Schedule December 2006

Received from John Van Gardner - Dec 4, 2006

1401 Maint Manual page 95

I was looking at the 1401 Maintenance Manual 225-6487-3 pages 180 and 181 which show scope pictures and set up to check the read brushes and impulse CBs. There is a good diagram on page 95. I wish I knew some way to capture one page of a .PDF file and send it The row bit cores are in the 1401 array and I marked with red where the -20 attaches. There is a chart on page 42.40.53.2 that shows the actual pin connections to the array. Also marked is a note that says, "Machines with serial numbers above 25000 have 1/2 write line removed. This allows the row bit core to set with full I from read brush". ALD page 42.40.51.1 has a chart that show the connections between row bit cores and the read brushes. There is a note at the bottom of this chart that says, "All brush signal lines have a 180 ohm series resistor before 01A1 edge connector termination on the paddle card connector". I wondered if this resistor value is the same for all serial number 1401s. When they did away with the 1/2 write line how did they increase the current through the brush? Assuming no other resistance 21 volts through a 180 ohm resistor = 117ma. If you have all 80 columns punched in the same row that's 9.3 amps from the supply and through the transistors driving the common brush. Any resistance in the common circuit could explain why it fails when there are lots of holes punched. Van Gardner

Robert B Garner wrote: John, Thx for your note. A 9.3-amp pulse to our old 1402 21V power supply could be our issue. I'm not familiar with required core switching currents (in general, and wrt 1401). Is 117 mA already a marginal value? The only cores that I actually knew what the switching currents were in the 737 memory on the 704. We had to scope the terminator resistors for the X and Y array drive lines and look for a voltage level that represented 410ma +or- 10ma. These X and Y drive lines only went through the hole in 64 cores one time. We did not have any vacuum tubes that could supply this amount of current so that's why they used switch cores to drive them. As cores became smaller with less mass it took less current to flip them. The cores in the 7302 memory on the 7090 could pass through the hole in a 737 core. Then the 360 cores could pass through the hole in the 7302 cores. What does it mean to "remove 1/2 write line"? Why would they do that? (cost optimization?) If you look at the left hand red arrow on the attached diagram you will see it points to a line labeled 1/2 write * that goes from the power transistor up through a resistor then over to the right and down through the row bit core. This is the line that was removed on the 25000 serial number machines. This would certainly help reduce the cost of the array as these were all hand wired at that time. There is a second line from the power transistor through the read brush then through a resistor then to the row bit core. Notice that when this line goes through the core it is wrapped around the core several times then to the -20 volts. The extra turns help flip the core with less current.

Robert B Garner wrote: Van, Thanks for your advice! I suspect it will help us immensely again. > We had to scope the terminator resistors for the X and Y > array drive lines and look for a voltage level that represented 410ma +or- 10ma. I've been trying to encourage the guys to do exactly this to find out what's wrong with our extended core memory. > There is a second line from the power transistor through > the read brush then through a resistor then to the row bit core. It's amazing that the current directly from the read brushes is used to flip a core in main memory! (Imagine all the junky noise that could get on it via the ground loop formed between the 1401 and the 1402 in a noisy environment due to nearby elevators, etc.). - Robert

Wednesday finally came, and seven dwarfs went to "work" -

Present were Ron Williams, Bob Erickson, Allen Palmer, Frank King, Glenn Lea, Chuck Kantman, Ed Thelen. Allen Palmer arrived with his pickup loaded with re-furbished parts from Grant Savier's work shop. Here the truck is about half unloaded. So much weight (many motors and clutches) on such a little cart. Frank King arrived with some cleaned card track parts. and we washed some more surface parts in a CHM vendor kitchen ;-)) Now to put the 083 sorter back together. Anyone remember how this thing came apart - and where are the screws? ;-)) Bob Erickson and Glenn Lea continued cutting and fitting plastic shielding for the 077 collator. The general philosophy is to prevent accidental touching of moving parts, not to completely encase the 077. Randy Neff came by and worried that if people reached around the shielding, bad things could happen. Ron Williams was bug shooting a problem in the 1401, but occasionally he and Ed Thelen looked at the 1402 card reader problem. I were surprised to find: The roller the brushes contact is a hard rubberoid substance, not bronze. The roller is normally at -21 volts, rising to about 0 volts during the 12 pulses of the card read cycle - the 80 write core wires in the card reader core are normally at -21 volts so maybe this might reduce hazard of smoking the limiting resistors in case of some fault. See December 4th diagram above. And a little study of the two read stations in the 1402. The read brush assembly of the second read station is removed for viewing. Ed talked some with Jim Sumers about the coming demo - Feb/March. He seemed pleased with the thoughts so far. Apparently the administration is contemplating demoing the operational machines (PDP-1 and projected IBM 1401) on alternate Saturdays - alternate being the PDP-1 one say even Saturdays and the 1401 on odd Saturdays - something like that? Jim was concerned about my projected visitor training time to operate a key punch to key punch their name into a card - to be read into the 1401 and printed in BIG letters, etc and a description of the 1401. (We hope to have 3 operational keypunches by formal demo time.) I had projected 5 minutes to get someone familiar with feeding a card and successfully keying their name. Jim wondered what we would do if we had say 15 visitors which might overwhelm that procedure. Maybe there would have to be a plan be for say 5 or more people, maybe a docent feeds and registers the card and lets the visitor operate the keys, or maybe I am a worry wart, or we need to get more creative - I showed Jim something like the following that now works with 1401 emulation under Ron Mak's ROPE :-)). This is currently coded in 1401 AutoCoder, could be recoded in the not so nice SPS format, the smaller less demanding 1401 assembler. The 700 character format table and the 700 character program are just not practical to keypunch in Object Card format. (I would really be great to get an assembler working, or a convenient method of getting object decks punched.) There are plenty of test decks that can make: - the card reader pass cards, - the printer bang - a tape move with the tape drive chattering loudly, *but* I think if a visitor 1) key punches his/her name into a card, 2) maybe sees the card go zinging through a 083 sorter 3) sees the 1401 read the card, 4) listens to the printer banging out his/her name, 5) and gets a printout of his/her name in BIG BOLD PRINT to take home and show friends 6) and gets the card he/she punched to take home that is not only charming and memorable, - it is lightning and thunder !! :-))