Gandalf LDS 120 Modem Innards?

[Martin Hepperle]

In the 1970s/80s, at the University, we were connected to the mainframes via terminals.
For this purpose we used small blue boxes (must have been Gandalf LDS 120 modems) to connect via 4-wire lines to remote locations.
You simply, switched the modem on and your connection at 9600 baud was established.

Internally these modems must have been rather simple - just a power supply, a modulator and a demodulator - no dialing etc intellgnece required.
Doe someone have such a box and could take some photographs of its innards?
I cannot find any technical information on the internet.

This is just to satisfy my curiosity - however, if I had a pair of them I would try to hook them up...

Martin

 

[cchhrriiss11]

Hey Martin,

Gandalf you say? I've got a bit of a Gandalf modem collection... they were Canadian, after all



The two larger modems on the bottom have some local history, they came out of BC Ferries and were used to connect the Tsawwassen Ferry Terminal to their head office, back in the 80s.

There's more info here on a post I made a year ago on Twitter:

https://twitter.com/x/status/1661132808256110597

Regards,

Chris

 

[Martin Hepperle]

Nice - the blue color and the characteristic font seem to have been part of the companies look-and-feel.

Hoever, the LDS-120 is a much smaller and simpler device...

Martin

 

[Gilatrout]

Are you still interested in this? I just grabbed several from a pc recycler and could provide details if you like

 

[Martin Hepperle]

Yes, it would be interesting if you could take the cover off and make a few photos of the PCB.
As I am in Europe, shipping costs are usually too high to make sense.
Usually one needs a pair of them or another larger modem (like a multi-port PACX) as counterpart.

The small LDS-120 were the bread and butter modems at my university when terminals located in buildings away from the computer center were connected to the mainframes.

Martin

 

[Gilatrout]

I posted a complete set of photos for each revision I had on Archive.org here. Curiously the logo got bigger for Rev. E for some reason. I will try and go back and grab the others and if they are different revs, document them too. If I can get the others, I'll bring them to VCFSW 2025 in a few weeks for anyone else interested in them.

 

[Martin Hepperle]

Thank you - that's quite some analog technology to de/modulate the phone line to RS 232C - looking at some pictures I now believe that we also had the LDS 125, which has a two digit select switch on the front panel like this one:

(taken from https://uwaterloo.ca/daily-bulletin/2023-05-11)

 

[Gary C]

Crikey

We have literally hundreds of LDS120's scattered around site where I work, some even still work ! We used them to connect GEM80 PLC's and D Robinson alarm units to the main computer system. Certainly robust units.

I also remember Preston Polytechnic had a PRIME computer that had a wall of these, connecting all the terminals around the campus to the machine. Looked very futuristic with its smoked perspex front and flashing red lights. Shame it was scrapped before anyone thought to preserve it.

 

[Gilatrout]

Thank you - that's quite some analog technology to de/modulate the phone line to RS 232C - looking at some pictures I now believe that we also had the LDS 125, which has a two digit select switch on the front panel like this one:
View attachment 1302007
(taken from https://uwaterloo.ca/daily-bulletin/2023-05-11)

Glad to help. Let me know if you need anything else.