atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems ITT 403 MOH practice

Does anybody have a copy of the practice for a 403A MOH isolation card? I just scored one and I don't want to guess. A quick google search was fruitless, as most searches for ITT practices seem to be for me. Sam, or any of the non-bell guys?? You must have put in a few of these.

As I recall, you had to remove A Battery from pins 3 & 18 and then you fed music in on that pair. It was only good for four(???) lines - I think.

I'll look to see if I have prints. I probably put in dozens.

But none more recently than 1975.

I'll look.

Sam

OK. I didn't even have to go down to the dreaded basement.

Here's the info:

https://www.wedophones.com/Manuals/Itt/ITT%201A2%20601-501A-512A-584C.PDF

It's on pages 17 & 18

Aha! It'll service 6 CO lines (not 4) BUT you will need a 20 pin card mounting apparatus (359 -single or 259 - double) to install it - it's a 20 pin card.

Or maybe not. Check. I do remember some butchered installations, but I can't recall if they were 403s or 414s (definitely 20 pin).

Twice, As I recall, I've seen butchered installations (because they didn't have a 20 pin slot). Once someone drilled a hole in the center of the card, screwed it to the backboard and then soldered wires onto he fingers of the card. That was the worst install I've ever seen.

Another time I found one installed in a 501 KSU and couldn't understand how. Closer examination revealed that the installer took a jeweler's saw and sawed off pins 1 & 20 (unused on the card) and fit it in to an 18 pin slot.

Unless your 1A2 system HAS a slot with 20 pins.

But I can't recall what it is. Or why ITT would tell you to mount it in a 259 - maybe because you've got to completely redo the wiring on the card.

I think that's it. You might have to strip the wiring off of a slot and then rewire most of it.

Sam

Well..."back in the day" a tech had to be certified on the ITT 1A2 equipment to purchase and install it. Since part of the certification was that the applicant had to promise "with the weight of any and all applicable laws" to NOT mess with their factory wiring. Hence the provision to mount the 403 in a 259 housing.

The simple thing is everyone that used the 403 just used an existing slot and cut off lands 1 and 20 or removed an 18 pin socket and replaced it with a 20 pin socket. After a while, ITT had a sixth 20 pin socket in their KSUs for 20 pin cards like the 403.

Rcaman

Thanks, guys! I've been using WECO 400D cards in my ITT KSU since the start, with a WECO 451B MOH card in a modified external card slot connected with a piece of 25pr to a 66 block. This will greatly neaten things up. I'll likely remove the factory wiring from the sixth slot and rewire it to accommodate the 403 card. Then I can go back to the 400E cards that I really like. The WECO MOH card depends on the imbalance created by the hold bridge on the 400D cards to work, and won't work with any other cards besides the 400G. Interestingly, the 403 requires A-battery. I'm assuming some kind of amplifier. The WECO 451B is a completely passive card.

The 403 has some integrated circuits to provide isolation as well as balance.

Rcaman

Count the pins on the card (before you cut anything off!). I really can't remember if it was an 18 or a 20 pin card.

Sam

It's a 20 pin card to prevent you from plugging it into a standard line card slot that is full of voltages, flashes, winks, etc. which will certainly blow out the isolation transformers. The 403 card supports seven CO lines (strange quantity). 14 pins are used for the isolated MOH outputs, two per line, two are used for MOH input and two are used for power.

Ed, I'm looking at a print for a 403A. Music In, 6 circuits music out AG/AB, 2 spares and.....maybe only 18 pins. If it is a 20 pin card then there are also no connections to pins 0 & 19 (or 1 & 20, depending on how you count them).

I hate this getting old sh*t. It's not that I don't remember anything, it's that I forgot half of what I knew - about everything.

Very annoying.

Sam

Just counted... 18 pins. I'd invent something before I hacked a card made of unobtanium.