Schedule April 2007

return to main 1401 Restoration Page
go to Team Bios

Wed April 04 - general, Sat April 06 - die hards
Wed April 11 - general, Sat April 14 - 2nd Sat., - Volunteer Day
Wed April 18 - general,
Wed April 25 - general, Sat April 28 - 4th Sat.

Wed April 04 - general

  • Present were Ron Williams, Frank King, Bob Erickson, Allen Palmer, Chuck Kantmann, Joe Preston. Robert Garner (brought the bagels as usual :-))) and Chuck's 14 year old grandson were there for about an hour.

  • e-mail from Frank King
    Since Bill Flora was out today I stole the feed knives from the punch side of the 1402 and put them on the 083 sorter. The dang thing kept on jamming with the same symptoms. Card turning sideways more than the feed path will allow. (column 1 getting behind column 80). So, my theory is all wet or at least very damp about the feed knifes. But, for the life of me I can't figure it out right now. But I will. I better before Bill gets back and finds the knifes are missing on his punch unit. I sent the 083 feed knives to Grant via Allen so he can sharpen them up. They are worn badly which was verified by Bob Erickson.

    Chuck's grand son, Ian came by today to hitch a ride from Mountain View to Morgan Hill. It's a good thing, cause I lost the nuts and washers from the feed knifes from the 1402 and his sharp eyes found them, along with a few extra washers we have dropped from time to time. I think he is about 14ish. Maybe we can get him on the team.


    - - - - - - Ron Williams provided the following - - - -

  • A Register latches, some were rather slow - output fast and inverted not-output slow, - playing around with it.

  • Some upper memory addresses dead - even hundreds 8000 to 11999. 8000 - 8009 bad, 8200-8209 bad, ... up through 11,999

    Bob Feretich and Ron Crane figured previous addressing problem - maybe they will have to work on this one.

  • Ron is saving a printer ribbon re-inking opportunity for Ed Thelen :-((

Sat April 07 - die hards - or maybe "energizer bunnies"?

Report by Mike Cheponis
I needed to help with the PDP-1 demonstrations on Saturday the 7th and I stopped by the 1401 room afterward, and lo and behold Ron Williams was there with scope a'blazing, debugging the "Z" instruction (MCS - Move Characters and Suppress Zeros, which is how his "powers of N" demo program prints the numbers). So I stayed a bit and generally lowered Ron's productivity.

Still, Ron found the problem and got it working. Here are some pictures:

Bad card:

After card replacement
See Slow Circuit below.

The signals should be mirror images of each other. The fact that the output signal (top trace) is so clean with a working board is Very Good. This signal is only used for the Z instruction. (The slow rise time seen on other signals in the machine that continues to cause intermittent Check Resets still needs to be debugged.)

The Bad card looks like this:

And the relevant schematic:

If I'm remembering correctly from the machine schematics, the section that is bad is the circuit with T4, so Tim, if you have a chance, it would be interesting to find out if only T4 on that board is bad (and just how bad T4 is).

The bad board was placed in a plastic baggie, tagged with a yellow stickie, and placed into the "bad boards" box. Ron made plenty of notes to document this in the various logbooks, etc.


p.s. to Tim: I got the initial loader program to work. Now I can get the full relocating loader going by using this absolute loader. It's pretty cool: no more piles of "setwm" instructions! It's 99 characters long.

Wed April 11 - general

Sat April 14 - 2nd Sat - Volunteer Day

During the weekend, Mike Cheponis worked on the slow circuit problem above - below are the e-mails
You may be surprised to learn that they [the speed up capacitors] are OK (!).

I tested them at 10 kHz on my cap meter, and at a higher freq.

Test setup for higher freq:

        | |           R=612 ohms
  >-----| |----+-----/\/\/\/\/---------- gnd
        | |    |
Vi            Vo

I set the sig gen to 10.0V p-p sin-wave, and then tweaked freq of sig gen until
     Vo = 5.0 V p-p  (meaning Xc = 612 ohms).  [1]

Xc=1/jwC so C=1/jwXc

For one cap, C1 was 396 pf @ 657 kHz   For other cap, C2 was 414 pf @ 628 kHz.


We can substitute in these "bad" caps for the other two "good" caps
and my bet is that we won't see any difference to the "good" sections
    - that is, these caps will work fine.

So I suspect the two transistors are hosed.


[1] The reason for the 612 ohm value was that's what I got when 470 series
with 150 ohms came out to, and the back-of-the-envelope said 1 MHz should
have been the same Xc;
   but the caps were larger than that so the point was lower in frequency.
So during a lull in tonight's 1620/PDP-1 meeting, Tim and I headed over to
the 1401 lab for some further checking.  Tim brought some 330 pf ceramic caps,
and one was quickly soldered in and tested and... no difference!
   No overshoot, like there should be.

After some further back and forth, we ended up re-installing the suspected
bad caps (so that now all the caps are original) and replaced T2 and T4
transistors with approved parts from the list for the 083 type transistor.

After those two transistors were replaced,
      the card appeared to work normally on the bench test setup.

The card is in the plastic baggie, and is placed on "Ron's" document holder
(which normally sits between the 1401 and 1403).  If he gets a moment,
maybe he can try this repaired card in the machine to make sure it works.


What's a little disturbing is that the curve tracer, operating at 60 Hz,
    didn't catch this transistor failure.

My guess at this point is that the bad transistors' Cbe (base to emitter
capacitance) is abnormally high, therefore, any HF energy that one might
expect from a Miller speed-up cap gets dumped into that junction.
I have the bad transistors and I'll work them up into a simple wideband amplifier
circuit and see what the frequency response turns out to be.

Ed Thelen's remark - Interesting!! Tim's curve tracer caught
some wierd effects at 60 Hz in 2005 where transistors acted similar to reactive components. (We were conjecturing these were heating effects?) Now it appears we must also test at rated speed to check for speed compliance. Interesting world!!

Wed April 18 - general

Please see Slow Circuit above, (appended after the Saturday report was posted)

  • Present were Ron Williams, Bob Erickson, Glenn Lea, Joe Preston, Robert Garner (thanks for the bagels), Ed Thelen.

  • Ron Williams explained some of the bugs that bad word mark circuitry can produce. In this example, the circuit failed during the summation of the 8 + 8 giving the 16. The zero suppress operation, reading from left to right hit a word mark and quit suppressing zeros, giving the leading zeros on the 16. The next add operation, adding the 16 + 16 hit a word mark at the 6 and added 6 + 16, giving the 22. The intermittent word mark circuit started working again, giving the rest of the page.

  • Bob Erickson had a change of mind about working on the sick IBM 513 Reproducing Punch above. Dag Spicer gave us permission to further evaluate the machine. Chris Garcia and ??? moved the machine into "our" 1401 Restoration Area.
    That mass of relays left of the shoe connector near Bob's leg is an add-on to disconnect the 513 from a driving machine when it is "off-line" doing reproducing rather than summary punching.

  • Glenn Lea just quietly worked on tape stuff, and didn't get rowdy with anyone ;-))

  • There was some kind of new problem with the 1406 add on memory. Joe Preston found an old cold solder joint that could move and be intermittent - Bob Erickson re-soldered it and that seemed a permanent fix for that problem.

  • Ron Williams restored the switch on the maintenance console to its original function. see Hot Wire above. He then carefully removed the masking tape label that had been applied so many years ago to indicate the field wired change.

  • While some of the above was going on, Ed Thelen was upstairs "Xerox"-ing two manuals. Bob Stetson came by and commented that is father had worked for IBM, and that Bob had some momentos in his office.

  • More problems remain in the upper 8,000 characters of memory. Here, the top signal, from a sense amp, is "good", a "one" and the lower signal, although looking rather good and of sufficient amplitude, is read as a "zero". We currently do not understand what is going on. Appropriate boards have been swapped and replaced, (we think - the schematics do not seem complete) and still the problem remains. (I didn't get a picture of the sample pulse.)
    The test setup on the right gives the repeating sequence for scoping as seen on the left.

  • Frank King (and others?) can also come in on Tuesdays as well as Wednesdays. This can better match the Tuesday (evening?) activities of the IBM 1620 and DEC PDP-1 groups - the members of which are providing more and more help to the 1401 group.

Wed April 25 - general

  • Present were Ron Williams, Bob Erickson, Joe Prescott, Grant Saviers, Robert Garner with bagels, and Ed Thelen. After noon Mike Cheponis came in.

  • The new key punch that Robert Garner purchased and had transported from the mid west arrived late last week.

    from left, Joe, Robert, Ron

    Actually looks not bad :-))
    Joe was vacuuming, and heard the rattle of something getting sucked in.
    Well, lets see what it is :-|

  • Dan McInnis has offered a Demo Assurance Program to help verify that the 1401 system is capable of performing intended demonstrations. His preliminary specification is here. Running this program (successfully) will help assure docents and demonstrators that the system is "OK".

  • The 513 card punch -

    Maintenance Manual

    A friendly looking group

    Examining Punch Dies

    wiring - The motor generator works,
    Ed Thelen gets no fun :-((
    some fun details -

    Special read brushes, four shown, when connected with the

    patch panel, can cause useful variations in punching

    The gear box - obviously needs oil

    and an oil change. ;-))
    note the pipe we uncapped and the tunafish oil drain can
    The coils of wire (upper left) is the start cycle relay

    Red Shield removed, Bob says all gears behind the shield have jerky motion to move the card between punch rows

    now for the gory details :-((
    This is the bar that Bob feels was left disconnected, and caused such devistating damage some years ago.
    Hard to miss warning

    Broken pawl to prevent someone from reversing machine and damaging read brushes

    Grant holding some of the about 10 broken punches of hardened steel

  • Three of Bob Erickson's grand"children" visited. (They appear to be in their late teens.) We had a great time. Bob got lots of huggs - I think the rest of us were a little jealous? Each of them keypunched their name into IBM cards, and the cards was placed in the "Visitor Big Print" deck and produced a printout similar to this. We had some excitement as we had forgotten that the first two cards of the deck do not work reliably. (We had to remove them to get the program to run - see below.

  • The memory clear pre-loader prepended onto object decks by the AutoCoder assembler does not work. We had to strip off the first two cards of the object deck generated by AutoCoder or face a HALT during the processing of the second card. (See investigation by Mike Cheponis below.)

  • Shortly thereafter, John Toole brought in a group, including Barry Boehm (see below). We keypunched Barry Boehm's name and he got a Big Print souvenir :-)) - That was a really interesting group - too bad their time was so short.

  • Ron and Bob worked some more on the 1406 extended memory

    And the job ain't finished
    'till the paper work is done :-|

  • Later - From Mike Cheponis
    Eric stopped up with me to the 1401 room this evening so I could try out some further quick test programs, in order to try to diagnose the latest problem that Ed discovered this afternoon.

    Ed was giving some of Bob's grandchildren some standard demo paper out w/the visitor's name when the first two cards of the program loader were causing a check reset light to go on.

    Further investigation showed that the initial 2 cards could be removed and the deck still loaded OK to print the demo.


    Afterward, it was determined that a "cs 15999" instruction was failing; Ron and I tried to narrow in the range. The program was:
    1: sw 8,12
    8: cs x999
    12: b 1
    the "x999" would be I9I (for 15999) R9I (for 14999) etc.

    The failure is: the "B" with a wordmark at location 12 is _completely_ gone - all bits in that location are turned off, not even a check bit is on; this is, of course, invalid as well as strange, as the clear storage instruction is only supposed to clear (up to) 100 positions of core, NOT to be wiping out op codes and turning the next instruction into an invalid blank!

    I made 16 cards that cleared storage on the addresses 15999, 14999, ...., 1999, 999 (these cards are now on top the 1402), and tried them one at a time. The rationale was that although it could be done via panel switches, that can be error-prone, and also because it was easy to try the 16 programs to see which ones worked, and this could be done systematically.

    If the address was 7999 or below, the program worked normally.

    If the address was 8999 or above, the program failed as described, above.

    (I did not try to clear storage of 8000 [should clear one location] to see if it also causes the problem - I suspect so).

    So it would seem that clearing storage on an address above 8000 causes the next instruction after the "cs" instruction to be replaced by all bits off.

    This is a new problem, as far as I know.

    p.s. John Toole brought Barry Boehm and entourage through the 1401 room this afternoon:
    [Barry also got a personalized

  • There is a rumor that the tape team, including Allen Palmer, is distracted by amateur rocketry. Apparently there is some rocketry meet in June that they are preparing for. (See formal correction here.)

Sat April 28 - 4th Sat

  • Present were Ron Williams, Bob Erickson, Tim Coslet, Ed Thelen.

  • As reported above, Ed Thelen is searching desperately for some reason to take the 513's motor-generator apart - for further "examination". ;-)) Unfortunately, the motor generator works, and looks in almost new condition. ;-(( Here is the almost new looking commutator and one of four almost new looking brushes. Probably a good idea to temporarily put Zerk fittings on the end bearing assemblies and inject some grease.
    Here is the field resistor for the 40 generator part of the 513's motor generator. It is shorted out by that black wire - we think that is not a good sign. Will test the no-load and loaded voltage output "next time".

  • Speaking of motors, look at the 513's starting capacitor that IBM moved. Why? To make room for the punch magnet assembly. As Ron Williams said, "I bet there were some bad words said about that."

  • 1406 Expanded Memory - Background - The 4,000 character core bank sense windings are connected to two amplifiers
    - a pre-amp, followed by a final amp.
    The preamp presents a terminating load on the sense winding of 400 ohms, and converts bipolar pulses to positive pulse currents.
    The positive pulse current is fed into the final amp, where it is ORed with the outputs of the other three core banks





  • Tim Coslet reported that his in-circuit tester found on the sick SenseFinal-AQX-Card:
    a) 3 of 4 transistors had a gain below 5, lowest he can measure - didn't fix what wasn't broke
    b) pin "G" - the one reported bad - did not diode between the base and emitter :-(( - replaced

  • Ron Williams found two more bad sense final amplifiers bad - always pin "G" - strange -

  • We are running low (like 3 left) of 083 transistors

Go to
May 2007
go to Team Bios