A networking tech confirms: Miracles can - and will - happen!

Flashback to the early 1980’s. I’m a relatively new tech working out of a remote one person field office. My task, to install four brand new dumb (and I do mean dumb) terminals on an existing mid range system. The system is located in the business school of a university, and it typically has all 20 or so terminals occupied with students. The mini-mainframe has a processor that looks like a microwave oven and four washing machine sized drives in one room. The four dumb terminals will go in an adjoining room on the opposite side of a concrete wall.

I arrive onsite and unbox the four terminals. They all power up and pass their very basic POST sequences. The maintenance folks at the university have already pulled four runs of coax through a conduit to connect the terminals. All I have to do is terminate the coax, connect the terminals, and get them up to a login prompt. Heck, they’re so simple, there’s not even any type of network address or ID to set. Just turn them on, there’s a funky little growling noise, then a screen appears that says “Welcome to the ARC”. ARC being Attached Resource Computing. I connect the four units, power up the first one and get the familiar growlllll, Welcome to the ARC. Power up number two, growlllll Welcome to the ARC. Power up number three….and the entire system halts! Rats, I’ve got a DOA terminal and 20 irate students. I power everything down, go into the computer room and IPL (remember those?) the system. Ten minutes later everything is back up and running normally. I go back into the room with the four new terminals and power up the last one, growlllll Welcome to the ARC. OK, it works. Now I’ve got to troubleshoot the defective one.

These terminals are super simple, just a power supply, logic board, display board, keyboard and picture tube. Figuring it has to be the logic board, I order one for overnight delivery. The next morning I’m back at the university with logic board in hand. I put it in, connect the coax and power up. Growlllll, Welcome to the ARC. Success! I reach over to the terminal next to me, power it on and growlllll, Welcome to the ARC. I lean over to the next terminal in line; flip the power switch….and the entire system halts! AGAIN! Now I’m confused. This thing was working fine yesterday. Could the logic board have fried when I powered up the “defective” unit yesterday? That’s about all I can think of, and with the symptom being a complete system halt, I’m not about to spend much time experimenting. So, another logic board goes on order.

Day three, the logic board gets replaced in the last unit that caused a system shut down. I power it on and growlllll, Welcome to the ARC. So far so good, but I’m not celebrating yet. I cautiously power up another terminal. Ok, there’s the familiar growlllll, Welcome to the ARC. I let them sit for a while, thinking it might be some type of heat or load related problem. Everything stays up. Finally, I get my nerve up to hit the power switch on another unit, and….the entire system halts! Now I’m not confused, I’m mad. It has to be a problem in the coaxial hub all along! As soon as a third unit is powered on, regardless of order, everything crashes. There never was a bad terminal. OK, re-IPL, apologize profusely to the professor and the students for the lost work, downtime, etc. and get a replacement hub on order for same day delivery.

Hub arrives late that afternoon and, thankfully, the computer room is empty of students. I replace the hub and confidently march into the adjoining room to power up those four troublesome terminals. Number one, growlllll, Welcome to the ARC. Number two, growlllll, Welcome to the ARC. Number three, uh, number three? Hello? Total system halt!

All I can do is pick my jaw up off of the floor and try to put the oozing brain matter back into my head, as I think about updating my resume. What in the world could be causing this? Well, in desperation I begin to more or less randomly disconnect cables at the hub end and try different combinations of terminals. Finally I power on one terminal, then think to myself “Dummy, you’ve got this coax disconnected at the hub. This thing isn’t going to work”…. growlllll, Welcome to the ARC!!!!! I FLEW into the other room, thinking that someone was in there messing with the cables. But low and behold, the very same cable that I had just used on that terminal was lying on the floor, disconnected. I had just witnessed a miracle! A disconnected terminal had just communicated with its host system! And this was long before the days of wireless. A few more minutes of head scratching and I had an idea. I moved all four terminals into the same room as the main system, built some short coax cables, and connected them up. Glory be, they all four came up and worked like champs! I called maintenance and told them to strip out the brand new cabling they had run, and put in some new coax FROM A DIFFERENT SPOOL. Yes folks, believe it or not, I had fallen victim to what is undoubtedly the only spool of badly shielded coax to ever leave the factory.

Oh, and the mysterious terminal that connected while its cable lay disconnected on the floor? Simple RF leakage from one of the other cables while they were running through the same conduit together.