This old modem

As I was rooting through the storage unit the other day, in search of something entirely unrelated to anything Apple II’ish, I stumbled across my very first modem.  I thought I’d disposed of this thing years ago and was happy to learn I was mistaken.  I was almost as happy to learn that I’d had the sense to make sure I packed the massive power brick along with the rest of it. I despise proprietary power connectors for this very reason.  I don’t blame developers for rolling their own but I’m terrible at keeping track of them, especially as the years begin to roll by.  The worst offenders are the companies who don’t bother to mark the brick with information about what it’s intended to couple to.  But that’s another rant…

My father originally brought this home from work when the company he worked for, NCR, bought his engineering department a handful of Apple ///’s so they could put in extra hours at home on the weekend.  My dad and a few other key personnel each got one and every Friday night, he would pack that 26 lb monster and all its accessories into the family Opal, drive it home, unpack it again and set it up in his study.  On Monday morning, back it would go.

When NCR replaced their ///’s with shiny new IBM PCs, he got to keep the modem and it integrated nicely into the family II Plus (and later, IIe).

To get back on topic, I plugged it into my IIe to see if it still worked.  Spoiler alert: it did not, so I decided to take it apart for a little quick & dirty troubleshooting.  Here are some photos and notes I took.

(Click on the thumbnails for full-size images.)

 

2012-07-14 10.38.32

The Racal-Vadic Auto-Dial VA3451 300 bps modem.  This little baby and me, plus my hacked up copy of ASCII Express Pro, made one lean, mean BBS-in’ machine.  The manual states that this model could also do 1200 bps out of the box, but I specifically remember that it would only do 300 for the first few years we had it.  It wasn’t until I bought a PROM upgrade that the blazing speed of 1200 characters per second was unlocked.

 

2012-07-14 10.39.26

Self-test instructions are clearly delineated on the bottom of the modem.  Note the lack of screws holding the unit together.

 

2012-07-14 10.39.58

Back of the modem, showing the switches, phone and power cables and the 25-pin serial connection.

 

2012-07-14 10.41.49

With the cover off, we can see that the modem is a two-board device with lots of chips.

(More after the jump.)

 

2012-07-14 10.42.17

A closer look at the LED bank and switches.

 

2012-07-14 10.51.38

A view from the side, near the front of the modem.

 

2012-07-14 10.52.37

The top and bottom boards connect electrically at these points.

 

2012-07-14 10.53.51

Top board removed.  The chip with the white label is the upgraded PROM I bought from Racal for about $50, if I recall correctly.  This allowed the modem to work at a screaming 1200 baud, nearly four times faster than the previous 300 baud limit.

The black plastic at the top left at first looked like RFI shielding, but it’s not – it hides the power unit and I assume removal constitutes a voided warranty.  Fortunately for us, the warranty ran out years ago.

 

2012-07-14 11.03.20

Cover off, we can see the modem’s power unit.  The red and green phone line connections are soldered to the board here as well.

 

2012-07-14 10.54.19

Close-up of the upgraded PROM.

 

2012-07-14 10.54.37

Heart of the beast.  The Racal-Vadic 3451S is powered by an Intel P8038 microcontroller from 1977.

 

2012-07-14 10.54.49

The business end of the phone line cord is directly soldered to points on the PCB.

 

2012-07-14 10.54.59

I believe that date code is the 47th week of 1980, or November 17th – 23rd.

 

2012-07-14 10.55.36

This switch bank allowed for greater control, and access to several functions normally off-limits to end users.  The chip is an Intel P8234 I/O expander.

 

2012-07-14 10.59.42

The modem entirely deconstructed.

 

2012-07-14 11.01.22

These orange stand-offs (foreground, and background in the upper right) provide the mounting for the second PCB.

 

2012-07-14 11.05.25

These pegs anchor the PBCs at the corners while still allowing them to be easily removed.

 

2012-07-14 10.52.07

In an interesting design decision, this is the only screw holding anything together in the modem.  Everything else is secured with stand-offs, clips and mount connections.  The screw goes through both PCB and sinks into a threaded hole in the bottom of the case.

 

2012-07-14 11.09.58

Threaded hole for the lone screw securing everything in place.

 

2012-07-14 11.11.14

These clips along the edge secure the two halves of the shell together.  The screw and the supports and stand-offs keep everything in place internally.

 

2012-07-14 11.12.482012-07-14 11.12.57

Another look at the operating instructions for the Rear Panel Controls.


In the end, the modem was easily returned to working order.  It only required re-soldering the phone line connections and re-seating the incoming power line connector.

Now the only thing that remains is who to call?  If I find a dial-up service that can still handle 1200 baud, maybe I’ll video myself connecting and post it somewhere…

I scanned and posted the manual here, if you’re interested in more detail.

 

One thought on “This old modem

Comments are closed.