Need Help Fixing a Teletype KSR 33

[eneas9904]

Hello! Incidentally, this is my first time on the forum and also my first time dealing with this sort of thing -- I was previously one to fix personal computers rather than larger machines like this, so teletypes are entirely new to me.

I recently bought a Teletype KSR 33, beautiful machine, all the working bits and bobs and even came with a 1968 revision manual as well as some... janky receiver card connected by speaker wire..?
Nevermind that. So I got this Teletype in the mail today, loaded some paper into it and went to switch it on:

Switching it to local was a bummer. Nothing turned on, no input, completely dead. Fine. But the issue was switching it to Line.
When I switched it to line, the Teletype would try and print nonstop -- it seemed like pressing a key down would offer some input, but it would not print onto the paper, would not advance, the carriage would just stay still and continually chatter to try and print.

How do I go about fixing this? Does it normally do this until I connect the other end to a mainframe? Is it the 20mA loop? I can provide images and a video of what I'm talking about if needed.
Probably stupid questions, but doesn't hurt to ask

 

[pbirkel]

Best source of information and parts: https://www.rtty.com/greenkeys.htm

 

[MauriceH]

Its a precise mechanical running machine, and after decades it needs some cleaning and some oil I think.

These machines also been modified by the lot, so you have to dig into it to see what been changed, added etc.
In local you just can type like a type writer, should be in any case work.

First look at that rubber hammer and see if that is still like a rubber pad, of not you damage the print head.
First fix that.

Machine keeps running without stopping:
Mostly it is a lever right side keyboard to the rest of mechanics that need to be adjusted.
Look down the tooth belt right side and notice a horizontal lever from keyboard .
Beware its a very narrow adjustment and due to shipping that machine this could be your problem.

"Normaly" its 20mA loop indeed, but again, so many modifications.

First the basics, running in local mode.

 

[djg]

When I switched it to line, the Teletype would try and print nonstop

This is normal for mine if the current loop isn't hooked up.

 

[eneas9904]

This is normal for mine if the current loop isn't hooked up.

Gotcha. Even though the ribbon is moving?

 

[eneas9904]

Its a precise mechanical running machine, and after decades it needs some cleaning and some oil I think.

These machines also been modified by the lot, so you have to dig into it to see what been changed, added etc.
In local you just can type like a type writer, should be in any case work.

First look at that rubber hammer and see if that is still like a rubber pad, of not you damage the print head.
First fix that.

Machine keeps running without stopping:
Mostly it is a lever right side keyboard to the rest of mechanics that need to be adjusted.
Look down the tooth belt right side and notice a horizontal lever from keyboard .
Beware its a very narrow adjustment and due to shipping that machine this could be your problem.

"Normaly" its 20mA loop indeed, but again, so many modifications.

First the basics, running in local mode.

Gah, I knew local mode would come back to me! I’ll definitely try cleaning it up, maybe some kind of WD40 to loosen up the printing mechanism a bit, though yeah, when I switch to local not a single thing happens. Ruh roh.

The good thing though is that it does have a perfectly intact rubber hammer — took a look this morning and, yup, still a good little pad on there.

I’ll come back on tonight to give an update to adjusting the lever you mentioned. Is that the one near that H clip I saw?

 

[eneas9904]

Here’s a short clip of what I’m encountering:

https://media.discordapp.net/attachments/989620401271361546/1387439412144766986/IMG_0611.mov?ex=685d5925&is=685c07a5&hm=20da3968d8fa08f4c17fc0fded31e9f9db4adc4e2442d588e4b33a4310e2bc96&

 

[djg]

Gotcha. Even though the ribbon is moving?

Yes mine does the same as yours.

Gah, I knew local mode would come back to me! I’ll definitely try cleaning it up, maybe some kind of WD40 to loosen up the printing mechanism a bit,

When I was a kid I used WD40 as lubricant. After seeing that anything I used it on was more gummed up after a couple months I switched to using proper lubricants. I would advise going slow since its easy to make things worse.

yup, still a good little pad on there.

I assume you mean by good it has proper rubber texture. Hard and it may disintegrate when you get it printing and too soft it will just flow out of the way. Did the previous owner replace it? By now you don't find too many that are still good.

 

[eneas9904]

Yes mine does the same as yours.


When I was a kid I used WD40 as lubricant. After seeing that anything I used it on was more gummed up after a couple months I switched to using proper lubricants. I would advise going slow since its easy to make things worse.

I assume you mean by good it has proper rubber texture. Hard and it may disintegrate when you get it printing and too soft it will just flow out of the way. Did the previous owner replace it? By now you don't find too many that are still good.

Yup, it does have a proper rubber texture. It looks like it may have been replaced, not entirely sure, though it’s definitely not a home modification. I’m pretty comfortable using what’s on there since it’s about as good as any.

When you connect it to, say, a PIDP-11 or something then does it stop chattering or continue on? Also, when you turn yours on and press keys down does it still advance and return the carriage? Does yours work as regular in local mode or does nothing happen too?

 

[m_thompson]

Here’s a short clip of what I’m encountering:

https://media.discordapp.net/attachments/989620401271361546/1387439412144766986/IMG_0611.mov?ex=685d5925&is=685c07a5&hm=20da3968d8fa08f4c17fc0fded31e9f9db4adc4e2442d588e4b33a4310e2bc96&

I assume that you have the knob at the right front in the clockwise position for LOCAL mode?
Is the selector magnet at the back left engaged?
If the selector magnet is not engaged, then you should debug the local power supply.

 

[eneas9904]

I assume that you have the knob at the right front in the clockwise position for LOCAL mode?
Is the selector magnet at the back left engaged?
If the selector magnet is not engaged, then you should debug the local power supply.

In the video it was set to line mode. Local mode did just about zilch nothing moving nothing inputting. I’ll have to check back later for the selector magnet since I’m at work, so bear with me.

 

[eneas9904]

So, part two. Tested selector trip mechanism and seems to work just fine — magnet I’m not too sure about, but it doesn’t seem to me like it’s engaged. Here’s a video of that: https://streamable.com/p8vowm




Otherwise I’m not sure if the selector mechanism is missing something or if I’m even looking in the wrong area for that.

Otherwise, for the adjustment under the spacing belt I’m not too sure which adjustment you mean, unless you mean the H bracket.

 

[MauriceH]

Indeed that mechanism start and stops the clutch ,as I recall.
When a key is pressed it starts the print mechanism and if print mechanism is ready print the character it
free the key's again for operating next key.

A ASR33 I had to repair it kept printing so never stopped,this was the issue to solve.
Also if moved this adjustment to far other way it never starts printing.

Due to fact the keyboard can move according the whole printer a little bit.
Or when unit is been apart.

By shipping by mail , you said, there could be a shift from whole printer unit.

You could also look for the 4 bolts that holds whole printer unit and loosen up and shift whole printer a bit.
See if ,in local mode, the machine starts print by it self.
Then you know you have to adjust this part of machine.

Can't find this adjustment right now in the adjustment manuals, but it should be noticed there.

 

[eneas9904]

Indeed that mechanism start and stops the clutch ,as I recall.
When a key is pressed it starts the print mechanism and if print mechanism is ready print the character it
free the key's again for operating next key.

A ASR33 I had to repair it kept printing so never stopped,this was the issue to solve.
Also if moved this adjustment to far other way it never starts printing.

Due to fact the keyboard can move according the whole printer a little bit.
Or when unit is been apart.

By shipping by mail , you said, there could be a shift from whole printer unit.

You could also look for the 4 bolts that holds whole printer unit and loosen up and shift whole printer a bit.
See if ,in local mode, the machine starts print by it self.
Then you know you have to adjust this part of machine.

Can't find this adjustment right now in the adjustment manuals, but it should be noticed there.

I don’t know if it’s just me, but it looks like I might be missing some kind of brace or bracket for the middle screw you pointed out. Is there something that is needed there?

 

[djg]

Note that there are hazardous voltages in various spots inside Teletypes. Avoid touching anything inside. Also the obvious mechanical hazards.

There are various schematics around. First is what referring to in this post.
https://www.pdp8online.com/pdp8cgi/query_docs/tifftopdf.pl/CHD/LT33_print_set.pdf
Also https://www.pdp8online.com/pdp8cgi/query_docs/tifftopdf.pl/pdp8prints/teletypeps.pdf
Page 10 of PDF has the transmit and receive paths. You can see with note 3 the relay that should connect stuff differently for local mode. When you say yours does nothing in local mode is that the motor running but keyboard does nothing?

There is a screw terminal block below all the plug connectors normally covered by a cardboard strip. Terminals are numbered on the cardboard. Leftmost is 1 if cover missing. In line mode you don't have loop power but on mine shorting 7 to 6 stopped it typing. There is .5V from the selector magnet driver.

You can connect 20mA power source + to 7, 6 to 4, 3 to 20mA power source - and it should work in line mode.

20mA power source can be 5V supply with 250 ohm resistor in series to limit current to 20mA. Note resistor will dissipate 100mW so 1/4W will get hot.

If this works and you want local mode you will need to figure out what is wrong with your local mode wiring/electronics.

 

[MauriceH]

Indeed looks like you miss something that is present in my ASR33.
But also be ware the lot of modifications, changes made etc etc.
Not 1 machine is the same.

Dive into the many manuals and start looking.
Tho a start tip is manual : 273B_Mod32_33_TechMan_Jan63.pdf
page 238, its a nice schematic flow-chart of how machine operates.

Also page 209 is shown that H-plate mechanism.

Take in mind there is a mechanical operation and an electrical,both can jam that local print function.
Its a very tidy precise operating mechanical wonder machine.
Due to old lubrication even a slightly friction of a bar or slice what ever could jam the whole thing.

How I repair the machine is mostly sitting and look at the machine.
Read manuals, start operate and look, good look.
I also had 1 sticky mech bar and it went off the rails.
Even my machine is been very well kept taken care off all those years.

The YT-ber Curious Marc spent many hours fixing his 33.
So find it and get to know how it all works.

Play list and find list "Teletype 33 ASR"

 

[eneas9904]

Thanks for the tips so far! One of the PDFs actually helped me a bit in making some adjustments to the line mode, and it seems like it’s now working according to the other forum posts and videos I’ve seen — at least without it plugged into anything for the 20mA loop. My concern was that the carriage would not advance or print while it was chunk-chunk-chunking away despite hearing the distributor move when a key was pressed, but I’m assuming that’s okay and that it will remedy itself when the current loop is connected on the other end.

Unfortunately, for the life of me I can’t seem to figure out what’s wrong with the local mode and why not a single thing — motor, distributor, carriage etc. works when local is selected. It has to be an electrical issue if they all worked for line mode, so I’m wondering if there’s any more info on what that local/line relay I read about looks like so I could tinker with it or if it could be a faulty connection somewhere.

Something just doesn’t seem right here since it’s more difficult to follow trying to figure out local mode.

On a side note, if there’s anything you guys recommend to connect to the Teletype let me know! Maybe if there’s some kind of PDP remake or even a simple 20mA receiver interface.

 

[johnx993]

I use a 20ma to RS-232 converter and just use a terminal emulator running to a serial port.

RS232 Current Loop Interface Converter - Telebyte Model 65A

 

[pbirkel]

I use a 20ma to RS-232 converter and just use a terminal emulator running to a serial port.

RS232 Current Loop Interface Converter - Telebyte Model 65A

Nice, but at $175 (DigiKey, if ever back in stock) rather over-priced. There have been a number of projects by Greenkeys members over the past decade that scratch this itch for both 60mA and 20mA current loop interfaces. Recommend checking them out. See earlier post: https://forum.vcfed.org/index.php?threads/need-help-fixing-a-teletype-ksr-33.1253508/post-1453496

 

[djg]

Unfortunately, for the life of me I can’t seem to figure out what’s wrong with the local mode and why not a single thing — motor, distributor, carriage etc. works when local is selected.

Start with motor since that is simple.

The second pdf I linked to page 9/FS-9 shows the AC distribution. It just the line/local switch providing power to the motor. Page 27 has the switch terminals labeled.

Is the motor connected to the terminal shown in the schematic? If so does the switch contacts close as labeled?