Philips PM 3266 - Page 130

135
Collector
Mesh
The
collector
mesh
G10
remains
at +150
V in
all
modes,
and
this
potential
is
derived
from
the +160
V
supplv
rail
via diode
V2457.
3rd
Collimator
The
3rd
collimator
is held
at +75
V
as
control
input
D2401-13
is at
logic
0. The
earth
potential
is
not
switched
to
output
D2401-2
and
so
the
base
of
V2449
is held
positive
by
the +5.6
V input
via
preset
R2404.
Transistor
V2449
is
therefore
more
conductive
and
limits
the
emitter
output
of V2451
to +75
V.
Collimator
2
The
2nd
collimator
is held
at a
potential
between +30
V and +90
V.
In this
mode,
output
9 of
AND
gate D2224
is
at logic
0
and therefore
V2419
is
non-conducting.
The
input
of
the
collimator
2
amplifier
is therefore
at
logic
1.
Transistor
V2462
conducts
and the
output
of
transistor
V2448
is
adjustable
between +30
V and +90
V by
preset R2523
in
its
base
circuit.
Collimator
1
The
1st
collimator
is held
at +30
V by
means
of the
positive
potential
applied
to
the base
of input
transistor
V2444
via feedback
resistor
R2518.
MEMORY
OFF
MODE
When
both
the WRITE
and
STORE
pushbuttons
(S24B, S24A)
are
depressed
together,
the MEM
OFF
or
NON-STORE
mode is
selected.
Logic
0 is
applied to
input D2202-14
and D2202-11
(and to D2201
inputs
4,
3
and 1
1)
to give logic ones on
outputs
D2202-1
5 and D2202-1
2. Input
1 and
8
of
AND gate D2201
are therefore
at
logic
1
,
and also
the
input
2
is
at logic
1
(FAST
input
at logic
1). Consequently,
there
is a logic 1
on output
D2201-9,
which
feeds
a logic
1
to flip-flop
input D2204-4.
This results
in
a
logic
1 on
the NON-STORE
output
D2204-2.
In
this mode,
all other
inputs
to the quadruple
flip-flop
D2204 are at logic
0,
therefore
the FAST,
WRITE and
STORE
outputs
are also
at logic 0.
The
logic 1 from
D2204-2 is
applied to
control
input D2403-5 to
switch
the
+1
1.2 V
on
pin 3 to pin
4
and via
R2418
to
the
base of V2414
at
the
input of the front
mesh preamplifier. This
transistor
switches
off and
V2416
conducts,
which
in turn switches
on V2418.
The drop in its
collector
potential
makes V2412
less
conductive.
The
negative potential
on
R2474
is routed via
series transistors
V2427,
V2426
and R2484 to give
—35
V on
the front mesh,
G12.
The
potentials to
the fast
mesh, the collector
mesh and
the collimators are
the same
as those for the
STORE
mode,
and the flood gun
accelerator is permanently
at
+20
V (i.e. no input
connected from
D2401).