Log of October 2006 events

Back to Home Page

Tuesday, October 17, Letter from Dick Oswald, Oct 25
Tuesday, October 31
Next scheduled (progress/problem) meeting is Tuesday November 14th.

and every other Tuesday after that.

Tuesday, October 17
Meeting - at CHM at 2 PM on Tuesday, October 17

e-mail from Dave Bennet, to Al Hoagland, Dick Oswald, Joe Feng, Jack Grogan, HERKY Hanson, Pat Connolly, Ed Thelen - dated 10/10/2006
I am calling a team meeting for next Tuesday, October 17 at 2PM at CHM. Al Hoagland has asked that we establish a timeline for demo capability for the new access control that Dick is designing. Al feels that the fact of accepting support money from IBM and Hitachi as well as increased scrutiny from CHM management will inevitably expose us to the need to keep things moving along at a predictable pace.

This may mean that we should recruit additional skills, such as perhaps electronics fabrication and programming. There is a talent pool among CHM volunteers just waiting to be tapped if need be. We should discuss this as a team.




Meeting Notes - October 17th

Preliminary, subject to review, enhancement, corrections, ...

From Dave Bennet 10/20/2006
Hi Team,

I had a very good chat with an engineer at Sensor Systems, heir to the Markite brand, and it is arranged that they will try to restore our track pot. I have an RMA authorization and this man, Willy Culkar, has agreed to be our interface throughout the repair process. He seems most interested in our project and wishes that his firm be identified as a contributor to our ultimate success. I think this is an auspicious start and can only hope that the outcome is as good.

I will plan to go to CHM, probably Monday, to remove the pot and send it on its way.

BTW I looked at the pot on the proto machine at Almaden and it is similar but not identical in physical form so that its use would be more of a last resort than a preferred path.


Letter from Dick Oswald, Oct 25

Commenting on new Track Pot Corrections

From: D Oswald [sdroswald@sbcglobal.net]
Sent: Wednesday, October 25, 2006 8:30 AM
To: Dick Oswald
Subject: Track pot

It should be possible to make the track pot work without the 80 tap, but the hardware implementation would be complex and the track location accuracy will suffer significantly. The way I see that might work is to replace the 20 tap resistor string and 20 position analog multiplexer with a 40 tap resistor string 40 position multiplexer. In addition the 2 end point tap select multiplexer will have to be changed to a 3 and the standard off the shelf logic parts for decode replaced by a special custom programmable CPLD to accomodate the exceptions needed to then access tracks 60 through 100; (it is greatly complicated by 100 not being integer divisible by 40 as it is with 20).

This in its self would degrade precision by something more than a factor of 2 just from the larger resistor ratio but the excitation voltage headroom limits will also reduce the allowable volts per track scale factor by 2 and increase the max source resistance by a factor of 2. The net result will be a reduction in accuracy of at least a factor of 4 and probably more like 6 or 7 at track 80 compared with the max at tracks 10, 30, 50--with the regular configuration using all taps.

I don't know the linearity of our particular pot and thus what the track position error budget actually is, but I suspect it is already near the about +/- 3/4 track out of 20 that would be the usefull limits of the odd-even dual pitch rack hardware in good adjustment. Its not like a track following servo where the pitch error would gradually change with track number in the problem range and thus be tolerable, but rather when the absolute error reaches a threshold, the detent will be 2 tracks off (if it even settles at the critical error) and would probably make the selection of tracks between 70 and 90 very questionable unless some kind of position check through the read channel, adjust and retry routine were added.

The other possible way I can visualize to correct the track positions to detent centers is to add a lookup table with an entry per track that would generate a correction of the null locations with a DAC. But this requires addition of at least a non-volatile (probably flash) memory and memory access logic which require a lot of extra parts and design effort.

Regarding another issue, is the moulded plastic on the pot really required and the only way to get the structural integrity needed, or could an alternative mounting method and flexible cable be used on a repaired pot? It would no longer be exactly original in appearance, but without a "before" and "after" reference it would probably not be noticed, and all the taps working is quite important for proper function and this would save a lot of design and construction time in the electronics.

Dick Oswald

dickoswald@ieee.org or


Meeting Notes of Tuesday, October 31

Present were Al Hoagland, Joe Feng, Dave Bennett, Dick Oswald, Ed Thelen.

The RAMAC track pot, which had been removed from the RAMAC, was physically presented and discussed as follows

  • The rubbery potting compound which contains the leads was examined in detail.

  • Folks were very concerned that trying to cut into the rubbery compound would be difficult and likely to cause more problems, but without cutting into the compound the existing problem (open track 80 wire) would remain.

  • Ed showed a disassembled cermet and a disassembled wirewound poteometer to give practical examples. We all agree that if the missing tap on the pot is broken at the presumed wirewound resistor of the pot, the required spotweld would be "interesting".


More on the RAMAC track pot - there are several possible trades/comparisons.

- Sindelfingen, Germany - connected to an IBM 650
- Plano, Texas, Ross Perot, Libby Craft
- Almaden - is connected to 305
- Hitachi ??

And around the table we go -

Al Hoagland

Last meeting we wanted a "total demo" in September. That means that we need to be ready a month ahead of time (late June) and have papers and reports published and ready to distribute, and well as head seeking and correct data channel (I/O) activity.
No need to meet original performance specs.

Joe Feng

- 10& of the RAMAC disk magnetic wave forms have been captured
- he has a couple of programs to convert the wave forms to BCD
- two basic conversion/detection schemes
- software peak detector
-zero crossing/template detector

We talked about the wave forms/protocol on the disk. Prreviously we had thought about using a UART, but there is no "stop bit" that UARTs expect - if there is no stop bit, the UART reports a framing error and will likely get confused.

There is the thought that after the current data on the disk is recovered, we can use any format we wish - and adding a stop bit to the protocol might be a reasonable idea.

There was a discussion of basic head alignment, top vs bottom head alignment -

and the point was made that after the current data is recovered we don't care about alignment. In the mean time, hand alignment is adequate to recover data.

Dave Bennet

- had 6 more copies of the 305 Reference Manual made by IBM Almaden. It is also on the website here IBM-305-227-3533-1-mostlyRAMAC-CE-RefMan.pdf .
- currently having 6 more copies of the 305 Manual of Instruction made, also at IBM Almaden. It is also on the website here IBM-227-3534-0-305-RAMAC-r.pdf .
- The noisy compressor situation
- the donated original RAMAC compressor (DeVilbiss - Toledo, Ohio) is much quieter than the modern compressor that is causing so much annoyance.
- Dave has made a new base for the DeBilbis and is working on a belt shield and
- maybe we should borrow an accoustic Db (loudness) meter?

Dave Bennet has some Beta video tapes of IBM history,

but no Beta VCR. Apparently CHM can't view Beta format either :-((
He got a Beta VCR via e-bay from some guy in L.A.
but it arrived with front knobs smashed due to poor packaging.
He is now looking for another Beta VCR.

Dick Oswald

Drawing about complete - but wants a good determination of the capability of the Disk Potentiometer. If the track 80 wire is not working, much more logic to work around the defect, and about half the current accuracy of head seeking.

He *does not* want to do two designs and/or change designs in mid stream.

Dick wishes to attain about half track capability to minimize detent impact and wear.

Dick has purchased plenty of 5 volt logic (0.1 inch centers) from Mouser.

Ed Thelen

Lots of documents on web site. If you know of others, please let me know so that I can add it.

Mechanical Help - Grant Saviers still in South Pacific.

Electrical construction - the prospect would rather design than construct other's design.

If you have comments or suggestions, Send e-mail to Ed Thelen

Back to Home Page