Datron 1061 - Rear (Power Supply) Pcb Assembly; General; Supply; Self Test Seouence

-
48
The
line
transformer
and
power
supply
components
are situated
at
the rear
right
hand
side
of
the
instrument'
when
viewed
from
the f-ront.
Transformers
T1
and
T2
are
of
toroidal
construction mounted
one
on
top
of
the
other and
bolted
to
the rear
panel.
T1
has
a
split
primary
comprising
two 115V
windinbs,
intended
for
either
series
or
parallel
connect¡on
depenãing
on
the
line
voltage'
An
earth screen
is interposed
between
primary
and
secondary
windings
to
minimise electrostatic
coupling,
and
is
grounded
to line
earth. The
second
transformer
T2
is
driven
from
T1.
lt
also
possesses an
electrostatic
screen,
this time
being
connected to
Guard.
3.13
REAR
(PowER
suPPLY)
PcB
ASSEMBLY
(Circuit
Drawing
No.
430295)
3.13.1
General
3.13.2 180V
Supply
3.13.3
5V Supply
All the
logic
circuitry
to
the
right of
the
central
printed circuit
board
is
powered from
the
supply
gener'
The
180V supply
is required
for
the
gas
discharge
display.
Bridge
rectifier Wl
and
C6
convert
the
200V
AC
from
the secãndary of
T1,
to
DC.
R6,
D3,
R4
and
02
act as a constant
current
source
being
regulated
by D4,
R5
and
01. The
+5V
line
(TP2l
is connected
to
the
dig¡tal
+5V
line
(TP3)
on
the
Display
Driver
assembly.
)
ated
from
the
two
8.8 volt
750m4
secondary
windings
on
transformer
T1.
The
centre
tap
(dígital
common)
is
linked
directly
to
line
ground
via
LK6. The
output
of
rectifying
diodes
Dl
and
D2
is
smoothed
by
C7
and C8
before
being
fed
to
regulator
Ml.
This
regulator
is capable
of
l
amp
output
and has
foldback
current limiting
and
thermal
shut-down,
to
provide
short
circuit
protection.
3.13.4
Jl5V
Supply
The output of
the
third secondary winding
of
trans'
former
Tl
(10V
AC)
is
input
to the
primarv
of
T2.
The
two
19.25V
outputs are
connected
in series,
with the
centre
tap
connected
to analog
common.
The
output
of
bridge
rectif¡er
W2
is fed
to
voltage
regulators M2 and
M3
(wired
in
seriesl,
to
produce
positive
and negative
15
volt supplies
to
power
the analog circuitry. These regulators
also
include
foldback
current
limiting
and thermal
shut-down,
to
provide short-circuit
protection.
3.14
SELF
TEST
SEOUENCE
Selection
of the TEST key
places
the
instrument
into a test
routine, checking the display
and basic
measur-
ing circuits.
A
flowchart for
the
routine
is
given
in
Fig.
3.53.
The
analog
circuitry conditions
for each
test
arec'
given
in the
last subsection of
the
circuit description
for
the
particular
board,
and the
range
'F.E.T.'
patterns
¡n
Appendix
l-8.
T1
T2
Blue
5
NEUTRAL
Black
200v
White
15
V¡olet
6
Grey
13
19 25V
7
MAINS
5V
Pink
White
16
8
10v
Mauve
17
SUPPLY
5V
9
Blue
14
Grey
19.25V
10
8.8V
G
18
LIVE
11
Green
Yellow
8.8V
Blue
12
20
GUARD
SCREEN
19
EARTH
SCREEN
LK3
(1tSV) 11sV
I
LK2(11svl
l1sv
Brown
Red
4
2
3
FIG.
3.52
LINE
TRANSFORMER