Friday, March 13, 2015

Identified problem at root of the 1442 card reader/punch problems, meanwhile continued wiring SAC interface box


It seems that cards are slowing or dragging as they move through the punch station. This causes both problems I am experiencing - a check condition as the card hasn't cleared the photocell area when it should have, and poor ejection into the cornering station for movement into the stackers.

I will remove the punch unit to get at the heart of the problems here - as was recommended by Peter Vaughan of the National Museum of Computing in the UK which has successfully restored an 1130 system.

Cable disconnected as first step to remove punch unit

After removal and examination, I discovered grease covered dust bunnies wedged in the card path, dust and oil mixture coating the bulk of the mechanism and an obvious problem. To describe the problem and my actions so far, I have to give a touch of background on the construction and operation of the punch station.

The punch station has a pair of very thin rubber wheels that will move the top and bottom strip of a punched card. A metal roller on a pivoting arm sits above each of the wheels - both rollers share a common arm. The arm is spring loaded to force the rollers onto the drive wheels, except when pushed out of the way by two pushrods coming up from the punch release lever. This is pushed manually to release cards stuck in the punch station, but also pushed by a long lever driven by a cam on the main card feed clutch axle.

In each feed cycle, the feed clutch axle will lift the rollers off the punch drive wheels at the beginning and end of a cycle, otherwise relaxing the pushrods so the card is squeezed by the wheel/roller duo and moves only when the drive wheel rotates.

When a card is heading into the punch station at the end of the feed cycle, the roller is lifted until the card comes to a stop at the right position for column 0, then the roller is allowed to press down on the drive wheel through the card.

When a card is moving out of the punch station and going to the cornering station, the roller is controlled to move the card out at the proper speed to stop precisely where it should in the cornering station .

On my punch unit, one of the pivot arms on the common axle is very stiff, too much for the spring to restore on its own, thus the roller is not properly moving to its two positions. This results in the improper card movement into the punch station, but also gives a weak ejection speed from the punch into the cornering station. If I solve this, it should solve both of the observed problems.

Punch unit out of the machine for investigation

Punch went here between the read station on left and cornering station on right

Front of reader where a belt powers the Incremental Drive which moves and punches column by column
I have been dripping oil everywhere that the gummy lubricant might be causing the excessive friction, but I have limited access to the inside surfaces. To pull this apart, clean it thoroughly and reassemble, I would have to almost completely disassemble the punch and incremental drive unit, which opens me up to a large number of very critical adjustments that will need to be made. I am going to hope I can free this up enough without having to 'go nuclear' and temporarily turn the punch into a large pile of teeny parts.

It may free up from a very large number of hand cycles of the pivot arm using both the release lever/pushrods and a screwdriver. I will work on this process for the next few days and hope I can restore normal pivoting.

As of the end of the day, I am guessing that it is about 20% looser than initially. Friction is still stronger than the spring force, but it is close to that point at least.


My connectors for the FPGA to circuit card cables should be arriving Saturday afternoon, when I can finish the wiring. Today I repaired the two broken leads onto the 160 pin connector, as well as verified that no others appear broken off. I had spare pins which didn't make the task too hard, particularly since the two that snapped were near the top and easily accessible.

This is frustrating, because I specifically switched to stranded wire for the connectors in the 160 pin unit to avoid the problems I was having with solid wires in connectors. The solid wire would snap more easily, while the individual strands in the other wire type are able to handle the stresses with less risk of breakage.

I realize my problems were caused by all the bending of wires I have had to do when unsoldering all the original boards, soldering the new boards, then resoldering the new boards to the proper points.I am going to try to minimize movement of the boards while I wire them up and then very carefully move them into their mountings.

I made up some colorful ribbon cable for the FPGA to circuit board connections. I wired up 30 of the 77 signals today, going slowly and carefully, As part of this task, I decided to reorganize my assignment of signals to FPGA pins, so that the cable is very straightforward and logical.

Ribbon cables being attached to circuit boards
I am using a 50 pin IDC connector to the ribbon cable, which is built as two rows of 25 pins, Knowing that the pin for row A, column 1 of the FPGA board is the leftmost wire on the ribbon cable, I could plan out the signals assigned to each wire. Some of the pins on the FPGA carry voltages or ground lines, for example pins 1 and 2 are 3.3V while pins 3 and 4 carry ground. I split the ribbon cable for most of its distance except for where it attaches to the FPGA as a single unit.

The first two wires are cut off, since they are 3.3V, and the next two were kept as a short pair for grounding. The next twelve wires are the signals going to board 1, so that group of twelve are together as a mini-ribbon going to board 1, the next twelve is another group that supports board 2, then I have a ground of six wires which are power and ground, another block of twelve for board 3 and then a few unassigned signals left alone for expansion.

Then, each mini-ribbon with twelve wires is split again for the last few inches near the circuit boards, into pairs of wires that match the double pin headers I built onto the circuit cards. I then began attaching the wire pairs.

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