Dug into the erratic contact in Documation reader, tested need for column 81 modification, stowed away

 REMOVING AND FIXING UP THE POWER SUPPLY AND DAUGHTER CARD

I found contacts that were bent and likely not making solid contact. I  did some straightening and adjusting to improve it, then remounted the power supply in the machine. I ran it a bit and it worked well, although with intermittent errors only the passage of time and many cards will remove any lingering doubts.

TESTING WHETHER MOD NEEDED TO HANDLE RIGHT SIDE DIAGONAL NOTCHED CARDS

I disconnected the connection from the MOSFET that is hooked to a wired-OR and at the time of the column 81 (CR81) signal, will force row 12 to appear to be dark. I had made this mod because I thought that light from a diagonal notch on the right side was reaching the row 12 phototransistor. 

I then ran a large batch of cards, about half of which had the notch on the right side, with no Read Checks being generated. This tells me that the reason the reader wouldn't tolerate right side notches was the modification made by previous owners that forced a dark check at column 82 in addition to the intended time at column 81. 

BACKING OUT THE MODIFICATIONS ON BOTH M1000 AND M600 READERS

I carefully removed the circuitry I engineered to 'solve' the right side column 81 issue, since it actually does not occur in a machine as it was designed by Documation. Thus I want to strip out the modifications that came with the machine as well as the mods I installed. 

Taking the MOSFET from the M1000 was pretty easy. The M600 had a small daughter PCB with a NAND gate that was wired to several points on the PCB. I had lifted pin 6 of a chip, broke a trace, put in a jumper to bring the pullup resistor to the correct side, and put my NAND gate between the pad under pin 6 and the lifted pin. I installed a new 7405 chip and jumpered over the cut trace, putting the card back in original condition. 

The other modification I had to back out was the cut trace and pullup resistor on the card that that creates the CR81 signal (and was producing the second pulse at column 82 time because of the mod). I had removed it on the M1000 by pulling the resistor and jumpering over the cut trace. I did the same fix to the card on the M600. 

I then grabbed a small batch of cards from a box that I had previously read and read them to be sure that all my tweaks didn't impair the successful operation of the reader. It performed perfectly. I stowed away the reader for future projects. 

RESTORATION UNDERWAY FOR M600 READER

I turned my attention to the M600 whose picker mechanism was in desperate need of renovation. I found that the shaft, which rotates between two roller bearings (at the top and underside of the picker casting), has a huge amount of vertical play. 

I inspected the upper bearing, which is the one riding up out of its socket. The notch on the shaft for a circlip is well above the top of the washer on the bearing. There may be another washer which is missing, or this may have been bad from when I bought it. I do have to measure the space between bearing and circlip notch, then buy washers of the proper diameter and thickness.