Thread by @ArtieMog

A while back I picked up a trash-picked Link MC5 serial terminal, which seemed to be working but was getting no power to the CRT. I finally got around to poking around in it a bit last night.

I even got the user's manual with it, which I've discovered that I can't find online anywhere. I'll get scans and upload them to archive.org as soon as I can

(Link was a company that made terminals and other things, and was bought by Wyse in the late '80s. Wyse mostly let them continue to operate independently—there aren't even references to Wyse in the manual—but even still, this swivel stand and keyboard both have Wyse branding)

Anyway, on to the teardown/repair attempt. There are only three screws on the bottom to take out, two of which hold on the stand. There are these two clips holding the outer case on, though, which were a pain to find and spring. But once sprung, the whole thing just slides off

Once inside, I discovered the probable cause of my issue pretty quickly. This whole board that's now plugged in to the back of the tube had come unplugged. You can see where the blob of hot glue that was supposed to hold it in place sheared in half. That's an easy fix!

Also looked up the model number on the tube. The MC5 was available with an amber, green, or white display, and from the model number, it looks like my tube has white phosphor. Darn, that's the most boring one!

But wait...does this say that this thing was just serviced in 2011???

Anyway, with the board replaced on the back of the tube (I'll secure it better later, although it didn't seem loose to me), I need to test to see if it's working now...except I accidentally broke the anode clip off while I was discharging the tube. Great, now I gotta fix that too

In my defense, this is the first time that I've dared work on a CRT. It should be relatively easy to fix, hopefully, but it'll have to wait until I can get out my wire strippers and soldering iron.

Well, in the meantime, let's see what we can do with this filthy keyboard.

Got almost all the screws out of the back, but it's still not coming open. I'm guessing there are two more hiding under these rubber feet.

Huh, apparently not. Hmmmmmm

Aww, crap. There's a screw under the label.

Well, I'll have to do some research to see if I can pull up that label without destroying it. If not, I may just try to clean the board as best I can without actually opening it, since it does work as far as I can tell.

In the meantime, I'll see again about repairing the anode

The anode clip has a little channel for the wire to go through, so it should be a simple matter to insert the clip and wire into their slots in the suction cup and then solder the wire in place from the underside. Just got to get all the old solder cleaned off of the clip first

Can't really get a clearer shot of the clip without a macro lens, but it's all nice and clean now!

I cleaned the suction cup with some soap and water too, because it was a bit grimy. I'll let that dry and then reassemble everything.

Alright, not my finest soldering work fixing the anode, and I may have burned myself on some molten solder, but IT WORKS! I guess it really just did that board plugged back in

Just need to fiddle with these pots a bit to get the picture looking right again. The one that I assume is for horizontal position doesn't seem to do anything, but I was still able to get the display adjusted pretty well.

Tested it out by calling The Heights BBS over the cable phone line I have available (since it has an 800 number and this line doesn't have long-distance). Had a bit of trouble connecting, but eventually got it to work at 1200 baud. They're not kidding about their time limits!

(This was using the 14.4 kbps dial-up modem that I've tweeted about before, btw)

Very excited that this thing is working now, and glad that the fix was so simple! Still have some work to do to clean it, but I'm very happy that this has all worked out.

(Excuse the potato quality...my phone camera has a hard time focusing on screens)

(And my other camera is a 35mm SLR…)

Tentatively found the terminal a spot on my desk, although it's a bit cozy. I've also discovered that my RS-232 to serial adapter, ironically, needs a gender change...

I need an edit button…three screws hold the casing in, and two more hold on the stand. Derp

Update: Acquired the required serial cable, only to discover that my adapter is no longer working. Fantastic.

Got most of the MC5 User's Guide scanned yesterday, but couldn't finish because I got kicked out of the library when it closed. They're also closed all day today, but I'll get the rest scanned as soon as I can.

In the meantime, I'm going to see about borrowing a USB adapter while I wait to get a new one. I won't be getting the Amazon special direct from China this time...I'm getting one recommended by FTDI. Hopefully that will prevent any future failures.

Okay, adapter and null modem cable are on their way, and I've borrowed one of each in the meantime. Getting this thing to work as a tty for Linux on my laptop has been waaaaaay more complicated than I expected, though., so I've been working on it a lot.

Some problems I noticed right away were:
1. Not all of the information was always making it onto the screen, or things were going on the screen in the wrong places
2. Some special characters (like frame graphics) were showing as garbage
3. Not all the keys were working

I thought the first problem was a lossy serial connection, but turning the baud rate down didn't fix it completely. The actual problems were that the MC5 was set for 25 rows when Linux was expecting 24, and when smooth scrolling is on, it seems to make its data buffer overflow =(

So yeah, pretty disappointed that I'll have to keep smooth scrolling off. I thought it was silly at first, but it grew on me very quickly. Seems like a huge design flaw that shouldn't have been allowed to escape into the factory. And this is in version 3.04 of the firmware!

(If you don't know what I mean by "smooth scrolling," see this wonderful @lazygamereviews video about the DEC VT320, the successor to the VT220 terminal mine is supposed to emulate)

Back to diagnostics: the second problem turned out to be the default UTF-8 encoding that Linux was trying to use. This terminal only supports either DEC-MCS or ISO-8859-1 encoding (which the setup menu calls "ISO Latin-1"), So I had to generate an en_US.iso88591 locale for it

I still have to figure out a good way to automatically switch that locale for this terminal. It'll probably involve an if statement in /etc/profile or something like that.

The third problem was perhaps the weirdest, though. A handful of F-keys and a few others like PgUp, Home, and End weren't working properly. This one had me scratching my head for a while, because the keyboard WAS working, and no setting change would fix the problem.

Eventually, I discovered that the problem was that the terminal wasn't sending the correct escape sequences! For example, PgUp is normally ESC [5~, but the MC5 was sending ESC [3~, which is the normal sequence for the Delete key! What?!

Wait a sec...those two keys are swapped on the VT220 keyboard! And, as it turns out, on the "ANSI" layout for this terminal (my keyboard has the "EPC" layout). But that's a pretty big snafu to be sending escape codes based on the key's physical location rather than its function!

...especially since the terminal _does_ correctly recognize those keys in the setup menu. Yet it still sends the wrong codes. Grrrrrrr

So to fix this one, I could either try remapping those keys' functions in the terminal or create a new terminfo file for the MC5.

I tried the terminfo route, copying the vt220 definition and modifying the appropriate "capabilities." That mostly worked, but there are still some programs (most notably irssi and weechat) that ignore the terminfo definitions entirely, and I've seen a few other glitches as well.

But even still, the terminal is MUCH more usable than before. I guess tomorrow I'll try the other method, since I'm getting a little out of my depth writing terminfo definitions. And it does kinda make more sense to fix it on the terminal side, since the terminal is the problem

Oh, by the way, I got the manual scanned! It's on archive.org here: archive.org/details/linkmc…