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FOREWORD
This manual provides information intended for use by persons who, in accordance with current
regulatory requirements, are qualified to install this equipment. Because installations vary depending
on a particular aircraft, this manual is intended as aguideline. If further information is required,
contact:
BFGoodrich Avionics Systems, Inc.
Attn: Field Service Engineering
5353 52ndStreet, S.E.
Grand Rapids, MI USA 49588-0873
Telephone: (800) 453-0288 or (616) 949-6600
Fax: (616) 977-6898
We welcome your comments concerning this manual. Although every effort has been made to keep
it free of errors, some may occur. When reporting a specific problem, please describe it briefly and
include the manual part number, the paragraph/figureltable number, and the page number. Sendyour
comments to:
BFGoodrich Avionics Systems, Inc.
Atto: Logistics Support
5353 52ndStreet, S.E.
Grand Rapids, MI USA 49588-0873
Telephone: (616) 285-4203
Fax: (616) 977-6898
©Copyright 1999
BFGoodrich Avionics Systems, Inc.
BFGoodrich Avionics Systems, Inc.
Component Maintenance Manual
P/N 501-1075-()
RECORD
ofREVISIONS
Assigned To: Locat on
Rev. Insertion By Rev. Insertion By Rev. Insertion By
No. Date No. Date No. Date
I
Retrin this record in the front of this manual. Upon receipt of arevision, insert the revised pages in this
manaal, enter the revision number, date of insertion and initialson this record of revisions.
Record of Revisions
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Revision A June 30, 1999
BFGoodrich Avionics Systems, Inc.
Component Maintenance Manual
P/N 501-1075-()
ListofManualChanges
Original June 15, 1972
Revision 1 July 1, 1973
Revision 2April 1, 1974
Revision 3 May 1, 1976
Revision 4 January 10, 1983
Revision 5 January 31, 1984
Reissue January l1, 1985
Revision 1 June 1, 1987
Revision 2September 29, 1987
Revision 3 July 15, 1991
Reissue September 30, 1991
Revision A June 30, 1999
NOTE: This manual is a new issue, which has incorporated all previous changes and revisions.
From this time on, BFGAS publications once referred to as "reissues" are now
"Revisions" and what was "revisions" are now called "Changes." Olderdocuments and
manuals still in circulation will manifest this change in practice after their next
"Revision" review. This manual supercedes and replaces all previous copies and
editions.
Listof Manual Changes
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Revision A June 30, 1999
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Component Maintenance Manual
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ListofEffectivePages
Page Effectivity
Title Page and ithrough ix June 30, 1999
lthrough 10 June 30, 1999
101 through 118 June 30, 1999
301 through 304 June 30, 1999
401 through 402 June 30, 1999
501 through 502 June 30, 1999
601 through 606 June 30, 1999
701 through 704 June 30, 1999
801 through 804 June 30, 1999
901 through 902 June 30, 1999
1001 through 1020 June 30, 1999
List of Effective Pages
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Component Maintenance Manual
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TableofContents Page
List of Revisions............................................................................................................................................ i
List of Effective Pages.................................................................................................................................iii
Table of Contents.......................................................................................................................................... v
List of Figures.............................................................................................................................................vii
Introduction ................................................................................................................................................. ix
List of Abbreviations.................................................................................................................................... x
Description and Operation
1. General..................................................................................................................................................................1
2. Purpose Of Manual...............................................................................................................................................l
3. Purpose Of Equipment..........................................................................................................................................l
4. Physical Description..............................................................................................................................................1
5. Functional Description...................................................................................................................,......................2
6. Specifications........................................................................................................................................................2
7. Model Variation....................................................................................................................................................3
8Theory of Operation..............................................................................................................................................5
Testing and Fault Isolation
1. General..............................................................................................................................................................10 1
2. Tools And Test Equipment...............................................................................................................................lO1
3. Emergency Power Supply Test Setup ...............................................................................................................106
4. Performance Test Standards..............................................................................................................................107
5. Battery Pack Test ..............................................................................................................................................108
A. Initial Battery Test Procedure...................................................................................................................... l08
B. Battey Pack Charging Procedure (in unit)..................................................................................................109
C. Batteg Pack and Cell Test Procedure ......................................................................................................... l 10
6. PS-823 Storage..................................................................................................................................................112
7. PS-823A through H Periodic Inspection and Charging.....................................................................................112
8. Emergency Power Supply Calibration ....................................................................................................,.........113
9. Emergency Power Supply Performance Test....................................................................................................113
10. Figures, Schematics and Modification Notes....................................................................................................114
Disassembly
I. General..............................................................................................................................................................301
2. Cover Removal............................................. .... ................. ...... ...................................... ..............................30 1
3. Battery Pack Removal............................... . ....... .......... .. . .. .... ..... ..............................................302
4. Circuit Card Assembly Removal............................................................ . . .... ...........................................303
5. Battery Test Circuit (if present) Removal from Circuit Card Assembly............................ ..............................303
6. Transistor/Heatsink Assembly Removal ............................. .... .. ......... ..... .................................................303
7. Diode Assembly Removal...........,................ ... . .... ..... ... ....... .. .................................................303
8. Fuse Holder Removal............................. . . .. .. .. ..... ......... .... .... ...... ..............................303
9. Chassis Disassembly ............................ ........ ...... .. ....... . ... ..... ... ....................... ..............................303
Cleaning
1. General............................. . . . ... .. . .. ............................401
2. Extemal Cleaning......................... ... ... .. ..... .............................40 1
3. Intemal Cleaning........................... .................................401
Table of Contents
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TableofContents(Cont,)
Checks
1. General............................. ............. .. ........ ...... ................. .... ... . .. .. .... ......................................501
2. Checks Prior to Repair (in aircraft) ............................. ................ .......... . ....... .... ....................................501
3. Check After Repair and During Reassembly ............................. .. .... ............. ... ........................................50 I
4. Inspection After Repair and During Reassembly............................. ...... .... ..... ...........................................502
5. PS-823 Storage........................................................................ .. . ....................................................................502
Repair
1. General..............................................................................................................................................................601
2. Circuit Card Assembly (CCA) Repair...............................................................................................................601
3. Performance Test ........................................................................ .....................................................................602
4. Moisture And Fungus Proofmg.........................................................................................................................602
5. Battery Pack Replacement ................................................................................................................................603
6. Individual Cell Replacement And Battery Pack Repair....................................................................................604
7. Power Supply Reassembly................................................................................................................................606
8. Perfornance Test ..............................................................................................................................................606
Assembly
1. General..............................................................................................................................................................701
2. Chassis Assembly..............................................................................................................................................70l
3. Mounting Fuse Holder ............................................................ ...... ................................................................701
4. Mounting Diode Assembly ...............................................................................................................................702
5. Mounting Transistor/Heatsink Assembly..........................................................................................................702
6. Battery Test Circuit Board Assembly ...............................................................................................................702
7. Circuit Card Assembly......................................................................................................................................702
8. Battery Pack Assembly .....................................................................................................................................702
9. Cover Assembly Replacement ............................................................................ ....... ....................................703
10. Preperation for Use or Storage..........................................................................................................................703
Fits and Clearances
1. General..............................................................................................................................................................80 1
2. Emergency Power Supply Location.................................................................. ...............................................80 1
3. Pre-Installation Inspection.................................................................................................................................80 l
4. Post Installation..................................................................,.............................. ..............................................802
5. Figures and Schematics............................................................. .. ................ .. ..............................................803
Special Tools, Fixtures and Equipment
I. General..............................................................................................................................................................90 1
2. Tools and Test Equipment.............................. ..... ............ ... ..... ........ .... ......................................................90 1
3. Illustrations.............................. .... .. ...... ....... ..... .... ..... ...................................................................902
Illustrated Parts Listing
1. General.................................. .. ................. ...... .. .. ... .. ..... ...... .. ...... . ..........................................,.1001
2. Numerical lndex............................ . ..... ... .. ........ ........ . .... ...... ......... .. ....... .. .... . ........................... l00 l
3. Part Reference Designator lndex....................................... .. ...... ...... ... .... ... ... .. .....................................10 13
4. Detailed Parts List ................................ ..... ............ .................. ................... ... ...........................................10 18
5. How To Use The Detailed Parts List................................ .. ...... ..... . .... .... .... ... .............................1019
6. Figures.............................. ... .... ...... . .. . ............ . . ... .. .. . .... . ...... .. ...........................1021
Table of Contents
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ListofFigures
Figure IllustrationDescription Page
1PS-823 Emergency Power Supply 3
2Emergency Power Supply Models 4
3Model PS-823 and Attitude Indicator Compatibility 4
4PS-823 Block Diagram. 9/10
101 Tools and Test Equipment 10l
102 JT-5 Emergency Power Supply Test Panel.. 102
103 Explanation of Controls, Indicators, and Connectors 102
104 JT-5-lA Test Set Adapter 104
105 Explanation of Test Adapter Controls and Connectors 104
106 PS-823 Basic Test Setup 106
107 Performance Standards 107
108 Batteg Acceptance Values and Discharge Curve 109
109 PS-823 Power Supply Charging 109
110 20-Cell Battery Pack Charging 111
11l Calibration with Test Setup 114
l 12 Performance Test with Test Setup 115
114 Calibration with JT-5 Test Set 124
l 15 Performance Test with JT-5 Test Set 125
116 Test Points and Settings 133
l l7 Waveforms Scope Frames 136
113 PS-823 Test Setup with Attitude Indicator 123
118 Waveform and Testpoint Schematic Diagram 14l/142
119 Batteg Circuit Variation Schematic Diagram l43
120 PS-823A and B Schematic Diagram 145/146
121 PS-823E and F Schematic Diagram 147/l48
122 PS-823C and D Schematic Diagram 149/l50
123 PS-823G and HSchematic Diagram 151-152
124 PS-823A/T and B/T Schematic Diagram 153/154
125 PS-823EIT and F/T Schematic Diagram 155/156
126 PS-823C/T and D/T Schematic Diagram 157/158
127 PS-823G/T and HTTSchematic Diagram 159/160
128 Schematic Diagram Notes for Models A, B, E, F, A\T, B/T, E/T, F/T 161
129 Schematic Diagram Notes for Models C, D, G, H, C\T, D/T, G/T, H/T 163
40l Cleaning Brush 402
List of Figures
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ListofFigures (Cont.)
Figure IllustratlonDescription Page
601 Battery Pack Assembly 604
602 Consumable Materials List 606
801 PS-823 Installation Drawing 803/804
802 AC Powered Attitude Indicator for PS-823A thru D, and A/T thru D/T 805/806
803 DC Powered Attitude Indicator for PS-823A thru D, and A/T thru D/T 807/808
804 AC Powered Attitude Indicator for PS-823E thru H, and E/T thru H/T 809/810
805 DC Powered Attitude Indicator for PS-823E thru H, and E/T thru H/T 811/812
90l Tools and Test Equipment 901
902 JT-5 Emergency Power Supply Test Panel 902
903 Explanation of Controls, Indicators, and Connectors 902
904 JT-5-lA Test Set Adapter 904
905 JT-5-lA Adapter Controls and Connections 906
IPL lPS-823 Emergency Power Supply Exploded View 1021/1022
IPL 2 Circuit Card Assembly 542-1254-01 &-02 1031/1032
IPL 3 Circuit Card Assembly 542-1255-01 &-02 1039/1040
IPL 4Circuit Card Assembly 542-1256-01 &-02 1047/1048
IPL 5Circuit Card Assembly 542-1257-01 &-02 1055/1056
IPL 6 Circuit Card Assembly, Battery Test A2 1063
IPL 7 Transistor/Heatsink Assembly 1066
IPL 8Diode Assembly 1067
List of Figures
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Component Maintenance Manual
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Introduction
This Component Maintenance Manual (CMM) is constructed according to the Specification for
Manufacturers' Technical Data #ATA-100 which dictates format and content. It contains the
information necessary for atrained technician to service the Model PS-823 Emergency Power
Supply manufactured by BFGoodrich Avionics Systems, Inc., 5353 52ndStreet SE, Grand Rapids,
Michigan 49588-0873.
Use this manual as acomprehensive resource for repair and acquisition of replacement parts.
The arrangement of material is by sections, numbered in amanner that provides visual cues for
locating information. The manual is sectionalized, tabbed and paginated as follows:
Roman Numerals General Information (Front Matter)
1-99 Description and Operation
101-199 Testing and Fault Isolation
301-399 Disassembly
401-499 Cleaning
501-499 Checks
601-699 Repair
701-799 Assembly
801-899 Fits and Clearances
901-999 Special Tools, Fixtures and Equipment
1001-1099 Illustrated Parts Listing
Illustrations are number assigned to correspond to the sections which they reside.
SB501-1075-1 SB501-1075-2
SB501-1075-3 SB501-1075-4
SB501-1075-5 SB501-1075-6
SB501-1075-7 SB501-1075-8
SB50l-1075-9 SB501-1075-10
SB501-1075-11 SB501-1075-12
SB501-1075-13 SB501-1075-14
SB501-1075-15 SB501-1075-16
SB501-1075-17 SBS01-l075-l8
SB501-1075-19 SB501-1075-20
SB501-1075-21 SB501-1075-22
SB501-1075-23 SB501-1075-24
SB501-1075-25 SB501-1075-26
SB501-1075-27 SB501-1075-28
Record of Applicable Service Bulletins incorporated in this manual.
Introduction
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ListofAbbreviations
Symbolor Definition Symbolor Definition
Abbreviation Abbreviation
AAmps or Assembly pPlug (Male pin or female
socket)
AC or ac Alternating Current
AH or Ah Amp-hours PH Pan Head
AP Attaching Parts P-P or PP Peak topeak
A/R or AR As required 9Transistor
BMotor RResistor
. . REF or RF Reference
BFGoodrich Aviomcs
BFGAS Systems, Inc. RMS Root mean square
°C Degrees Celsius SSwitch
CCapacitor SEL Selected component
CB Circuit Breaker TTransformer
CCA Circuit Card Assembly TP Test Point
CR Diode (Crystal Rectifier) uF Microfarad
DC or de Direct Current VVolt (AC or DC)
DS Indicator Lamp VR Voltage Regulator (Zener
diode)
ESubassembly termination
other than aconnector. WWatts
°F Degrees Fahrenheit
FFuse
FH Flat Head
HHenry
Hd Head
Hz Hertz
Jack (Male pin or female
socket)
Kilohms (Ohms times
K1,000)
LInductor
mA Milliamps (AC or DC)
mV Milivolt (AC or DC)
Megohm (Ohms times
Meg 1,000,000)
NHA Next Higher Assembly
In-phase, or phase
OOut-of-phase, or anti-phase
Introduction
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DescriptionandOperation
1. General
The PS-823 Emergency Power Supply provides 28.0Vdc and 115.0Vac 3-phase power for DC or
AC Standby Attitude Indicators.
2. Purpose Of Manual
This manual contains operation instructions, maintenance instructions and parts support information
for the Model PS-823 Emergency Power Supply (Figure 1).
3. Purpose Of Equipment
The Model PS-823 operates from internal nickel-cadmium batteries or aircraft 28Vdc power. The
outputs are l l5.0Vac, 400 Hz, 3-phase at 100VA (capacitor-shifted power for third phase); 26.0Vac,
1-phase; and 4.5Vac, 1-phase. All output power is inthe form of asquare wave that is filtered to
meet RFI requirements. The power supply provides network shifted-phase power for a controlled
time to start 3-phase gyro motors such as Model AI-804 Standby Attitude Indicator. Abattery
charging circuit provides astepped-up charge rate whenever the PS-823 inverter isturned ON. The
inverter will provide power output from internal battery with voltages between 22.0Vdc and
27.0Vdc. Using fully charged batteries, the Emergency Power Supply will drive the respective
indicator for the following specified time:
Model Indicator *Time(Hr)
PS823A & E 2inch(3 inch) 2.1 (1.0)
PS823ATI' &E/T 2inch (3 inch) 2.1 (1.0)
PS823B &F2inch (3 inch) 4.2 (2.0)
PS823B/T &F/T 2 inch (3 inch) 4.2 (2.0)
PS823C &G3inch 1.0
PS823C/T &G/T 3 inch 1.0
PS823D &H3inch 2.0
PS823D/T &H/T 3 inch 2.0
*Derate time 1percent/degree centigrade for ambients above or below 25 degrees C.
4. Physical Description
The Model PS-823A, C, Eand G contain sealed nickel-cadmium batteries having a rating of 1.9
Ampere-hours (Ah), while the PS-823B,D,F and H contain sealed nickel-cadmium batteries having a
rating of 3.8Ah.
The Model PS-823 consists of a chassis, two circuit card assemblies (CCAs) and associated
hardware, interconnecting wire, and electronic components. High power transistors are mounted
flush on heat sinks and CCAs are mounted directly behind the heat sinks. Connector pins pass
through the printed-circuit board assembly before being soldered directly to the circuit card.
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5. Functional Description
Model PS-823 Emergency Power Supply consists of an adjustable oscillator that drives four power
transistors in an H-bridge configuration. The current flow between them passes through a
transformer that develops a square wave signal. Part of the output is stepped-down and rectified to
provide charging current to internal batteries. Atiming circuit maintains added shifted-phase
voltage for starting 3-phase gyro motors. The inverter within Model PS-823 will not operate if both
the aircraft and internal battery voltage are below 20.0Vdc. Normal input voltage to the inverteris
between 22.0 to 32.0Vde; from the aircraft DC bus or the Model PS-823 internal batteries.
The PS-823E, F, G and Hmodels have some internal rewiring and removal of the 5Amp fuse and
fuseholder to accommodate revision of the manual emergency bypass circuits to comply with FAA
requirements.
6. Specifications
Weight: PS-823A/C/E/G, 7.6 pounds*
PS-823B/D/F/H, 11.2 pounds*
*(Add 0.4 pounds for /T units)
Dimensions (Includinghandle)
(Inches) 2.4W x 7.62H x 14.llL
(cm) 6.2W x 19.4 x 36L
Rack Size: 1/4 ATR Short. Rack No. 404-.25-S-1/DPXB-0
Input: 28.0Vde nominal (4.6 Amperes per 100VA output). Normal operating range 22.0-
32.0Vde
Output: 115.0Vac +7%, -10% for maximum load of 100Va.
26.0Vac +7%, -10% for maximum loadof 20Va
4.6Vac +7%, -10% for maximum load of 10Va
Additional 5% tolerance, 26 and 32Vde inputs
24Vde minimum with fully charged batteries and inverter operating
Frequency: 400 ±8Hz for 20.0-32.0Vde input
Waveshape: Square wave
Efficiency 75% at full rated load
Temperature: -30 to +55 degrees C(Batteg only)
-55 to +71 degrees C(Inverter)
Humidity: 0 to 95%
Batteg Charger: Automatic as long as inverter operates
35mA from aircraft 28.0Vde
145mA from inverter
RFI: Intemal suppression on output and 28.0Vde line.
Meets Cat. A of TSO-C73 and Cat. A/Z of DO-138.
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7. Model Variation
Model PS-823 is available in eight models. See Figures 2 and 3.
Note: 5amp fuse and fuse
holder are removed on the
PS-823E-H and E/T-H/T
PS-823 501-1075-xx PS-823 501-1075-xx
A-01 E-09
B-02 F-10
C-03 G-11
D-04 H-12
A/T -05 E/T -l3
B/T -06 F/T -14
CIT -07 G/T -15
D/T -08 H/T -l6
PS-823 Emergency Power Supply
Figure 1
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Number
PS-823
Model NI-CAD AmpereHours(Ah) BatteryTest Application
Cells
Aand E 20 1.9 No Drive 2-inch Al-804 or 3- inch Al-904 JET
indicators.
A/T and E/T 20 1.9 Yes
Band F40 3.8 No Drive 2-inch Al-804 or 3- inch Al-904 JET
indicators.
B/T and F/T 40 3.8 Yes
Cand G20 1.9 No Drive 3-inch3- phase JETor SFENA
indicators
C/T and G/T 20 1.9 Yes
D and H40 3.8 No Drive 3-inch3- phase JET or SFENA
indicators
D/T and H/T 40 3.8 Yes
Emergency Power Supply Models
Figure 2
PS-823
Model J.E.T. SFENA A.I.M. 28.0Vdc
Aand EAl-804 705 500ECF YES
A/T and E/T (30, 2") (lØ, 3") (10, 3")
Band FAl-904
B/T and F/T (10, 3")
Cand GAl-904 705
C/T and G/T (30, 3") (30, 3") (30, 3")
D and H
D/T and H/T
Compatible Indicators and Manufacturers
Figure 3
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1. Theory Of Operation
A. General
This section provides ageneral theory of operation for Model PS-823 Emergency Power
Supply. Ablock diagram (Figure 4) is included to support the text. For detailed circuit
descriptions refer to schematic diagrams in the Testing and Fault Isolation section.
B. Power Input
Aircraft 28.0Vde is connected to the emergency power bus through diode A2CRl8. Diode
A2CR18 isolates the internal batteries in case of a short circuit on the aircraft main DC bus. If
aircraft power is lost, the emergency switch is placed in emergency position.
C. Oscillator
Application of 28.0Vde to connector pin 13 activates a voltage divider consisting of resistors
AlR12, AlR13 and zener diode AlCR8. Transistor AlQ5is avoltage regulator that holdsthe
DC voltage on the oscillator at 16 volts. Current flow through capacitor AlCl and resistors
AlR1 and AlR2 is gradually decreased as capacitor AlCl charges. The junctionof capacitor
AlCl and resistor AlR1 reaches a point where transistor AlQl will fire. Current flow through
thejunctiondischarges capacitor A1Cl and develops anegative spike on transistor AlQ2base.
Transistor AlQ2conducts for the duration of the spike and develops apositive pulse at
capacitor AlC2 and diodes AlCR5 and AlCR7.
The switching portion ofthe oscillator consists of transistors AlQ3and AlQ4. The
unijunction transistor AlQl fires at 800 pulses per second. Each spike determines the startof a
half-cycle of square-wave on transformer Tl. An 800pps spike frequency then produces a
400Hz square-wave on transformer Tl to drive the output transistors.
To understand the operations of the free-running oscillator consider one cycle without the
application of pulses. When power is initially applied, the natural unbalance of the components
starts either transistors AlQ3or AlQ4conducting. (The example will start with AlQ3
conducting). The initial current flow is through diode AlCR3, transistor AlQ3and halfof
transformer Tl to ground. Transformer Tl saturates immediately and terminal P3 becomes
+16Vdc. As current continues to increase, transformer action causes the opposite halfof
transformer Tl to become -16.0Vde at terminal Pl, which turns AlQ3ON. When current can
no longer continue to increase, transformer Tl no longer presents ahigh reactance and terminal
P3 becomes more negative. The magnetic field of transformer T1 then collapses and reverses
the voltages on its two halves. Terminal Pl becomes +16.0Vde and terminal P3 becomes -16.0
Vdc. The positive voltage from terminal Pl shuts OFF AlQ3and the negative voltage onP3
turns transistor AlQ4ON. As current through transistor AlQ4increases, the same sequence
occurs as described above. This is the second half-cycle and the polarities ontransformer Tl
are opposite those of the first half-cycle. The time duration of each half-cycle is determined by
transformer Tl.
To operate at 400Hz, the oscillator functions as described above, except that the time duration
for each half-cycle is determined by the frequency ofthe spikes from transistor AlQ2.A
positive spike applied to both bases of transistors AlQ3and AlQ4will turn the conducting
transistor OFF. This triggers the same events described above on each half-cycle. The result is
a400Hz square wave on transformer Tl.
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D. Power Regulation And Output
The 28Vdc applied to connector pin 13 is divided by the network consisting of resistors AlR12
and AlR13, and zener diode AlCR8. Transistor AlQ6will conduct as longas the iriput
voltage to pin 13 exceeds 20Vdc. Transistor AlQ6completes the path for current flow through
zener diode AlCR10, diode AlCR11 and resistor AlR15. This biases transistor A1Q7to an
ON condition that, in turn, completes current paths for transistor A1Q8.
The DC voltage at transistor A1Q9collector must reach 16 VDC before regulation begins. No
voltage appears on transistor AlQ11and AlQl3 collectors until transistor AlQ9is turnedON.
When input voltage exceeds 16Vde, zener diode CR9 passes current to transistor A1Q9.The
voltage appears on transistor AlQ9emitter and divides across resistors AlR16, AlR17 and
AlRl8. The arm of resistor A1R17 connects transistor A1Q7base to the voltage divider and
AlQ7conducts. Transistor A1Q7turns transistor AlQ8ON. Transistor AlQ9now conducts
and the DC line voltage is applied to the output transistors AlQll and AlQ13. The voltage on
transistor AlQ9emitter is adjusted by resistor AlR17 to remain at23.5Vdc. Changes in load
or aircraft bus voltage change the conduction of transistor A1Q9to compensate.
The square wave developed across transformer T1 (described in paragraph 2) is applied to the
bases of transistors A1Ql0,A1Q11,
A1Ql2and AlQl3. The polarity is suchthat transistors
Q10and Ql3conduct simultaneously on one half-cycle and transistors AlQll and AlQl2 on
the other half-cycle. Current flow on each half-cycle will cause avoltage dropacross
transformer T2. Terminal T2-1 is positive when transistors AlQ11and AlQ12conduct, and
terminal T2-2 is positive when transistors A1Ql0and A1Q13conduct. The secondary of
transformer T2 provides the ll5Vac, 26Vac and 4.5Vac outputs to the connector.
E. Start/Run Power
Added shifted phase voltage is provided by atime delay circuit consisting of transistors
AlQ14,AlQl5,AlQl6 and AlQl7. When DC voltage is applied, current flow begins through
capacitor A1C8 and resistors AlR23, A1R24 and AlR38. As capacitor AlC8 charges, current
flow decreases and transistor Q14base becomes more negative. As transistor AlQ14base
becomes negative it will conduct and connect transistor AlQ15base to a more negative
voltage. Transistor AlQl5 begins to divert the current through transistor AlQ16.Transistor
AlQl6 collector becomes more negative until transistor AlQl7 gate is no longerpositive
enough to conduct. This removes capacitor A1C9 from the circuit and the shifted-phase
voltage is reduced.
F. Battery Isolation And Charging
The voltage divider described in paragraph 3biases transistor AlQ6to an ONcondition. The
battery charging potential through A2CRl 6and A2CR17 applied by A2R33 and A2R34 tobias
A2Ql9and A2Q20OFF. As long as aircraft 28.0Vdc is applied to connector pin 10,
transistors A2Q18
and A2Q20
are OFF and the batteries are isolated from the emergency bus,
pin 11. If aircraft 28Vdc is interrupted, transistors A2Ql8and A2Q20
will connect the internal
batteries to the emergency bus. A2CR24 and A2CR25 provide battery isolation.
Battery charging results from tapping and rectifying part of the output voltage. Transformer
T2, terminals 8 and 10, and diodes A2CR16 and A2CRl7 provide approximately 40Vdc while
the inverter is operating. The charging current is approximately 145mA fromthe inverter
charger and 45 mA from the external 28Vdc. The external path through A2CR22 allows a
trickle charge although the inverter may be OFF, as is often the case during periodic inspection.
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BFGoodrich Avionics Systems, Inc.
Component Maintenance Manual
P/N 501-1075-()
G. Battery Test Circuit (if present)
The Battery Test Circuit is present on unit models designated _/T. The assembly level
designation is A3 as indicated in Figure 4of this section, the schematics for /T models inthe
Fault Isolation section and IPL Figure 6 in the Illustrated Parts List section.
CAUTION: IMPROPEROPERATIONOFTHETESTCIRCUITCANDAMAGETHEUNIT
ANDMAKE
THE
TESTINDICATOR
USELESS.DONOTATTEMPTTHETESTAGAINFOR2TO3 MINUTES.
SEETHECHECKSSECTION
OFTHISMANUALFORPROPEROPERATION.
The battery test circuit operation is initiated by depressing the test button, typically mounted in
the cockpit. When the test button is depressed, 28Vdc is applied to relay A3Kl and to the
bases of transistors A3Q3and A3Q4biases the 400Hz oscillator OFF during the battery test.
Relay A3Kl is energized when the 28Vde applied through resistor A3R1 biases transistor
A3Q1ON completing a current path from power ground through diode A3CR2, transistor
A3Q1,and relay winding A3Kl to the test switch and 28Vdc. Relay A3Kl contacts 3and4
open disconnecting the 28Vde input from pin J1-10. Contacts 7and 8close completing a
current path from the emitter of transistor A3Q5through relay A3K lto power ground. When
ground is connected to transistor A3Q5,
a resistive load made up of resistor A3R6 and A3R7 is
simultaneously connected between the battery output and power ground. Current flow through
resistors A3R7 and A3R8 develops apositive voltage at the junctionof capacitor A3C2 and
zener diode A3CR5. Capacitor A3C2 charges to acalibrated voltage representative of the
battery output voltage. If the battery voltage is within calibrated limits, zener diode A3CR5
will apply apositive voltage to the base of transistor A3Q4.The conduction of transistor A3Q4
causes apositive voltage drop across resistor A3R10 that in turn biases transistor A3Q5on.
Electron current flow is from power ground through relay A3Kl, contacts 7and 8, through
transistor A3Q5,and diode A3CR6 to the test lamp. The test lamp, mounted near the test
button, will illuminate indicating that the battery output voltage is acceptable.
When the positive voltage on capacitor A3Cl reaches a sufficient level, zener diode A3CR3
applies the voltage to the base of transistor A3Q3biasing the transistor ON. Current flow
through resistor A3R2 develops apositive voltage on the base of transistor A3Ql. The positive
voltage on the base of transistor A3Qlwill bias the transistor OFF. Current flow through
transistor A3Qland the winding of relay A3Kl will be zero. Relay A3Kl will de-energize
disconnecting the resistive load from the battery and reconnecting the 28Vdc input at pin Jl-10.
Note that relay A3Kl is automatically de-energized after approximately 4seconds after the
beginning of the test in this paragraph. However, the 400Hz oscillator will be biased OFF as
long as the test switch is ON. To recycle the battery test circuit, it is necessary to momentarily
open the test switch so that capacitor A3Cl can discharge sufficiently to tum transistors A3Q3
and A3Q2OFF.
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