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TICI.II{ICAL OIJIDI FOR $IRI|ICI
TROUBLE SHOOTING METHODS IN
SOLID STATE MAIN AMPLIFIER
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PIONEER'
\/ SERVICE DEPARTMENT INTERNATIONAL DIVISION
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3.
WE ARE GOING TO STUDY HOW TO CHECK THE COMPLEMENTARY
MAIN AMPLIFIER CIRCUITS WITH THE AID OF THIS SLIDE.
4.
THIS IS THE MOST BASIC AND COMMONLY USED COMPLEMENTARY
CIRCUIT.
5.
ON THIS BASIC DIAGRAM, TRANSISTOR 1 IS FOR THE PRIMARY.
STAGE AMPLIFICATION. TRANSISTOR 2IS FOR THE PRE-DRIVING
PURPOSE, TRANSISTORS 3 AND 4 ARE FOR THE DRIVE-STAGE, AND
TRANSISTORS 5 AND 6 ARE FOR THE POWER STAGE.
6.
HERE, WE WILL OMIT FROM OUR STUDIES THE PRIMARY.STAGE
AMPLIFIER SECTION OF TRANSISTOR 1, SINCE IT IS A VERY COMMON
CI RCU IT OF CAPACI TOR-COUPL ED, EM ITTER.GROUND ED TYP E.
7.
TRANSISTORS 3 AND 5 AS WELL AS TRANSISTORS 4 AND 6 ARE OF
DARLINGTON.CONNECTION, SO THAT THEY MAY BE CONSIDERED
AS N.P-N AND P-N-P TRANSISTORS, RESPECTIVELY.
8.
SINCE THERE IS NO DIFFERENCE, AT LEAST THE DC FUNCTION IS
CONCERNED, WHETHER TRANSISTORS 5 AND 6 ARE CONNECTED
OR NOT,LET'S PROCEED WITH OUR SLIDE STUDIES WITH TRANSIS-
TORS 5 AND 6 DISCONNECTED.
9.
NOW LET'S CONSIDER THE DIRECT CURRENT FUNCTION OF THIS
clRcUlT. lF Vcc lS APPLIED, A BlAs VOLTAGE tS GTVEN To TRANSIS-
ToR 3 BY MEANS oF THE RESlsroRS R6 AND Rlo. THEN THE col-
LECTOR CURRENT OF TRANSTSTOR 3, OR tg3, FLOWS, AND A VOLT_
AGE ARISES AT THE CENTER POINT.
10_
A BIAS VOLTAGE IS GIVEN TO TRANSISTOR 2 FROM THE CENTER
POINT THROUGH vRr wHtcH ts FoR REGULATTNG THE CENTER
VOLTAGE. THEN THE COLLECTOR CURRENT FOR TRANSISTOR 2.
oR tcz, STARTS TO FLOW, AND THE COLLECTOR VOLTAGE, OR
vc2, DROPS.
11.
THE COLLECTOR OF TRANSISTOR 2 IS DIRECTLY CONNECTED TO
THE BASE OF TRANSISTOR 4 SO THAT THE BASE VOLTAGE, OR
vB4, oF TRANSTSTOR 4 ALSO DROPS,
12.
SINCE TRANSISTOR 4 IS A P.N-P TYPE, A BIAS VOLTAGE IS IN FACT
GIVEN TO TRANSISTOR 4, AND CURRENT THUS FLOWS TO TRANSIS-
TOR 4.
13.
THE lNsrANT vcc ls APPL|ED, THE VOLTAGE AT THE GENTER porNT
BEcoMES ALMosr AS HlcH As vcc trsELF,BECAUSE A BIAS voLTAGE
IS GIVEN TO TRANSISTOR 3.
14.
BUT AS TRANSISTOR 2 BEGINS TO FUNCTION, AND FURTHER,
TRANSISTOR 4 FUNCTIONS, THE VOLTAGE OF THE CENTER POINT
GRADUALLY DROPS FROM THE VALUE CLOSE TO Vcc.
15.
NOW, LET'S CONSIDER THE CASE WHERE THE CENTER VOLTAGE
HAS DECREASED AND t{AS BECOME LOWER THAN ll2vcc. THE BIAS
VOLTAGE FOR TRANSISTOR 2 BECOMES INSUFFICIENT, BECAUSE OF
THE DIRECT.CURRENT FEEDBACK FROM THE CENTER POINT THROUGH
vRl TO TRANSISTOR 2. THE COLLECTOR CURRENT, lc2, DECREASES
AND THE COLLECTOR VOLTAGE Vcz GETS HIGHER.
16.
FOR THIS REASON, THE BIAS VOLTAGE FOR TRANSISTOR 4 BECOMES
SMALLER, AND THE VOLTAGE DROP BETWEEN THE COLLECTOR AND
THE EMITTER BECOMES LARGER WHICH TENDS TO RAISE THE
CENTER VOLTAGE.
17.
THUS, THE CENTER VOLTAGE CHANGES AS YOU CHANGE THE BIAS
OF TRANSISTOR 2. SO THAT IF THE CENTER VOLTAGE IS SET AT
112 vcc BY ADJUSTING vRl, THEN THE CENTER VOLTAGE cAN AL-
WAYS BE MAINTAINED AT 112 vcc BY MEANS oF THE Dc FEEDBACK.
18.
THE CONDITION UNDER WHICH THE CENTEB VOLTAGE BECOMES
1l2Vcc tS WHEN THE DC CURRENT rN UPPER AND LOWER PORTIONS
IS THE SAME.
IN OTHER WORDS, IT IS WHEN THE INTERNAL BESISTANCE BETWEEN
THE COLLECTOR AND THE EMITTER OF TRANSISTORS 3 AND 4 IS
APPROXIMATELY EOUAL AND WHEN THE BIAS VOLTAGE IS GIVEN IN
SUCH A WAY.
NOW THAT YOU HAVE UNDERSTOOD THE DIRECT CURRENT FUNC-
TION UP TO NOW, LET'S CONSIDER ABOUT THE WAYS OF CHECKING
THE CIRCUIT.
19.
WHEN CHECKING THE COMPLEMENTARY MAIN AMPLIFIER CIRCUIT.
FIRST, MEASURE THE CENTER VOLTAGE, AND THEN, CONSIDER
SEPARATELY THE CASES WHERE IT IS HIGHER THAN THE NORMAL
VALUE OF 112 Vcc AND WHEN lT lS LOWER.
20.
wHEN THE CENTER VOLTAGE tS HtcHER THAN 112Vcc,lT MAy BE
THAT THE VOLTAGE BETWEEN THE COLLECTOR AND THE EMITTER
oF TRANSTSTOR 3, OR Vces, tS LOW, OR, ON THE CONTRARY, tT MAy
BE THAT THE VOLTAGE BETWEEN THE COLLECTOR AND THE EMIT.
TER OF TRANSTSTOR 4, OR Vcea,lS H|GH.
21.
WHEN THE CENTER VOLTAGE tS LOWER THAN 1/2Vcc, tT MAy BE
THAT THE VOLTAGE BETWEEN THE COLLECTOR AND THE EMITTER
oF TRANslsroR 3, oR Vc e 3, ls HIGH, oR lr MAY BE THAT THE voLT-
AGE BETWEEN THE COLLECTOR AND THE EMITTER OF TRANSISTOR
4,OR Vcec, lS LOW.
LET'S HYPOTHESIZE ACTUAL TROUBLE SPOTS AND SEE HOW THE
CENTER VOLTAGE CHANGES ACCORDI NGLY.
22.
LET'S CONSIDER THE CASE WHERE THE COLLECTOR AND THE EMIT.
TER OF TRANSISTOR 2, ARE SHORTED.
23.
WHEN THE COLLECTOR AND THE EMITTER OF TRANSISTOR 2 ARE
SHORTED. THE COLLECTOR VOLTAGE OF TRANSISTOR 2 BECOMES
LOW, THUS THE BIAS VOLTAGE OF TRANSISTOR 4 BECOMES LARGER.
THEN, THE VOLTAGE DROP BETWEEN THE COLLECTOR AND THE EMIT-
TER OF TRANSISTOR 4 GETS SMALLER. THEREFORE, THE CENTER
VOLTAGE ALSO GETS LOWER.
24.
WHAT IF THE COLLECTOR AND THE EMITTER IS OPEN?
WHEN THE COLLECTOR AND THE EMITTER
IS OPEN, THE COLLEC.
TOR VOLTAGE OF TRANSISTOR 2 GETS HIGHER.
AS A RESULT, THE
BIAS FOR TRANSISTOR 4 BECOMES SMALL AND THE VOLTAGE BE-
TWEEN THE COLLECTOR AND THE EMITTER
RISES.
26.
ON THE OTHER HAND, THE BIAS IN TRANSISTOR 3 BECOMES LARGER,
AND THE VOLTAGE BETWEEN THE COLLECTOR AND THE EMITTER
DROPS. AND THE CENTER VOLTAGE BECOMES HIGHER THAN THE
NORMAL VALUE OF 1/2Vcc.
27.
WHAT IF THE COLLECTOR AND THE EMITTER OF TRANSISTOR 3 BE.
COME SHORTED?
28.
WHEN THE COLLECTOR AND THE EMITTER OF TRANSTSTOR
3 BE-
COME SHORTED, THE VOLTAGE BETWEEN THE COLLECTOR AND
THE EMITTER BECOMES ZERO (OV), AND AS CURRENT
FLOWS DIRECT-
LY To rHE CENTER PoINT FROM vcc THRoucH Rl1, THE voLTAGE
AT THE CENTER POINT BECOMES HIGHER. IN THIS CASE. THE
BIAS
FOR TRANS|STOR 4 BECOMES LARGER, CAUSING
AN INCREASE IN THE
COLLECTOR CURRENT, THEREFORE, EVERY CAUTION
IS NECESSARY
TO PREVENT TRANSISTOR 4 FROM BEING DAMAGED.
29.
WHAT IF THE COLLECTOR AND THE EMITTER OF TRANSISTOR 3 IS
OPEN?
30.
IT MAY SEEM THAT WHEN THE COLLECTOR AND THE EMITTER OF
TRANSISTOR 3 IS OPEN, NO VOLTAGE WOULD APPEAR AT THE CENTER
POINT, BECAUSE NO COLLECTOR CURRENT FLOWS TO TRANSISTOR
3 EVEN THOUGH THE BIAS IS GIVEN TO IT.
31.
ACTUALLY, HOWEVER, VOLTAGE APPEARS AT THE CENTER POINT
BY THE BASE CURRENT IN TRANSISTOR 3.
THE BIAS VOLTAGE IS GIVEN TO TRANSISTOR 2,THEN THE CURRENT
FLOWS IN TRANSISTOR 2, AND THE VOLTAGE BETWEEN THE COL-
LECTOR AND THE EMITTER OF TRANSISTOR 4 DROPS. AS A RESULT
THE CENTER VOLTAGE DROPS, TOO.
32.
WHAT IF THE COLLECTOR AND THE EMITTER OF TRANSISTOR 4 ARE
SHORTED?
WHEN THE COLLECTOR AND THE EMITTER ARE SHORTED, THE
VOLTAGE BETWEEN THE COLLECTOR AND THE EMITTER OF TRANSIS.
TOR 4 BECOMES OV AND THE VOLTAGE AT THE CENTER POINT GETS
LOWER.
34.
IT SHOULD BE EMPHASIZED THAT IN THIS CASE, AS THE COLLECTOR
AND THE EMITTER OF TRANSISTOR 4 GET SHORTED THE TRANSISTOR
3 MAY ALSO BE DAMAGED DUE TO INCREASE IN BIAS OF TRANSISTOR 3.
35.
WHEN THE COLLECTOR AND EMITTER OF TRANSISTOR 4 BECOME
OPEN, WHAT WILL HAPPEN?
36.
IN THIS CASE, NO CURRENT FLOWS BETWEEN THE COLLECTOR AND
EMITTER, AND SINCE THE BIAS VOLTAGE IS APPLIED TO TRANSISTOR
3, A HIGH VOLTAGE APPEARS AT THE CENTER POINT.
37.
WHAT WILL HAPPEN WHEN TFIE TEMPERATURE COMPENS,ATING
DIODE IS SHORTED?
38.
WHEN THE DIODE IS SHORTED, THE BIAS VOLTAGE IN THE DRIVE-
STAGE AND POWER.STAGE BECOMES SMALL, CAUSING THE FUNCTION
POTNT SHTFT ONTO THE NON-L|NEAR PORTION OF THE Ve.tc CHARAC-
TERISTIC.
AS A RESULT. THE CROSS-OVER DISTORTION OCCURS.
39.
THEN. WHAT WILL HAPPEN WHEN THE DIODE OR VR2 IS OPEN?
40.
IN THIS CASE. THE COLLECTOR CURRENT OF TRANSISTOR 2 DOES
NOT FLOW, THEREFORE, AS THE BASE VOLTAGE OF TRANSISTOR
3 INCREASES. THE BIAS VOLTAGE OF TRANSISTOR 3 GETS LARGER.
CONSEOUENTLY THE VOLTAGE BETWEEN THE COLLECTOR AND EMIT-
TER BECOMES LOWER, AND THE VOLTAGE AT THE CENTER POINT
BECOMES HTGHER THAN 1l2Vcc.
41.
HOWEVER, SINCE THE BIAS VOLTAGE IS APPLIED TO TRANSISTOR 2,
THE BASE CURRENT OF TRANSISTOR 4 FLOWS INTO THE COLLECTOR
OF TRANSISTOR 2, MAKING THE BIAS VOLTAGE OF TRANSISTOR 4
LARGER. IN THIS CASE, EVERY CAUTION IS NECESSARY, BECAUSE
A LARGE CURRENT FLOWS INTO TRANSISTORS 3 AND 4, CAUSING
THEM TO BREAK DOWN.
42.
WHAT WILL HAPPEN WHEN VRl IS OPEN?
rt3.
lF vRl ts oPEN, tT W|LL NOT ALLOW TO G|VE B|AS VOLTAGE TO
TRANSISTOR 2. THEREFORE, THE COLLECTOR CURRENT OF TRAN.
SISTOR 2 DECREASES, CAUSING THE COLLECTOR VOLTAGE TO IN-
CREASE.
THE BIAS VOLTAGE FOR TRANSISTOR 3 BECOMES LARGER, AND THE
BIAS VOLTAGE FOR TRANSISTOR 4 BECOMES SMALLER, THUS THE
CENTER VOLTAGE BECOMES HtcHER THAN 112Vcc.
4. WHAT WILL HAPPEN WHEN THE RESISTOR R8 IS OPEN?
45.
wHEN THE RESTSTOR R8 tS OPEN, THE B|AS VOLTAGE OF TRANSTSTOR
2 BECOMES LARGER, LOWERING THE COLLECTOR VOLTAGE. AC.
CORDINGLY, THE BIAS VOLTAGE OF TRANSISTOR 3 BECOMES SMAL-
LER, AND THAT OF TRANSISTOR 4 BECOMES LARGER, AND AS A
RESULT, THE CENTER VOLTAGE BECOMES LOWER TH.AN 112 Vcc.
M.
WHAT ABOUT THE CASE WHEN THE RESTSTOR Re tS OPEN?
47.
IN THIS CASE, NO CURRENT FLOWS INTO TRANSISTOR 2, MAKING
ITS COLLECTOR VOLTAGE HIGHER. THE BIAS VOLTAGE OF TRAN-
SISTOR 3 BECOMES LARGER, WHILE THAT OF TRANSISTOR 4 BECOMES
SMALLER, AND AS A RESULT THE CENTER VOLTAGE BECOMES
HTGHER THAN 112Vcc.
48.
WHAT WtLL HAppEN WHEN THE LOAD RESTSTOR RI oOF TRANSTSTOR
2 IS OPEN?
49.
IN THIS CASE, IT MAY SEEM THAT NO VOLTAGE IS PRODUCED AT THE
CENTER POINT SINCE NO BIAS VOLTAGE IS APPLIED TO TRANSISTOR
3. HOWEVER, ACTUALLY, A VOLTAGE IS PRODUCED AT THE CENTER
POTNT BECAUSE OF tsge3, THE COLLECTOR CUT-OFF CURRENT OF
TRANSISTOR 3, WHICH IS THE COLLECTOR-EMITTER CURRENT WHEN
THE BASE IS OPEN.
THEREFORE, TRANSISTORS 2 AND 4 WILL FUNCTION IN SUCH A WAY
THAT IT WILL REDUCE THE CENTER VOLTAGE TO LOWER THAN 1/2
Vc c.
50.
WHAT ABOUT THE CASE WHEN THE RESTSTOR Rl1tS OPEN?
51.
WHEN THE RESISTOR Rl1 lS OPEN lN THIS CIRCUIT WHERE TRANSIS-
TOR 5 IS NOT CONNECTED, THE CENTER VOLTAGE WILL NOT APPEAR.
52.
HOWEVER, IN ACTUAL CIRCUITS, TRANSISTOR 5 IS ALWAYS CON-
NECTED. THEREFOHE, THE EMITTER VOLTAGE OF TRANSISTOR 3
BECOMES THE BASE CURRENT OF TRANSiSTOR 5, MAINTAINING
THE CENTER VOLTAGE AT ll2vcc OF THE NORMAL VALUE.
WHAT WtLL HAppEN WHEN THE RESISTOR Rl2 tS OPEN?
54.
WHEN THE RESTSTOR Rr z tS OPEN, THE EMTTTER CURRENT OF
TRANSISTOR 4 BECOMES ZERO.
SINCE BIAS IS APPLIED TO TRANSISTOR 3, THE CENTER VOLTAGE
BECOMES HIGHER.
55.
IF TRANSISTOR 6 IS CONNECTED IN THIS CIRCUIT, THE COLLECTOR
BASE GURRENT lceeo WHEN THE EMlrrER oF TRANSISTOR 4 ts
OPEN BECOMES THE BASE CURRENT OF TRANSISTOR 6.
HOWEVER, THIS VALUE OF IcEBo IS EXTREMELY SMALL, THERE.
FORE, THIS SERVES AS ALMOST NO BIAS FOR TRANSISTOR 6.
56.
TH|S tcEeo OF TRANSTSTOR 4 CHANGES DEPEND|NG UPON THE
INPUT SIGNAL. ACCORDINGLY, THE BIAS VOLTAGE OF TRANSISTOR
6 ALSO CHANGES, THE CENTER VOLTAGE VARYING FROM HIGH TO
NEAR 1l2Vcc rN ACCORDANCE W|TH THE tNPUT STGNAL STRENGTH.
57.
NEXT, WHAT ABOUT THE CASE WHEN THE RESISTOR Rl3 tS OPEN?
58.
WHEN THE RESTSTOR RI3 tS OPEN AND ALSO tF TRANSTSTOR 6 tS
NOT CONNECTED. THEN THE COLLECTOR CURRENT OF TRANSISTOR
4 BECOMES ZERO. AS A RESULT, THE CENTER VOLTAGE WILL GET
HIGHER.
59.
IF TRANSISTOR 6 IS CONNECTED IN THE CIRCUIT, THE COLLECTOR
CURRENT OF TRANSISTOR 4 BECOMES THE BASE CURRENT OF
TRANSTSTOR 6, MAINTAINING THE CENTER VOLTAGE AT 112 Vcc
OR THE NORMAL VALUE.
60.
WHAT WILL THEN HAPPEN WHEN THE POWER STAGE, TR.ANSISTOR 5
OR 6IS OPEN?
61.
IN THIS CASE, NO ABNORMALITY OCCURS AT LEAST DC-WISE.
THE CENTER VOLTAGE WILL BE KEPT ATA NORMAL VALUE OF 112
Vcc. FRoM THE vlEWPolNT oF Ac, THERE ls No PROBLEM wHEN
THE OUTPUT IS VERY SMALL. HOWEVER, LARGE OUTPUT CANNOT
BE PRODUCED, DUE TO CLIPPING.
62.
WHAT WILL HAPPEN WHEN THE PROTECTTVE RESISTOR Rr+ OR
Rl5 FOR TRANSTSTORS 5 OR 6 BECOMES OPEN?
63.
THERE IS HARDLY ANY PROBLEM AS FAR AS THE DC IS CONCERNED.
BECAUSE THE SITUATION IS THE SAME AS THE CASE WHEN TRAN-
SISTOR 5 OR 6 IS OPEN.
SINCE NO CURRENT FLOWS INTO THE POWER TRANSISTORS, TRAN-
SISTORS 3 AND 4 WILL FUNCTION INSTEAD.
HOWEVER, THEY WILL NOT BE CAPABLE OF PRODUCING LARGE OUT
PUT.
M.
HOW ABOUT THE CASE WHEN POWER TRANSISTOR 5 OR 6 IS SHORT.
ED? WHEN EITHER ONE OF THE POWER TRANSISTORS IS SHORTED,
THE FUSE WILL BLOW IMMEDIATELY, MAKING IT IMPOSSIBLE TO
CHECK THE CONDITION BY MEANS OF VOLTAGE.
65.
IN THIS INSTANCE, REMOVE THE POWER TRANSISTORS AND CHECK
tF THE CENTER VOLTAGE tS SET AT 1l2Vcc.
IF THE VOLTAGE IS NORMAL, THEN INSTALL A NEW POWER TRAN-
SISTOR.
66.
THIS WILL CONCLUDE THE SLIDE STUDY ON HOW TO LOCATE
TROUBLES IN THE TRANSISTOR AMPLIFIER CIRCUIT.
YOU HAVE SO FAR LEARNED HOW TO CHECK THE CAPACITOR-
CONNECTED COMMON-EMITTER TYPE CI RCUIT, DIRECT-COUPLED AM-
PLIFIER CIRCUIT AND THE COMPLEMENTARY MAIN AMPLIFIER CIR.
CUIT.
67.
WE HOPE YOU WILL GET A CORRECT UNDERSTANDING OF THESE
BASIC THEORIES, BECAUSE THEY WILL PROVE U'*Y HELPFUL
'O ''
IN YOUR FURTHER STUDY.
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