Schedule June 2009

return to main 1401 Restoration Page
go to Team Bios


Wed June 3 - General, Thurs June 4 - Tape Team
Wed June 10 - General, Thurs June 11 - Tape Team, Sat June 13 - 2nd Sat
Wed June 17 - General, Thurs June 18 - Tape Team, Sat June 20
Wed June 24 - General, Thurs June 25 - Tape Team, Sat June 27 - 4th Sat

Wed June 03 - general

Thursday June 04 - Tape Team

TAU Debug Status - 6/4/09 - (Sam S. & I)
  • Last week we noticed  that the Overlap STAR would sometimes be ORed into other STARs when the various STAR buttons were pressed on the DE 1401's operators panel. Today we troubleshot that bug first. We found that the a microswitch behind the Overlap button was vibration sensitive. Sometimes the pressing of other buttons on the panel caused the "normally closed" contacts of this switch to open. There are two microswitches behind the Overlap STAR button and one of them was unused. So, we moved the wires from the failing microswitch to the other one. This appears to have fixed the problem.
  • The DE 1401 was unable to perform reads or writes to tape. The TAU was failing solidly, hanging in the first part (Read Delay) of Read operations. We found that the Delay Counter was unable to toggle the 8 bit.While probing we noticed that Delay Counter bit 4 had an asymmetrical up/down waveform and the trigger +output had a bad up level. We replaced the trigger card. The levels the new card produced were good, but bit 4 still had an asymmetrical up/down waveform and bit 8 still would not toggle.
    We then found that a gate that controlled bit 4 was not functioning. We replaced that card and the Read operations stopped hanging, but would complete with errors and the Delay Counter would not stop after the operation.
  • We found another bad card (bad output level) in the DC Drive circuit. Replacing this card permitted tape operations to complete without errors.
  • We then booted the Autocoder assembler and it ran successfully to completion.
The bad level on the DC bit 4 trigger could have been with us for a long time, but the other two failures occurred (or degraded to the point of solid failures) over the last week.

If the DE 1401 shows signs of stability, we will move the 729 Emulator to the CT system. We need to position the Emulator monitor in a spot where it is visible from the operators console. Any suggestions on where we should move our table.

Bob Feretich

Wednesday June 10 - General

Thursday June 11 - Tape Team

There was no meeting -

Saturday June 13 - 2nd Saturday

Ron Williams, Bob Erickson, Bill Newman and Stan Paddock showed up today for the second Saturday work day.

When we arrived, all of the CHM parking lots were FULL! They even hired people to provide valet parking.

I saw Jim's E-mail on the Saturday work but missed the fact that it has been moved to NEXT Saturday. Well, we had a nice lunch cross the street.

Ron and Bob are close on the trial of the CT system's memory problem.

Bill and I continued our work on removing the "skip printing" wiring that had been done to the DE machine. We removed and installed the last of the revision changes and the machine is operational again as wired from the factory.

We had a return visitor from Australia who knows about the "Sterling" option installed on the DE machine.

The "Sterling" option was to handle the following problem.

Prior to decimalization, the pound was divided into 20 shillings and each shilling into 12 pence, making 240 pence to the pound. The symbol for the shilling was "s" not from the first letter of the word, but from the Latin solidus. The symbol for the penny was "d", from the French denier, from the Latin denarius (the solidus and denarius were Roman coins). A mixed sum of shillings and pence such as 3 shillings and 6 pence was written as "3/6" or "3s 6d" and spoken as "three and six". 5 shillings was written as "5s" or, more commonly, "5/-". The stroke, /, indicating shillings, was originally an adaptation of the long s.

Various coin denominations had, and in some cases continue to have, special names such as "crown", "farthing", "sovereign" and "guinea". In February, 1971, the British switched to the decimal system eliminating this problem. On the DE machine, the floating $ option of the 1401 Edit instruction does not work with small amounts . Ron and the Australian visitor believe there might be a conflict between the Sterling option and the Edit instruction. (To be continued)

Stan Paddock
San Jose, CA

Wednesday June 17 - General

  • Present were: Ron Williams, Bob Erickson Bill Flora, Frank King, Glenn Lea, George Ahearn, Joe Preston, Stan Paddock, Don Luke, Mathias Goerner (down from Berkeley), Ed Thelen, Robert Garner. - The museum was full of INTEL people, so we ate our lunch at tables on the north lawn :-))

  • Jim (Chip) Hunt, [JimHunt at Pacbell dot net], came for the day. Jim knew Robert Garner from SUN days. Jim also worked on attack submarines, and has wonderful, wild and wooly tales to tell ;-)) (And he seems to have a very practical working knowledge of electronics :-))

  • Glenn Lea was curious about the state of replacements for the 1402 card pocket clutch springs. Judith has taken a sabbatical, and we were not sure what folks had found. A call to Helander Products revealed that the pictures of the springs and clutch assembly Judith sent did not match the old IBM units available at Helander. We (Bill Flora) will send a sample so that several more spares can be fabricated. Hopefully they have the correct spring stock.

  • A new? problem? - temperature and vibration sensitivity in a 1406 12,000 character core memory. The 1406 supplies the upper 12,000 of the 16,000 programmer accessible memory location. Suddenly?, there was a problem - different bits of different characters were unreliable under different conditions of tapping SMS cards and temperature. Ron Williams found inconsistencies in the voltage patterns in the switch cores in the address switching matrix.


  • A Detailed Overview of the memory Ron's study sketch, looks as though he has to struggle with this stuff like the "rest of us".

  • Details of the temperature sensitive switches three in middle are the series resistors. Like warm ;-))

  • Jim Hunt had a fine time verifying that the temperature switches worked at different temperatures. He found the middle switch of one spare AKB card with a 50 ohm "closed" resistance, should be about 0.1 ohm :-|

  • There was a lot more going on - Printers, Tapes, ... , but I got involved with sorting spare SMS cards :-((
    Sorry to slight a lot of other folks :-((

Thursday June 18 - Tape Team

Saturday June 20

from George Ahearn

Bill Worthington was kind enough to conduct a private tour of the CHM for my visiting relatives.

Thanks Bill

Wednesday June 24 - General

Thursday June 25 - Tape Team

from Bob Feretich and Sam S.

TAU Debug Status Report 6-25-09 - (Sam S. and me)

First, we verified that 5 Tape Autocoder still ran on the DE System. No problem, it worked.

Then we disconnected the 729 Emulator and moved it to the CT System. To place the Emulator where we needed it, we had to move the two CT tape drives a couple tiles to the right. When Sam tried to attach the power cable to the rightmost drive, one of the pins got pushed in. Further examination found that it had been being held in place with electrical tape. While Sam replaced the pin with one from the donor drive, I coupled the two data cables together (bypassing the drive) and tested the Emulator connection.

I found that multiple errors were occurring on the READ Bus. Bit A was shorted to ground, and other bits had intermittent errors. Close examination of the short (drive-to-drive) data cable revealed that the head end biscuit connector was broken all the way across. The crack went through the cluster of READ Bus contacts. Pressure on the biscuit connector opened the crack allowing the contacts to move. Several were partially pushed in. One was partially out and shorting to its neighbor. We replaced the cable with the one that was stowed under the floor.

Once the repairs were made, we tested basic tape operations, then ran the 5-tape Autocoder application. The basic tests (just some reads and writes from the TAU control panel) worked without errors. The Autocoder runs to a successful completion 30% of the time. A machine check occurs 60% of the time with a "all zeros with bad parity" OPCODE being loaded. The other 10% of the time the TAU hangs in a Backspace operation.

We did not try using any of the 729s on the CT system.

Ron W. tried using the left 729 on the DE system. It would not load tape.



from Sam Sjogen

Hey, I'm not "just" a software guy! Ironically, today I ended up spending most of the day fixing a 729's power connector.

Chris, note carefully that the power connectors on these drives are fragile. In rearranging our drives while moving our emulator from one 1401 system to the other we ended up with some damage to the pins on one drive and it took the rest of the day to repair it.

Using an "organ donor" drive I was able to obtain some pins and retention clips to do the job. Note that the pins are of various lengths, with the most precious being the one used for ground (longest, so as to make contact before the others). There seems to be a mix of signal and power pins, the latter being thicker than the rest and requiring different extraction tools.

We didn't have a pin extractor of exactly the right size, even for the signal and ground pins, so some improvisation was employed. Most of the retention clips were damaged in the extraction process. Each clip has three grab points, you're doing OK if you keep two of the three intact during an extraction. As you don't have spare drives, you might figure on using any extra power cables you're able to obtain as spares just for pins for the power connectors on your drive.


Here are a few photos illustrating the power pin issue. Note in the close-up that the retainer clips are missing their teeth.

Saturday June 27 - 4th Saturday

Go to
July 2009
go to Team Bios