Brüel & Kjær 2131 User manual

BRUEL & KJA:R
Natrum - Denmark
Service Instruction
2131
2131
Digital Frequency Analyzer
Valid from serial no. 824523
037 · 0260
Trouble Shooting
If any faults should occur please check the instrument according to the
Checking Procedure .
When a fault has been traced and corrected . the voltages and adjust-
ments influenced by the correction must be rechecked. The complete in-
strument should then be tested to make sure that all bas ic functions are
operative .
The tolerances given in these notes are intended for use as guide for ad-
justments .
Before correcting any apparent deviation make sure that the measuring
i nstrument has tolerances small e nough not to affect the measurement .
Modifications
Due to the constant technical progress the instrument will be modified
from time to time in order to provide continuously improved perfor-
mance .
For this reason there may be small d itte rencies between the instrument
and the Service Instruction .
However . the local Representative S ervice is in possession of all i nforma-
tion regarding the mod i fications that have been made .
Spare Pans
Please state type an d serial number of the instrument when ordering
spare parts .

Service Instruction 21 31
Consisting of: -
dot.
Consisting of : (continued) page
dot.
Service Instruction
0-1 10 . 79
ZD 0097 Digital Interface 2.
76
0-2 10 . 79
0-3
10 . 76
ZD 0098 Digital I/ O 1 2.
76
2 2.
76
Checking Procedure
1-1
10 . 76
3 2.
76
1-2 10 . 76
1-3 10 . 79
ZD 0099 Analog Output
1 2.
76
1-4
10 . 79
2 2.
76
3 2.
76
Power Supply
2-1
1. 76
2-2
1.76
ZD 0100 Display Control I 1 2.
76
2 2.
76
Front Panel Control
3-1
4. 76
3-2 4. 76
ZD 0101 Display Control II
1 2.
76
3-3
4.76
2
2.76
3-4 4.76
ZD 0102 Spectrum Memory 1
2.76
Display Unit
4-1
1.78
2
p6
4-2
1.78
4-3
1. 78
ZD 0103 Lin / Log Converter 1
2.76
4-4
1. 78
2 2.
76
4-5
1. 78
3 2.
76
4-6
1. 78
ZD 0104 Multioctave Averager 1 2.
76
dB Lines and Characters
5-1 3. 76
2 2.
76
5-2 3. 76
5-3
3.76
ZD 0105 Squaring Circuit and 1 2.
76
5-4
3. 76
Singleoctave Averager 2 2.
76
5-5 3. 76
5-6 3.76
ZD 0106 Master Control 1
2.76
2 2.
76
Input and Filter 6-1
10 . 79
6-2
10 . 79
ZD 0107 Digital Filters 1 10 . 79
6-3 4. 76
ZD 0111
2
10 . 79
6-4 4. 76
3 10 . 79
6-5 4. 76
6-6
4. 76
ZD 0112 Front Panel Control I 1 3.
76
6-7
5.76
2 3.
76
6-8 5. 76
3 2.
76
RMS and Average
7-1
5. 76
ZD 01 T3 Front Panel Control II
1 2.
76
7-2
5. 76
2 3.
76
7-3
7. 76
7-4
7. 76
ZD 0115 Front Panel Selector 3.
76
7-5
7. 76
ZD 0116 Board I and II
7- 6 7.
76
7-7
7. 76
ZD 0162 IEC Standard Interface 1 9. 76
7-8
7. 76
2 9.
76
7-9
7. 76
ZD 0245 A I D Converter
10 . 79
Display Control Section
B-1
7. 76
8-2
7. 76
ZE 0148 Preamplifier 1 3.
76
8-3
7. 76
2 3.
76
8-4
7. 76
3 4.
76
Analog Output
9-1 8. 76
ZG 0104 Power Supply and Ref. Generator
9. 78
9-2 8. 76
9-3
8. 76
ZT 0051 LP .Filter/ A Filter 1 3.
76
9-4 8. 76
2 3.
76
Digital Input/Output
10-1
9. 76 N 0002 Display Unit 1 1.
78
10-2
9. 76
2 1.
78
10-3
9. 76
3
1.78
10-4
9. 76
4 1.
78
10-5
9. 76
ZZ 0043 Power Supply
10-6
9. 76
1 2. 76
10-7
7. 77
2 2.
76
10-8 7. 77
3 2.
76
10-9
7. 77
10-10
7 . 77
10-11
7 . 77
Interconnection Diagram I
11-1 10 . 79
with Parts Lists
Interconnection Diagram
II
11-2
4. 76
with Parts Lists

GV 0968
FB 0345
Fe 6177
DH0163 -~
Fe 6179
YQ 8089 ......... lit
2pes. Ci'P'
YQ 80U ,,_
2pes . r:P
GV 0994
FC 0070
2pes .
~DZ9069
2 pes .
~DF 7015}
®--YO 0335 L pes.
Jr-YV 3327
DH 0162
Cover for circuit board cassette
Wooden Box
Rack Mounting Set
DO 0182
KA 0058
KS 0027
Fe 6180
ZV0002-+-
Upper Control Section
lower Control Section
(II. pag.ll-l)
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BROa & KJA:R
Nrerum - Denmark
Checking Procedure
2131 .1
Front Panel Control (Stationary signals)
I
Power Supply
I
dB Lines and Characters
Display Unit
Input and Filter RMS and Average
Display Control
I : :
Sian I Lin/Log
,
: AID I Digital
Di splay: Store I ,
Analog
RMS
' I I and :Spectrum
, : Filter :
Average I Mellory I Square
Section
:Converter, System
I I System '-Roo-i
Counter I Update : Memory
F ,I
Digital I/O
11 11 11
"l
I Crystal
Clock Control
( Dynamic
signals)
I I
Analog Output
I
As it appears from the Block Diagram the instrument is built up in sec-
tions . where each section has a specific function . A
quick check of the most important functions is carried out by means of
a low distortion LF - Oscillator with an output of exactly 100 mV at
1000Hz .
The checking Procedure has been arranged in the same way , and it
should be possible from the procedure to point out in which section a
possible fault may be found . A
more thoroughgoing check can be made by using two LF-Oscillators ,
Level
Recorder and Digital Equipment such as Tape Punch , Tape Reader
and Computer .
Cooling
Basic Checking Procedure
Reference Adjust . dB: "0"
G ai n Control: "Cal. "
Power to " On"
Channel Selector to " 1. 00 kHz"
Input All . to " 40dB " (bollom line)
In order to provide sufficient cooling of the instrument, the Dust Filter for the Ventilator
should be kept clean .
Ac cess to the Du st F ilte r is obtained by sliding the right sideplate backwards .
Exactly
100 mV RMS at 1, 00 kHz from a low di stortion Oscillator to " Direct Input " .
The instrument should automatica lly preset as follows :
Input
Input All . 0 to 100 dB
Av eraging St a rt
Av eraging Control
Averaging Time S
Fr eque n cy Ran ge Hz
F
ilter Bandwidt h Octave
Input Control
Output Control
Output Spec trum Selector
Input Sp ect rum Function
Chann el S ele c to r
R
efe r ence 100 dBI'V RMS
A - Weighting
" Dir ect"
" 50 "
"Exp."
"Pro
ceed"
" 1"
" 25 - 20k "
" 1/ 3"
" Anal og"
"
Stop "
"
Input Spectr ."
"
Con!. "
" 1
,6 Hz"
"Off"
"Off'"
With the excep tion of Input. Reference and A -W eig hting the " System Reset" will reset all
the se functi ons to the same sellings .
A
few mom ents afte r switch on the Di splay Screen will begin to operate, and "Scale Br ight-
ness" and " Int ensity " should be used to adju st for an a dequate ap pearance of the display .
Adjust "Direct Sensitivity " for a level of 100 .0 dB.
The Oisplay Scr een should now look lik e the two pic tures on the rear of this page.

2131 .1 Checking Procedure
100
CenttrFrrqueiq.: UXlk Hz
l,ftI:l00.0 d
90
80
70
60
50
IB
40
15 18 21 24 27 JO 33 36 39 42 ·W
Filter 8andwidth Octa", to "1/3"
Frequency Range Hz to "1 , 6-1.25 k"
System Reset
Channel Selector to "1 . 00 kHz"
Reference: "In"
A-Weighting : "In"
A- Weighting : "Out"'
Input Att . to "30 dB" (bottom line)
A·Weighting to "In "
Gain Control to ··Cal."·
A·Weighting to "Out""
SystAm Reset
Reference: "In"
Averaging Control to "Reset"'
Averaging Time s to " B"
System Reset
Filter
Bandwidth Octave to " 1/ 1"
6B% Confidence Level to " u = O, 5dB "
5B% Confidence Level
10 "u = 2 dB"
lOG c.e.r F,.....cy:l.00kih
l, •• 1:100,Od.
98-----------4~*---------~
U--~------_+EI__----~
70 ------------~~----------~
iO------+JII>J------t1
Filter Bandwidth Octaw to "lit"
If not the Trouble Shooting on page 1-4 should be consulted before further steps are taken.
If yes, the Checking Procedure continues as follows:
The instrument should now indicate' channel numbers from 03 to 30 instead of 15 to 42.
and the picture should move to the right side of the Display Screen.
The 1.00 kHz signal on the Display should now be 10 dB below full scale, and the Level read·
ing 100.0dB .
The Level should again read 100.0 dB ± 0.2 dB, the picture should look almost the same as
before.
but with harmonics from the reference oscillator (f. inst. third ham . in channel 35 at
approx.
50 dB corresponding to 1% of distortion).
Level reading 100 ,OdB ±0 . 2dB .
Adjust "Gain Control" and check that the Display is intensified by Overload at a Level indica·
tion between 95 .7 and 96dB .
Check that the Display is intensified between 95,7 and 96 dB
If any of the specifications are out of tolerance see page 6-3 for adjustments .
Check the Linearity by selecting suitable positions of " Input Alt. " .
From 0 to 30 dB below FSD the Level reading should be 1OO,OdB ± 0,2 dB.
At 40dB below FSD the reading should be 1OO,OdB t 0.4 dB.
At 50dB below FSD the reading should be 100 ,OdB t o.adB , but due to the A I D converter
principle
there may be a small measuring error .
This
error can be avoided by using two Oscillators as described on page 1- 3.
Disconnect "Direct
Input " signal.
Each time " Averaging Start lin " is pushed, "Averaging Control" will go to "Reset " for a
short period.
then to "Proceed" for the "Averaging Time s" (here I sec.) and finally to
"Stop" .
Push "Averaging Start lin ." and check that "Proceed" is on for Bs.
The same check can be carried
out for any number of "Averaging Time s ". but selection can
be made only
with "Averaging Control Reset ".
When " Reference" is selected In and Out it should be checked that channel 30 and Ware
operating with equal time constant .
With "'Reference" to In and Out channel 30 and W should operate with different time con·
stants (W much faster).
The channels ;;hould now operate with much faster time constants.
If the Averager System is not operating correctly consult 8'.1'> ,-

' System Reset
System Reset
Gain Control to " 0"
System Reset
Filter Bandwidth Octave to " 1/ 1"
System Reset
Input to "Preamp ."
Reference: " Out"
Input Att.: "As required"
Input : " Direct"
Reference: " Out "
A- Weighting : " Out "
System Reset
Oscilla tor 1
Freq , 1000 Hz
Output Alt. O,3V
Channel Selector to " 1, 00 kHz"
Checking Procedure 2131.1
Select "Hold" and check that the picture is "frozen ".
Select " Max . Hold" and check that the picture follows when " Gain Control" is turned up , but
remains at its max. position when "Gain Control" is turned down .
Turn " Gain Control" back to " Cal." and push "Store".
Select " Alternate Slow " and check that the picture alternates between the previous stored
1/ 3 Octave Spectrum and a continuously updated 1/ 1 Octave Spectrum .
If the Memory functions are not operating correctly consult Display Control section B.
Connect a
suitable Preamplifier with Microphone to "Preamp . Input " and check that the in-
strument operates with Microphone . (This test ensures that supply -and polarization vol-
tages are provided by the instrument.)
LINEARITY CHECK (using two Oscillators)
-OSCillator 2
10kn.
Freq. 250 Hz
Output Alt. 3V
Output Voltage to 0
o
~ ..
m~
2131
Adjust Output Voltage on Oscillator 1 for 100 ,0 dB deflection on 2131 (10 dB below FSD).
Check the Linearity by selecting suitable pOSitions of "Input Att ." .
From 0 to 30dB below FSD the Level reading should be 100 ,OdB ±0,2 dB.
At 40 dB below FSD the reading should be 1 OO , OdB ±0,4 dB .
At 50 dB below FSO the reading should be 100,0 dB ±O,S dJ Output Voltage on Oscillator 2
adjusted
for approx. half scale
At 60dB below FSD the reading should be 100 ,OdS ± 2, Od on the 250Hz channel.
If out of tolerance disconnect the input signal, select 1/ 1 Octave mode and check that W
channel remains sufficiently low .
If W is visible by more than 1 dS see page 6- 2 for adjustment of Off-set.
Page 6- 2 also describes Input Attenuator adjustment which can improve linearity in Att . po-
sition 30 dB bottom line .
INPUT/OUTPUT
2131 has Analog Outputs for Level Recorder and X/ Y Recorder as well as Digital Input/Out -
put which are used with Puncher , Reader, Computer etc.
A detailed describtion
of cable connections and pushbutton settings will be found in the In-
struction Manual of 21 31 .

2131 .1 Checking Procedure
Front Panel
Display Screen
dB Lines and Characters
Signal Information
TROUBLE SHOOTING
It should be noted that the Flips Flops and pushbutton lamps for Input, Reference and A-
Weighting are powered from a small 5 V Supply positioned on A/D Convener ZD 0245 in
the left side of the instrument. while the rest of the Front is powered from the 5 V Head Sup-
ply ZZ 0043 in the right side of the instrument .
Thus , just by switching ' on and operating the Front Panel it appears immediately whether a
possible fault should be traced in one of the two Power Supplies or in the Front Panel Con-
trol ci rcuits .
Consult Circuit and Layout Diagrams ZD 0245, Power Supply section 2 or Front Panel Con-
trol section 3.
If there is no operation at all on the screen it should be checked whether + and -22 V unre-
gulated and + 5 V are supplied from ZZ 0043 in the right side of the instrument. All other
supplies are made internally in the Display Unit .
However. two logic Signals are imponant to operate the Display Unit, namely Line Syncroni-
zation and Picture Syncronization .
These
two signals are provided by Display Control I board ZD 0100 , where LSYNE is found
in TP2 and PSYNE in TP5 .
"'~t----21,96 ms
PSYNE U
=4..F-
~1~'-----'60~s----~.~1
1.32 ms
Consult Power Supply section 2, TP2 and 5 on ZD 0100 in the top of the instrument or Dis-
play Unit section 4.
This information is supplied as logic signals from ZD 0100 in the top of the instrument and a
Video Mixer inside the Display Unit control the C. R. T.
In case of missing or wrong information consult dB Lines and Characters section 5 or Dis-
play Unit section 4.
A possible signal
fault is more compli cated to diagnosticate , since the signal is conditioned
by a large number of circuits .
However , the following information will prove helpful:
On the rear of the instrument will be found a BNC socket "To Exp. Unit" which is an analog
output from the Input Amplifier with an output voltage of approx. 1, 73 V (50 dB range) corre-
sponding to full scale deflection on the Display Screen .
The W channel is not passed through the Digital Filter System at all.
The 3 channels in the 16kHz octave are passed through the Digital Band Pass Filters only
and not through the Digital low Pass Filters .
All the Filter c!,annel and the W channel are squared in the RMS circuit .
Wand the 16 kHz octave are averaged in a separate Averager called the Si ngle Octave Sys-
tem .
All other octaves are averaged in the Multi Octave System .
The Slave Memory System positiones the Fi lter channels in the correct Channel Numbers .
The Lin /Log and Square Root circuit as well as the whole Display Control are used in a simi-
lar way for all channels .
Consult Input and Filter section 6, RMS and Average section 7 or Display Control section 8.
It should be noted that a Pink Noise input si gnal or a swept Sine Wave in " Max . Hold " will
be very useful for checking Filter function and Averaging ti me .

BRUF:L & KJ~R
Naerum -Denmark
Power Supply
2131.2
OGHO
+5V!:0,1V (Adjust Pl if nee. nary)
Zl
AGHO
C4
> > > >
-:1-
~ ~
'" '"
0
...
...
'j
"+
z
I + CI
(I) (I) (I)
<D 0
(9
(I) (I)
<S> <D
(9 (9 (I) e
(9
(I)
<9 <D
e (I)
,---- -I
Blowing Fan
UH 0006 1 I I T 2 1
, 1
' _____ 1
T 1
F7
General
C>
'"
r-
..
The Power Supply unit zz. 0043 converts a main supply of 100 to 240 V
AC into a number of DC supplies which are used in the instrument .
Through an ordinary mains transformer with associated rectifier circuit s
are produc ed unregulated voltages of approx . + and - 24 V as well as +
approx . 420V .
Furthermore the + and -24 V a re applied to integrated voltage regula-
tors which supply + and -15 V.
However , the + 5 V supply for all the TIL circuits in the instrument is pro-
duc ed by a different type of supply which is called a Switching Po wer
Supply .
Dismantling
When servic ing the Power Supply the right side plate should be removed
and the instrument posit io ned with its right side towards the operator.
Now unplug the mains lead and remove the rear fuse cap:
After removal of the three screws in the upper profile and three in the
lower the whole chaSSIS c an carefully be swung out and laid down on
the table .
ZG 0112
_,,~. .; I .;
6HO= pin 2
ZG 0110
Frequlncy 44 kHz! 2 kHz
D I 74132 I I 74101 I
~~
~
ZO 0120
HE 555 ~djust P2) i:d~~~tl~~) ~
8 8 P 1 L... _____ ....
Put back the fuse cap and plug in the mains lead and the Power Supply
can now be operated lying on the table .
The drawing shown on this page can be used to identify components and
measur ing points , and it should be noticed that small deviations on the
+ 5 V supply can be cured by adjustments while all other troubles will
prob ab ly be ca used by one or more defective components.
Adjustment Procedure
Adju stment of the three potentiometers is explained on the drawing ,
however . a certain order must be followed :
P 3
first , the n P 2 and finally P 1
Trouble Shooting
The rear page co ntains simplified diagrams and a technical description of
the Power Supply and a detailed Circuit D iagra m with complete compo-
nent Layout Diagram of the two printed ci rcuit boards as well as a Parts
List will be found on page ZZ 0043 .

2131 .2 Power Supply
Switching Supply
74132
44kHz
Osc .
V1
P2
NE555
V3
Pul .. Width
Control
'5
74107
: 2
V4
Q
+I5V
1----------- -----------
1 F7
I
I
I
I 280 V
I'----",~..., 1
1 2WVN
1
C7
1 ---0 I
I ./1
--~--~I~--~~~~~~----~--------~ I
I ~ 1
1- ______ ______________ _
Q3
Q4
~----------------------------------------~_.--~------------------~~+5V/25A
+Vref
In the Switching Power Supply the mains transformer is used only as an
Auto Transformer from which a 220V AC signal is provided directly for
rectification.
As it appears from the simplified diagram the rectified voltage will be ap,
pro)(. 2S0V which is applied to the two switching transistors V 3 and V
4.
These switching transistors are switched on and off by a circuit wh ich op.
erates as follows:
A 44 kHz oscillator provides trigger pulses for a monostable multivibrator
which has a variable pulse width controlled by a voltage comparator V 2.
By means of a
2· divider and a gating system suitable pulses are created
for
push·pull operation of V S and V 9, which are acting as drivers for
the
output switching transistors V 3 and V 4.
On the secondary of T 2 will appear a signal like shown on the osc·lIo·
gram , and the DC value of the double rectification will be dependent on
the pulse
width and amplitude .
Now as the DC value is applied to the voltage comparator which controls
the pulse
width it can be seen that any change in DC value will change
Protection
+15V ------ .... -............V
+5V -v"---'l-
Sense
R25
P3
--"'---+5V Y
ee
for VI,) and 4
The
switching supply is protected by two different means:
If the + 5 V l ine for some reason should increase to appro)(. + 7 V the
SCR' V 5 will switch on and disconnect the internal Vee supply on the
ZG 0110 circuit board, by which the switching pulses will stop immedi·
ately.
To reset V 5
the Power Switch on the front of the i nstrument has to be
sw itched off for a moment .
Another way of protection is arranged by a bistable temperature depend-
ent resistor R 25 which is also coupled to disconnect the internal Vee .
This resistor is high impedance at temperatures below 65°C and will sud·
denly change to a very low impedance when the temperature increases
to mer e than 65 °C.
VI pin 8
Vl pin 3
V1 pin 6
V1 pin)
Q 3 anode
(T 2 secondary)
(100mVp ·p ripple)
TTl
T
20 V
i.
the pulse width and in this way compensate for variations of load and
mains supply.
Note
Allthough this regulator system can work over a wide range there has to
be a load on the + 5 V supply of not less than 3 A in order to remain
within regulation.
Protections referred to ZZ 0043 Circuit Dillgram
Another thermal arrangement will be found in connecti on with the Slow-
ing Fan, where a thermo switch 0 2 is mounted with thermal connection
to the V 3 and 4 heatsink.
When this heatsink gets too hot the speed of the Slowing Fan will be in-
creased for more efficient cooling.
Finally a last protection associated with relay 0 3 should be mentioned.
When the i nstrument is switched on the charging current to C 1 is li-
mited by R 11 and R 12 . After approx. 200 ms 03 is engaged and R 11
and
12 are shortcircuited.
This arrangement is a protection
of the Power Switch N 1 which can
take a
current of max. 5 A .
The resistor R 1 also connected
to relay 0 3 is used to discharge C 1
when the instrument is switched off .

BROEL & KJA:R
Naerum - Denmark
Front Panel Control
2131
Genera l
--
, _ _ tIl
--
_ . ... 110. ""
T he Fr o nt Panel switc hes are fou nd on ZD 01 15 and ZD 0 1 16 whe reas
th
eir res pect ive cont rol l ogic is l ocate d on ZD 01 12 and ZD 0 1 13 .
The fr ont panel logic cou ld be oper ate d ma nu ally fr om the swi tches or au·
tom at i call y fr om th e Digital I nte rf ace. Th er efore th ey have been divided
in to di ffe rent gr oups in orde r to minimi ze the wiri ng, The gr oup control is
descr ibed in the Di g ital p art of th is sec tio n.
Basically each
manual sw i tch w i ll set a flip ·flop which in turn s wit ches
on a co
rr espond in g LED and provides the necessary c ont rol si gnals , but
most
of the flip· flo ps may onl y be set un der certai n con ditions , The set-
ting co nd it io ns of each gro up are described in t he M an ual part of this
section.
dB S' 2 1
50
0 1 0 1
ZO 0115
40
0 1 0 0
30 0 0 1 1
FC
20
0 0 1 0
10
0 0 0 1
Digital
Common
Sign
Ref. L
0 0 0 0 0
-10 1 1 1 1
Adjustm . 2
1
-20 1 1 1 0
Fa
- ]0
1 1 0 1
- 40 1 1 0 0
- 50
1 0 1 1
J 1
Ref,~tar
ZG 0104
Jl
----
' ... JIl I
4
5
~- __ -[jrcluo 10
9
L---'..:.L.---II-,[jrouo 11
.
' .' .
, .
. - .'
.
'...
"
Group
~~~-------- __ --urouo2
--l_-{U 0115
T he Digital R ef. Adjustme nt pr ovides a digital va lu e which is added te
the refe re nce value . The v alues are obtai ned f rom the sw itch ac cord i n ~
to the below table .
Notice
The Input C ir cui t in clusi ve th e gai n c ontr ol is dea lt within th e Inp ut anc
Filt
er Sectio n 6 whi le the Display inc !. th e Scale Br ightn es s a nd Int ens it\
is described in the D isplay Un it, Sectio n 4 .
ZO 0112 ZO 0113
ZO 0116
Jl
FD
Fr."t
Front
Panel
J 2
Pa".l
Centro l C
... tral
Jl
r n
J1 FE
J4 J5
"8
Me
"H ME
.....
" "
v
Matt..r 80erd

Front Panel Control 2 13 1.3
Group O. Time Constants and Fixed Cont . levels
Funct10n:
Selects 1 of 13 time constants or 1 of 3 confidence le-
vels.
Sy stem Reset: 1 sec.
Switch Select: In ··Exp."' is no limitations while in "Lin " the 13 averag·
ing time constants could be exchanged . but only during
Averaging Control "Reset" .
Operat ing
Conditions :
Logic :
Common is supplied both groups of switches In "Exp ."
from ZO 0112 . In "Lin" common is supplied the T ime
Con stant switches only a nd only in "Reset"
The individua l T ime Constant are selected by setting the
matching flip-flop .
FC 13 arid FC 16 = 0 when " d ' Lin . Averaging " = 1.
FC 13 = 0 when " 0 Lin . Averaging " = 0 and "0 Reset" =
O. " 5 8 seconds" =0 implies "0 8 seconds" =O.
Digital Entry : See page 1-4
Group 1. Attenuator Control
Fu hction :
Shifts the display range in ste ps of 10 dB.
System Reset: 50 dB - 110 dB displayed .
Switch Select: Unconditionally .
Operating
Conditions:
Notice :
Logic:
Digital Entry :
The 10 dB shift is performed when the matching flip-flop
is set causing a Schmitt-Tr i gger to count a presetable Up-
D own Counter . The ou tput refers to the bottom level of
the display and could be all binary values from 0 to 10 .
When the output is 0 the count - down Schmitt-trigger IS
i nh ibited whereas the co unt-up is simila rly inh ibited
when the output reaches 10 .
"System Reset" will load a 5 into the Counter carre·
s pondin g to 50 dB.
The ou tput is led to the Spectrum Output Zo 0102
where the Digital Reference Adjust. is added. But as the
low est signal is 0 dB. the lowest range must also be 0 dB
why the display will not change below this value .
A
high-to-low transition of " S Att . - 10 dB- " will count-
down the output of the Cou nt er V 302 .
A similar transition of " S Att. + 10 dB- " will count-up V
302 .
V
509 -9 (1 when off)
Group 2. Averaging Control
Fun c tion : Selects 1 of 3 Co ntrol modes .
Syste m Reset: Proceed
Switch Select : " Reset" and "Proceed" is activated unconditionally .
Operating
Conditions :
"
Stop " can o nly be selected in " Lin ."
Whenever "Exp." or " Lin " is activated the "Reset" flip-
flop and a IImer V 205 is set . When the timer expires
the " Proceed" flip-flop Will be set and the "Reset" flip-
flop is reset.
The
same thing will happen when activating ' 1/ 3 o ct ."
or " 1/ 1 oct ." (l o gic pOSitioned on ZO 0113) .
The timer IS omitted when the flip·flops are selected from
thei r respective switches .
The "Pr oceed " flip-flop wi ll simultaneously give a s tart to
the Averaging Circuit ( ZO 0104 and ZO 0105) while the
"Res et" flip - flop Will reset th is ci rcuit.
Man ual
Logic:
In "Li n" the averaging could be stopped and later pro -
ceeded and when the . averaging is finished AVFNL + goes
high and sets the " Stop " flip - flop . The result should be
reset before t he next averaging. otherwise an addition
w ill take place .
" Common on S Stop " = 0 when "0 Lin ." = O. 0 on " S
Exp. Averaging Start " or "5 Lin . Averaging Start " im plies
o Reset (AVREL -) = 0 until V 205 expires and sets " 0
Reset" = 1
and " 0 Proceed" (AVSTL- =1).
When the averagi ng is finished in " Lin ." AVFNL + = 1
thus setting "0 Stop" = 0 (AVSTL- = 1) .
o on RESBL- ( from ZO 0113) i mpl ies AVREL- = 0 as
above.
Digital
Entry : V 106 -6 =V 106-08 =V 106 -1 2 = when off .
AVEXL -= 1 when off .
V 508-B (on ZO 0113) = 1 when off .
Group 3. Averaging Start
Funct i on :
Selects Exponential or Linear Aver ag ing
System Reset: Exp.
Sw i tch Select: Unconditionally .
Operating
Conditions :
Logic:
The averaging mode is selected by setting the matching
flip - flop . The flip'- flop infl uences on the Averaging Control
as d escribed in group 2.
" S Exp. Averaging " =0 implies " 0 Exp. Averaging " =O.
Digital Entry : V 206-1 and V 206-4 (1 when off) .
Group 4 . Filter Bandwidth
Fur.cti on " Sele
cts 1/ 3 or 1/ 1 octave filt er bandwidth .
System Reset: 1 .1 3
SWitch Select : Uncondi t ionally
Operating
Conditions :
Logic:
The filter bandwidth is selected by se tting the matching
flip - flop . Th e flip -flop influences on the Averaging Control
as described in group 2.
"S 1/ 3 octave " = 0 implies " 0 1/ 3 octave" = 0
Di gital Entry V 508 - 10 and V 50B -l 3 (1 when off)
Group 5. Frequency Range
Function :
Selects the 1.6 - 1. 25 kHz range or the 25 - 20 kHz
range .
System Reset: 25 - 20 kHz
Sw itch Selec t: Unconditionally
Operating
Co nditi o ns : The
frequency range consists of 3 groups of ranges of
which o nly two . Frequ ency Range Lower and - Middl e.
c ould be activated from the front plate by setting the
ma tching flip -flop. The F requency Range Upp er IS em ·
played only when an expansion unit is co nn ected. Each
of the range sele ct si gnals will reset the other flip - flops .
When a read- out is in progress the lower range is se-
lected. but wh en the 16th channel address is reached
(SCASL + on ZO 0100) . GFRML + wil l set th~ ~ -- " : " "n " :·'
Range Middle flip -flop.

::.,
Logic: o
on "s 1.6 - 1. 25 kHz" . "S 25 - 20 kHz" or
"GFRUL-" implies 0 on FROLL- . FROML - . or
FROUL- respectively .
(GFRML + = 1 implies FROML- =1 O.
Digital Entry ' V 506 -12. V 506-6. V 506 ·8 (1 when off)
Group 6. Input Spectrum Function
Function:
Sel ects 1 of 3 H old functions .
Sy s tem Reset: Continuous
Switch Select: Unconditionally .
Operating
Conditions :
Logic :
The Hold modes a re selected by activating their respec-
tive flip-flops.
However . if " Digital Input" is selected the " Store " mode
is always on .
o on "s Continuous ". " S Hold ". or "s Max . Hold " im-
plies 0 on "D Continuous " . " HOLDL - " . or "MH LDL- "
respectively . 1 on " DIMOL ." implies 0 on " HOLDL- ".
Digital Entry : V 507-12 . V 507-6. V 507-8 (1 when off ).
Group 7. Memory Function
Function: " Store " will store an instant spectrum in one of the mem-
ories provided "Protect" is not activated.
System Reset: " Prote ct" off .
Logic :
Front Panel Control 21 31 . ~
ALTFL- . ALTSL -. and STSPL- is the control signal,
for the alternating locic on ZD 0099 while SESSL - i,
the return signal.
When the alternate function is inactive the " Stored Spec
trum " s ignal STSPL -is decisive for the SESSL -sig
naL Otherwise SESSL -is changed according to the al
ternating logic .
o on the "S" inputs implies 0 on the respective " D" out
puts . ALTFL- and ALTSL- = 1 implies STSPL-
SESSL- . ALTFL- or ALTSL- = 0 implies SESSL- i,
changing .
Digital Entry : V 206 - 12 . V 206-6 . V 206-8. V 408-8 . (1 when off) .
Group 9. Input Control
Function : Selects Analog or Digital data input.
System Reset: Analog
Switch Select : Uncondit io nally
Operatin g
Conditions :
Logic '
The logic level of DIMOL + decides whether the corre
sponding flip-flop is set to Analog or Digital mode .
GISPL + is ' normally low. but goes ' high in D igit al modi
when data corresponding to one spectrum is read in thu '
forcing the flip-flop to Analog mode.
"s Analog Input" = 0 implies DIMOL + = O.
GISPL + = 1
implies DIMOL + = 0 and GISPL + goes lov
again .
Switch Select: Uncond itio nally . SEDIL - = 1 (Normally not used).
Operating
Conditions :
Logi c:
Provided System Reset is activated last the 0 utput Spec-
trum Sele c tor (group 8) is forced to display the Input . The
" Stored Sp ect rum " can be displayed only when data has
been stored.
When "S tore" is ac tivat ed one of the two memories on
ZD 0102 is erased and an instant spectrum is stored. Si-
mult a ne ously the Input Spectrum Fun cti on will go into
" Continuous " mode and the other memory will contain
the varying input va lue s. The next activation will reverse
the memory functions.
If " Protect" is activated the co nt ents of the stored me-
mory is protected fr om being superseded until the next
activation resets the protection.
"Prote ct" can not be set before "Store " has been acti-
vated.
"s Stor e -" = 0 implies " D Store " and "D Conti nu ous "
= O. When "s Protect - " goes low V 104-6 Will change
pr ovided " Store " has been ac tiv ated. V 104-6 = 0 im-
plies that SPERL + will not change .
Digital Entr y: V 107-13 and V 107 -10 (1 when off).
Group 8. Output Spectrum Selector
Fun ction:
Selects 1 of 4 display output modes
System Reset: Input Spectrum
Switch Select: Unconditionally
Operating
Conditions :
The individual output modes are selected by setting the
matching flip - flop . and the other will be reset .
Digital Entry V 603-13 . V 60~-1 O. (1 when off) .
Group 10 . Output Control
Function:
Selects 1 of 3 data ou tput modes .
System Reset: Stop
Switch Select : Output is selected unconditionally . Analog Output 'f ou"
be selected in Outpu t Stop mode while Di gital Outpu
could be selected in Output Stop mode provided not in AI
ternate mode (group 8).
Operating
Conditions:
Lo gic :
Di gital Entry :
The individua l outp ut modes a re selected by setting thei
matching flip - flop .
GOPSL + is
normally low. but goes high in Digi tal modi
when data corresponding to one spec trum IS read au
thus forCing the flip-flop to Output Stop mode .
SEDOL - is normally l ow but goes high when a spec
trum read- out is demanded from the digital output (fran
ZD 0097)
o on the " S" inputs implies 0 on the respective " D" out
puts . GOPSL + = 1 impli es " D Output Stop" = 0 an!
GOPSL + goes
low again.
V 306 · 12. V 306 ·6. V 306-8 (1 when off) .
Group 11 . Channel Selector
Function: Selects a cha nn el on the display.
System Reset: Reset to 1.6 Hz via SYRTL- ZD 0099 - 10RPL- ZD 0 10
Switch Select: Unconditionally

Front Panel Control 2131 .3
Op e rating
Conditi o ns :
When either th e " Up " or the " Down " sw itc h is activated
MSCUL + or MSCDL + resp ec ti vely enables the S elected
Channel Count er Con t ro l (ZD 0099) .
FCCx L-
E
F
G
H
FCCSL -
FeREL -
A
8
C
D
FCSEL -
AA
V401
Group
041
Decoder
-u-
Enabl.
---+--, I/O Bus
Driver
The co nt ro ls may be set and read auto matically. The Fro nt Co ntr ol Char-
acter lines provides togethe r with Fro nt Charac ter Read and Front Charac-
ter Set the necessa ry data system for the co ntr ol.
The digital control is enab led whe n S goes low . Then the status of E -
H select
one of the groups and a 0 on FCREL - or F CS EL -decides
I
Group O. Time Constants and Fixed ConI .
FCSEL-
FCREL -
FCCxL-
A.
B
C
D
V304
.--------iA
.--------fB 1: 16Line 0-15
.----lC Se l ector -u-
Control
Circuit
Group 0
Gr oup 0 Enable
Bus Driver
8 -15
When G roup 0 En a bl e and FCSEL -goes low on e of th e Time Constant
flip - flop s is set by th e Bus Driv er code. Each fl ip- flop is given a numb er
wh ic h is c onv e rt ed in to a Binary -code by 2 encode rs w he re the enabl e
ou
tput Eo prov ides t he mo st signif ic ant digit . The encoder is en a bled
Digi tal
Logic "S Channel Selector Up -" or "s Channel Selector Down -"
= 0 implies 1 on MSCUL + or MSCDL + respectively .
D
igital Entry V 505 -8. V 505 -6. (1 wh en off) .
"'If' Control Circuits
Group 0-11
To Group Oood 1
To
F=======> Internal
Logic
~----~~,------~
Bus Driver
whethe r t he data is going o ut or in . Exce pt for group 0 whi ch is d e-
scribed below a nd group 1 t he 4 p ossib le pe rm u tat ions of the A a nd B
line select 1 of max . 4 f un c ti ons in side each gr ou p.
In group 1 A - 0 is the 10 dB code wh ic h is loaded when FC SEL -and
Group 1 E nab le IS active.
l Z8-lsec~
r;::=======================================~ > 1M _ l/n To
lL 15-
and Fi xed ploy
ConI . ZOOn5
r----~:~:~J - To
.----TlCC L- ~te~~al
TlCDL - OQI
Encoder
Aotl~j=~i
V608 Al
EI Eff
Z
t-+--·-I._';
wh en E, is l ow and w hen all i np uts a re high. Eo is low .
A Read-o
ut is in pr ogress w he n Group 0 Enable and F Cp <: 1
t he Binar y-c ode is gated o nt o th e bus. .

BRUt:L & KJA:R Display
Unit
2131.
Ncerum - Denmark
OA0049~
V.rt .width P
Focus P
12
Dismantling
Turn power off .
P 13 C.R.T. Cut-off
L 1 Vert . li nearity
Unscrew the two unbraco screws YO 0007 and YO 0011 in both sides
of the chassis and remove the bearings . Then lift the Display Unit and
push it out through the front plate of the 2131 . Half out the three con-
nectors should be removed . Place the Display Unit beside the 2131 and
reconnect the connectors.
Now . all adjustment potentiometers are accessible through the side
plates . For trouble shooting purpos es the printed circuits could be drawn
backwards and placed with their printed c ircuit side towards the table
without any disconn ectio ns.
~ ~ ~ ~ ~ ~ ~ ~ ~
••
~ ~ ~ ~ ~ ~ ~ ~ ~
•••
@ •
Horizontal Frequency P2
Trapezium Correction P 8
Pi ncush io n Correction P 7
10 kV Adjust ment P 1
Warning
II
• •
•••
••
~--T.H-;;:::::::;;;:::==::;:=t Pp~ Horizontal lin.ar ,
I left 0 •
right
o-o- ___ -t,P5 Horizontal width
0-0-- -- ;--;- P6 Horizontal Positi,
[5]1====
11nl
~
~I==:==
D~§:::::::::
P9 P 10
Intensit y
It should be ens ur ed. es pecially when reassembli ng the instrument. th,
the connecto rs are properly inserted . as it is p ossib le to invert or displac ,
them even in spite of c ode pins in two of the connectors .

2131 .4 Displav Unit
Block Diagram
-----------------~---------,-----------------
I ZI 0018 I Z(j 0127 200 HA. I ZIOI79
I
I
jM
,...,
1:J9
I
lJ5I4 IOKV
I T IJ1I5 O-IOIlV
Refer.nce
~
1J511 E. HI
I Elelllfnt
Driv'r
I Suptlly IJ
717 3SO-"400V
I
l-
I
~13
I--
UlJI
I +80V
~
J I I
LSnE- : I
IJ5I7
y I
Jl/III I
Y- Deflection
1J8/1
,,~l!J)V\
I torrelationl
1J5/8
X y
I
JII~~
IIot used +
SOV
Circuit
1-----4
I I
J1I51
2dB Linrs
~~
I I
10 dB lines
I (j2
~~
low Inlen Video I
+22V
, I
J7/4
h~'
I T I
Jill
Mixer I
15V RIg " "
High In len
II~
lJ JP'I
li,
6()V
~~
Column Tenl.
J!1t-
Char . Hod .
I
J2/5.l.'icn1e art
r
J214 'Intensity
r---
Blanking
I
I
I
I
1JU:
PSYNE - I X-Deflection
and S-Correction
J1I91
I
I
I
IJ6
I
I I
I I
I I
1)5/5
1J71l
I I
I I
I
______ ----~
I
I
AMplifier I J4/5
X-Deflection I
r I
lJ414
: 1 !
6, 63
,n
Lx
Centering
Magnets
~
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
L ____________________________ L ___________________ ~
The C.R. T. converls the digital data into visuality by accelerating e!ec·
trons from the cathode to the fluorescent anode. This may happen only
on the assumption that a synchronization logic provides the necessary
voltages and beam
deflection for the C.R.T.
The E.H/ T.
supply provides the voltages for the C.R. T. Here, the anode
voltage
of 10 kV accelerates the electrons from the cathode, while Gate
2- 4
perform an electronic lense in order to focus the electrons in as
small a spot as possible on the anode.
The Y-
deflect i on coil will move the light spot in vertical direction and the
X-deflection coil in horizontal di rection . This is done by creating an elec-
tromagnetic field around the coils and thus it is possible to influence the
pictura by turning the coil as well as by adding some extra magnets to
the magnet ic field.
If a deflection coil has been replaced or if the position of the centering
magnets have been altered for some reas on it might be necessary to
carry out a
magnetic adjustment as described in the adjustment proce-
dure .
The Y·
deflection is maintained by the Line Sync. signal LSYNE- which
also provides the timing to the E.H.T. The X· deflection is controlled by
the Picture Sync. signal PSYNE -.
When PSYNE -is low a return trace is in progress. During this time
Gate 1 will be negative compared to the cathode thus inhibiting the flow
of electrons to the anode.
The
LSYNE- and PSYNE- signals as well as CHMOL- . LR02L- . and
LR 1 OL -are originated on the ZD 0100 board and a detailed description
could be found in
the chapter handl i ng the dB-lines and characters.
Sim ilarly, LlNTL- , HINTL- , and COTLL-is orig inated on the ZD 0101
board and the description is found in the chapter dealing with the Dis·
play Control and Store/Update.
Checlcing Procedure
The checking procedure is carried out visually . The pic ture should be lin-
ear and steady and the columns should stand perpendic ular on the raster
lines . Then the picture sh ould be 5 mm from the borders of the front
frame and mu st not be suppressed. Finally the junctions of different sig-
nals on the screen should give a resulting increased light intensity also
in Overload mode.
"Scale Brightness " should vary the raster line intensity while "Intensity "
concerns with the overall picture light .
Trouble Shooting
In case of a missing signal the waveforms on the diagrams (ZI 0038 and
ZG 0127) should be measured in order to localize the error in a defined
circuit .
In case of an e rror with the E.H.T. supply J5 pin 9 could be connected to
ground . Then the voltages marked with an asterisk on the main diagram
indicates the approx.
DC values.
When an error has been remedied it should be decided whether an ad-
iustme nt is necessary. If so, refer to the Adjustment Procedure.

Ref.
Ellmlnt
LSYNE -
Ampl.
Rigulator
.15V
EHT Supply
Drivlr
The Line Sync. signal LSYNE- provides the driver input Vl with a
16.666 kHz pulse train which is amplified and led to the driver output
transistor V3 . The transformer T1 splits up the ' signal into a part being
used
for the Y-deflection and another for the E.H.T. The current neces-
sary to drive the E.H.T. drive transistor V38 is obtained from a current
generator V5-7 .
The E.H.T. stage is designed as an AC-coupled impulse amplifier where
V38 is sw itched On and Off thus generating a voltage across the primary
of T2 . Then the capacitors C29 and C33 in connection with the primary
creates a damped oscillation.
In T2 not only the voltages for Gate 2. Gate 4. and the anode of the
C.R.T. are created.
but also the + 80V supply to the Video Mixer .Hence.
th e E.H.T. is essential to the functioning of the display.
Display Unit 2131.4
200 MIl.
lakY
E. H.T.
Anode
T2
lSO-LOOV
.2 1/2 '11:
21W
Gat02
):"
LkV
CGotlL
'I
0-100V
I
~ .80 V
The secondary is tuned-in to the 3. harm . wi th a resulting 4 kV voltage
which is voltage doubled resulting in a DC voltage of 10 kV to the anode .
A feed-back
through a 200 MO resistor to the positive input of a Regula-
tor Amplifier ensures a steady output voltage. The input is normally tied
to OV by means of a Reference Element . and a change in the anode vol-
tage. will regulate the current generator in accordance with the change
thus compensating the variations .
Notice.
that an extensive short circuiting of the anode voltage to ground
may damage the Switching Regulator in defiance of the two pr otection di-
odes 02 and 03 .
Y -Deflection
as c ~~~~:~::_T.O_R_"~tu~r_n_T_r_O_C";.i=i~nro='=\.
~. Suppr.
From Driver
Blanking
When the power is turned off the Display is blanked immediately by V41
the output of which is kept high when the supply disappears as long as
C46 and C47 is charged.
The Y-deflec
tion circuit is also an AC-coupled impulse amplifier where
V35 is switched On and Off .
During a forward trace the capaci tor C25 . which has been charged by
the pulse from the Driver transformer . will discharge through L1. C26
and Ly. a nd the created current will correspond to the Y- deflection .
During a return trace the capacitor C25 will be shortened by V35 thus in-
creasing the discharge. Simultaneou sly the display will be suppressed by
the pulse to the Return Trace·Suppressi on .
The supply of the circuit is maintain ed by V36 and V37 where the posi-
tion of Pll decides the level of the max. Y- deflection . A small contribu -
tion from the Correlation Circuit overrides th e level adjustment so that
t he resulting supply becomes greater in the edges of the pi cture where
the distan ce from the cathode to the anode is the longest.
The value
of C25 decides the picture level on the C.R. T.
During the ret ur n trace tim e of the X- deflection the display should be in-
hibited as well. Hence. the signals are ORed in two diodes controlling a
switch transistor V39 . P13 pr ovides the voltage to Gate 1 thus deciding
the C.R.T. cut - off during the normal display ti me .

21 31 .4 Display Unit
X-Deflection and S- Correction
Rom p ro./Mrator
o E
o t-U---"--i
Qll
Pho .. Inverter
Corr.lotion Circuit
to
Y-Defl. H
~
:V Hor .
.---n-...... 7V Pos .
5 ms -15V
PSYHE
Her.
Frequency
Synchronously with the vertical deflection the spot should be moved in
the horizontal direction . Every picture consists of 344 Y-lines followed by
22 more during which the X-trace returns and as a complete Y -turn is
60llS the PSYNE frequency should be approx. 22 mS.
When a forward trace is starting PSYNE- is high and the comparator in-
put V12-2 is zero while the output is kept on -7V by 08 and 09 . But
then C9 will discharge through R25-P2 - R26 and as the Ramp Genera-
tor input V13-2 becomes more negative the output becomes positive
thus oerforminq the ramo.
If nothing happens the Ramp Generator would continue until the output
reaches the value as is the output of V12 and then cease to stop. But as
the X-deflection must be synchronized with the Y-deflection PSYNE-
goes low just before the end of the ramp. This changes the output of
V12 to + 7 V and C9 will charge through R25-0 10 and when V13-6
and V12 ·6 are equal the Comparator will start a new forward trace.
Hereby follows, that R25 represents the return trace while
R25-P2-'-R26 represents the forward trace. As the high-to-Iow trans-
ition of PSYNE- is the synchronization time , P2 should be adjusted so
that the jump expires immediately afterwards . A positive Comparator out-
put will inhibit the display .
Now, the distance from the cathode to the anode in the C.R.T. is not lin-
ear as the edges of the screen is further away than the center. In order
to compensate a S-slobe is impeded onto the ramp by means of a ~hase
Inverter and a full-wave rectifier .
LA02L-
LR10L-
Video Mixer
The pi cture on the C.R. T. is composed of spcts a rran ged in a matrix of X
Hor.
Width
to
....... i'" CircuIt
Correlation Circuit
At the start of the X-deflection V13-6 is most negative and C9 will dis-
charge, but the Phase Inverter supplies current through a11 thus delay -
ing the discharge . However , as the ramp is rising the amount from the
feed-back decreases and the discharge will increase until the ramp
reaches zero. Then all will stop and 012 will start to delay the dis-
charge again.
The
ramp output is then controlling the current for the X-deflection coil
through a differential amplifier . The feed-back via R53 and R54 ensures
that the output current is proportional to the input voltage . The input vol-
tage level is decided by P5, whereas the current necessary is provided by
P6 .
In order to linearize the picture further the Y -deflection could be im-
pressed by the S-correction . The ramp output and the inversion is ap-
plied each end of P7 and P8 and when they are adjusted to outweigh
each other the output of V15 will be zero and the Y-deflection is not af-
fected. But when f. inst. the Trapezium potentiometer is employed the
vertical deflection is squeezed in one side of the picture while increased
in the other thus performing a trapezium.
Similarly the Pincushion potentiometer will force the Y-deflection low , or
high respectively, in the middle of the screen.
tlcular spot is decided in the Video Mixer where the composants are
summed up to create the cathode voltage of the C.R.T.
The signals
to the Video Mixer are
LR02L -
LR10L -
lINTL -
HINTL-
COTLL-
CHMOL-
2 dB Line Raster
10 dB Line Raster
Low Intensity
High Intensity
Column Te rminati on
Character
Mod
Intensity
Scale Brightn ess
V26 and V27 are buffer gates with three-state output. This means that a
low enable sig nal will tran s fer the I nput to the output and current is
routed through the resistors R56-61 thus c oncerned . Then V31 and
V33 is closed correspondingly and the voltage drop across R69 decides
the light intensity .
Where two signals are merging in the same spot the resis tors concerned
will be parallelled and an increased light will result .
The
line raster intensity is independently controlled by the Scale Bright-
ness potentIometer which controls t he current flow via V29 and V ')
The picture i ntensity is si milarly controlled by the Im e '-'
wh;r.h cO 'll rois th e nase voltaqe of V33 h·, ~ ,,- ..