[GreenKeys] Troubleshooting papertape reader

Fri Apr 24 10:20:13 EDT 2015

Bill,
If the distributor spins when the LF position on the tape is read, then some serial sequence of bits IS being sent by distributor. It may not be a valid LF, it may not even be a validly framed character, however, some sequence of electrical pulses at 110 baud is being sent.
What did you use to capture the output of the Teletype into the file you've been looking at? I noticed it stripped out CRs. Is there any possibility the capture operation is stripping out other non-printable characters (e.g., whatever garbage character the Teletype might be transmitting when the LF position on the tape is read)? If so, a new capture operation with a different program would let us see what bit pattern is actually coming in when the distributor spins out the LF it read from tape.
If you're 100% sure your data capture didn't filter out any characters, then I would set up a digital scope (not a logic analyzer) and capture characters on the scope as you manually force each reach from the tape. Set the scope timebase so a full character fits on the screen. You'll be able to see if when LF is read and transmitted, it's generating a framing error or if it's an electrical issue (e.g., carbon wipers or copper contact plates of the distributor not making good contact).
Mike 

     On Friday, April 24, 2015 8:46 AM, B Degnan <billdeg at aol.com> wrote:

 Mike and Wayne,
To recap
1.  Capture of data shows missing LF's occasionally when reading a tape.  No other chars seem to be getting dropped.
2.  When in local mode. By quickly pressing the switch in the back near where the two reader wires connect to the motor I advance the reader one character at a time.  This way I can See if the form feed mechanism is activated when a LF character is present on the tape. I watch as chars print on the paper, and I can see the tape advance one click at a time.  Some of the time the LF's do not occur.  The form feed arm is not activated.  
3.  I repeated this test in LINE mode, knowing the printer would not print to see what if anything would be different from a distributor perspective.

Mike asked me to check the distributor under line and local modes while testing.  The distributor spins just like any other character, there is nothing especially different about how the distributor acts when a LF is sent from the tape that I can see.

What I am thinking is that the LF "builds up" enough go pressure eventually to fire, and it may be that certain ASCII characters that precede it make it "harder" to activate, but this just a theory.

Bill

-----Original Message-----
From: teletypeparts <teletypeparts at comcast.net>
To: Douglas, Mike <deramp5113 at yahoo.com>
Cc: B Degnan <billdeg at aol.com>; GREENKEYS BULLETIN BOARD <greenkeys at mailman.qth.net>
Sent: Thu, Apr 23, 2015 3:52 pm
Subject: Re: [GreenKeys] Troubleshooting papertape reader

  Bill, 
     Dont spray contact cleaner into any 33 wire contacts unless you are absolutely sure is it safe for plastics!     Better to do visual check on contacts after you isolate the trouble as Mike suggests.     Wayne   
    From: "Mike Douglas via GreenKeys" <greenkeys at mailman.qth.net> 
 To: "B Degnan" <billdeg at aol.com>, greenkeys at mailman.qth.net 
 Sent: Thursday, April 23, 2015 12:56:04 PM 
 Subject: Re: [GreenKeys] Troubleshooting papertape reader 

    Bill,   
   I would still recommend starting with a capture of tape data. From that, you'll be able to compare to the original data and see if a particular bit position is the one that is always failing. Knowing a bit position to look for helps when tracing down the problem in the Teletype.   
   In the Teletype, the reader, keyboard and answer-back wheel are all wired in parallel. It's not unusual for one these parallel paths to be causing the problem. Of course, the actual reader may have a bad contact / probe pin as well. Have you tried contact cleaner on the gold contact pins in the reader recently?   
   Mike   

       On Thursday, April 23, 2015 11:38 AM, B Degnan <billdeg at aol.com> wrote:

     On the punched tape there are CR then LF characters in each S1 (data line).  I confirmed this.  The tape is OK.

There is a relay in the back of the TTY that when you press down release quickly it moves the reader one click at a time, and prints the input char to the page (or space or CR or LF, etc).  From this I can see that the bad unit does not "respond" to to the LF character when it comes up on the tape, at least some of the time.  There are also occasional bad characters.  If you could imagine a "clean" Motorola S record file with each line starting with S11300000000...   On the bad machine you'd notice occasionally the printout appears to have lines that typed over themselves.

On my good teletype it prints from the tape correctly both one char at a time and in "start" mode on the reader.  I read the tape and it prints the correct thing to the printer.

If I was to load in the tape using the good teletype into the computer (BASIC) and then switch to the TTY with the reader problem the TTY seems to work correctly, no lost characters or misprints.   I am no expert.  I checked the form-out mechanism on the teletype with the issue and I did not see anything wrong with it.  I always get a LF when I call it from the typewriter to the printer or if I am using teletype through a computer.

This is why I think the problem is with the reader.  I am baffled because the problem does not happen consistently.   

Bill

   -----Original Message----- 
From: Mike Douglas <deramp5113 at yahoo.com> 
To: B Degnan <billdeg at aol.com>; greenkeys <greenkeys at mailman.qth.net> 
Sent: Thu, Apr 23, 2015 12:13 pm 
Subject: Re: [GreenKeys] Troubleshooting papertape reader 

     Bill,   
  You're going to want to start by isolating this problem to the reader or the printer mechanism. I'd read the tape into a file on your PC and see whether or not the LFs are being lost/garbled by the reader. If not, then you're really just chasing a printer mechanism issue with this particular symptom.   
  Use a terminal emulator like TeraTerm and capture the received data into a binary file. Do you still have a PC with a native serial port instead of a USB-serial adapter? Many serial adapters have problems at 110 baud.   
  Mike   

      On Thursday, April 23, 2015 10:44 AM, B Degnan via GreenKeys <greenkeys at mailman.qth.net> wrote:

   Hi all,
I have a question about reading a papertape.

Let's say I have two machines,  both in local mode.

I want to read in a papertape that has the following data on it:
S10400F3FF09
S11300000D7600F37E18F97E033C00004838002C7E
S113001000000000000000000000000000000000DC
S113002000000000000000000000000000000000CC
S113003000000000000000000000000000000000BC
S113004000000000000000000000000000000000AC
S1130050000000000000000000000000000000009C
S1130060000000000000000000000000000000008C
S9

Machine #1 - run the tape in the reader I get
S10400F3FF09
S11300000D7600F37E18F97E033C00004838002C7E
S113001000000000000000000000000000000000DC
S113002000000000000000000000000000000000CC
S113003000000000000000000000000000000000BC
S113004000000000000000000000000000000000AC
S1130050000000000000000000000000000000009C
S1130060000000000000000000000000000000008C

Machine #2 - run the same tape in the reader and a number of the lines do not line feed, typing over the line.  
This happens in the very beginning and every so often but enough to make it impossible to load a long program from the reader.

I have checked the reader and the form out mechanism.  Nothing obvious appears wrong to me, the unit is clean and oiled but not too much.

I welcome your suggestions.  What could be wrong?

Best
Bill Degnan
vintagecomputer.net

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