Terminal Repairs
Two of my terminals have been complaining about uninitialized settings on power up. It's time I took care of that.
First up is my Wyse WY-55. I've tried opening this one before, but never could figure it out and there are no service manuals to be found. It only has two screws on the back, but something holds it together on the top. I eventually found it has two rather large plastic clips on the back case that extend into the front case.
Removing the back case requires pushing down the clips far enough to clear the studs protruding from the inside of the front case without cracking 30 year old plastic.
With the case finally removed I could see the battery … soldered into place beneath the CRT.
This terminal was clearly designed to reduce costs whereever possible. It only has a single board that includes power supply, logic, and the CRT driving circuitry. Removing it requires discharging the CRT, disconnecting the yoke, pulling the connector off the neck of the CRT, then removing the bottom two screws from the CRT. This will free up the bottom case with board attached. A few screws secure the PCB but it also has plastic clips and alignment pins molded into the bottom case to keep it in place.
With the board out, I could desolder the original battery and replace it. I don't have any vertical coin cell holders and the original battery placement is inconvenient, so I decided to run some wires and put the battery holder towards the back of the board. I used some double-sided thermal tape (it's what I had on hand) to insulate the socket pins & attach it to the back side of the aux serial port, and held down the wires with some polyimide tape.
It might not be the prettiest repair job, but it works and it puts the battery where it can be replaced without completely removing the board next time.
Next up was my Esprit Opus2 terminal. This one was easier to get into. Four screws on the back case, and then the foot hinge slides forward to a slot where it can slip loose of the foot. Fortunately this terminal has a separate logic board and analog board.
Unfortunately —
Its soldered-in coin cell battery had leaked.
Coin cell batteries don't leak often, but they certainly can. Thankfully when they do leak, damage is typically not so catastrophic as with the larger alkaline batteries in used in older computers. In this case there was no sign of any corroded traces, just three bad pins on the main bus transceiver. It wasn't even enough to prevent the terminal from functioning (yet).
I clipped the battery leads to get it out of the way, then cleaned the board. It was a cheaply made board with quite a bit of old flux residue so I cleaned that off with some alcohol wipes while I had it out. Once it had dried, I brushed some flux on the back side of the pins for that bus transceiver to start removing it.
That went well until I started heating the corroded pins. Something exploded. Bright flash of light, a deafening pop, and ringing ears.
There was no smoke. There was no visible damage. The chip was still intact. There wasn't even any kind of a residue flash across the board like often happens with a component releases its magic smoke.
I can only guess some of the alcohol had soaked into the board and was set off by the burning flux. Or perhaps something to do with lithium from the battery. I've never had anything like that happen before when working on a board.
I tried to be more careful, but still managed to get a second explosion removing those corroded pins.
The chip was out though. I soldered in some machine pin strips to serve as a socket (without any further explosions), and dropped in a 74ALS245 (the closest I had on hand to the original 74LS245; much faster, but should be fine). This board had the footprint for a battery socket so I gave it one.
And that did it!
Now both of these terminals are able to retain their settings across power cycles, and both should be just a little easier to maintain in the future. I was a little late diving into the Opus2, but thankfully the damage was minimal. I am rather fond of my terminals so I am glad to have them all back to being fully functional.
