Tait T889 User manual

M889-00 1
Copyright TEL 02/10/95
T889 Power Amplifier
UHF FM 800-870MHz
Issue 100 October 1995
M889-00-100

2M889-00
02/10/95 Copyright TEL
Head Office
New Zealand
Tait Electronics Ltd
558 Wairakei Road
P.O. Box 1645
Christchurch
New Zealand
Phone: [phone]
Fax: [phone]
Australia
Tait Electronics (Aust) Pty Ltd
275 Toombul Road
Northgate 4013
P.O. Box 679
Virginia
Queensland 4014
Australia
Phone: [phone]
Toll Free: 1800 077-112
Fax: [phone]
Canada
Tait Mobile Radio Inc.
Unit 5, 158 Anderson Avenue
Markham
Ontario L6E1A9
Canada
Phone: [phone]
Toll Free: 1 800 890-8248
Fax: [phone]
France
Tait France Sarl
2 Avenue de la Cristallerie
92 316 Sèvres, Cedex
France
Phone: [phone]
Fax: [phone]
Germany
Tait Mobilfunk GmbH
Willstätterstraße 50
D-90449 Nürnberg 60
Germany
Phone: [phone]
Fax: [phone]
New Zealand
Tait Communications Ltd
Unit 4, 75 Blenheim Road
P.O. Box 1185
Christchurch
Phone: [phone]
Fax: [phone]
Singapore
Tait Electronics (Far East) Pte Ltd
4 Leng Kee Road
SIS Building #05-11A
Singapore 159088
Phone: [phone]
Fax: [phone]
United Kingdom
Tait Mobile Radio Ltd
Ermine Business Park
Ermine Road
Huntingdon
Cambridgeshire PE18 6YA
United Kingdom
Phone: [phone]
Fax: [phone]
USA
Tait Electronics (USA) Inc.
9434 Old Katy Road
Suite 110
Houston
Texas 77055
USA
Phone: [phone]
Toll Free: 1 800 222-1255
Fax: [phone]

M889-00 3
Copyright TEL 02/10/95
About This Manual
Scope This manual contains general, technical and servicing informa-
tion on the T889 Power Amplifier.
Revision Control Each page in this manual has a date of issue. This is to comply
with various Quality Standards, but will also serve to identify
which pages have been updated and when. Each page and its
publication date is listed in the “List of Effective Pages”.
Any portion of text that has been changed is marked by a verti-
cal line (as shown at left) in the outer margin of the page. Where
the removal of an entire paragraph means there is no text left to
mark, an arrow (as shown at left) will appear in the outer mar-
gin. The number beside the arrow will indicate how many para-
graphs have been deleted.
The manual issue and revision status are indicated by the last
three digits of the manual IPN. These digits start at 100 and will
increment through 200, 300, etc., as the manual is updated and
republished, e.g:
The last two digits are used for manuals published in an updata-
ble ring binder format and do not apply to this manual.
PCB Information PCB information is provided for all current issue PCBs, as well
as all previous issue PCBs manufactured in production quanti-
ties, and is grouped according to PCB. Thus, you will find the
parts list, grid reference index (if necessary), PCB layouts and
circuit diagram(s) for each individual PCB grouped together.
Errors If you find an error in this manual, or have a suggestion on how
it might be improved, please do not hesitate to contact the Tech-
nical Writer, Radio Infrastructure Division, Tait Electronics Ltd,
P.O. Box 1645, Christchurch, New Zealand.
Technical Information
Any enquiries regarding this manual or the equipment it describes should be addressed
in the first instance to your nearest approved Tait Dealer or Service Centre. Further
technical assistance may be obtained from the Customer Support Group, Radio Infra-
structure Division, Tait Electronics Ltd, Christchurch, New Zealand.
Updating Equipment And Manuals
In the interests of improving performance, reliability or servicing, Tait Electronics Ltd
reserve the right to update their equipment and/or manuals without prior notice.
2
1 0 0
issue status revision status

4M889-00
02/10/95 Copyright TEL
Copyright
All information contained in this manual is the property of Tait Electronics Ltd. All
rights are reserved. This manual may not, in whole or part, be copied, photocopied,
reproduced, translated stored or reduced to any electronic medium or machine readable
form without prior written permission from Tait Electronics Ltd.
Ordering Tait Service Manuals
Service Manuals should be ordered from your nearest Tait Branch or approved Dealer.
When ordering, quote the Tait Internal Part Number (IPN) and, where applicable, the
version.
Date Of Issue
IPN M889-00-100 T889 Power Amplifier Service Manual
Issue 100 published October 1995

M889-00 5
Copyright TEL 02/10/95
Table Of Contents
This manual is divided into seven Sections as listed below. There is a detailed table of
contents at the start of each Section.
Section Title
1 General Information
2 Circuit Operation
3 Introduction To Servicing
4 Initial Tuning & Adjustment
5 Fault Finding
6 Installation
7 PCB Information

6M889-00
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The total number of pages in this Manual is 64, as listed below.
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M889-00 General Information 1.1
Copyright TEL 02/10/95
1 General Information
This section provides a brief description of the T889 PA, along with detailed specifica-
tions and a list of variants available.
The following topics are covered in this section.
Section Title Page
1.1 Introduction 1.3
1.2
1.2.1
1.2.2
Specifications
Introduction
General
1.4
1.4
1.4
1.3 Versions 1.6

1.2 General Information M889-00
02/10/95 Copyright TEL

M889-00 General Information 1.3
Copyright TEL 02/10/95
1.1 Introduction
The T889 is an FM base station power amplifier designed for single or multichannel
operation within the frequency range 800 to 870MHz. The output power capability is 20
to 100W.
The PA comprises a broad band, two stage drive amplifier whose output is split to drive
four separate output stages. The outputs from these final stages are then recombined
and filtered before being fed to the output socket. This type of balanced output stage
offers two advantages over single ended types:
- improved intermodulation performance in the presence of high signal levels
from adjacent transmitters;
- enhanced reliability: if one of the four output stages fails, the transmitter can
still produce half its rated power.
VSWR and thermal protection is incorporated into the basic design, while monitoring
and alarm signals are available for both forward and reverse power. The output power
is adjustable from the front panel.
The main PCB is mounted directly on a die-cast chassis/heatsink. For long-term relia-
bility, four high quality, low loss Teflon PCBs are sweated to the main PCB in areas of
high RF current. Extensive use is also made of the latest surface mount technology.
Forced air cooling for the heatsink is provided on the T889 by a fan, which is activated
whenever the transmitter is keyed. Thermal sensors will also activate the fan automati-
cally if the internal temperature reaches an unacceptable level.
The T889 has a width of 120mm, occupying a double module in a Tait rack shelf
(T99-770) which will accommodate up to seven standard modules to give an attractive
and convenient installation.

1.4 General Information M889-00
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1.2 Specifications
1.2.1 Introduction
The performance figures given are minimum figures, unless otherwise indicated, for
equipment tuned with the maximum switching band and operating at standard room
temperature (+22°C to +28°C).
Where applicable, the test methods used to obtain the following performance figures are
those described in the EIA specification. However, there are several parameters for
which performance according to the CEPT specification is given.
Details of test methods and the conditions which apply for Type Approval testing in all
countries can be obtained from Tait Electronics Ltd.
1.2.2 General
Power Output:
Rated Power .. 90W
Range Of Adjustment .. 20 to 100W (typical)
Duty Cycle Rating: .. 90W continuous to +60°C
Intermodulation .. -70dBc or -40dBi1with 25dB isolation
(PA with output isolator) & interfering signal of -30dBc
Mismatch Capability:
Ruggedness .. infinite VSWR
Stability .. 5:1 VSWR (all phase angles)
Supply Voltage:
Operating Voltage .. 10.8 to 16V DC
Standard Test Voltage .. 13.8V DC
Polarity .. negative earth only
Polarity Protection .. diode
Supply Current:
Standby .. 50mA
Transmit .. 27A (20A typical @ 850MHz)
1. dBi denotes the level of the intermodulation product relative to the interfering signal.

M889-00 General Information 1.5
Copyright TEL 02/10/95
Spurious Emissions:
Conducted - Transmit .. -36dBm to 1GHz
-30dBm to 4GHz
- Standby .. -57dBm to 1GHz
-47dBm to 4GHz
Radiated - Transmit .. -36dBm to 1GHz
-30dBm to 4GHz
- Standby .. -57dBm to 1GHz
-47dBm to 4GHz
Dimensions:
Height .. 191mm
Width .. 120mm
Length .. 340mm
Weight: .. 3.5kg

1.6 General Information M889-00
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1.3 Versions
Description Version
10
800-870MHz

M889-00 Circuit Operation 2.1
Copyright TEL 02/10/95
2 Circuit Operation
This section provides a basic description of the circuit operation of the T889 PA.
The following topics are covered in this section.
Section Title Page
2.1 Introduction 2.3
2.2 RF Circuitry 2.3
2.3
2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
2.3.6
Control Circuitry
Power Control
Driver Power Level
Thermal Protection
Forward And Reverse Power Alarms
Forward And Reverse Power Metering
Fan Control Circuitry
2.4
2.5
2.5
2.5
2.5
2.6
2.6
Figure Title Page
2.1
2.2
2.3
High Level Block Diagram
Control Circuitry Block Diagram
Fan Control Logic Diagram
2.3
2.4
2.6

2.2 Circuit Operation M889-00
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M889-00 Circuit Operation 2.3
Copyright TEL 02/10/95
2.1 Introduction
Figure 2.1 High Level Block Diagram
The T889 comprises a three stage RF power amplifier with extensive control circuitry.
The final stage is composed of four transistors (Q3, Q4, Q5 & Q6) whose outputs are
combined to provide the rated output power.
The configuration of each of the main circuit blocks may be seen on a functional level in
Figure 2.1.
2.2 RF Circuitry
The driver stage of the T889 consists of a two stage transistor amplifier (Q1, Q2) which
delivers a minimum of 40W. This signal is split via three 3dB couplers (L13, L14 & L15)
and used to drive the four final amplifiers (Q3, Q4, Q5 & Q6). These outputs are recom-
bined by L40, L41 & L42 and passed to the antenna socket via the directional coupler
and low pass filter.
The directional coupler senses forward and reflected power, which is rectified (D1, D2)
and passed to the control circuitry for metering, alarm and power control purposes.
Power control is via a series pass transistor (Q16), which controls the supply voltage on
the collector of the driver transistor (Q1).
RF Out
Q1 Q2
Pad
RF In LPF
4W 40W
Q3
Q4
Q5
Q6
30W
30W
30W
30W
60W
60W
120W 100W
Power
Control Vsupply
Q16
L40L13
L15 L42
L14 L41
Directional
Coupler

2.4 Circuit Operation M889-00
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2.3 Control Circuitry
Figure 2.2 Control Circuitry Block Diagram
REF

M889-00 Circuit Operation 2.5
Copyright TEL 02/10/95
2.3.1 Power Control
The DC voltages from the directional coupler representing forward and reflected power
are buffered by the two voltage followers, IC3 pins 1, 2 & 3 and pins 5, 6 & 7. Their out-
puts are summed at an integrator (IC1 pins 8, 9 & 10), which drives the series pass con-
trol element (Q16).
Forward and reflected power are summed so that, under high output VSWR, the power
control turns the PA down. This is because the control loop adjusts for the same DC
voltage from the directional coupler that would have been present if there were no
reflected power.
2.3.2 Driver Power Level
The maximum output power of the T889 can be limited by placing a ceiling on the
driver output power level using RV69 (accessible through the side cover). For example,
if RV69 is set for a maximum output power of 50W, the range of adjustment using RV63
(front panel power adjust) will be 20 to 50W.
2.3.3 Thermal Protection
At excessively high temperatures, the output power will automatically reduce to a pre-
set level (set by RV74), thus preventing the PA from overheating.
A thermistor controlled voltage divider (R68, R72) applies a voltage to a comparator
with hysteresis (IC1 pins 12, 13 & 14).
The output current from the comparator is summed into the power control network via
RV74 so that the power level to which the PA must turn down may be set.
2.3.4 Forward And Reverse Power Alarms
If forward power drops below, or reverse power rises above, presettable limits, alarms
may be triggered.
The alarm outputs are open drain configuration and are low under normal conditions
(i.e. forward and reverse power levels are normal).
IC1 pins 1, 2 & 3 and pins 5, 6 & 7 form comparators with thresholds adjusted via RV48
and RV52 respectively. The inputs are from the forward and reverse power signals from
the directional coupler, buffered by IC3 pins 1, 2 & 3 and pins 5, 6 & 7. Thus, the power
levels at which the forward and reverse power alarms are triggered are defined by RV48
and RV52 respectively.

2.6 Circuit Operation M889-00
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2.3.5 Forward And Reverse Power Metering
Forward and reverse power signals from the two IC3 buffers are available for metering
purposes. The output currents are adjustable via RV43 (forward power) and RV57
(reverse power).
2.3.6 Fan Control Circuitry
Figure 2.3 Fan Control Logic Diagram
Comparator IC3 pins 8, 9 & 10 are set to trigger at heatsink temperatures greater than
+70°C, and pins 12, 13 & 14 at temperatures greater than -10°C.
A logic AND function is applied to the comparator outputs by Q20 and Q21, thereby
turning on the fan unconditionally (via Q17 and Q18) if the heatsink temperature
exceeds +70°C.
A logic OR function is applied to comparator IC3 pins 8, 9 & 10 and Tx KEY signals,
thereby turning on the fan when the transmitter is keyed and the temperature is
between -10°C and +70°C.
If the temperature drops below -10°C, Q21 is turned off, preventing either Q19 or Q20
from activating the fan.
Q17 Q18 Fan
Ref
+
High Temp.
Sense
Comparator
IC3C
R72
Ref
+
Low Temp.
Sense
Comparator
IC3D
R116
NTC
NTC
Tx Key
Invert
Q19 OR
Q20,
R106, R107
NAND
Q20, Q21,
R119, R120 Fan Driver
13.8V
Filtered

M889-00 Introduction To Servicing 3.1
Copyright TEL 02/10/95
3 Introduction To Servicing
This section provides some general and advisory information on servicing procedures.
The following topics are covered in this section.
Section Title Page
3.1
3.1.1
3.1.2
3.1.3
General
Caution: CMOS Devices
Caution: Aerial Load
Caution: Beryllium Oxide & Power Transistors
3.3
3.3
3.3
3.4
3.2
3.2.1
3.2.2
3.2.3
3.2.4
Mechanical
Pozidriv Recess Head Screws
UNC Thread Screws
Screw Torques
Disassembly/Reassembly
3.5
3.5
3.5
3.5
3.5
3.3
3.3.1
3.3.1.1
3.3.1.2
3.3.2
Component Replacement
Leaded Components
Desoldering Iron Method
Component Cutting Method
Surface Mount Devices
3.6
3.6
3.6
3.6
3.7
3.4
3.4.1
3.4.1.1
3.4.1.2
3.4.2
To Replace PA Transistors
Capacitor /Transistor Spacing
Q1 (2SC2933 Pre-Driver)
Q2, Q3, Q4, Q5 & Q6 (SD1414)
Replacement Procedure
3.8
3.8
3.8
3.8
3.8
3.5 To Remove The PCB From The Heatsink 3.10
3.6 To Remove Cased Mica Capacitors 3.10
Figure Title Page
3.1 Typical Anti-static Bench Set-up 3.3
3.2 Typical Transistor/Capacitor Spacing (Q1 & Q2 Shown) 3.9

3.2 Introduction To Servicing M889-00
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