Wednesday, May 25, 2016

Investigating possible causes of 1442 punch lacing during NPRO


The punch unit has three cams rotating in synchronization, moving mechanical parts. There is a main or punch cam, an interposer restoring cam, and a punch restoring cam. In addition, twelve solenoids will either pull an interposer back out of the punch path or let it pop out by spring pressure. The solenoid has a constant hold current which pulls the interposer back and another winding that neutralizes the pull of the hold current when an interposer is to be released into the punch path.

The punch cam pushes down on 12 spring loaded rods, one per row of the card. If a spring loaded interposer has moved out into the path of that downward rod, then the rod pushes the interposer down which pushes on the spring loaded punch itself. This pushes the punch down through the card and into a punch-shaped die below.

The punch restoring cam will push all the punches back up, pulling them out of the die and through the card to reach their original raised position. Thus, the punch restoring cam is timed to push up after the punch cam itself has finished pushing down. The final cam is the interposer restoring cam which pulls the interposer back against its spring load, so that the hold current in its solenoid can keep it retracted. Thus it stays until it is next selected by the neutralizing counterwound current.

This means that when power is off to the 1442, all twelve interposers are pushed into the path of the punch rods and all twelve punches will push down through a card and into the dies. When power is on, all twelve should have only hold current applied and thus all twelve interposers are kept out of the punch path. No punch should descend with hold current on.

The only way a punch should descend when power is on is when the counterwound coil current is also applied, allowing interposers to spring out into the punch path.  Since the punch unit and its three cams are constantly turning whenever the 1442 motor is turned on, it is only by way of the hold coil current and absence of counterwound coil current that the punches do not descend.

My first power up test had punches for rows 4 through 8 descending on every rotation of the punch cam, which should be caused by one of three cases assuming no mechanical failures:

  1. The hold coils are not energized for those five rows
  2. Hold is energized but so is the counterwound selection coil
  3. I have assembled the punch incorrectly which is blocking those interposers from retracting

I think that the hold coils are all wired in parallel, with one source of energizing power. Unless the coil is defective, all should be energized and either all twelve punch or all twelve don't. I can test for magnetic attraction on the ends of the twelve solenoids using a metal rod or screwdriver.

The counterwound coil is driven by an amplifier/driver card in the punch based on signals coming over the cable from the 1131 adapter logic cards. I could have a bad card in either location or the cable might not be fully engaged. I will check all these conditions when I get to the machine tomorrow. Today, I am working on the 729 tape drives on the 1401 computers at the Computer History Museum.


Waiting for the metalworker to respond to my specs and request for an estimate. By the weekend without a response, I will go find another metalworker.

Waiting for the hard drive recovery service to complete its attempt and tell me whether my files are recovered. They would be delivered by FTP so once they respond and if I pay, I can be accessing them immediately.


  1. Thank you for the clear description of the punch unit. I've always thought card equipment was awesome from a mechanical-engineering standpoint. Just to underscore the awesomeness, can you say what speed this unit works at? That is, how many punch cycles per second it runs at? Which would tell how many milliseconds are involved in that cycle of interposer movement, out and then back. Not very many, I'm guessing...

  2. Hi David

    The punch operates at 160 cards per minute, while reading cards takes place at 400 cpm. Cards usually move at the 400cpm rate, but when they get to the punch station, rather than a punch operation triggering a card movement through normal transport, the incremental drive on the front side of the punch unit will pull the card column by column then have a transport move it to the stackers.

    Normal transport speed is 150 milliseconds per card at full speed, but punching takes 375 ms. This tells me that the process of punching 80 columns takes about 225 ms using the incremental drive, or about 2.8 milliseconds per column punched.

    Interposer speed is not directly a factor. The machine has neutralized the magnet in advanced of a column, letting the spring pull the interposer out in the path of the punch. The exact timing dependency is the cam shape roller that drives the punch hammers down at a special point in each cycle. If the interposer is in the way, the punch hammer is pushign through the interposer to push the punch itself down.

    A second cam shaped roller pulls the interposers back to the magnets where they will hold as long as the neutralizing coil is not active. A third cam will pull the punches up out of the die by tilting a lever with 12 prongs that grab the 12 punches.