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Contents
26.5.8 Contamination
26.5.9 Solder Bridges
26.5.10 Arcing
26.5.11 Digital Circuitry
26.5.12 Replacing Parts
26.6 After the Repairs
26.6.1 All Units
26.6.2 Transmitter Checkout
26.6.3 Other Repaired Circuits
26.6.4 Button It Up
26.7 Professional Repairs
26.7.1 Packing Equipment
26.8 Typical Symptoms and Faults
26.8.1 Power Supplies
26.8.2 Amplifier Circuits
26.8.3 Oscillators
26.8.4 Transmit Amplifier Modules
26.9 Radio Troubleshooting Hints
26.9.1 Receivers
26.9.2 Transmitters
26.9.3 Transceivers
26.9.4 Amplifiers
26.10 Antenna Systems
26.10.1 Basic Antenna System Troubleshooting
26.10.2 General Antenna System Troubleshooting
26.11 Repair and Restoration of Vintage Equipment
26.11.1 Component Replacement
26.11.2 Powering Up the Equipment
26.11.3 Alignment
26.11.4 Using Vintage Receivers
26.11.5 Plastic Restoration
26.12 References and Bibliography
26.1 Test Equipment
26.1.1 Senses
26.1.2 Internal Equipment
26.1.3 Bench Equipment
26.2 Components
26.2.1 Check the Circuit
26.2.2 Fuses
26.2.3 Wires and Cables
26.2.4 Connectors
26.2.5 Resistors
26.2.6 Capacitors
26.2.7 Inductors and Transformers
26.2.8 Relays
26.2.9 Semiconductors
26.2.10 Tubes
26.3 Getting Started
26.3.1 The Systematic Approach
26.3.2 Assessing the Symptoms
26.3.3 External Inspection
26.4 Inside the Equipment
26.4.1 Documentation
26.4.2 Disassembly
26.4.3 Internal Inspection
26.4.4 Signal Tracing and Signal Injection
26.4.5 Microprocessor-Controlled Equipment
26.5 Testing at the Circuit Level
26.5.1 Voltage Levels
26.5.2 Noise
26.5.3 Oscillations
26.5.4 Amplitude Distortion
26.5.5 Frequency Response
26.5.6 Distortion Measurement
26.5.7 Alignment
Chapter 26 —
CD-ROM Content
Supplemental Articles
•
“Troubleshooting Radios” by Mel Eiselman, NC4L
•
“Building a Modern Signal Tracer” by Curt Terwilliger, W6XJ
•
“Hands-on Radio — Power Supply Analysis” by Ward Silver, NØAX
•
“Ampliier Care and Maintenance” by Ward Silver, NØAX
•
“Diode and Transistor Test Circuits” by Ed Hare, W1RFI
PC Board Templates
•
Crystal controlled signal source template
•
AF/RF signal injector template
Chapter
26
Troubleshooting and
Maintenance
This chapter is organized in three groups of sections to be consulted as required for any
particular troubleshooting need. You will not need to read it from end-to-end in order to
troubleshoot successfully. The first group of sections covers test equipment details, pertinent
information about components, and safety practices. The second group presents general
guidelines and techniques for effective troubleshooting. The third group presents specific
advice and information on equipment that is commonly repaired by amateurs.
The robust and self-reliant ethic
of Amateur Radio is nowhere
stronger than in the amateur’s
ability to maintain, troubleshoot
and repair electronic equipment.
Amateurs work with not just
radios, but all sorts of equipment
from computers and software to
antennas and transmission lines.
This lexibility and resilience are
keys to fulilling the Basis and
Purpose for Amateur Radio.
The sections on troubleshooting
approaches, tools and techniques
build on earlier material written by
Ed Hare, W1RFI. They will help
you approach troubleshooting
in an organized and effective
manner, appropriate to your level
of technical experience and tools
at hand. This material shows
how to get started and ask the
right questions — often the most
important part of troubleshooting.
Additional sections on
troubleshooting power supplies,
ampliiers, radios and antenna
systems (contributed by Tom
Schiller, N6BT, Ted Thrift, VK2ARA,
and Ross Pittard, VK3CE) tackle
the most common troubleshooting
needs. Restoring and maintaining
vintage equipment is a popular
part of ham radio and so there
are some sections by John
Fitzsimmons, W3JN, and Pat
Bunsold, WA6MHZ, on the special
needs of this equipment.
TROUBLESHOOTING — ART OR SCIENCE?
Although some say troubleshooting is as much art as it is science, the repair of electronic
gear is not magic. It is more like detective work as you work carefully to uncover each clue.
Knowledge of advanced math or electronics theory is not required. However, you must have,
or develop, a good grasp of basic electronics and simple measurements, guided by the ability
to read a schematic diagram and to visualize signal flow through the circuit. As with most
skills, these abilities will develop with practice.
Not everyone is an electronics wizard; your gear may end up at the repair shop in spite of
your best efforts. The theory you learned for the FCC examinations and the information in
this
Handbook
can help you decide if you can fix it yourself. Even if the problem appears to
be complex, most problems have simple causes. Why not give troubleshooting a try to the
best of your abilities? Maybe you can avoid the effort and expense of shipping the radio to
the manufacturer. It is gratifying to save time and money, but the experience and confidence
you gain by fixing it yourself may prove even more valuable.
SAFETY FIRST! — SWITCH TO SAFETY
Always! Death is permanent. A review of safety must be the first thing discussed in a
troubleshooting chapter. Some of the voltages found in amateur equipment can be fatal! Only
50 mA flowing through the body is painful; 100 to 500 mA is usually fatal. Under certain
conditions, as little as 24 V can kill. RF exposure in a high-power amplifier can create severe
burns very quickly. Batteries can deliver huge amounts of power that can melt tools and wires
or create an explosion when short-circuited. Charging lead-acid cells can create a buildup of
explosive hydrogen gas, as well.
Make sure you are 100% familiar with all safety rules and the dangerous conditions
that might exist in the equipment you are servicing. A list of safety rules can be found in
Table 26.1
. You should also read the
Safety
chapter of this
Handbook
— all of it — before
you begin to work on equipment.
Remember, if the equipment is not working properly, dangerous conditions may exist where
you don’t expect them. Treat every component as potentially “live.” Some older equipment
uses “ac/dc” circuitry. In this circuit, one side of the chassis is connected directly to the ac
line, a condition unexpected by today’s amateurs who are accustomed to modern safety
standards and practices. This is an electric shock waiting to happen.
The maximum voltage rating of voltmeters and oscilloscopes is not often noted by the
hobbyist but it is crucial to safety when working on voltages higher than the household ac line
voltage. Test equipment designed to measure voltage always has a maximum safe voltage rating
Troubleshooting and Maintenance
26.1
complicated — turn out to have a simple root
cause found by understanding the fundamen-
tals and methods of one of these categories.
Table 26.1
Safety Rules
1. Keep one hand in your pocket when working on live circuits or checking to see that
capacitors are discharged.
2. Include a conveniently located ground-fault current interrupter (GFCI) circuit breaker in
the workbench wiring.
3. Use only grounded plugs and receptacles.
4. Use a GFCI protected circuit when working outdoors, on a concrete or dirt loor, in wet
areas, or near ixtures or appliances connected to water lines, or within six feet of any
exposed grounded building feature.
5. Use a fused, power limiting isolation transformer when working on ac/dc devices.
6. Switch off the power, disconnect equipment from the power source, ground the output
of the internal dc power supply, and discharge capacitors when making circuit changes.
7. Do not subject electrolytic capacitors to excessive voltage, ac voltage or reverse voltage.
8. Test leads should be well insulated and without cracks, fraying, or exposed conductors
9. Do not work alone!
10. Wear safety glasses for protection against sparks and metal or solder fragments.
11. Be careful with tools that may cause short circuits.
12. Replace fuses only with those having proper ratings.
13. Never use test equipment to measure voltages above its maximum rating.
GETTING HELP
Other hams may be able to help you with
your troubleshooting and repair problems,
either with a manual or technical help. Check
with your local club or repeater group. You
may get lucky and find a troubleshooting
wizard. (On the other hand, you may get some
advice that is downright dangerous, so be se-
lective.) Most clubs have one or two trouble-
shooting gurus who can provide guidance and
advice, if not some on-the-workbench help.
There is a wealth of information available
online, too. Many of the popular brands of
equipment and even specific models have
their own online communities or user’s
groups. The archives of these groups — al-
most universally free to join — contain much
valuable troubleshooting, modification and
operating information. If the problem doesn’t
appear to have been described, you can ask
the group.
The Technology area of the ARRL’s web-
site also has an extensive section on Servicing
Equipment (
www.arrl.org/servicing-
equipment
). That page features articles and
other resources, including links to schematic
databases.
Your fellow hams in the ARRL Field
organization may also help. Technical
Coordinators (TC) and Technical Specialists
(TS) are volunteers who are willing to help
hams with technical questions. For the name
and address of a local TC or TS, contact your
Section Manager (listed in the front of any
recent issue of
QST
).
between the circuit being measured and the
equipment user — you! This is particularly
important in handheld equipment in which
there is no metal enclosure connected to an
ac safety ground. Excessive voltage can result
in a flashover to the user from the internal
electronics, probes, or test leads, resulting in
electric shock. Know and respect this rating.
If you are using an external high voltage
probe, make sure it is in good condition with
no cracks in the body. The test lead insulation
should be in good condition — flexible and
with no cracks or wire exposed. If practical,
do not make measurements while holding
the probe or meter. Attach the probe with the
voltage discharged and then turn the power
on. Turn power off and discharge the voltage
before touching the probe again. Treat high
voltage equipment with care and respect!
you are experiencing. Knowing how circuits
are supposed to work will help you to notice
things that are out of place or that indicate
a problem.
To be an effective troubleshooter, review
and understand the following topics dis-
cussed elsewhere in this book:
Ohms law and basic resistor circuits
(
Electrical Fundamentals
)
Basic transistor and diode characteristics
(
Analog Basics
)
Fundamental digital logic and logic sig-
nals (
Digital Basics
)
Voltage and current measurements (
Test
Equipment and Measurements
)
SWR and RF power measurement
(
Transmission Lines
)
You would be surprised at how many
problems — even problems that appear
Soldering Safety
Remember that soldering tools and melted
solder can be hot and dangerous! Wear pro-
tective goggles and clothing when soldering.
A full course in first aid is beyond the scope of
this chapter, but if you burn your skin, run the
burn immediately under cold water and seek
first aid or medical attention. Always seek
medical attention if you burn your eyes; even
a small burn can develop into serious trouble.
Using Search Engines for Troubleshooting
The power of Internet search engines can save huge amounts of time when trou-
bleshooting equipment. The key is in knowing how to construct the right list of words
for them to ind. Precision is your friend — be exact and use words others are likely
to use if they had the same problem. Use the primary model number without sufixes
to avoid being too speciic. For example, when troubleshooting the well-known PLL
potting compound problem exhibited by Kenwood TS-440 transceivers, entering the
search string “TS-440 display dots” immediately inds many web pages dealing with
the problem, while simply entering “Kenwood transceiver blank display” returns dozen
of unrelated links.
Start with a very speciic description of the problem and gradually use less exact
terms if you don’t ind what you want. Learn how to use the “Advanced Search” func-
tions of the search engine, too.
UNDERSTANDING THE BASICS
To fix electronic equipment, you need to
understand the system and circuits you are
troubleshooting. A working knowledge of
electronic theory, circuitry and components
is an important part of the process. When
you are troubleshooting, you are looking for
specific conditions that cause the symptoms
26.2
Chapter 26
26.1 Test Equipment
Many of the steps involved in effiicient
troubleshooting require the use of test equip-
ment. We cannot see electricity directly, but
we can measure its characteristics and effects.
Our test equipment becomes our electrical
senses.
The
Test Equipment and Measurements
chapter is where you can find out more about
various common types of equipment, how to
operate it, and even how to build some of your
own. There are many articles in
QST
and in
books and websites that explain test equip-
ment and offer build-it-yourself projects,
too. Surplus equipment of excellent quality
is widely available at a fraction of its new cost.
You need not purchase or build every type
of test equipment. Specialty equipment such
as spectrum analyzers or UHF frequency
counters can often be borrowed from a club
member or friend — maybe one of those
troubleshooting gurus mentioned earlier. If
you own the basic instruments and know how
to use them, you’ll be able to do quite a bit of
troubleshooting before you need the special
instruments.
Brain
— More troubleshooting problems
have been solved with a multimeter and a
brain than with the most expensive spectrum
analyzer. You must use your brain to analyze
data collected by other instruments.
are sometimes communicated through pat-
terns of beeps or flashing of LEDs. Each
sequence has a specific meaning that is de-
scribed in the operating or service manual.
26.1.3 Bench Equipment
The following is a list of the most common
and useful test instruments for troubleshoot-
ing. Some items serve several purposes and
may substitute for others on the list. The the-
ory and operation of most of this equipment
is discussed in detail in the
Test
Equipment
and Measurements
chapter. Notes about the
equipment’s use for troubleshooting are listed
here.
Multimeters
—The most often used piece
of test equipment, the digital multimeter or
DMM, can often test capacitors of most val-
ues in addition to voltage, current and resis-
tance. Most can test diodes and transistors on
a go/no-go basis, while some can measure
gain. Some can even measure frequency or
use an external probe to measure temperature.
Some DMMs are affected by RF, so most
technicians keep an old-style analog moving-
needle VOM (volt-ohm-meter) on hand for
use in strong RF fields. Some technicians
prefer the moving needle for peaking or null-
ing adjustments.
26.1.2 Internal Equipment
Some test equipment is included in the
equipment you repair. Nearly all receivers
include a speaker. An S meter is usually con-
nected ahead of the audio chain. If the S meter
shows signals, that indicates that the RF and
IF circuitry is probably functioning. Trans-
mitters often have a power supply voltage
and current meter, along with power output,
SWR, ALC and speech compression read-
ings that give valuable clues about what is
happening inside the equipment.
The equipment also has visual indica-
tor lights that provide additional informa-
tion such as transmit status, high SWR, low
voltage, squelch status, and so forth. These
readings or indicators are often specifically
referenced by the troubleshooting sections of
manuals to help sort out problems.
Microprocessor-controlled equipment
often provides error indications, either
through a display or by indicator lights. In ad-
dition, faults detected by the control software
26.1.1 Senses
Although they are not test equipment in
the classic sense, your own senses will tell
you as much about the equipment you are
trying to fix as the most-expensive spectrum
analyzer. We each have some of these natural
test instruments.
Eyes
— Use them constantly. Look for
evidence of heat and arcing, burned compo-
nents, broken connections or wires, poor sol-
der joints or other obvious visual problems.
Ears
— Severe audio distortion can be
detected by ear. The snaps and pops of arcing
or the sizzling of a burning component may
help you track down circuit faults. An expe-
rienced troubleshooter can diagnose some
circuit problems by the sound they make.
For example, a bad audio-output IC sounds
slightly different from a defective speaker.
Nose
— Your nose can tell you a lot. With
experience, the smells of ozone, an overheat-
ing transformer, and a burned resistor or PC
board trace each become unique and distinc-
tive. Many troubleshooting sessions begin
with “something smells hot!”
Finger
— After using a voltmeter to ensure
no hazardous voltages are present, you can
use a fingertip to determine low heat levels—
never do this in a high-voltage circuit. Use a
temperature probe if using a finger is unsafe.
Small-signal transistors can be fairly warm,
but being very hot indicates a circuit problem.
Warm or hot capacitors are always suspect.
High-power devices and resistors can be quite
hot during normal operation.
Fig 26.1 — An array of test probes for use with various test instruments.
Troubleshooting and Maintenance
26.3
Test or clip leads
— Keep an assortment
of these wires with insulated alligator clips.
Commercially-made leads have a high failure
rate because they use small wire that is not
soldered to the clips, just crimped. You can
slip off the clip jackets and solder the wire
yourself for better reliability. Making a set of
heavier-gauge leads is a good idea for currents
above several hundred milliamps.
Individual wire leads (
Fig 26.1A
) are good
for dc measurements, but they can pick up
unwanted RF energy. This problem is reduced
somewhat if the leads are twisted together
(Fig 26.1B). Coaxial cable test leads can
avoid RF pickup but also place a small capaci-
tance across the circuit being measured. The
added capacitance may affect performance.
Test probes
— The most common probe
is the low-capacitance (×10) oscilloscope
probe shown in Fig 26.1C. This probe iso-
lates the oscilloscope from the circuit under
test, preventing the scope’s input and test-
probe capacitance from affecting the circuit
and changing the reading. A network in the
probe serves as a 10:1 divider and compen-
sates for frequency distortion in the cable
and test instrument.
Demodulator probes (see the
Test
Equip-
ment and Measurements
chapter and the
schematic shown in Fig 26.1D) are used to
demodulate or detect RF signals, converting
modulated RF signals to audio that can be
heard in a signal tracer or seen on a low-
bandwidth scope.
You can make a probe for inductive cou-
pling as shown in Fig 26.1E. Connect a two
or three-turn loop across the center conduc-
tor and shield before sealing the end. The
inductive pickup is useful for coupling to
high-current points and can also be used as
a sniffer probe to pick up RF signals without
contacting a circuit directly.
Other common types of probes are the
non-contact clamp-on probes shown in
Fig 26.2
that use magnetic fields to measure
current. A high-voltage probe for use with
DMMs or VOMs is shown in
Fig 26.3
and
is discussed more in this chapter’s section on
power supply troubleshooting.
Thermocouple and active temperature
sensor probes are also commonly available.
These display temperature directly on the
meter in °F or °C.
RF power and SWR meters
— Simple
meters indicate relative power SWR and are
fine for adjusting matching networks and
monitoring transmission line conditions for
problems. However, if you want to make ac-
curate measurements, a calibrated directional
RF wattmeter with the proper sensing ele-
ments for the frequencies of signals being
measured is required.
Dummy load
— Do not put a signal on
the air while repairing equipment. Defective
equipment can generate signals that interfere
Fig 26.2 — A clamp-on meter probe is used with a digital multimeter for measuring ac
current (left). Meters are also available integrated with the clamp-on probe (right).
with other hams or other radio services. A
dummy load also provides a known, matched
load (usually 50 W) for use during adjustments
and test measurements. See the
Transmitters
and Transceivers
chapter.
Dip meter
— As described in the
Test
Equipment and Measurements
chapter,
dip meters are used to adjust and trouble-
shoot resonant circuits. Many can perform
as an absorption frequency meter, as well.
Dip meters can be used as low-power signal
sources but are not very stable.
New dip meters are fairly rare. When pur-
chasing a dip meter, look for one that is me-
chanically and electrically stable. All of the
coils should be present and in good condition.
A headphone connection is helpful. Battery
operated models are easier to use for antenna
measurements. Dip meters are not nearly as
common as they once were.
Oscilloscope
— The oscilloscope, or
scope, is the second most often used piece
of test equipment, although a lot of repairs
can be accomplished without one. The trace
of a scope can give us a lot of information
about a signal at a glance. For example, when
signals from the input and output of a stage
are displayed on a dual-trace scope, stage
linearity and phase shift can be checked (see
Fig 26.4
).
Fig 26.3 — A probe
used for measuring
high-voltage with
a standard multi-
meter.
26.4
Chapter 26
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