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TECI|NICAL OUIDE TOR SERI|ICE

TROUBLE SHOOTING

PROTECTION CIRCUITS

I
I
I
1

t
I

PIONEEFI'
SERVICE DEPARTMENT INTERNATIONAL DIVISION
TROUBLE SHOOTING METHODS
FOR

PROTECTION CIRCUIT

r'I()NEEFI'

SERVICE DEPARTMENT INTERNATIONAL DIVISION
3.
THE MAIN PURPOSE OF HAVING PROTECTION CIRCUITS IN AUDIO
EOUIPMENT IS TO PROTECT THE POWER TRANSISTORS IN THE MAIN

AMPLIFIER. HOWEVER, IN THE CASE OF OUTPUT CAPACITOR LESS

(O.C.L.) MAIN AMPLIFIER CIRCUITS, LOUDSPEAKERS ARE DIRECTLY

COUPLED TO THE AMPLIFIER. FOR THIS REASON WE MUST ALSO

PROTECT THE SPEAKERS.
+84tV
Ra
Rn

Rr
Cn
Qa

OCL }4AIN AMP CIRCT'IT

4.
IN ORDER TO MEET THESE REOUIREMENTS, WE DESIGNED A CIRCUIT
THAT WOULD DETECT A DEFECTIVE MAIN AMPLIFIER BY SENSING IF
THERE IS A D.C. VOLTAGE PRESENT AT THE SPEAKER TERMINALS.
THIS ALSO SENSES EXCESSIVE CURRENT IN THE OUTPUT STAGE.

(5 THROUGH 9 NOT USED)
PROIECTION CIRCUIT

fl"tcTR0il
MAIN AMP CIRCUIT

CIRCU IT

(
SPEATT

POWER
SUPPLY
CIRCUIT

5.
IN PIONEER O.C.L. MAIN AMP'S A "CUT OFF LOAD SYSTEM" IS

EMPLOYED. THIS IS AN ELECTRIC SENSING CIRCUIT AND RELAY

WHICH DISCONNECTS THE SPEAKERS FROM THE AMP WHENEVER THE

AMPLIFIER OR SPEAKER MAY BE DEFECTIVE.

THE PROTECTION CIRCUIT OF THIS TYPE WORKS EFFECTIVELY ON OCL MAIN AMPLIFIER
AND, AT THE SAME TIME. THE ACTION IS VERY STABILIZED.
6.
IN THESE NEXT SLIDES WE WILL LEARN HOW THE PROTECTION

CIRCUITS OPERATE. AS AN EXAMPLE WE WILL USE THE PROTECTION

UNIT FROM A SA-1OOO AMPLIFIER.
DETECTIVE SECTION RELAY DRIVE SECTION

7.
THE PROTECTION UNIT IS COMPOSED OF THREE DIFFERENT CIRCUITS

DESIGNED TO DETECT ANY ABNORMAL OPERATION IN THE AMP.

LIFIER, SUCH AS EXCESSIVE CURRENT OR D.C. VOLTAGE ATSPEAKER

TERMINALS. THERE IS ALSO A SECTION TO DRIVE THE PROTECTION

RELAY.
SPEAKER

8.
WE CAN DIVIDE THE PROTECTION UNIT INTO THREE SECTIONS,

CONSISTING OF TRANSISTORS O-1 AND O.2, O-3 AND O.4 AND 0-5,0.6,

o-7.

O-1 AND O.2 DETECT EXCESSIVE CURRENT DRAWN THRU THE POWER

TRANSISTORS OF THE MAIN AMP. ONE TRANSISTOR IS FOR THE
RIGHT CHANNEL AND THE OTHER IS FOR THE LEFT. O.3 AND O-4

DETECT ANY D.C. VOLTAGE PRESENT AT THE OUTPUT TERMINALS.

EITHER OF THESE CONDITIONS WILL PRODUCE A SIGNAL TO ACTUATE

THE PROTECTION RELAY.
THE EXCESSIVE CURE
THE EXCESSIVE CURRENT SIGNAL CAN BE DETECTED AT O.1 CIRCUIT FOR L-CHANNEL AND
O.2 FOR R-CHANNEL.
IN CASE OF LOWER SIDE POWER TRANSISTOR, THE RESISTOR IS CONNECTED TO THE
COLLECTOR, SUCH A
CIRCUIT. AS THAT IS CONSISTING FOR THE PURPOSE OF GETTING
THE SIGNAL FOR DETECTING EXCESSIVE CURRENT.
Qr

Rto

Re
RELAY DRIVE CIRCU IT

9.
THE PROTECTION RELAY IS DRIVEN BY A SCHMIT TRIGGER CIRCUIT

coNstsTtNG oF o-5, 0-6 AND O-7.
SPEAKER +35V

RELAY

ls----J
Ra

Cz
CURRENT
R+
TOR

SPEAKER

10.
HERE WE WILL EXPLAIN IN DETAIL HOW EACH OF THE crRcutTs
WORK. WE WILL START WITH THE CURRENT OVERLOAD SENSING
CIRCUIT. AS YOU CAN SEE O.1 AND O-2 ARE THE SAME. ONE FOR
EACH CHANNEL, SO WE WILL EXPLAIN ONLY ONE SIDE.
mwEn o
TR P0srTtvE
HALF SYCLES

NEEATI V E
P{}WER
HALF SYCLES
TR

1t.
THE OUTPUT SIGNAL TO THE SPEAKER IS DEVELOPED ACROSS THE
TWO EMITTER RESISTORS CONNECTED AT POINTS ''A" ,"b" AND
'IC'f. SINCE WE ARE USING A CLASS "b" PUSH.PULL AMPLIFIER,THE
,,A" SIDE OF THE AMP HANDLES THE POSTTIVE COMPONENTS OF
THE SIGNAL BEING AMPLIFIED AND THE "C" SIDE HANDLES THE
NEGATIVE.
12.
01'S CIRCUIT MAY BE RE.DRAWN AS TWO COMBINED BRIDGE CIRCUITS.

WHEN ONE BRIDGE CONSISTING OF POINTS ''d", ''b'" ''f '' AND "d"
AND THE OTHER OF "b", "C", "et' AND "f " ARE BALANCED THEN

THE POTENTIALS AT POINT ''b'" ''d", AND "E" ARE EOUAL. WHEN

THE BRIDGE IS BALANCED IN THIS MANNER, NO POTENTIAL DIF-
FERENCE IS PRESENT BETWEEN THE EMITTER AND BASE OF O-1.

THEREFORE, THERE IS NO COLLECTOR CURRENT THRU O.1 AND NO

SIGNAL TO OPERATE THE PROTECTION RELAY.
o,-
13.
TO SIMPLIFY THE EXPLANATION OF OPERATION WE HAVE RE-DRAWN

THE CIRCUIT AS SHOWN. IN THIS SCHEMATIC, THE EMITTER OF O.1

IS CONNECTED TO POINT "b" BECAUSE THE CIRCUIT IS CONSIDERED

TO BE BALANCED WHEN THE AMPLIFIER IS OPERATING NORMAtLY.
THEREFORE, FOINTS "b" AND "e" ARE ELECTRICALLY THE SAME.
O-1 WILL STILL DETECT ANY CURRENT VARIATION.

lF THE BRIDGE ClRcUlT {b}, (c}, (e} AND (f} ARE BALANCED, POINT (e} AND POINT (b)
ARE AT THE S,AME POTENTIAL AND IT CAN BE CONFIRMED THAT THEY ARE CONNECTED.
SHO

14.
LET'S ASSUME A CASE WHERE R.L. HAS SHORT CIRCUITED OR R.L.

IS A VERY LOW IMPEDANCE. IN THIS CASE, THE CIRCUIT WILL
BECOME IMBALANCED, POTENTIAL AT THE BASE OF O-1 INCREASES

WITH RESPECT TO THE EMITTER, AND COLLECTOR CURRENT WILL
FLOW THRU O.1 OPERATING THE RELAY.
+B/tlV

IDLE
CURRENT
INCREASE

OUT

Rss
Rst

f crs
,?2.
R+r

EXCESS IVE OUTPUT

15.
IF THE POTENTIAL OF POINT ''A" INCREASES BECAUSE OF EXCESSIVE

OUTPUT OR HIGH IDLE CURRENT OR IMPROPER BIAS, EXCESSIVE

CURRENT WILL FLOW THRU THE POWER TRANSISTORS CAUSING A

LARGER VOLTAGE DROP ACROSS THE EMITTER RESISTORS. BECAUSE

OF THIS, THE POTENTIAL AT POINT "b" WILL INCREASE CAUSING
AN IMBALANCE OF THE BRIDGE CIRCUIT, WHICH WILL ACUATE THE

PROTECTION RELAY.
SHORTED

t6.
NOW WE WILL LOOK AT THE PORTION OF THE CIRCUIT MADE UP OF

''C", ''b,,, ,,C" AND "f ". REMEMBER IN THE SA-1OOO PROTECTION

UNIT, THE BASE OF O-1 IS CONNECTED TO POINT "b" IN THE
SCHEMATIC. THIS IS BECAUSE WHEN THE BRIDGE IS IN A BALANCED

CONDITION, POINTS "b'' AND "d'' ARE AT THE SAME POTENTIAL AND

MAY BE CONSIDERED TO BE CONNECTED TOGETHER. NOW IF THE
R.L. IS SHORTED, POTENTIAL AT THE BASE OF O.1 BECOMES THE SAME

AS GROUND. SINCE THE EMITTER IS NEGATIVELY CHARGED, COL.
LECTOR CURRENT WILL FLOW THRU O-1 ACTIVATING THE RELAY.
P0s,ER
o
TR
f d

Dr
Ds
Qr
OUT

Ul- Dsl

fi/ e
pgril5p \5r
TR
e

17.
THE DIODES, D.l AND D-3 ARE USED FOR TEMPERATURE

COMPENSATION AND MORE STABLE OPERATION WITHOUT BEING
SENSITIVE TO TEMPERATURE. CAPACITOR C-1 CONNECTED BETWEEN

THE BASE AND EMITTER OF O-1 IS TO DECREASE SENSITIVITY OF

THE PROTECTION UNIT AT HIGH FREOUENCIES. THIS IS TO PREVENT

IMPROPER OPERATION DUE TO HIGH FREOUENCY NOISES OR POPS.
POWER TR
SPEAKER + 35V

RELAY
Ct

Cs C+ I Rrr

DC VOLTAEg
Cz DETECTOR
R+

SPEAKER

18.
NOW. WE WILL CONSIDER THE OPERATION OF THE D.C. VOLTAGE
DETECTION CIRCUIT. THIS CIRCUIT IS COMPOSED OF TRANSISTORS

O.3 AND O-4. IT IS DESIGNED TO OPERATE THE PROTECTION RELAY

WHENEVER THERE IS D.C. VOLTAGE PRESENT AT THE SPEAKER

TERMINALS. O-3 AND O-4 ARE A MATCHED PAIR FORMING A DIF-

FERENTIAL AMPLIFIER. A BIAS ADJUSTING CIRCUIT IS PROVIDED TO

COMPENSATE FOR MINOR CIRCUIT VARIATIONS AND TO BALANCE

THE DIFFERENTIAL AMP.
L

-r3v

19.
AS CAN BE SEEN IN THE SCHEMATIC, THE BASES OF O-3 AND O-4 ARE

CONNECTED TO CAPACITORS C-3 AND C.4. THESE CAPACITORS ARE

CONNECTED IN SERIES. BY ITS DESIGN, A DIFFERENTIAL AMPLIFIER

ONLY HAS OUTPUT WITH A DIFFERENCE IN INPUT. SINCE WE NEED

SOME METHOD OF SENSING THIS DIFFERENCE, NECESSARY FOR
OPERATION, WE HAVE INSTALLED THESE CAPACITORS AT THIS POINT

IN THE CIRCUIT.
TPr TPz

L* I9nu
R

HICH
qefo Qft -ft, qft
L0w 4e 4(''
a b c

20.
THE REACTANCE OF C-3 AND C.4 MAY BE DISREGARDED AT ANY
FREOUENCY OVER A FEW HERTZ. SINCE THE BASES OF O-3 AND O-4

ARE FED THE SAME SIGNAL, THERE IS NO DIFFERENCE SIGNAL

PRESENT AND NO OUTPUT. HOWEVER, FOR SIGNALS BELOW A FEW

HERTZ OR DIRECT CURRENT THE REACTANCE OF C-3 AND C.4 CANNOT

BE DISREGARDED. THEREFORE, A DIFFERENCE SIGNAL WILL BE

PRESENT BETWEEN THE BASES OF O-3 AND O.4. THIS WILL CAUSE

OPERATION OF THE RELAY.

1
THE REACTANCE Xc OF CAPACITOR CAN BE SHOWN AS Xc = AS THE FORMULA
*"
SHOWS, lF TllE FREOUENCY (fl BECOMES HlcHER, THE VALUE OF Xc WILL BECOME
SMALLER; lF THE FREOUENCY BECOMES LOWER, THE VALUE OF Xc WILL BECOME LARGER.
lN CASE OF DIRECT CURRENT, THE VALUE OF Xc BECOMES INFINITE SINCETHE FREOUENCY
IS ZERO IN THAT CASE.
TPr TPe
+35V

)i-
4
DECREASE I NCREASE
@"
b
Q+ .O
L.OUT*

R.OUT

-t3v

21.
NOW WE WILL DISCUSS WHAT TAKES PLACE WHEN A POSITIVE D.C.
VOLTAGE IS PRESENT AT POINT "A'" SINCE A CAPACITOR IS CON-
NECTED TO POINT ''b", THE VOLTAGE AT POINT ''A'' WILL NOT
AFFECT POINT "b". THE SAME SIGNAL AT POINT "A " IS ALSO PRESENT
AT POINT "C'" SINCE THE POTENTIAL POINTS "b" AND "C" ARE
NO LONGER EOUAL, THE DIFFERENCE SIGNAL PRESENT AT POINT
,,C,'WILL AFFECT THE COLLECTOR CURRENT OF O-4. THE POTENTIAL
AT POINT "E'' WILL IN PROPORTION TO THE INCREASE
DECREASE
OF COLLECTOR CURRENT OF O.4. THE DECREASE AT POINT "C''
WILL FORWARD BIAS DIODE D.7. THIS WILL DECREASE POTENTIAL
AT POINT ''f", WHICH WILL TURN O-5 ON, OPERATING THE PRO-
TECTION RELAY.
*---T
-- "--|r-j- tF potNT (a) BECoMES pLUS voLTAGE AGAINsr porNT (b), DroDE BEcoMEs
,ON'AND THE ELECTRIC CURRENT FLOWS. IN THIS
CASE,-DIODE IS "BIASED
IN FORWARD DIRECTION." IN CASEOF ABOVE PHOTOGRAPH, POINT{f}BECOMES
'PLUS' COMPARED WITH POINT (el SINCE THE VOLTAGE AT POINT (el DECLINES.
+35V

INCREASE DECREASE
e^d,
0g
kcO
L.0UT*

R. OUT
Rrr ? JRrz
t lRrs m

-t3v

'22.
IF NEGATIVE VOLTAGE IS APPLIED TO POINT ''A'" THE COLLECTOR
CURRENT OF O-4 WILL DECREASE IN PROPORTION TO THE VOLTAGE
AT THE BASE, WHILE THE COLLECTOR CURRENT OF O-3 WILL
INCREASE. THIS INCREASE WILL CAUSE THE POTENTIAL AT POINT
''d,' TO DECREASE IN INVERSE PROPORTION TO THE COLLECTOR
CURRENT AT O-3. AGAIN THIS WILL FORWARD BIAS THE DIODE
D-6 WHICH WILL REDUCE POTENTIAL AT POINT "f '" TURNING O-5
ON AND OPERATING THE RELAY.
AS A CHARACTERISTIC OF THE DIFFERENTIAL AMPLIFIER CIRCUIT,
lo lS ALWAYS CONSTANT. I\CCORDINGLY. THERE lS THE RELATION OF
"lo = 11 + 12." HERE, lF SIGNAL lS ADDED TO lNl TO INCREASE 11, 12 WILL
DECREASE lN ACCORDANCE WITH 11 SINCE lo lS CONSTANT. ALSO, lN
cAsE THE STGNAL tS ADDED TO tN2, tl CHANGES tN ACCORDANCE W|TH 12.
lN cAsE THE SAME STGNAL lS ADDED TO lNl AND lN2, NO CHANGE WILL
HAPPEN ON tl AND t2.
PROTECTION crRcutT

'\
MAIN AMP
CIRCUIT

P()IT'ER
SUPPLY
crRcurT

23.
IN THIS MANNER, WHENEVER A POSITIVE OR NAGATIVE VOLTAGE
IS PRESENT AT THE OUTPUT TERMINALS, O-5 WILL CONDUCT.

ACTUATING THE RELAY TO DISCONNECT THE SPEAKERS.
FP0H r{Ailt A}tP

R3
TO SPAI(ER
R9

Rlo

r Ds

24.
NEXT WE'LL SEE HOW THE RELAY DRIVE CIRCUIT OPERATES. IF
COLLECTOR CURRENT FLOWS IN O-1, O.2, O-3, OR O.4 THE DIODE

CONNECTED TO THEIR COLLECTOR IS FORWARD BIASED AND THIS

CAUSES A VOLTAGE DROP ACROSS R.16. THIS VOLTAGE DROP WILL

DECREASE THE POTENTIAL AT THE BASE OF O-5 BY AN AMOUNT
EOUAL TO THE DROP ACROSS R.16.

THE PROTECTION IS CARRIED OUT BY CUTTING THE RELAY WHICH CONNECT FOR OUT
TERMINAL OF MAIN AMPLIFIER AND THE SPEAKER TERMINAL.
FPOM }.IAIN AFIP
TPr TPz

RELAY

TO SPEAKER

i-oJ-'

25.
SINCE O-5 IS A P.N.P. TRANSISTOR, IT WILL TURN ON WHENEVER ITS
BASE VOLTAGE DECREASES. WHENEVER O.5 IS ON, BASE CURRENT

WILL FLOW IN 0-6 CAUSING COLLECTOR CURRENT TO FLOW,

IN CASE OF PNP TYPE TRANSISTOR, IF THE BASE VOLTAGE BECOMES MINUS K LESS THAN
EMITTER VOLTAGE, THE TRANSISTOR BECOMES'ON'AND THE COLLECTOR CURRENT FLOWS.
FR(I}"I MAIN AI.IP
+35V
De

Dg
I
t
I Rzo a
I
I RE LAY

DS L*Jil I
lr
ll
lr
I
TO SPEAKER
iR 22

26.
WHEN COLLECTOR CURRENT FLOWS THRU 0-6 A LARGE VOLTAGE

DROP WILL APPEAR ACROSS R-21, CAUSING A BASE VOLTAGE DROP

AT O.7. THIS WILL CUT.OFF COLLECTOR CURRENT WHICH WILL

OISCOruruCCT TFIE AMPLIFIER FROM THE SPEAKERS.
mt't xAlr gp
FR(lM MAIN AMP +35V

L
OVER

l0 SPEATER
'l
I
I
I
I
t

27.
WHENEVER THE RELAY IS NOT ENERGIZED, THE CURRENT DETECTION

CIRCUIT, CONSISTING OF O-1 AND O-2 WILL TURN OFF WHICH
INCREASE THE BASE POTENTIAL AT O.5. THIS TURNS OFF O.5 AND
0-6. O.7 WILL TURN ON, ENERGIZING THE RELAY WHICH CONNECTS

THE SPEAKERS AND AMP. IF THE ORIGINAL PROBLEM WHICH CAUSED

THE RELAY TO OPEN IN THE FIRST PLACE STILL EXSISTS THEN
THE CIRCUIT WILL CYCLE ON AND OFF UNTIL THE PROBLEM IS
CORRECTED.

IN THE RELAY IS CUT, THE AMPLIFIER SECTION AND LOAD ARE CUT OFF, EMITTER VOLTAGE
OF O-1 BECOMES HIGHER THAN BASE VOLTAGE AND O-1 BECOMES 'OFF." AS A RESULT,
THE ELECTRTC CURRENT DOES NOT FLOW THROUGH D5 AND THE BASE VOLTAGE ANDO-
5 RISES.
FROM MAIII AI-IP
TPt TPz +35V

RELAY

SPEAKER
Drl

l- ou-
-'

28.
TO SERVE AS A TURN.ON PULSE NOISE ELIMINATOR R-21 AND C.6

ARE CONNECTED TO THE BASE OF O.7. THEY HAVE A TIME CONSTANT

OF APPROXIMATELY FIVE SECONDS. O-7 CANNOT TURN ON DURING

THIS TIME AND THE DELAY SERVES AS A MUTING CIRCUIT AT THE

TIME THE POWER IS TURNED ON.

KEEP RELEASING THE RELAY FOR A WHILE EVEN AFTER THE POWER SWITCH IS TURNED
,ON" ACTIVE RELAY AFTER THE MAIN AMPLIFIER CIRCUIT IS STABILIZED. BY DOING SO,
THE UNNECESSARY NOISE CAN BE PREVENTED FROM THE SPEAKER SYSTEM.
POWER TR
SPEAKER Pr TPz + 35V

RELAY
Cr

Cz
DC VOLTAEE
R+ DETECTOR

SPEAKER
-l3v

29.
IF ANY D.C. VOLTAGE IS PRESENT AT THE OUTPUT TERMINALS OF
THE AMPLIFIER, THE RELAY WILL REMAIN OPEN. UNTIL THE
PROBLEM IS CORRECTED, SPEAKERS REMAIN DISCONNECTED SO NO

DAMAGE IS POSSIBLE.

IN CASE THE BALANCE OF DIRECT CURRENT OF MAIN AMPLIFIER IS BROKEN, THE DIRECT
CURRENT VOLTAGE APPEARS.
30.
NOW WE WILL CONSIDER THE TROUBLE SHOOTING PROCEDURE FOR

PROTECTION CIRCUITS. YOU MUST, OF COURSE, CAREFULLY

OBSERVE ALL SYMPTOMS OF FAILURE AND FOLLOW A LOGICAL

PROCEDURE TO A REPAIR.
PROTECTIOII CIRCUIT

RELAY
MAIN AMP
CIRCUIT
ilr
(
SPEAI(E

POWER
SUPPLY
CIRCUIT

31.
THE PROTECTION CIRCUIT MAY OPERATE DUE TO FAILURES EITHER

IN THE MAIN AMP OR IN THE PROTECTION CIRCUTT ITSELF. TO

COMMENCE TROUBLE SHOOTING, IT IS NECESSARY TO DECIDE IN
WHICH CIRCUIT THE PROBLEM EXSISTS.
+B4IV
Rzr OVER
CURRENT
Rrg

Rrz
Crg
Qs
o,ur o
0r
Rsl
:iC
Rsg
o
rs
L
R+v

-B r 45V
-84IV

32.
FIRST WE WILL CONSIDER THE AMPLIFIER AS HAVING THE DEFECT.

TWO CAUSES OF PROTECTION CIRCUIT OPERATION ARE POSSIBLE.
(1) D.C. VOLTAGE tS PRESENT AT AMpLtF|ER OUTPUT. (2) EXCESSIVE

CURRENT IS FLOWING THRU THE OUTPUT TRANSISTORS.
TO SPEAKER

Cr C+ J Rrr

'L2
R4

33.
NOW WE WILL CONSIDER THE PROTECTION UNIT ITSELF: IF FOR

ANY REASON, O.1, O-2, O-3, ORO.4 TURNS ON. THEN THIS WILL LOWER

THE BASE POTENTIAL OF O-5 WHICH WILL TURN OFF THE RELAY
BY TURNING ON O-5 AND 0.6 AND TURNING OFF O-7.
PROTECTION CIRCUIT

MAIN AMP
CIRCUIT

SPEAKE

POWER
SUPPLY
CIRCUIT

34.
GENERALLY SPEAKING, YOU CAN DECIDE IF THE PROBLEM EXSISTS

IN THE AMPLIFIER OR THE PROTECTION CIRCUIT, BY SEEING IF THE

RELAY OPERATES OR NOT.
PROTECTION CIRCUIT DOES NOT WORK AT ALL

RELAY CLOSES IMMEDIATELY AFTER TURNING THE AMP ON

IT REMAINS IN ACTUATED STATE

IT REPEATS PROTECTIVE OPERATIONS
AT INTERVALS OF ABOUT 5 SECONDS

IT IS IN CRITICAL STATE

IT WORKS WITH THE LAPSE OF TIME

35.
THERE ARE 6 MAIN SYMPTOMS THAT ARE CLUES TO THE PROBLEM IN
A PROTECTION CIRCUIT. THESE ARE: 1. PROTECTION CIRCUIT DOES

NOT OPERATE AT ALL (RELAY WILL NOT ENERGIZE). 2. RELAY

CLOSES IMMEDIATELY AFTER TURNING THE AMP ON. 3. (OF No.38)

PROTECTION CIRCUIT REMAINS ON AT ALL TIMES (RELAY WILL NOT

DROP OUT WHEN IT IS SUPPOSED TO}. 4. THE PROTECTION CIRCUIT

CYCLES ON AND OFF AT INTERVALS OF APPROXIMATELY (5) FIVE
SECONDS. 5. THE PROTECTION CIRCUIT IS TOO SENSITIVE AND
OPERATES TOO EASILY. 6. THE PROTECTION CIRCUIT OPERATES
AFTER THE AMPLIFTER HAS BEEN ON FOR THE SOME TIME AND
APPEARS TO HAVE BEEN WORKING NORMALLY. (TEMPERATURE

SENSITIVE}.
36.
IF THE PROTECTION CIRCUIT DOES NOT OPERATE AT ALL, THEN

CHECK TO SEE IF IT IS RECEIVING POWER FROM THE POWER SUPPLY.

$EE CUT 28 AS TO THE EXPLANATION OF MUTING ACTION.
Cs C+ I Rrr

37.
IF THE RELAY OPERATES AS SOON AS THE AMP IS TURNED ON,
THEN THERE MAY BE A COLLECTOR.EMITTER SHORT IN O-7, OR

C-6 IS OPEN.
Rl

Rro

RELAY
Cz RETURNS
OR N()T
R4

-t3 V

38.
HOWEVER, IF THE MUTING ACTION IS NORMAL, THAT IS IF THE
RELAY OPERATES APPROXIMATELY FIVE SECONDS AFTER TURN ON,

WE CAN VERIFY NORMAL OPERATION OF O.5, 0.6 AND O-7 AND
POSSIBLE FAILURE IN THE DETECTION SIDE O.1 THRU O-4.
TPt TPz +35V

LI
sr0ts
ll
1s

iro

cz?

39.
TO CHECK THE RELAY OPERATION WE CAN TURN O-5 ON BY CON.

NECTINGA SOKO 1/2WRESISTOR FROM THE BASE OF O-5 TO GROUND.
RELEASE

DETECTOR RELAY

CI RCUI T

DETECTOR CIRCUIT IS DEFECTIVE
DRIVE
CIRCUIT
I
N{}T RELEASE

ili
DETECTOR RELAY
DRIVE
crRcutT CIRCU IT

RELAY DRIVE CIRCU IT IS DEFECTIVE

40.
IF THE RELAY OPENS AND DISCONNECTS THE SPEAKERS, THEN THE

RELAY DRIVE CIRCUIT IS O.K. THE FAILURE MUST BE IN THE
DETECTION CIRCUITS.
COT{NECT A RESISTOR
BETVI/EEN BASE OF Q5 AI\D GROUND

DOES RELAY
RELEASE ?

TROT.'BLE 15

TROUBLE IS IN IN REI-AY
DETECTOR CIRCUIT DRIVE EIRCUIT

41.
CONNECT A SOKO RESISTOR BETWEEN THE BASE OF O-5 AND GROUND.

IF THE RELAY OPENS AND DISCONNECTS THE SPEAKERS, THEN THE
FAILURE IS IN THE DETECTIVE CIRCUITS. IF THE RELAY DOES NOT

OPEN, THEN THE RELAY DRIVE CIRCUIT IS DEFECTIVE.
Rz

OVER CURRENT
DETECTOR

42.
IF YOU DETERMINE THE DETECTION CIRCUITS ARE AT FAULT, WE
WILL SHOW YOU HOW TO JUDGE IF IT IS THE VOLTAGE OR CURRENT

clRcutTs.
43.
TO CHECK THE D.C. VOLTAGE DETECTION CIRCUIT, CONNECT A

MULTIMETER SET FOR D.C. VOLTS BETWEEN TP-l AND TP-2. TURN

VR-l IN BOTH DIRECTIONS.
ffirr I
-13 v

44.
WHEN YOU TURN VR-1 CLOCKWISE AND COUNTER.CLOCKWISE, IF
THE CIRCUIT IS NORMAL, AT SOME POINT, IN THE ROTATION, YOU
WILL GET A VOLTAGE READING BETWEEN TP-l AND TP-2. ALSO, THE
RELAY SHOULD OPEN. IF WHEN YOU FIRST CHECK THE VOLTAGE

READING AND ROTATING VR-1 HAS NO AFFECT, THEN O.3 OR O-4

MAY BE DEFECTIVE.
-t3 v

45.
IF ROTATING VR-l AFFECTS YOUR METER READING BUT THE RELAY
STILL DOES NOT OPERATE THEN THE DIODE D.6 OR D.7 MAY BE

DEFECTIVE.

AFTER MAKING THE CHECK, BE SURE TO ADJUST THE VR-l SO THAT

THE POTENTIAL BETWEEN TP-l AND TP.2 BECOMES ZERO.
T0 0s

0r
(02)

FEED
SICNAL
SLOWLY OVER CURRENT
DETECTOR
SH()RTED

46.
TO CHECK THE EXCESSIVE CURRENT DETECTION CIRCUIT INSURE

THAT NO SIGNAL IS FED INTO THE AMPLIFIER. SHORT CIRCUIT
BOTH OUTPUT TERMINALS AND VERY SLOWLY FEED A SIGNAL TO THE

INPUT. YOU SHOULD BE CHECKING WITH YOUR MULTIMETER THAT
THE COLLECTOR VOLTAGE OF O-1 AND O.2 DECREASES OUICKLY
AS THEY TURN ON.
Vcl or Vea
DECREASES BY
0r or Qr 0t

47.
IF THE COLLECTOR VOLTAGE DECREASES, THEN THE CIRCUIT IS

O.K. IF NOT THEN O-1 OR O-2 MAY BE DEFECTIVE, OR C-1 OR C.2

MAY BE SHORTED. BE SURE NOT TO INCREASE THE INPUT SIGNAL

RAPIDLY AS YOU MAY DAMAGE THE POWER TRANSISTORS.
48.
NOW WE WILL CONSIDER THE PROBLEM OF THE PROTECTION CIRCUIT

REMAINING ACTUATED ALL THE TIME. THIS IS PROBABLY CAUSED

BY D.C. VOLTAGE AT THE OUTPUT TERMINALS.

SEE CUT 24 THRU 33 AS TO THE DETAILS.
TPr IPz

Re
CIRCUIT
Cz
DC VOLTASE
R+ DTECTOR

49.
OTHER POSSIBLE CAUSES FOR NON.OPERATION OF THE RELAY MAY

ALSO BE A FAILURE OF THE RELAY DRIVE CIRCUIT OR THE D.C.

VOLTAGE DETECTION CIRCUIT.
+B4IV
Rzs R+t
OVER
Rrs
0rs
CURRENT
Res
Rrr Dr
Crg
Qg t our@
0r
Rs

Rst
e
JRrr
Raz
Cs

50.
IF A POWER TRANSISTOR SHORTS IN THE MAIN AMP IT WILL UN-

BALANCE THE AMPLIFIER AND A D.C. VOLTAGE WILL APPEAR ACROSS
THE OUTPUT TERMINALS. ALSO, EXCESSIVE CURRENT WILL FLOW
THRU THE TRANSISTORS TO GROUND.
-l3v

51.
NOW WE WILL CONSIDER TROUBLE.SHOOTING THE PROTECTION

CIRCUIT WHEN THE MAIN AMP UNIT IS O.K.

CONNECT A MULTIMETER BETWEEN TP-l AND TP.2 OF THE VOLTAGE

DETECTION CIRCUIT O.3 AND O.4, AND BALANCE THE CIRCUIT BY

ADJUSTING VR.l UNTIL YOU GET A ZERO VOLTAGE READING ON

YOUR METER. IF THE RELAY NOW WORKS, THEN THE PROBLEM

WAS MISADJUSTMENT OF VR.l..
m RAN

+35V

Qs Qo Sv

9r "cr u
L RSLAY SREVE
Rlo
gtfficu6T
R

-t3 v

52.
IF BALANCE CANNOT BE OBTAINED BY ADJUSTING VR-1, THEN THE
D.C. VOLTAGE DETECTION CIRCUIT MUST BE DEFECTIVE. ALSO, IF

THE RELAY DOES NOT WORK EVEN THOUGH THE CIRCUIT IS

BALANCED, THEN THE RELAY DRIVE CIRCUIT MAY BE DEFECTIVE.

POSSIBLE CAUSES MAY BE A SHORT IN O.5 OR 0-6 OR AN OPEN IN O-7.

IF THE SHORT CIRCUIT HAPPENS ON O.5 OR 0.6, THE ELECTRIC CURRENT FLOWS THROUGH
THE COLLECTOR OF 0-6, THE BASE VOLTAGE OF O.7 DECLINES AND O.7 IS CUT OFF, THE
ELECTRIC CURRENT DOES NOT FLOW THROUGH THE RELAY AND NO ACTION TAKES PLACE.
LIKEWISE, IN CASE O.7 IS OPEN, THE ELECTRIC CURRENT DOES NOT FLOW THROUGH THE
RELAY AND NO ACTION TAKES PLA,CE.
53.
NEXT, LET'S CONSIDER THE CASE IN WI-IICH TFIE RELAY REPEATS

ACTIONS AT INTERVALS OF ABOUT 5 SECONDS. SINCE THE RELAY

WORKS IN THIS CASE, THE RELAY DRIVE CIRCUIT IS NORMAL.
IPr l?t
Rr

TEUY
Ct

Cc C+ I Rrr

OC VOLTASE
DETECTOR
Cz

54.
NORMALLY IF SOMETHING IS DEFECTIVE IN THE D.C. VOLTAGE
DETECTION CIRCUIT THE RELAY WILL NOT CONNECT THE SPEAKERS

TO THE AMP. NOW WE WILL INVESTIGATE THE PROBLEM OF THE
PROTECTION CIRCUIT ACTUATING EVERY FIVE SECONDS.
(}YER
CURRENT RE LAY
DETECTOR
(0r ot 0z 0ll)

55.
WHEN AN EXCESSIVE CURRENT FLOWS THRU THE LOAD VIA THE

N4AIN AMP, THE EXCESSIVE CURRENT SENSOR ACUATES THE RELAY
AND DISCONNECTS THE LOAD FROM THE AMPLIFIER. NO EXCESS

CURRENT WILL FLOW THRU THE POWER STAGE.
WER EURRNT
MAIN AMP
DETECT(lR
0r or Qz (}ff)

c0t{NEcT
THE LOAD

l3
R9

Rro

56.
WHEN THE EXCESSIVE LOAD IS SENSED BY THE CURRENT CIRCUIT,

IT WILL TURN OFF O.1 OR O.2 AND ALSO TURN OFF O-5 AND 0.6
WHICH WILL TURN ON Q-7. THIS WILL CLOSE THE RELAY AND AGAIN

CONNECT THE LOAD TO THE AMP.

1} THE ACTIVATE OF RELAY AT EVERY FIVE SECONDS IS DUE TO THE TIME CONSTANT OF
MUTING CIRCUIT. SEE CUT 28 AS TO THE DETAILS.
2} AS THE CAUSE OF MAIN AMPLIFIER SIDE, THERE IS THE ABNORMAL INCREASE OF IDLE
CURRENT, AND AS THE CAUSES OF LOAD SIDE, THERE ARE THE SHORT CIRCUIT OF
LOAD, CONNECTION OF VERY LOW VALUE LOAD, ETC.
COXNECT
THE LOAD

57.
AS SOON AS THE LOAD IS CONNECTED, EXCESSIVE CURRENT WILL
FLOW AND THE RELAY WILL DISCONNECT.
co$rNEcT
T}iE LOAD

FELAYI
,{qs!$ql
SEPARATE
TliE r0A0

58.
IN THIS MANNER, THE PROTECTION RELAY WILL CYCLE ABOUT
EVERY FIVE SECONDS. WHENEVER THIS SYMPTOM IS NOTED THE

PROBLEM IS EITHER IN THE MAIN AMP OR THE LOAD.
59.
OUR NEXT PROBLEM IS TO CONSIDER A PROTECTON UNIT THAT IS

TOO SENSITIVE. THE OPERATING RANGE OF THE PROTECTION
CIRCUIT MAY BE TOO NARROW.
POWER TR
fPr TPz

DC VOLTACE
Cz
DETECTOR
R+

60.
MOST LIKELY THIS IS CAUSED BY AN UNBALANCED DIFFERENTIAL

AMP IN D.C. DETECTION CIRCUIT.
Io
I
-l'

BALANCED

ACTION RANGE ACTION RANOE
BICOMES WIDE BECOMES NARROW

DC VOLTAQE
+ DC VOLTAGE
+

A B

61.
IF THE CIRCUIT IS BALANCED, AS SHOWN, IF FIG. A THEN WE HAVE
A WIDE OPERATING RANGE SO THE UNIT DOES NOT OPERATE UNLESS
IT IS SUPPOSED TO. IF THE CIRCUIT IS UNBALANCED THE OPERATING

RANGE IS NARROW AND ANY INPUT WHATSOEVER WILL ACTIVATE

THE RELAY.
: ->BgcsMg$ 0v
FE RAtr&g

ft*u

62.
THE REMEDY FOR THIS PROBLEM IS SIMPLE. JUST ADJUST VR.l
WITH YOUR METER SET TO CHECK D.C. VOLTAGE BETWEEN PINS

TP.1 AND TP-2. SET VR-l SO YOU HAVE A ZERO VOLTAGE READING.
63.
OUR LAST PROBLEM IS WHEN THE PROTECTION CIRCUIT OPERATES
AFTER THE UNIT HAS BEEN ON AWHILE AND WARSM UP. THIS MAY

BE CAUSED BY TEMPERATURE SENSITIVITY OF SOME COMPONENTS
IN THE PROTECTION UNIT.
Rr

RELAY DRIVE
ctRcutT
Re

Cz
DETECTIVE
R4 SECTION

64.
TO TELL WHICH SIDE HAS THE PROBLEM YOU MUST SEPARATE THE
RELA,Y DRIVE CIRCUIT FROM THE DETECTION CIRCUIT. THE RELAY

ITSELF WILL GIVE YOU A CLUE AS TO WHICH SIDE IS BAD.
cllAl0f ...-ErEcnrE sgnolt D0 mr cilAfleE...naAY

DETECTIVE
SECTION

65.
IF, AFTER YOU DISCONNECT THE TWO CIRCUITS THE RELAY STAYS
THE SAME AS IT WAS BEFORE YOU SEPARATED THE TWO UNITS, THEN

THE RELAY CIRCUIT MAY BE DEFECTIVE. IF THE RELAY RETURNS TO

NORMAL OPERATION THE DETECTTON CIRCUIT IS PROBABLY AT
FAULT.
RELAY DRIVE
ct Rcu tr

66.
MOST TEMPERATURE SENSITIVITY PROBLEMS IN THE RELAY DRIVE

CIRCUIT ARE CAUSED BY O.5 OR D-8 AND D-9.
Rr

DETECTIVE
Cz SECTION

R+

67.
POSSIBLE CAUSES FOR TEMPERATURE SENSITIVITY IN THE

DETECTION CIRCUIT ARE AN UNBALANCING OF THE DIFFERENTIAL

AMPLIFIER CAUSED BY O.3, O-4 OR D-1 THRU D.4.
{
*d

w
4#

68.
AS YOU HAVE JUST SEEN. IT IS IMPORTANT TO NOTICE FAILURE
SYMPTOMS CAREFULLY AND FOLLOW A LOGICAL PROCEDURE TO
REPAIR PROTECTION UNITS.
69.
END MUSIC.
I

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I
1

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