Can the wrong keyboard type damage a terminal?

[Rubix]

Hi all, asking this question here because I think this area of the forum has the most members who are familiar with terminal keyboards. I have a Morrow MDT 60 terminal with no keyboard. Someone told me that any keyboard with the same connector will probably work. I tried a Unisys keyboard, but nothing came up on the screen. Now, with no keyboard attached, the terminal shows no signs of life anymore, where it used to show a text "No keyboard attached". Can the wrong type of keyboard damage a terminal and if so, what component(s) could it likely be?

 

[DeltaDon]

Back in the days of terminals there was very little standardization of things like keyboard pin outs. That mostly came about with the IBM PC's controlling the PC market and clones following IBM's lead. Finding the correct keyboard these days may be a problem since keyboard cutters have been chopping up old terminal keybords up for repurposing their key switches for years. Plus the MDT60 wasn't a main stream terminal sold but the thousands, IMHO.

Since some form of power has to get to the keyboard's circuitry I guess there's a chance therefore that the terminal's power supply could have been damaged with the incorrect keyboard shorting something in the terminal - maybe nothing more than a blown fuse. But it could also be some more severe blown components. The only way to tell would to open the terminal and see. Do be very careful since there's 15K-20K voltage on the CRT and it's power circuits. I would hazard a 2nd guess that signal input pins to the terminal expect high/low voltage changes as data flows and therefore less likely to have suffered damage the input circuit. But that's all a guesses on my part.

 

[Eudimorphodon]

Someone told me that any keyboard with the same connector will probably work.

That *may* be true for a single manufacturer (but even then not really a sure thing), but it’s definitely *not* true in general. There was absolutely no standardization across the industry prior to… well, I was going to say USB, but PS/2 keyboard ports were also pretty common by the mid-90’s. But DIN/modular/D-shell connectors? Forget about it. You absolutely could let the magic smoke out by trying to mix and match.

 

[Rubix]

The terminal does power on because when I switch it off, I sometimes see a garbled line flash really quickly. I'm afraid some controller chip may be damaged.

 

[Al Kossow]

Someone told me that any keyboard with the same connector will probably work.

Fortunately, I wasn't drinking anything when I read that.
There are NO protocol or input voltage standards between different vendor's terminal keyboards
beyond those that used PS/2 kbs.
They may not even be the same between the same company's terminal.
If you plug in a keyboard expecting 5v onto a terminal supplying 12, you'll be SOL.
The worse example I can think of is a certain brand of twinax terminals with DIN5 connectors
that replaced 5 volts with 12.

 

[Rubix]

Fortunately, I wasn't drinking anything when I read that.
There are NO protocol or input voltage standards between different vendor's terminal keyboards
beyond those that used PS/2 kbs.
They may not even be the same between the same company's terminal.
If you plug in a keyboard expecting 5v onto a terminal supplying 12, you'll be SOL.
The worse example I can think of is a certain brand of twinax terminals with DIN5 connectors
that replaced 5 volts with 12.

That's what I was afraid of, and I understand it could've damaged the keyboard. But how could that have damaged the terminal? By directly connecting a voltage rail to ground or something?

 

[Al Kossow]

the terminal is completely documented in http://bitsavers.org/pdf/morrow/terminal/MDT60_Service_Manual_1984.pdf

there is a complete schematic, and the keyboard is sent +8.5v
the keyboard I/O goes into ttl chips, so it may be something simple
obviously, check the voltages on the power supply connector first

 

[Rubix]

Thank you! I was looking for that, but somehow I only found the user manual on Bitsavers. You think it could be one of the TTL chips that's shot?

 

[GearTechWolf]

The early all-in-one Macs with the RJ11 jacks (same form-factor as corded-phone handsets) for the keyboards had a similar problem.
The cable from Apple had it so that the connections at each end of the cable were flipped, whereas a phone-handset has them mirrored.
Use the wrong one and it would send voltage to the data pins, damaging keyboard and/or related circuits in the computer.
Form-factor means very little, pin-out is most important! (in such cases)
Anyhow, anecdotes aside, hope your terminal is easily/inexpensively repaired!
(a hacked/modified cable might allow a keyboard from a different terminal to work, if voltages and data protocols match)

 

[Caleb Hansberry]

The Morrow MDT-60 uses the same keyboard as the Zenith Z-29, Z-39, and Heathkit H29, and it's a pretty specific keyboard. I'm using one on my Z-39 right now. If that helps you find schematics or information about the way the keyboard works. I know it's pretty intelligent, it basically communicated with the keyboard using serial, and it is powered.