televideo model 925

[lighthugger]

Hi All,

Just discovered this excellent forum and thought someone might be able answer some of my questions

I rescued a Televideo model 925 from a dumpster a while back (my wife calls it junk!) and I've decided to do something with it. The goal is to connect it up to one of my linux machines as it would make a nice retro tty.

The system turns on, some ascii appears in the botton and a cursor appears in what I think is the "home" location. The manual mentions this.
When I follow the instructions for the self test SHIFT + SETUP 1 it moves the cursor to the status bar on the bottom, but doesn't launch into the display testing routine.

Before I invest too much time into it I'm wondering what the behaviour of it should be without an RS232 cable connected to my linux machine? Should I at least be able to get into this self test mode?

I'm going to look at the S1/S2/S3 settings in the next couple of days to see if maybe they aren't set correctly.

Regards
Richard

[sirpaul484]

Welcome to the forum, Lighthugger!

Congratulations on the find! I wish I could find something like that in my dumpster.  Sadly, no luck.

Unfortunately, I have zero experience with video display terminals, so I have no idea.  I am a fifth degree black belt in Googling, though, and I will see what I can find online.

[lighthugger]

Thanks Sirpaul! I've tried using my google-fu as well but it's a very old unit, 3 years younger than me!

I removed the case last night and couldn't find the internal switch... That confused me as I was 100% sure this was a model 925 as it looks identical to the wiki article. Maybe a later board revision removed the internal switch? We'll never know I guess.

I've managed to "toogle" some information on the status bar, but it doesn't display anything resembling text, rather @00@P, ASCII like that. It's almost like few bits have flipped in the video circuits because seems to respond to the commands it should, just with gibberish.

-Richard

[t3hfr3ak]

Although I have no particular experience with video terminals such as that, I am familiar with most computer workings.

In my experience, when the output video looks as though it should but with gibberish in random spots, in most cases this would be a fault within the video card/output on the originating machine. If thats the case, that sucks!


Also! WELCOME TO THE FORUMS!

[lighthugger]

Although I have no particular experience with video terminals such as that, I am familiar with most computer workings.

In my experience, when the output video looks as though it should but with gibberish in random spots, in most cases this would be a fault within the video card/output on the originating machine. If thats the case, that sucks!


Also! WELCOME TO THE FORUMS!

Hey t3hfr3ak. I think you're correct somethings screwed up with the video subsystem (it's basically a VT terminal with a different protocol).
Anyway I'm going to build a serial cable according to the specs in the manual (pins 2 and 3 cross, just like standard consoles) and i'll let you all know how it goes! 

[t3hfr3ak]

Sounds good!

Hey if you get the chance, you should put up a couple pictures of the terminal. Inside and such, be interesting to take a look

[lighthugger]

Sounds good!

Hey if you get the chance, you should put up a couple pictures of the terminal. Inside and such, be interesting to take a look

Sure here they are!

[lighthugger]

Sure here they are!

damn, sorry for how big the attachments are.. should have checked that

[RedWolf]

Very cool, lighthugger!  Welcome to the forum, by the way.

That terminal is a rare prize (well, rare in the sense that you don't see one every day).  I'm somewhat a video terminal fan myself, so I can definitely appreciate your acquisition.

I myself hook terminals up to Linux boxes all the time.  You need to build a null modem serial cable and setup the AGETTY or MGETTY (forgot which one) on the Linux end to look for the terminal on the serial port.  I believe I follow the SERIAL HOW-TO when I forgot what to do.  Here are a few links that should help:

http://tldp.org/HOWTO/Serial-HOWTO.html
http://www.vanemery.com/Linux/Serial/serial-console.html

I personally troubleshoot terminals with a Hayes-compatible serial modem, which is easy to hook up.  You just type in ATA, and look for "OK".  You need a straight-through serial cable for that, though.

--

Now, that being said, it looks like your terminal's display is garbled.  It may be because the character ROM or the display chip is bad or badly seated.  Lucky for you, it looks like most of the major chips on the terminal's motherboard are socketed.  You should very, very carefully clean the motherboard (dust or vacuum with a dry brush or paper towel), then very very carefully unsocket each chip with a special tool for it or a flat blade screwdriver (careful not to break the pins - it is very easy to do) and look for corrosion on any of the pins or sockets.  If they're dirty, scrub them gently with a wire brush and dust them off.

Go through all the chips like this, one at a time (make sure you remember the right orientation when you resocket them, so do them one at a time.  Also make sure the pins are straight and going in the right holes when you push them down, or the pins will break) and when you're done, it may just work.  Also, unplug and replug all removable connectors inside the terminal.

In my experience, connections are the first to go (they just need to be cleaned and re-connected).  Second to go are capacitors.  But try resocketing the chips first.

[lighthugger]

I myself hook terminals up to Linux boxes all the time.  You need to build a null modem serial cable and setup the AGETTY or MGETTY (forgot which one) on the Linux end to look for the terminal on the serial port.  I believe I follow the SERIAL HOW-TO when I forgot what to do.  Here are a few links that should help:

http://tldp.org/HOWTO/Serial-HOWTO.html
http://www.vanemery.com/Linux/Serial/serial-console.html

Thanks Redwolf! I've got a console cable I created for sun machines (pins 2/3 crossed) so I'm hoping it works, and getty is all setup and ready to roll.

Now, that being said, it looks like your terminal's display is garbled.  It may be because the character ROM or the display chip is bad or badly seated.  Lucky for you, it looks like most of the major chips on the terminal's motherboard are socketed.  You should very, very carefully clean the motherboard (dust or vacuum with a dry brush or paper towel), then very very carefully unsocket each chip with a special tool for it or a flat blade screwdriver (careful not to break the pins - it is very easy to do) and look for corrosion on any of the pins or sockets.  If they're dirty, scrub them gently with a wire brush and dust them off.

Go through all the chips like this, one at a time (make sure you remember the right orientation when you resocket them, so do them one at a time.  Also make sure the pins are straight and going in the right holes when you push them down, or the pins will break) and when you're done, it may just work.  Also, unplug and replug all removable connectors inside the terminal.

But as you've pointed out the display is very very garbled... (thats the screen self test you see there)

I'll try your suggestions this weekend but my only concern is zapping myself as the CRT is so close the motherboard, I just have to slip a little and well you know ...
Maybe leaving the terminal unplugged for a few days will make me feel better.

[RedWolf]

I'll try your suggestions this weekend but my only concern is zapping myself as the CRT is so close the motherboard, I just have to slip a little and well you know ...
Maybe leaving the terminal unplugged for a few days will make me feel better.

You can always discharge the CRT yourself.  You need a long screwdriver and an alligator clip lead. Attach one end of the clip lead to the screwdriver metal and the other end to to a the machine's metal chassis (to ground).  Carefully pull back the rubber suction cup connected to the tube and gingerly (don't scratch the CRT glass) stick the screwdriver down in there to touch the metal contacts that normally go into the CRT.  If you hear a small pop then it has discharged.  If nothing happens, then it was already discharged because of a bleed resistor in the circuit.

Or you can shock yourself.  It will hurt, but it probably won't kill you.

Benj

[Stull]

Or you can shock yourself.  It will hurt, but it probably won't kill you.

 

I always wanted to play around with dumb terminals but have never had the opportunity. I remember going to a vintage computer warehouse (or rather, junk-house) in the late '90s that had a couple but $15 for one seemed like a lot back then.

I ran across this years ago and thought it was neat: The Metatron.

[lighthugger]

Or you can shock yourself.  It will hurt, but it probably won't kill you.

If you hear from me next week I'm still alive

[RedWolf]

I always wanted to play around with dumb terminals but have never had the opportunity. I remember going to a vintage computer warehouse (or rather, junk-house) in the late '90s that had a couple but $15 for one seemed like a lot back then.

I ran across this years ago and thought it was neat: The Metatron.

That is neat, Stull.  (Welcome to the forum, by the way!)  There are all kinds of neat things you can do with serial terminals.  Here is one of them, StarTTY:

http://www.vintagecomputing.com/index.php/archives/263

And lighthugger, please do be careful!

[Stull]

Are there any dumb terminals that, I don't know, stand above the rest? Like a make/model that would be ideal? Or any that should definitely be avoided?