown fuse). Get a replacement fuse and move the wire to the right hand terminal.

I'll have to check about the taped wires, but I don't think they go to the PS.

The jumper you're talking about was between the R1 leads (individual line ringers) and the CA (common audible) connection. This was done if you wanted an easy way to get multiple lines to ring on the same phone.

Sam

Thanks for the help. Any ideas on a source for those fuses ? The masking taped wires go into the bundle of wires that feed the line cards, do they need to be terminated somewhere ?

The taped wires are just optional leads from each card slot's pins 3 and 18. They aren't normally used for anything.

You can probably find the fuses on eBay. I'll look and see if I have some.

Ed's on the $. Some cards required 24V DC Talk battery on pins 3 & 18 (manual intercom, ring down cards, etc.)

Sam

And you may need an ac generator, to ring all lines to a common bell.

Maybe this will help:

BSP for Shoebox

Some observations from your photos:

The original type 28-type power unit is not present, and has been replaced with the external 20B2 unit. Sam is correct that there are a couple of open fuses, and they need to be attended to.

The extra wires are, as Ed has said, the -24Vdc filtered and ground wires to allow a manual intercom card (401-type) to be plugged into any of the 4 slots. The factory wiring allows only the 4th slot to be used for that type of card.

The convention for wiring a power unit is as follows:

Blue/White pair for "A" TALK battery / ground with the tip (white) being the ground and the ring (blue) being used for the -24. (filtered)

Orange/White for "B" SIGNAL battery / ground, with the white being ground and the orange being the -24. (unfiltered)

***NOTE that "signal" supply in phone company equipment does not mean "noisemaker" supply. It means the juice that operates the relays.

Green/White for the LAMP supply / ground. White for ground, green for 10Vac. (also used for the interrupter motor)

Brown/White, spare

Slate/White, ringing generator supply. White ground, slate 105Vac.

Red/Blue spare

Notice that the 6-pair that interconnects your KSU and power unit is wired using a reversed color code. This is no big deal, since it's wrong at both ends, but you might want to correct it at some point.

The Slate/W pair that is terminated on the generator output screws gets punched down at the extreme bottom right of the 66 block, on the terminals marked RG and RB. That will allow you to use common ringing in your key sets. You don't need to add a ringing generator, since there is already one right there in the 20B2 supply, all wired up and ready to go.

You also need to ground the KSU (using the three screws at the top) to an electrical ground or a cold water pipe. This will ensure reliable ringup using the WE 400D KTU's (line cards) that you have there.

As it is wired now (with those fuses bypassed) I am getting a click from the line card when the phone goes off hook (or when I short the a/a1 punchdowns) but I am getting no light on the phone set or the line card. I am also unable to get the interrupter to "run" when the set on hold.

The wiring from the 551a to the 20b2 was wiring I did a while ago when I started then abandoned this project. I will re-do it to spec.

The whole reason for reconnecting this stuff is simply that I love the 1a2 system and I have a great 2830 speakerphone that works far better than any phone I have ever used and I would like to begin using it again.

Thanks again for the help.

The wiring looks like it would work, regardless of the weird color code. It seems that all the wires are punched down at the correct spots.

Do you have a digital volt meter?

If so, take a reading from any of the ground screws at the bottom of the power unit (they are all common) to the screw where the white/blue wire is terminated. 10 volts AC?

If so, take a reading from the terminals where the white/blue power wires are terminated in the KSU. 10Vac?

If so, short the A & A1 terminals of the first line card and take a reading from the Lamp/Lamp Ground terminals. Count down to the 5th and 6th terminals in the left row of the 66 block. 10 Vac?

The click is normal, when you short the A leads. That's the sound of the A relay in the line card operating.

The (two) 10 Vac outputs of the power unit would be the least likely to fail, because they are both just direct transformations of the primary supply, and do not run through a rectifier, which is easily blown out through shorts or bad wiring. if the screw where the white/blue wire is attached is dead, try the screw right above it. It's another 10Vac output.

"Upon further review..."

I just expanded the photo of the power unit about 300% and I notice that the white/blue and white/orange leads in the 6-pair are not actually terminated on any screws. They seem to be just pushed down into the hole where the metal fuse contact is. Pull them out, strip the ends to get fresh copper, and tighten them under the screw heads. Then see if you get lamps.

I was able to get it to work. The wires were pushed into the holes which I put under the screws on the power supply but the real problem was that there were a few bad punchdown terminations.

All is working now except common audible ringing.

Sorry Arthur as well as being blind in one eye, and stupid; I missed the external power supply and the Gen. Taps. Maybe I'll just give this s**it up.

I'm not sure what you mean by "missed the external power supply."

If you punch down the two wires at the correct spot (bottom 2 terminals, right side) then the CMB should work.

No reason to quit now, you're almost done.

wh8428:

I have spares of the 3 amp fuses here on my desk but none of the 2 amp. PM me with your mailing address and I'll put some 3 amps in the mail to you.

Mark

3-amp fuses might not work. Some of the fuses that are rated for more than 2 amps have slots that are smaller (and fit screws that are smaller) so that higher-ampacity fuses cannot be used to protect a 2-amp supply. This was done so that the diode bridge (the most volatile of the various components in the DC part of the supply) would be protected against high currents.

I'll look to see if I have any 2 amp fuses, but......

If we were out in the field and did not have the right fuse with us, as a temporary measure, we would put in a thin piece of solder. In the event of a short the solder would melt and protect the equipment.

Sam