Rear (Power Supply) Pcb Assembly; General; Supply; Self Test Seouence - Datron 1061 Calibration And Servicing Handbook

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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