Was: PDP-8/A transformer hum Is: VXT-2000 stuff. - test-drb@ccmp.vtda.org

18 Jun 2020

...

 On 6/9/2020 11:51 AM, Glen Slick via cctalk wrote:
  On Tue, Jun 9, 2020 at 9:04 AM Bill Gunshannon
via cctalk
 <cctalk at classiccmp.org> wrote:

 For the VXT-2000 with an H7109-B the rated voltage and current values
 are printed right on the power supply label:

 +5.1V, 7.81A
 +12.1V, 0.62A
 -12.1V, 0.46A
 -9V, 0.2A

 Fixed width character pinout diagram:

        +=================+
    -9V | Yellow | Orange | +12.1V
        +--------+--------+
    ??? | White  | Black  | Gnd
        +--------+--------+
 +5.1V | Red    | Blue   | -12.1V
        +--------+--------+
 +5.1V | Red    | Black  | Gnd
        +--------+--------+
    Gnd | Black  | Black  | Gnd
        +=================+

 The mystery is the White wire. The power supply label only lists 4
 output voltages. The White wire appears to be routed to the Ethernet
 daughter board. The measured voltage appears that it might be floating
 slightly negative, somewhere around -1.5V when the Ethernet daughter
 board is installed and around -5V when it is removed. Maybe it is a
 high impedance earth ground connection? It appears to be connected to
 the shield of the Ethernet BNC, which measures around 1M-Ohm to the
 chassis ground when the power supply is disconnected from the main
 board, and around 0.75M-Ohm when the power supply is connected.
  As long as we are talking VXT-2000, I have this on file, figure it would 
 be useful for future googling of the list if
 this were here as well.? May be a repeat of info from an earlier post, 
 or maybe elsewhere.

 I didn't save the source of the info, but looks like someone named Matt 
 Millman did it.

 The setup is as follows: HP Envy laptop running MOP boot daemon, 
 connected to Lantronix LTX-C twisted pair
 ethernet to AUI converter (not the same as a twisted pair MAU). This is 
 then connected to a cabletron coax
 MAU with a 10BASE5 vampire tap. The coax runs over to another MAU, which 
 is connected via an AUI cable to
 my VXT2000. I didn't think of it, but it would have been nice to have a 
 real DEC MAU on the VXT2000, I've
 got several DEC h4000's I could have used.

 https://www.youtube.com/watch?v=A5T2GlAN2N4

 http://tech.mattmillman.com/projects/10base5/ 
The first link is mine actually. (Hi, I'm Joe from Joe's Vax Repair and 
More). I have a VXT-2000 and have had it setup and booting on a few 
occasions. I also happened into some 10BASE5 equipment a few years back 
and the VXT2000 was one of the only AUI devices I had at the time. I'm 
not Matt Millman, but I did reference that site to find the existence of 
the Lantronix LTX-C and similar devices.

Now that I have more AUI gear, I plan to put different gear on the 
3-node AUI segment (cisco 2511 router, media converter to 10BASE2, 
VAXStation 3200) and move the other 10Mb equipment to a 10BASE2 segment. 
The whole mess will be joined to the main network via T1 on a Kentrox 
CSU/DSU on the 2511.

You can boot the VXT2000 using MOP or BOOTP and TFTP actually. MOP was 
the first thing I managed to get working, but BOOTP and TFTP worked 
equally well once I had it set up correctly. Unfortunately my bootptab 
file is on a roommate's MicroVAX II...

Anyway, see the links section here for the software: 
https://terminals-wiki.org/wiki/index.php/DEC_VXT2000

There's also theoretically OpenBSD and NetBSD support for the VXT2000, 
but in my experience the netboot stuff is pretty broken on VAX for 
whatever reason. There's at least one bug for the SGEC ethernet chip 
driver, and I could only get older versions of the network boot mop file 
to load. Of course, the older versions wouldn't support the newer kernel 
format, which apparently changed at some point. Or maybe I'm just doing 
something wrong.

If the machine in question gets repaired, feel free to contact me with 
any questions. If you're familiar with netbooting VAX systems, it's not 
too hard to figure out though.

I'll add that the note about the 9V supply being isolated sounds 
reasonable. It could be used as the supply for the built-in 10BASE2 MAU 
on some units. I can't confirm as my unit has 10BASET instead which has 
no requirement for an isolated supply.