Adding power switch to 3b1 monitor.

[Bill Mayhew]

Thanks to Gary for re-posting the article I wrote about 3b1 monitor
switches.

I should add a couple of things.  There are several defferent
monitor types on 3b1/7300s, as I subsequently discovered.  My
personal 3b1 happened to be easy to usurp the power because it
happened to have a glass mini fuse in a clip holder.  Several
moniorts I've seen since then don't have a clip-in fuse; they have
soldered-in microfuses.

The pin-outs for the video connector are on sheet 8 of the Rev J
schematics, with functions as follows:

JV-1     Video V Sync
JV-2     GND
JV-3     Video H Sync
JV-4     GND
JV-5     Video Out
JV-6     GND
JV-7     +12 VDC Power
JV-8     GND
JV-9     +12 VDC Power
JV-10    GND
JV-11    8 ohm speaker, lead 1     (see sheet 26)
JV-12    8 ohm speaker, lead 2


The video clock rate is 20 MHz.
The screen oganization is 720 bits wide x 348 bits tall.
The screen is scanned non-interlaced starting at top left.
H Sync and retrace is 11 word times (16 * 11 * 50 nS) = 8.8 uS
V Sync and retrace is 1079 word times ( 863 uS)
The video field rate is 60 fields/sec.

The Unix PC video system is discussed on pages 2-78 through 2-86 of
the Unix PC Technical Reference Manual.


Remember, if you decide to work on your minotr that you need to
follow proper electrical safety and tube implosion avoidance
procedures.  Untrained persons should not atttempt modifications or
repairs.


Hope this info helps,
==Bill==
-- 
Bill Mayhew      NEOUCOM Computer Services Department
Rootstown, OH  44272-9995  USA    phone: 216-325-2511
wtm at uhura.neoucom.edu   ....!uunet!aablue!neoucom!wtm
via internet: (140.220.001.001)