[vcf-midatlantic] 11/9 & 11/10 Workshop

David Gesswein djg at pdp8online.com
Tue Nov 12 21:21:55 EST 2019

   I got the Museum 3B1 operating again. The hard drive wasn't spinning up.
I took the dead drive home and did a quick poke at it. Its not a stiction
type problem, it just doesn't seem to be trying to spin up. The original
drive was 40 MB. I put in a MFM hard drive emulator emulating the biggest
drive the machine supports without modifications, 67 MB. I installed the
OS, development tools, some games we had on our machine, utilities such as
less, compress compatible with "current" compress etc, script to allow
setting Y2k date, Kermit, and some demo programs which display slides with
sales/promotional material. The basic I found was a DD copy which I haven't
figured out the magic to write it to a floppy that can be used to install
it. I ran out of time to install some of the things discussed such as Emacs.

The emulator does loose the distinctive sounds of the MFM drives. What
do people think of emulated sounds? I've thought about adding it to the
emulator but wasn't sure if it was just a gimmick.

I also replaced the soldered in coin cell battery with a battery holder and 
coin cell. The information I found online said it used a 2325. I put in a
BR2330. The actual battery I found in the machine was a CR2430 which has
slightly higher capacity. My understanding is BR batteries are a little less
likely to leak so I like to use them though they have slightly less capacity.

I cleaned the dust out and it still worked. The foam that they put in instead
of a left side fan is starting to deteriorate. It does not spring back if
touched but isn't quite to turning to dust. I will replace it next time I
open the case.

My original plan was to route an Ethernet cable from the emulator down into 
an unused expansion slot to allow easy access to update/backup the image on 
the emulator. I found the machine had all the slots full so couldn't do that.
One has a memory board, the second a RS-232 & memory board, and the third 
the DOS-73 PC DOS board. For now the cable tucked behind the drive which 
requires the case to be opened to get to it. If we decide that we want 
better access there are a couple options.

1) Snake a cable out through the case such as the non used left side fan.
Its convenient and won't be too visible but probably not the best option
since I can be seen.

2) See if a smaller cable such as USB can still be snaked into the center
expansion slot which has an easy to remove cover. The beaglebone in the
emulator supports Ethernet over USB.

3) Wireless. The 3B1 has extensive shielding so probably would have to 
remote the antenna to outside the metal drive enclosure. This is probably

I gave a quick walk-through to Jeff on what can currently be demoed.

Future plans are to finish installing useful programs for demo on an
emulator at home and update the image in the museum machine next time I visit.
I'll also document what is installed and how to demo.

I also checked out the straight 8. The programs in memory were corrupted
but it seemed to work fine when I reloaded them. I left it with the moving
AC bits program and the punch letters on paper tape program loaded.

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