Suggestions for VT103?

[Jerome H. Fine]

 >Tony Duell wrote:

>>Upgrading the back plane to 22 bits is easy and probably would take Tony 
>>Duell only 15 minutes.  It will
>>
>About 1 minute per connection on average? That sounds right :-)
>  
>
Jerome Fine replies:

Glad to know that my appraisal of your ability to solder was accurate.  
I figured that dividing
my time by about 100 would be a good estimate.

>>usually take everyone else a few hours.  Wire wrap is probably the least 
>>difficult to use with a small soldering
>>iron.  You will need to use lead based solder.  A total of 16 points 
>>need to be soldered - 4 for each wire
>>to connect address bits 19, 20, 21 and 22.  Leave the insulation on the 
>>wire wrap except where the soldering
>>takes place.  Probably Al Kossow has a manual with a diagram for the 
>>VT103 back plane which show where
>>address bits 19, 20, 21 and 22 are located.
>>
>The only thing to watch for when doing a modification like this is to 
>make sure that hte pins you're connecting to have not been used for some 
>other singal (and connected by PCB traces). I don't think this is a 
>problem with the VT103, but I've never seen one.
>  
>
As far I my experience is worth, the upgrade to a 22 bit backplane with 
the version DEC
provides in the VT103 works VERY well.  I watched over at least 6 VT103s 
having the
modification and all responded as expected.  I also tested each point on 
the backplane
before they were soldered and all points showed an open circuit to 
everything else.

 >Glen Slick wrote:

>On Sun, Dec 28, 2008 at 5:15 AM, Jerome H. Fine wrote:
>  
>
>>>Address bits 18 - 21 are on BC1 - BF1 (SSPARE4 - SSPARE7)
>>>
>>>BC1 - BDAL18L
>>>BD1 - BDAL19L
>>>BE1 - BDAL20L
>>>BF1 - BDAL21L
>>>
>>>      
>>>
>>A diagram would be helpful to identify the required points on the backplane.
>>
>>    
>>
>
>http://www.bitsavers.org/pdf/dec/terminal/vt103/MP00731_VT103_Aug80.pdf
>
>Page 73 of 76, VT103 BACKPLANE
>
And as final confirmation, the pdf should confirm that the 4 address 
points in each AB portion
of the backplane are not connected to anything else.

The really cool reason to use a VT103 is that a hard drive can be placed 
right under the CRT.
For someone who does not look closely, the VT103 will look identical to 
a normal VT100.
Thus, when the VT103 is powered up and boots into one of the PDP-11 
operating systems,
the look of surprise is quite evident when they are told there are a 
pair of small monkeys
inside who are answering the responses typed into the keyboard. :-)

The one problem of using the VT103 is that the power supply is really 
too limited, although with
only 4 slots, not a lot of power needed.  Tony, perhaps you might be 
able to suggest how
the 5 amp supply could be enhanced?  On the other hand, with a BA23 
being relatively easy
to locate, perhaps it is not worth while even asking.  I recently 
managed to acquire a 3rd BA123
box (with 12 slots) to be a spare in case one of the other 2 power 
supplies on the other BA123
boxes fails.

As for modes of failure, how often should a power supply be used to be 
sure that keeping it out
of service does not cause a failure when the power supply is used after 
a few years?  Does anyone
have any recommendations?

Sincerely yours,

Jerome Fine