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OQ NBS TECHNICAL NOTE 1109

^^fiEAU O^
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3. 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system. (2) scientitlc and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL .MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement: coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry

and commerce: conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government: provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

.Absolute Physical Quantities- — Radiation Research — Thermodynamics and

Molecular Science — .Analytical Chemistry — Materials Science. THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems: conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes: develops and proposes new engineering practices;

and de\elops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers;

Applied Mathematics — Electronics and Electrical Engineering- — Mechanical

Engineering and Process Technology- — Building Technology — Fire Research —

Consumer Pro'duct Technology — Field Methods.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection,

acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 L'.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

pro\ides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

Programming Science and Technolog\ — Computer S\stems Engineering,

'Headquarters and Laboratories at Gaithersburg. MD. unless otherwise noted; mailing address Washington. DC 20234. Some divisions within the center are located at Boulder, CO 80303.
OCT 2 2 "'^

OCtoO

Characterization of Electrical Ignition U6i^

Sources Within Television Receivers no

George J. Rogers

Center for Electronics and Electrical Engineering

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

and

David D. Evans

Center for Fire Research

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

Report to:

U.S. Consumer Product Safety Commission

Washington, DC 20207

,t^^ o-^ Co,

^

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Luther H. Hodges, Jr., Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

\l^ NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued October 1979
National Bureau of Standards Technical Note 1109

Nat. Bur. Stand. (U.S.), Tech. Note 1109, 60 pages (Oct. 1979) CODEN;NBTNAE

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1979

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

StoclcNo.003-O03-02119-9 Price $2.50

(Add 25 percent additional for other than U.S. mailing)
TABLE OF CONTENTS

i

' Page

LIST OF FIGURES V

ILIST OF TABLES vi

[ABSTRACT 1

1. INTRODUCTION 1

2. SELECTION OF TELEVISION RECEIVERS 2

3. EXPERIMENTAL APPROACH 3

4. DOCUMENTATION 3

5. PREPARATION OF RECEIVERS 4

6. EXPERIMENTAL RESULTS 4 6.1 Summary 4 6.2 30.5-cm (12-in) Black and White TV Receiver 5 6.2.1 Short Circuit in the Output of the 125-volt

Supply (Test 1) 6 6.2.2 Short Circuit in the Output of the 100-volt

Supply (Tests 2 and 6) 6

6.2.3 Short Circuit in the Output of the

140-volt Supply (Tests 3 and 7) 6 6.2.4 Short-circuited Winding in the

High-voltage Transformer (Test 9) 7 6.2.5 Short Circuit in the Output of the

15-volt Supply (Test 1) 7 6.2.6 Effect of Dust Conditioning 7 6.3 48.3-cm (19-in) Black and White TV Receiver 8 6.3.1 Short Circuit at the Output of the

24-volt Supply (Tests 4 and 10) 8 6.3.2 Further Tests on 24-volt Supply (Test 13) 8 6.3.3 Short Circuit in the 26-volt Supply to the

Low-power Horizontal Circuits (Test 5) 9 6.3.4 Short Circuit in the 24-volt Supply to the

Vertical Amplifiers (Test 11) 9 6.3.5 Short-circuited Winding in High-voltage

Transformer (Test 14) 9 6.4 48.3-cm (19-in) Color TV Receiver 10

6.4.1 Short Circuit in Decoupling Network to

Horizontal Driver (Tests 15 and 19) 10

6.4.2 Short Circuit in Decoupling Network to

Sound Module (Test 18) 11

6.4.3 Short-circuited Zener Diode in the X-ray

Protection Circuit (Test 16) 11

6.4.4 Short Circuit at the Output of the

11.2-volt Regulator (Test 17) 11

6.4.5 Overloaded Resistor in 40-volt Supply

(Tests 20 and 21) 11

6.4.6 Short-circuited X-ray Protection Winding

(Test 22) 12

111
TABLE OF CONTENTS (continued)

Page

6.5 63.5-cm (25-in) Color TV Receiver 12

6.5.1 Short-circuited Decoupling Network in

Horizontal Driver Circuit (Test 23) 13

6.5.2 Short-circuited Network in Audio

Output Module (Test 24) 13

6.5.3 Overloaded 26-volt Supply (Test 25) 13

6.5.4 Short-circuited Decoupling Network in

IF/audio Module (Test 26) 14

6.5.5 Overloaded 23-volt Power Supply (Test 27) 14

7. REDUCED VENTILATION TESTS 15

8. VOLUNTARY STANDARD UL 1410 15

8.1 UL 94 Test 15

8.2 Measurement of Ignition Source 16

8.3 Comparison of Television and UL 1410 Ignition Sources .... 16

9. CONCLUSIONS 17

10. REFERENCES 17

IV
LIST OF FIGURES

Figure Page

1. Equipment for television receiver tests 2 3

2. 30.5-cin black and white receiver, back cover removed 24

3. Partial schematic diagram of 30.5-cm black and white

TV receiver 2 5

4. Test 2, 30.5-cm black and white, temperature of resistor R5 . . 26

5. 30.5-cm black and white, placement of resistor Rl 27

6. Test 3, 30.5-cm black and white, temperature of resistor Rl . . 2 8

7. Smoke produced by resistor Rl 29

8. 48.3-cm black and white receiver, back cover removed 30

9. Partial schematic diagram of 48.3-cra black and white

TV receiver 31

10. Tests 4 and 10, 48.3-cm black and white, temperature

of resistor R14 32

11. Test 13, 48.3-cm black and white, temperature of resistor R14 . 33

12. Test 5, 48.3-cm black and white, temperature of resistor R13. . 34

13. Test 11, 48.3-cm black and white, temperature of resistor R12 . 35

14. Test 14, 48.3-cm black and white, temperatures of resistors

RIO and Rll 36

15. 4 8.3-cm color receiver, back cover removed 37

16. Partial schematic diagram of 48.3-cm color TV receiver 38

17. Test 15, 48.3-cm color, temperature of resistor R23 39

18. Test 19, 48.3-cm color, temperature of resistor R22 40

19. Test 18, 48.3-cm color, temperature of resistor R23 41

20. Tests 20 and 21, 48.3-cm color, temperature of resistor R26 . . 42

21. 63.5-cm color receiver, back cover removed 4 3 22. Partial schematic diagram of 63.5-cm color TV receiver 44

23. Test 23, 63.5-cm color, temperature of resistor R31 45

24. Test 24, 63.5-cm color, temperature of resistors R32 and R33. . 46

25. Test 25, 63.5-cm color, temperature of resistor R32 47

26. Test 26, 63.5-cm color, temperature of resistor R35 48

27. Test 27, 63.5-cm color, temperature of resistor R34 49
LIST OF FIGURES (cont.)

Figure Page

28. 48.3-cm black and white receiver, sealed for reduced

ventilation test 50

29. 1.9-cm (3/4-in) UL 94 test flame 51

30. Test equipment for energy release rate measurements 52

31. Copper slug UL 94 sample in flame 53

LIST OF TABLES

Page

Table 1. Summary of tests 18

Table 2 . Range of component operating temperatures 21

Table 3. Effect of ventilation on temperatures of selected

components 22

Table in text, Television receivers tested 2

VI
CHARACTERIZATION OF ELECTRICAL IGNITION SOURCES

WITHIN TELEVISION RECEIVERS

George J. Rogers and David D. Evans

The ignition of television receivers initiated

by electrical failures in the circuitry was examined

by studying four receivers. They were: two black

and white portables, a color portable, and a color

console receiver. Selected locations within the

circuitry were stressed by introducing full or partial

short circuits to simulate the failure of electronic

components. The temperatures and increased power

dissipation generated by short-circuited components

were recorded. Although component temperatures

greater than 500°C were achieved, no flaming ignition

sources were generated.

For comparative purposes the energy release rate

of the ignition source specified in the UL 1410 test

procedure was measured. Supplemental measurements on the operating temperatures of chassis components under

varying ventilation conditions were also made.

Key words: Electrical failure; fire containment;

ignition; television fire.

1. INTRODUCTION

This study of television receivers was initiated at the National Bureau

of Standards (NBS) to provide technical support to the U.S. Consumer Product

Safety Commission (CPSC) . The study was designed to provide data relevant

to the containment of television receiver fires and to the existing voluntary

flammability standards. The present flammability requirements are contained

in the Underwriters Laboratories publication, "Standard for Television

Receivers and Video Products," (UL 1410) [1]1.

The entire program of study was to be divided into two phases. In the

first phase, the television receiver market would be analyzed to determine the

various available construction types and sizes being sold. Then experiments

were to be conducted to document the burning characteristics of the various

current television receiver constructions. In phase two of the study, this

information would be used to facilitate defining levels of containment, and

to develop performance fire tests to assure the achievement of containment.

In June 1978, the Center for Fire Research at NBS, Gaithersburg,

Maryland, and Factory Mutual Research Corporation (FMRC) , Norwood, Massachusetts, began a cooperative study to supply the data requested as part of the

phase-one CPSC program. The work at NBS was to continue through September

1978.

To satisfy the objectives of phase one, NBS was to study the ignition

of television receiver components by simulated electrical failures in the

circuitry.

Numbers in brackets refer to the literature references listed at the end

of this report.
FMRC was to study the fire growth and propagation from a sustained

flaming ignition source in various locations on the receiver chassis. Simply,

NBS would investigate means of obtaining an ignition source and FMRC would

study the growth of the fire given that a flaming ignition source had been

generated. Since the phase-one study was concerned with the intensity of the

fire that could develop from the interior components comprising a television

chassis, all the plastic television receiver enclosures would be replaced by

materials that would not contribute to the fire in the FHRC tests. The NBS

tests, only concerned with ignition, would be terminated at the initiation

of fire spread from the ignition source. During the studies, NBS would be responsible for determining the energy

release rate of the ignition source specified in the UL 1410 test procedure

[1] and obtaining operating temperature data for unventilated television

receivers. In the course of the FMRC study a method for simulating television

aging and dust deposits was to be developed. FMRC would also attempt to

develop a classification system for television receiver chassis.

The data gathered in these phase-one studies will contribute to a better

perception than existed previously of the ignition and fire spread resistance

of television receivers currently being marketed. These data can also serve

as the basis for the phase-two study of television receiver fire containment.

2. SELECTION OF TELEVISION RECEIVERS

Four television receivers were purchased for use in the four-month

phase-one study at NBS. An effort was made to obtain receivers that would

characterize the common household receivers being marketed. All the receivers

purchased used solid-state circuitry and none had the "instant on" feature;

each was made by a different U.S. manufacturer. As shown in the table below,

two were color receivers: one large 63.5-cm (25-in) diagonal screen size

console model manufactured in January 1977 and a smaller 48.3-cm (19-in)

portable manufactured in March 1978. The remaining two receivers were black

and white portables, one 48.3-cm (19-in) manufactured in May 1978 and the

other a 30.5-cm {12-in) manufactured in December 1976. The nominal power

consumption at 120 volts for the receivers was 200W, 89W, 55W, and SOW

respectively. These four different popular brand name receivers were purchased from local distributors. The selection of specific brands was based on the type of circuity used, the availability of circuit diagrams,

the ease of obtaining factory replacement components, and the willingness

of the distributor to accept a government purchase order.

TELEVISION RECEIVERS TESTED

Type

Diagonal

Screen

Size

Date

Manufactured

January 1977

Rated

Power

color 63.5-cm 2 0W

color 48. 3-cm March 19 79 8 9W

B/W 48. 3-cm Hay 19 7 9 55W

B/W 30. 5-cm December 1976 SOW
3. EXPERIMENTAL APPROACH

Electrical failures within the television receiver can lead to a fire

condition. The cause may be a complete or partial short in a capacitor or transformer which caused increased power consumption in other circuit com- ponents, often leading to an increase in operating temperature or failure.

In this testing program deliberate shorts were introduced into the television

receiver circuit at capacitor and transformer connection points. During any

test, only one short was introduced. Documenting the physical and electrical

response of the receiver to this type of fault was the primary objective of

each test in the program. No work was done to simulate arcing or glowing

connection failures.

In each of the television receivers obtained for study in this program,

chassis components that might serve as ignition sources needed to be located.

As a first step, statistics on past television fires were reviewed to obtain

data on the frequency of fires identified as starting in various sections of

the television chassis. The best source of this type of data was Harwood '

report, "Analysis of Subpoenaed Television Data" [2]. The data in this report

were to be analyzed fully as part of the FMRC program. A cursory review of

the report showed that when television fires occurred, the frequent locations

identified as the source were the power supply, high voltage, and switch areas. Making use of this information, the testing in the NBS program was predominantly

devoted to analysis of the power supply and high—voltage sections of the

television circuitry.

Several considerations were made in determining which components to

stress in the selected areas of the chassis. Components with normally high

operating temperatures were identified by probing the chassis under normal

operating conditions. By studying circuit diagrams, means to overload these

high temperature components by simulating circuit failures were determined.

In addition, consideration was also given to introducing a circuit failure

that would lead to overheating components in proximity to flammable materials,

such as, plastic wire tie downs, plastic terminal connectors, and wire bundles.

Again study of circuit diagrams and analysis of the normal operating conditions

determined the practical choices for testing.

These failures were tested in a sequence of least to most electrically

destructive. After each failure mode was tested, necessary repairs were made

to return the television to its normal operating condition using factory

replacement parts where possible. It should be pointed out that the generation of fires within a television receiver started by electrical failures is

a process that involves chance. It should also be clear from the above

discussion that no attempt was made to exhaust all of the possibilities for

electrical failure within the receivers.

In addition to testing circuits and components in-situ, tests of bench-top

circuit mockups were performed to determine the response of components to con- trolled levels of electrical overload. In particular, surface temperature and

deterioration measurements were made on several specific components like those

overstressed in the receiver tests.

4. DOCUMENTATION

To document all the experimental work on the four television receivers,

color video tapes were made of each test. The typical experimental setup is

shown in figure 1. (Notice in figure 1, that for tests with the back cover

of the television enclosure in place, circuitry was viewed through a polycarbonate window.) Temperature data in selected locations on the television

chassis and enclosure were probed using thermocouples and monitored using a digital data acquisition system.
5. PREPARATION OF RECEIVERS

In preparation for testing, the normal operating conditions of each of

the four television receivers were thoroughly studied. Each receiver was instrumented with up to 8, 0.025-cm diameter, type K thermocouples many of

which were wrapped circumferentially around key resistors and secured using

high temperature cement. The temperatures of transformer cases, fuse holders,

wire bundles, and the television receiver cabinet were measured in some tests.

As part of the FMRC study, methods of aging components to simulate 12

years of use and methods to deposit dust and grease throughout the chassis

were developed. None of the televisions tested in the NBS program were

exposed to an environment designed to simulate acfing. Copying the method of

dust and grease deposition developed by FMRC 2 , a small number of tests were

run with the dust-conditioned 30.5-cm (12-in) black and white portable. These

tests results were compared to identical tests conducted without dust.

In tests where the full television enclosure was used, a section of the

back cover was sacrificed and replaced by a polycarbonate window through which

the circuitry could be viewed. This window was molded to fit the contours of

the television enclosure and perforated to allow for ventilation equal to the

section it replaced. In some cases, the television receiver was tested with

the back of the enclosure removed. This condition was not considered detrimental to the test results, as the maximum difference in component temperature

between the entire enclosure in place, and the back removed, was 20°C (see

table 3)

.

6. EXPERIMENTAL RESULTS

6 . 1 Summary

The four television receivers used in this study of ignition sources represented different types of construction. Most of the circuits of the

black and white sets were mounted on a single printed circuit board placed

horizontally in the 30.5-cm (12-in) set and vertically in the 48.3-cm (19-in)

set. The color sets used modular construction with some of the printed circuit

modules mounted horizontally and some mounted vertically in each case. In the

48,3-cm (19-in) color set, most of the modules were mounted horizontally while

in the 63.5-cm (25-in) set, most were mounted vertically. The 63.5-cm (25-in)

set differed from the others in that the circuits were assembled in three

separate units.

These receivers used different design approaches to obtain DC voltages.

Power transformers were used to furnish all DC voltages except the anode and

screen voltages of the kinescope (picture tube) in the 48.3-cm (19-in) black

and white set and in the 63.5-cm (25-in) color set. The 30.5-cm (12-in)

black and white and 48.3-cm (19-in) color sets obtained DC voltages for most

of the low-voltage circuits from one of the secondaries of the high—voltage

transformer. In the 30.5-cm (12-in) set a half-wave rectifier was used to

obtain DC voltages from the 110-volt supply for the horizontal circuits and

audio and video output circuits. DC voltages for the remainder of the

circuits were obtained from the secondary of the high-voltage transformer

once the horizontal circuits were operational. The 48.3-cm (19-in) color set

employed a bridge rectifier to obtain DC voltage for the horizontal driver

and start-up voltages for the remainder of the horizontal circuits; after

start up, all DC voltages except the collector supply to the horizontal driver

were obtained from the high-voltage transformer.

2 Household dust is deposited on a layer of grease remaining from spraying the

receiver with a mist from a mixture of 1 part lard, 1 part corn oil, and 500

parts acetone.
Kinescope heater voltage was obtained from the high-voltage transformer

in the 30.5-cm (12-in) black and white and 48.3-cm (19-in) color sets, and

from the power transformer in the 48.3-cm (19-in) black and white and 63.5-cm

(25-in) color sets.

The number of tests that could be performed was limited by the time

available. Since power supply circuits and high-voltage transformers were

reported as frequent sources of fires in television receivers, testing was limited to these circuits or to circuits which would overload them. The test

method chosen was to introduce short circuits into the set at locations where

such faults would be likely to occur, such as across filter or decoupling

capacitors, and where the resulting increase in current would stress resistors

or transformers beyond their normal ratings. Thermocouples were bonded to

components to record temperature changes. Direct current (DC) voltage and

current measurements were made to record the electrical conditions, and were

used to calculate power dissipation. Where possible, components chosen for

overstressing were near connectors, wire bundles, or other flammable parts.

Because of the interaction between circuits in a television receiver,

short circuits which overstressed components in one part of the set often

caused a reduction of voltages and currents elsewhere. The result was that

in many of the tests the overstressed component was damaged or destroyed

without causing power to the set to be interrupted by a blown fuse or open

circuit breaker. In all cases tested, however, there was a noticeable change

in audio and/or video performance of the receiver. In those cases in which

a short circuit caused one of the protective devices to interrupt power,

resistive loads were introduced to simulate partial short circuits. These

were chosen to produce maximum overheating without interrupting power to

the circuit. In some of these cases, bench tests were made on components of

the same type to determine the maximum temperature that could be reached

before the component was destroyed.

By these methods, temperatures near 500 °C were produced in all of the

sets, and temperatures over 600 °C were observed in the two black and white

TV receivers. The results are summarized in table 1. A number of components

were destroyed or damaged enough to require replacement. In some cases, the

damage was accompanied by the emission of smoke but no flaming ignition was

generated. Most of the components failed by increasing in resistance or burning out, so that the failures tended to interrupt circuit operation and

did not spread to other components. Ceramic-coated resistors often showed

little change while they were hot, but cracked after they cooled.

It is not possible to foresee every type of failure that might occur,

or to attempt to reproduce them in limited tests of this type. The method

used in these tests to produce failures tends to produce the non-spreading

type of failure noted above as opposed to the over-voltage type of stress

which is likely to produce a domino type of reaction in which the failure

of one component leads to the successive failure of others. The short-circuited capacitor or short-circuited turn or winding is more likely to occur

in power supply and high-voltage transformer circuits. In addition, it was

felt that a sustained heat such as produced by these tests was more likely

to lead to ignition than the momentary surge that would be produced by the

over-voltage type of stress.

6.2 30.5-cm (12-in) Black and White TV Receiver

Except for the tuner assembly and picture controls, all components of

the 30.5-cm (12-in) black and white TV receiver were mounted on a 15 by 33-cm

printed circuit board which was mounted horizontally below the picture tube

neck (fig. 2) . A half-wave rectifier derived most of the DC voltages used

in the set directly from the 120-volt AC supply (fig. 3). From this source,

appropriate filter networks were used to obtain 140 volts for the video

output and vertical control circuits, 125 volts for the horizontal output
circuit, 100 volts for the horizontal driver, audio output and sync separator

circuits, and 15 volts for the horizontal oscillator. A second half-wave

rectifier in series with a low-voltage winding on the high-voltage transformer was a source of 35 volts for the vertical circuits, and 20 volts for

the tuner assembly, IF and AGC circuits. Heater current for the kinescope

(picture tube) was obtained from another low-voltage winding on the highvoltage transformer. The set was protected by a single 1.5-ampere slow-blow

fuse in the 110-volt input.

6.2.1 Short Circuit in the Output of the 125-volt Supply (Test 1)

The 125-volt supply furnishes power to the horizontal output circuit

through a decoupling network comprising a 56-ohm, 5-watt wirewound resistor

(R4, fig. 3) and a 0.1 yF capacitor (C4) . Capacitor C4 was short-circuited

to simulate a short circuit in the capacitor or a short circuit to ground in

the collector circuit of the output transistor. The increase in current blew

the fuse and interrupted the power to the set. There was no damage to the

set other than the blown fuse.

In the five seconds before power was interrupted, the temperature of

R3 had increased from 147°C to 160 °C, and the temperature of R4 from 125°C

to 187°C. Later bench tests on resistors of the type of R4 indicated that

the temperature of this resistor would have risen to over 600°C if the fuse

had not blown.

6.2.2 Short Circuit in the Output of the

100-volt Supply (Tests 2 and 6)

A short circuit in the filter capacitor at the output of the 100-volt

supply, C5, or a short circuit elsewhere in the circuits drawing current from

this supply was simulated by short-circuiting the filter capacitor. This

caused the current flowing through the 470-ohm, 3-watt wirewound decoupling

resistor in this circuit (R5, fig. 3) to increase from 47 mA to 255 mA, with

a resulting increase in dissipation from 1 watt to about 30 watts (test 2)

.

Within a minute the temperature of R5 had increased from the normal 93°C

to 500°C reaching a peak of 585°C 1 minute later (fig. 4) . This temperature

had decreased to 570°C when the test was terminated after 10 minutes. There was a slight trace of smoke for about 1 minute after the short circuit was

applied. There was no raster during the test.

When the short circuit was removed after 10 minutes, the raster was restored, and no visible damage was found anywhere in the set. The resistance of R5 was measured and found to have decreased to 100 ohms. Later it was discovered that a crack had developed in R5 and that the resistance had

increased to 1220 ohms.

Short-circuiting the 100-volt supply stops the signal to the high-voltage

transformer and not only interrupts the high voltage but also the 20 and

35-volt supplies derived from one of the transformer windings. This results

in decreases in current in other parts of the set which offset the more than

five-fold increase in current in R5 so that the fuse did not open during this

test. In the second test (test 6) , it was found that the increase in the

temperature of R5 was accompanied by decreases in the temperature of R2 , R3,

and R4.

6.2.3 Short Circuit in the Output of the

140-volt Supply (Tests 3 and 7)

The filter circuit of the 140-volt supply consists of a 470-ohm, 1-watt

resistor (Rl, fig. 3) and a 30-yF capacitor (CI) . The resistor is a carbon

resistor, rather than one of the wirewound types used elsewhere in the power

supply circuits. It is supported by its leads about one-half centimeter above

the printed circuit board on which it is mounted between R2 and R3 (fig. 5)

,

6
both of which are ceramic encapsulated, wirewound types. Current through Rl

is normally about 10 mA and the power dissipation less than 0.05 watt.

A short-circuited filter capacitor, CI, or short circuits to ground in

the collector circuits of the video output or vertical driver stages increased

the current in Rl to more than 200 mA and the power dissipation to more than

20 watts. This conditon was simulated by short-circuiting the filter capacitor

with similar results in each of three tests (two tests documented in test

number 3 and one in test number 7)

In the first test, the temperature of Rl had increased from the normal

50°C to 635°C within 30 to 40 seconds (fig. 6) accompanied by considerable

smoke (fig. 7). Both Rl and R2 , the latter, a 5-ohm fusible resistor, burned

out. The fusible resistor was replaced by a wirewound resistor, and only Rl

burned out in the succeeding tests. In the test number 7, the load on the

140-volt supply was increased by connecting a 500-ohm resistor across the

output. The overload caused the temperature of Rl to rise to 370 °C and the

resistance to decrease to less than 100 ohms, but did not blow the fuse.

In each of these tests Rl was destroyed. It first charred and then

cracked, opening the circuit. No other components in the vicinity of Rl

were damaged. The excess current caused fusible resistor R2 to open on the

first test; this would probably also have occurred on the succeeding tests

if Rl had been replaced by another fusible resistor. This and the blown

fuse were the only damage to the set. Operation was restored to normal after

these components were replaced.

Several 470-ohra, 1-watt carbon resistors were bench tested to subject them

to gradually increasing stresses. It was found that the resistors were stable

when the dissipation was less than 2 watts, at which dissipation they operated

at a temperature of about 125°C. Between 2 and 4 watts, the resistance

tripled, and at dissipations greater than 4 watts the resistance decreased

until the resistor was destroyed at dissipations between 6 and 7 watts.

McLximiam temperature reached in the bench tests was 420 °C.

6.2.4 Short-circuited Winding in the

High-voltage Transformer (Test 9)

In separate tests, the kinescope heater winding and the AGC winding of

the high-voltage transformer were short-circuited to determine the effect of

a short circuit in the high-voltage transformer. Power into the high-voltage

transformer increased 2 to 4% and the temperature of R4 increased about 25°C,

but there was no permanent damage to the set.

6.2.5 Short Circuit in the Output of

the 15-volt Supply (Test 1)

Short-circuiting the output of the 15-volt supply stopped the horizontal

oscillator and disrupted the operation of the set but did no permanent damage.

The increase in dissipation in R6 (fig. 3) was well within the wattage rating

of that resistor.

6.2.6 Effect of Dust Conditioning

Tests 6 and 7 were repetitions of tests 2 and 3 after the set had been

dust-conditioned by depositing household dust on the residue of grease

remaining after the interior of the set had been sprayed with a fine mist

from a mixture of 1 gram lard and 1 gram corn oil dissolved in 500 ml acetone.

Comparison of the results of tests 6 and 2 and of tests 7 and 3 reveals no differences that can be attributed to the presence of household dust. Test 8 in which the cabinet was sealed, and test 9 in which the heater winding of

the high-voltage transformer was short-circuited were also made after the
set had been dust-conditioned. The presence of dust had no effect on the

results of these tests. The 30.5-cm black and white receiver was the only

dust-conditioned set tested.

6.3 48.3-cm (19-in) Black and White TV Receiver

Except for the tuner and picture controls, the circuits of the 48.3-cm

(19-in) black and white TV receiver are located on two chassis extending across

the back and underneath the neck of the picture tube (fig. 8) . Mounted on a

9 by 37-cm horizontal chassis are, from left to right when viewed from the

rear of the set, the IF amplifier on a vertical printed circuit board, the

power transformer, the rectifiers and filter of the 135-volt supply, and the

high-voltage transformer. In figure 8 this chassis is hidden by the vertical

printed circuit board on which the rest of the components are mounted. This

10 by 30-cm board is mounted in a frame which is hinged at the bottom to the

horizontal chassis to permit access to the horizontal chassis and to the

back of the printed circuit board. The components are mounted on the side of

the board that faces the rear of the set.

The power transformer is the source of all DC voltages used by the set

except the kinescope anode voltage (fig. 9) . The 135-volt supply is obtained

by full-wave rectification of the output of one of the transformer secondaries.

A full-wave rectifier is used to obtain 32 volts from taps on the same secondary, and a half-wave rectifier is used to obtain 11 volts from another tap.

The other transformer secondary furnishes heater power for the kinescope. The

transformer primary is protected by a 0.6-ampere fuse which is soldered into

the circuit.

6.3.1 Short Circuit at the Output of the

24-volt Supply (Tests 4 and 10)

The normal output of the 24-volt supply to the RF, IF and vertical

oscillator circuits is about 110 mA. The power dissipated in the 56-ohm,

2-watt wirewound decoupling a temperature of about 80°C. A short circuit

at the output of this supply (across C14) is the severest overload that could

occur. This has the same effect as a short circuit in filter capacitor C14

or a short circuit to ground in one of the circuits which receives power from

this source. The short circuit increased the load on the supply to 520 mA and increased

the dissipation in R14 to about 16 watts. In test 4, the temperature of R14

climbed to 560°C in 3 minutes and had stabilized at about 570°C when the test was terminated after 5 minutes (fig. 10) . In test 10, the temperature climbed

at about the same rate to 475°C after 1 minute 20 seconds, and thereafter

decreased. At the same time resistor R14 was observed to move slightly, probably indicating that the heat conducted through the leads had loosened the

solder holding the resistor to the printed circuit board. The drop in the

temperature of the resistor following this occurrence probably indicates that

the resistance had begun to change at this point.

Disruption of the operation of the circuits connected to the 24-volt

supply, and possibly the overload on the transformer, caused currents in

other parts of the set to decrease. Temperatures of RIO and R12 dropped

20 °C and 30°C, respectively; temperatures of Rll and R13 dropped less than

10°C. The resistance of R14 did not change during test 4, but after test 10

had increased to 1700 ohms. There was no permanent damage to any other part

of the set.

6.3.2 Further Tests on 24-volt Supply (Test 13)

The output of the 24-volt supply was again overloaded in a two-step test

in which an additional 50-ohm load was connected across the output of the

supply for 10 minutes followed by short-circuiting the output of the supply

at C14. The 50-ohm load increased the current through R14 to 325 mA, but

8
decreased the current to the rest of the 24-volt circuits. Power dissipated

in R14 increased to about 6 watts and the temperature increased to 215°C

(fig. 11) . When the 24-volt supply was short-circuited completely, dissipation

increased to 16 watts as before, and the temperature increased to a peak of

530°C after 4 minutes followed by a gradual decrease to about 400°C when the

test was terminated at the end of 10 minutes (fig. 11)

.

The gradual decrease in temperature probably indicates an increase in

the resistance of R14 , although there was no appreciable change in resistance

noted at the close of the test. The printed circuit board underneath R14 was slightly charred (R14 was mounted by its leads about 1-cm above the board)

.

Other than that, there was no permanent damage to the set.

During the test, thermocouples on the case, fuse, transformer and neck

of the picture tube each showed an increase in temperature between 1°C and

3°C. Temperature of components in the 32 and 135-volt supplies decreased

20°C to 25°C.

6.3.3 Short Circuit in the 2 6-volt Supply to the

Low-power Horizontal Circuits (Test 5)

The 26-volt supply furnishes about 30 mA to the horizontal oscillator and

driver circuits through a 150-ohm, 1/2 -watt film resistor (R13, fig. 9). A

short-circuit in capacitor C13, or a short circuit to ground in the collector

circuit of the horizontal oscillator or driver would draw maximum current from

this source. When the circuit was short-circuited to ground at the junction of R13 and

C13, the current in R13 increased to 200 mA and the power dissipation to about

6 watts (from a normal 0.15 watt). The temperature of R13 rose to 645°C in

the first 2 minutes then declined gradually to about 610°C after 5 minutes

when the test was terminated (fig. 12) . Temperatures in other parts of the

set decreased as much as 50°C because the short circuit disabled the signal

from the horizontal oscillator and shut down the high-voltage supply.

6.3.4 Short Circuit in the 24-volt Supply

to the Vertical Amplifiers (Test 11)

The collector voltage of the vertical amplifiers is supplied through a decoupling network consisting of a 30-ohm, 5-watt wirewound resistor (R12,

fig. 9) and a 470 uF capacitor (C12) . A short circuit in this capacitor or

a short circuit to ground in one of the collector circuits of the vertical

amplifiers, which was simulated by placing a short circuit across capacitor

C12, caused the current through the resistor to increase from 200 to 900 mA

and the power dissipation to increase from 1.5 watts to 24 watts.

Within 3 minutes, the temperature of R12 had reached about 450°C (fig. 13).

This was followed by a more gradual increase to 48 5°C at the end of the 10-

minute test. Temperatures in other parts of the set changed less than + 10 °C

except the temperature of R13 which increased from 86°C to 163°C in the first

5 minutes and for the remainder of the test remained near that temperature.

During the test the raster was reduced to a single horizontal line,

indicating that the horizontal circuits and high-voltage supply were still

operating. The set recovered with no permanent damage after the short circuit

was removed.

6.3.5 Short-circuited Winding in High-voltage

Transformer (Test 14)

The AFC winding of the high-voltage transformer was short-circuited to

observe the effect on the circuits associated with the transformer. The

short circuit resulted in a 40% increase in power to the transformer and an
increase in current to the horizontal driver from about 150 itiA to 500 itiA. Power dissipation in each of the decoupling resistors (RIO and ^11, fig. 9)

in the 135-volt supply to the horizontal driver increased from 1,5 to 23 watts,

In the first test, the short circuit was removed after 2 minutes. The

temperature of decoupling resistor Rll increased from about 130°C to nearly

500°C, and that of RIO increased from about 100°C to about 320°C (fig. 14).

The second test terminated when the 0.6-ampere fuse blew at the end of 3-1/2

minutes. At that time, the temperature of RIO had leveled off at 320°C, but

the temperature of Rll v/as over 540 °C and still rising.

Each time the circuit was interrupted, the temperature rate of rise

increased momentarily before decreasing, probably caused by interference from

the horizontal output stage. Temperatures in other parts of the set rose 30°C

or less. Other than the blown fuse there was no permanent damage to the set.

6.4 48.3-cm (19-in) Color TV Receiver

Except for the tuner, picture controls, and convergence assembly, the

circuits of the 48.3-cm (19-in) color set v/ere mounted on a U-shaped chassis

frame to the rear of and parallel with the bottom of the picture tube. The

tuner and picture controls V7ere mounted on the front panel of the set, and

the convergence assembly was mounted on the neck of the picture tube. The IF

and sound modules were mounted vertically on the left upright of the chassis

frame (v7hen viewed from the rear as in figure 15) . Five modules -- chroma,

luminance/sync, video drive, horizontal oscillator, and vertical drive — were mounted horizontally on the base of the chassis frame, and the horizontal

output, high-voltage transformer and deflection circuits v;ere mounted on the

right upright.

Except for the 150-volt supply to the collector of the horizontal output

transistor, all DC supply voltages are obtained from the high-voltage transformer (fig. 16) . A bridge rectifier is used to obtain 150 volts DC from the

110-volt AC input and also to provide a 27-volt start-up supply to furnish

power to the horizontal oscillator and driver.

Basic protection for the circuit is provided by a 7-ampere fuse in the

AC line; a 3-arapere fuse is used to protect the kinescope heaters. Two over- voltage protection circuits guard against excessive high voltage and over- voltage in the 27-volt supply by disabling the horizontal oscillator if such

over-voltages occur. R21 is a 3.9-ohm fusible resistor in the input of the

bridge rectifiers.

6.4.1 Short Circuit in Decoupling Network to Horizontal

Driver (Tests 15 and 19)

Because of the multiplicity of protection circuits, tests on the 48.3-cm

(19-in) color set did not always have the expected results. The filter

capacitor, C22, in the decoupling network in the 27-volt supply to the

horizontal driver was short-circuited with the intention of overloading the

associated resistor, R22. The short circuit was accompanied by a momentary

surge of current in R22, but the temperature rise v/as less than 5°C during

the 5-minute test.

Within 30 seconds, however, the temperature of the decoupling resistor

in the 27-volt supply to the sound module, R23, had reached a peak of 470°C

before dropping to 260°C at the conclusion of the test (fig. 17) . At the same time the resistance of R23 increased tenfold, so that it had to be

replaced after the test. Temperature increase in other components v/as less

than 10°C.

10
Later the test was repeated by connecting a lOO-ohm resistor across C22

to increase the current through R22 from the normal 70 mA to 180 mA. Pov/er

dissipated in R22 increased from about 1/3 watt to 2 watts with a resulting

temperature increase from 65°C to 230°C (fig. 18) . During this test the

temperature of R21 increased 2 0°C; all other temperature changes were less

than 10°C.

6.4.2 Short Circuit in Decoupling Network

to Sound Module (Test 18)

In test 18, the load on the 27-volt supply was increased in three steps

by connecting additional resistances across the output of the decoupling network to the sound module, i.e., across C23 in figure 16. After test 15, the

original 27-ohm, 1/2-watt film resistor R23 had been replaced by a 27-ohm,

1-watt film resistor.

Additional loads of 100, 71 and 50 ohms across C2 3 increased the current

through R23 to 220, 280 and 360 mA, respectively, with corresponding increases

in dissipation to 1.3, 2.1 and 3.3 watts. The normal current in R2 3 was 30 mA

and the normal dissipation about 1/40 watt. Maximum temperatures recorded for

R23 were 140°C, 160°C and 170°C for the three loads, as indicated in figure 19.

Since the original resistor had a 1/2-watt rating, higher temperatures would

have been expected if the original resistor or an exact replacement had been

used.

6.4.3 Short-circuited Zener Diode in the X-ray

Protection Circuit (Test 16)

A voltage obtained from a low-voltage winding on the high-voltage

transformer is compared with a reference voltage in the x-ray protection circuit and used to interrupt the high-voltage supply if the high voltage exceeds

safe limits. The zener diode in the x-ray protection circuit was shortcircuited to overload resistors R2 8 and R29 in the input to that circuit. One

of these, R29, was located on the deflection circuit board and the other, R28,

in the horizontal drive module. Both were in close proximity to other com- ponents. The increased dissipation was well within the dissipation rating of

both resistors, and no temperature increases greater than 10 °C were recorded.

6.4.4 Short Circuit at the Output of the

11.2-volt Regulator (Test 17)

The output of the 11.2-volt regulator in the chroma module was shortcircuited by shorting capacitor C25, thereby increasing the load on R24 and

R25 (fig. 16). The increase was insufficient to overstress the resistors.

The temperature of R24 increased 26°C but no other temperature increases

greater than 5°C were recorded.

6.4.5 Overloaded Resistor in 40-volt Supply

(Tests 20 and 21)

The decoupling network in the 40-volt suoply to the vertical drive

module was overloaded by connecting a resistor in parallel with C26, and

then short-circuiting C27 when the temperature of R26 had stabilized.

Capacitor C26 was paralleled by a lOO-ohm resistor in test 20, and by a 50-ohm resistor in test 21.

Normal dissipation in R26, a 4.7-ohm, 2-watt wirewound resistor, is about

0.1 watt. When a lOO-ohm resistor was connected across C26 in test 20, the

dissipation in R26 increased to about 1/3 watt and the temperature leveled

off at 77°C (fig. 20) . When C27 was short-circuited, dissipation in R26

increased to 6 watts and the temperature stabilized at 405 °C. During the

test, the temperature of R27 increased from 44°C to 137°C, and of R21 from

105°C to 211°C. No other significant temperature changes were recorded.

11
when a 50-ohm resistor was connected in parallel with C26 (test 21) and

then 0.21 short-circuited, dissipation in R26 increased to 8 watts. The temperature of R26 increased from 53°C at the beginning of the test to 115°C

after 5 minutes v/ith 50 ohms paralleling C26, and then increased to 440°C

when C27 was short-circuited. The resistor opened a little more than 2 minutes after the short circuit was applied.

Temperatures in other parts of the set were similar to those recorded in

test 20. The circuit board near R26 was discolored slightly, but no permanent

damage was done and circuit operation was restored after R26 was replaced.

6.4.6 Short-circuited X-ray Protection

Winding (Test 22)

To determine the effect of a short-circuited winding on the high-voltage

transformer, the low-voltage winding which furnishes input to the x-ray protection circuit was short-circuited. The transformer began smoking and the

set became inoperative within 30 seconds. The x-ray protection winding of the

transformer was damaged, and the high-voltage winding opened. The horizontal

output transformer was destroyed, and possibly the regulator module and silicon

controlled rectifier were damaged. During the 30 seconds before the circuit

opened, the temperature of R21 increased from 104°C to 148°C. Temperatures

in other parts of the set decreased.

6.5 63.5-cm (25-in) Color TV Receiver

The circuits of the 63.5-cm (25-in) set were mounted in four groups which

v/ere well separated from each other and which were connected together by

detachable cables. The tuner and picture controls were mounted on the front

panel of the set to the left of the picture tube when viewed from the rear of

the set (fig. 21) . An assembly containing the power transformer and the power

supply circuits was mounted at the left rear. The low-voltage assembly was mounted between this chassis and the neck of the picture tube. This assembly

consisted of a vertical interconnect board into which were connected the

IF/audio chroma video, audio output, horizontal oscillator, and RGB drive

modules. The printed circuit chassis of these modules were mounted vertically,

three on one side of the vertical support and two on the other. The highvoltage assembly was located to the right of the neck of the picture tube.

It contained horizontal drive and output circuits, the high-voltage transformer, vertical drive and sweep interconnect modules mounted vertically, and

the convergence module mounted horizontally at the top of the unit.

The power transformer and associated rectifier circuits furnished DC

power to all circuits of the set except anode and focusing voltages for the

kinescope, which were obtained from the high-voltage transformer (fig. 22)

.

The primary of the power transformer was protected by a 2 . 5-ampere slow-blow

fuse. A circuit breaker in the- primary lead of the power transformer opened

the 143-volt supply when tripped, and a 1-ampere fuse protected the 30, 26

and 2 3-volt supplies which v/ere obtained from the same transformer winding.

A 6.3-volt winding on the power transformer furnished heater current to the

kinescope

.

Possible heat sources chosen for study in this set were decoupling

resistors in the high-voltage assembly, audio output and IF/audio modules,

and four decoupling resistors in the power supply assembly. The temperature

of each of these resistors (R31, R32, R33, R34, R35, R36 and R37, fig. 22) was monitored by means of thermocouples. In addition, the temperature of

the wood composition cabinet was monitored near the power transformer.

12

ii
6.5.1 Short-circuited Decoupling Network

in Horizontal Driver Circuit (Test 23)

The 143-volt supply furnishes power to the vertical oscillator, horizontal

driver and output circuits and the picture tube yoke. Current to the horizontal driver circuit is supplied through a decoupling network consisting of a 1300-ohm, 10-watt wirewound resistor (R31, fig. 22) and a 0.1-uF capacitor,

{C31) . The resistor is mounted below the pincushion transformer and near sev- eral plastic connectors used to connect leads from the high-voltage transformer

to the rest of the circuit.

When decoupling capacitor C31 was short-circuited, the current through

the decoupling resistor, R31, increased from 60 mA to 110 mA, and the power

dissipated in the resistor increased from the normal 4.6 watts to 16 watts.

The temperature of R31, which was 157°C under normal operating conditons,

stabilized at 350°C after about 8 minutes (fig. 23). Temperatures in other

parts of the set increased no more than 1°C to 5°C. During the test, the

raster disappeared, but sound remained normal.

When the short circuit was removed after 10 minutes, operation of the set

returned to normal. The resistance of R31 had changed from 1307 to 1320 ohms,

but the resistor was not damaged. There was no visible damage to the set.

6.5.2 Short-circuited Network in Audio

Output Module (Test 24)

The 26-volt supply is obtained from the 30-volt winding of the power

transformer through a 40-ohm, 3-watt, film decoupling resistor in the power

supply circuit (R32, fig. 22). It furnishes power to the audio output module

only. Current enters the audio output module through a decoupling network

consisting of an 18-ohm, 2-watt resistor (R33, fig. 22) and a 470 yP capacitor

(C33) . The module is mounted at the top of the left side of the low-voltage

assembly and the decoupling resistor is at the top rear corner of the module

near one of the cables interconnecting the modules. The 40-ohm resistor is

under the power transformer near some of the transformer leads.

Normal current in this circuit is about 13 mA. Power dissipation in the

filter and decoupling resistors, R32 and R33, is normally less than 10 mW; the

resistors normally operate at a temperature of 35°C to 40°C.

When decoupling capacitor C33 was short-circuited, current in this circuit

jumped to 0.5 ampere. Under these conditions the power dissipated in R32 was

10 watts and in R33 was 4.5 watts. After about 5 minutes, the temperature

stabilized at about 370°C for R32 and about 220°C for R33 (fig. 24) . Temperatures registered by the other thermocouples increased 2°C to 10°C. During

the test, the picture was undisturbed, but sound was completely silenced.

After the short circuit was removed, sound was restored. There was no visible damage to the set or to the wires or other components near the over- heated resistors. The resistances did not change.

6.5.3 Overloaded 26-volt Supply (Test 25)

The decoupling resistor in the 26-volt supply (R32, fig. 22) was further

stressed by adding an extra 10-ohm load to the output of the supply (point A,

fig. 22) . Such an overload could be caused by a defect in the audio output

module or a partial short circuit in the cabling connecting the module and the

power supply. The 550 mA increase in current caused a 2-volt reduction in

the output voltages of the 26 and 23-volt supplies and increased the current

through the 1-ampere fuse to 0.9 ampere. Power dissipated in R32 increased

to more than 13 watts causing an increase in its temperature to 435°C after

about 5 minutes (fig. 25) . The reduction in the output of the 23-volt supply

13
resulted in a reduction of 7°C and 1°C in the temperatures of R34 and R35,

respectively. Other thermocouples registered changes in temperature between

-2.5°C and +2,5^C. Sound volume was reduced.

When the short circuit was removed after 10 minutes, operation of the set

returned to normal. There was no visible damage to resistor R42, the transformer wires, or other components near R32.

6.5.4 Short-circuited Decoupling Network

in IF/audio Module (Test 26)

The 2 3-volt supply furnishes power to the IF/audio module through several

decoupling networks located on the module. The network which filters current

to the IF/AGC integrated circuit consists of a 360-ohm, 1/2-watt carbon resistor

(R35, fig. 22) and a 447 yF capacitor (C35) and is located near the bottom of

the vertically mounted, printed circuit chassis.

When capacitor C35 was short-circuited, the current through R35 increased

from the normal 30 mA to 70 mA and the power dissipated in the resistor increased

from 0.25 to 1.6 watts. The temperature of the resistor increased from 55°C to

140 °C in about 3 minutes and remained stable for the duration of the test (fig.

26). The short circuit eliminated both picture and sound.

The increase in current produced a slight increase in the dissipation of

the decoupling resistor in the 23-volt supply (R34, fig. 22) whose temperature

increased from 138°C to 152°C during the test. The temperature of the decoupling network in the horizontal driver circuit (R31) increased about 7°C; other

temperatures increased less than 2°C.

When the short circuit was removed after 5 minutes, operation of the set

returned to normal. The resistance of R35 did not change, and there was no visible damage to the chassis or other components mounted on the module.

6.5.5 Overloaded 23-volt Power Supply (Test 27)

The 2 3-volt supply is the principal source of low-voltage power for the

set. Defects in any of the circuits which receive power from this supply may

increase the current that it is required to deliver, and therefore increase

the dissipation in the associated 20-ohm, 5-watt wirewound decoupling resistor

(R34, fig. 22). Resistor R34 is located on the printed circuit board at the rear of the power supply assembly, and is within 2.6-cm of the fiberboard back

of the set.

The load on the 2 3-volt supply was increased in three steps by connecting

40, 20 and 10-ohm resistors across its output at point B, figure 22, at 10-

minute intervals and observing the effect on the set. The 40-ohm resistor

increased the current through R34 from the normal 370 mA to 650 mA and increased

the dissipation from 2.8 to 8.8 watts. The temperature of R34 increased from

137 °C to 295 °C in about 6 minutes and remained there until the load was changed

(fig. 27). After 10 minutes, the load was changed to 20 ohms causing a further

increase in current to 800 mA and an increase in dissipation to 13.5 watts.

After 5 minutes at this current, the temperature of R34 had increased to 380°C

where it remained. After a total elapsed time of 2 minutes, the load was changed to 10 ohms. Current in R34 increased to 965 mA and the power dissipation to 20 watts. The temperature had reached 470°C when the fuse blew after

a total time of 2 8.5 minutes (about 7 minutes after increasing the current to

965 mA)

.

During these tests there was no picture or sound except for a pronounced

120 Hz hum. Maximum temperature increase in the other circuits was about

4°C. The temperatures registered by the thermocouples not associated with

the 23 or 26-volt supplies decreased between 7°C and 40°C.

14
Except for the blown fuse, there was no damage to resistor R34 or to

other parts of the set. Operation of the set returned to normal after the

fuse was replaced.

7. REDUCED VENTILATION TESTS

Supplemental to the basic ignition source measurements made in this

program, measurements of the increase in operating temperature for the four

solid-state (except for the picture tube) television receivers were made with

all of the ventilation ports blocked. These data were requested by the CPSC

to aid them in present discussions of design changes associated with fire

containment.

Experimentally, the operating temperatures of selected components were

measured under normal conditions and with all ventilation openings in the

cabinet sealed with 0.3-mm thick duct tape (fig. 28). The data are summarized

and tabulated in tables 2 and 3. The temperature increase caused by restricted

ventilation was higher in the smaller, more compact sets, but in all cases was

less than 20 °C. It should be noted that although the cabinet openings were

sealed in the blocked ventilation tests, circulation of air around the cabinets

themselves was not restricted. Air flow about the receiver may have been

enhanced by the ventilation of the hood under which all tests were performed.

8. VOLUNTARY STANDARD UL 1410

The UL 1410 Standard for Television Receivers and Video Products covers

the fire performance requirements for materials used in enclosures or parts

of enclosures, barriers, and other applications. Of particular interest for

this study are the requirements for the polymeric enclosure materials. Depending on the location, size, and intended service of the enclosure, a flammability classification of 94V-0 or 94V-1 is required. For a major component

such as the polymeric television receiver cabinet, the more stringent 94V-0

rating is required.

8.1 UL 94 Test

The 94V-0 rating is assigned to materials based on the results of the

UL 94 Tests for Flammability of Plastic Materials for Parts in Devices and

Appliances [3] . Briefly, the UL 94 vertical burning tests are run on five

specimens in a draft-free chamber. In most cases, these specimens are flatstock bar samples 13.7-cm long by 1.27-cm wide. The test allows for thicknesses up to 1.27-cm to be tested. For the test each specimen is supported

from the upper 0.63-cm with the longitudinal axis vertical so that the lower

edge is at the mid-height of the 1.9-cm high blue ignition flame on top of

the burner tube and 30.5-cm above a 0.64-cm thick horizontal layer of dry

absorbent surgical cotton. Each specimen is exposed to the flame for 10 seconds. Then the flame is withdrawn. The duration of flaming of the specimen

is recorded. When flaming ceases the test flame is immediately placed under

the specimen for a final 10 seconds exposure and then withdrawn. The duration

of flaming and glowing is recorded.

To achieve a 94V-0 rating, section 3.2 of the standard states that the

five test specimens shall

a. Not have any specimen which burns with flaming combustion for more

than 10 seconds after each application of the test flame.

b. Not have a total flaming combustion time exceeding 50 seconds for

the 10 flame applications for each set of five specimens.

c. Not have any specimen which burns with flaming or glowing combustion

up to the holding clamp.

15
d. Not have any specimen which drips flaming particles that ignite the

dry absorbent surgical cotton located 30.5-cm (12-in) below the

test specimen.

e. Not have any specimens with glowing combustion which persists beyond

30 seconds after the second removal of the test flame.

8.2 Measurement of Ignition Source

For comparison purposes with the measurements of energy release rates

from ignition sources within the television receiver, it was of interest to

determine the energy release rate of the test flame specified in the UL 94

test procedure.

The ignition source specified in section 3.2 of the UL 94 standard [3],

is a 1.9-cm high blue flame produced by burning technical grade methane

gas with a Tirrill burner having a tube length of 10.16-cm and an inside

diameter of 0.95-cm. The burner is not equipped with an end attachment or stabilizer. The flame is produced by adjusting the gas supply and the air

parts of the burner until a 1.9-cm yellow-tipped blue flame is produced and

then increasing the air supply until the yellow tip disappears. Following

this procedure the test flame shown in figure 29 was produced on the burner

(shown fully in figure 30) built to comply with the specifications of the test

procedure.

To evaluate the energy release rate in the flame, the methane gas flow

rate was measured using a piston gas flow rate meter, shown in figure 30. The

flow rate of gas to the burner was adjusted with an in-line needle valve.

After a 1.9-cm high blue flame had been established by following the recom- mended procedure, the gas flow was diverted from the burner and the flow rate

measured with the piston meter. Using the measured gas flow rate and the

lower heat of combustion for methane, at 25°C (802 kJ/g-mole) , the rate of

energy release in the flame was calculated assuming complete combustion for

each of the 18 trials. From these measurements the energy release rate from

the burner was determined with 95% confidence to be in the interval of

60+8 watts.

In the UL 94 test, the tip of a bar-shaped plastic sample is placed in

the center of the test flame cone. For completeness sake, tests were run to

determine the percentage of energy, release in the flame that is transferred

to a sample. An approximate, but adequate, way to determine this quantity is

to measure the rate of temperature rise for a copper slug of known mass shaped like a test sample and placed in the flame as shown in figure 31.

Measurements were made on two copper samples, one a 2.5 x 1.27 x 0.63-cm rod

and the other a 6.1 x 1.27 x 0.63-cm rod, each mounted on a rigid plastic

support to bring the overall dimensions to 12.7 x 1.27 x 0.6 3-cm. The two

measurements were in good agreement with each other, and showed that 40% to

50% of the energy released in the flame could be expected to be transferred

to the UL 94 test sample.

8.3 Comparison of Television and UL 1410 Ignition Sources

A primary goal of this program of study was to collect sufficient data

to compare the energy release rate of the ignition sources that could be

generated within a television receiver with the ignition source specified in

the UL 1410 standard. Comparison of these ignition sources was complicated

by the fact that the UL 1410 ignition source was a small flame and all of the

ignition sources generated in the television receivers were non-flaming hot

spots.

As reported in the previous sections the energy release rate from the

burner specified in the UL 1410 standard is approximately 60 watts. The

16
temperature in the flame, although not measured, should be in the neighborhood

of 1900°C. For comparison, maximum component temperatures and power dissipation

recorded in the television tests are tabulated in table 1.

Generally speaking, ignition sources with the same order of magnitude of

energy release as the flame were generated during the test. The temperatures

of the stressed components were of course lower than the methane-air burner

flame specified in the UL 1410 standard. The combination of highest temperature

and highest power dissipation occurred in test 3 in which resistor Rl reached

635°C dissipating 40 watts. In test 3, this condition lasted for only a brief

time (see fig. 6) . The worst case recorded was test 2 on the 12-in black and

white portable where the receiver operated continuously with resistor "^5 dissipating 30 watts at temperatures in excess of 550°C (see fig, 4).

From the measurements made it has been verified that the ignition source specified in the UL 1410 standard has an energy release rate the same order

of magnitude as ignition sources that can be generated by electric failures

in the television receiver. This, of course, is not sufficient evidence to

verify that the UL 1410 ignition source or test procedure is a good simulation

of the television ignition problem, because of the difference in the character

of the sources. In the UL 1410 (UL 94) test procedure, a combustible is

exposed to a flame for 10 seconds. In the television receiver the same material may be exposed continuously to a hot spot at temperatures in excess of

500°C.

9. CONCLUSIONS

In the four television receivers studied in this program, no flaming

ignition sources were generated by introducing electrical failures in the

circuitry. It was possible to generate hot spots having temperatures in

excess of 500°C. Dust contamination applied artificially to one black and

white receiver was shown to have negligible effect in the tests. The effect

of material aging or long term deterioration was not examined. Although every

possible failure mode could not be examined, the resistance of the receivers

to ignition from electrical overload failure was found to be good in the tests

conducted. No work was done to simulate arcing failures or glowing connections.

The energy release rate from the gas burner ignition source specified in

the UL 1410 standard was estimated to be 60 +8 watts. This is the same order

of magnitude as the energy dissipated from stressed components in a television

receiver with an electrical fault present. However, this is not offered as justification that the UL 1410 ignition source or test procedure is a good

simulation of the television ignition problem.

Supplementary tests were conducted to measure the increase in operating

temperature for these television receivers with the enclosure vents blocked.

These tests showed that an increase of less than 20 °C occurred in the operating

temperature of electronic components in the sealed enclosures.

10. REFERENCES

[1] UL 1410 Standard for Television Receivers and Video Products, 13th edition,

revised June 13, 1978, Underwriters Laboratories Inc, Northbrook, 111.

12] Harwood, Beatrice, Analysis of Subpoenaed Television Data, HIA Special

Report, U.S. Consumer Product Safety Commission, March 1978.

[3] UL 94 Tests for Flammability of Plastic Materials for Parts in Devices

and Appliances, 2nd edition, revised July 30, 1976, Underwriters

Laboratories Inc, Northbrook, 111.

17
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Table 2

.

Range of component operating temperatures

Set Normal operation Cabinet sealed

30.5-cm B&W 60 to 144°C 76 to 157°C

48.3-cm B&W 55 to 128 60 to 139

48.3-cm color 44 to 122 *

63.5-cm color 39 to 163 48 to 166

* Extensive damage to the receiver in test 22 did not permit these

measurements to be made.

21
Table 3. Effect of ventilation on temoeratures of selected comoonents

Black and White Receivers

Receiver Thermocouple Cabinet open C abinet closed Cabinet sealed

size location (No rmal operation)

Degrees C 1 Degrees C Degrees C

30. 5-cm cabinet 38 49

wire bundle 43 50 59

to CRT socket

Rl(a) 52 60 76

R2 92 108 120

R5 98 106 115

R4 112 121 136

R3 126 139 151

R7 142 144 157

48. 3- cm cabinet 36 42

fuse 56 55 60

power 59 63 74

transformer

CRT neck 56 69 78

R13(b) 75 79 88

R14 68 79 91

RIO 98 96 106

R12 113 117 126

Rll 125 128 139

B. Color Receivers

4 8. 3- cm R28 (c)

R27

R26

R22

R24

R29

R21

40

41

52

51

75

85

103

44

44

54

62

75

94

122

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R33

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R37

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55

96

119

140

155

34

39

41

58

102

122

149

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34

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43

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107

125

150

166

(a) Components identified in figure 3 (b) Components identified in figure 9 (c) Components identified in figure 16

(d) Components identified in figure 22

(e) Extensive damage to the receiver in test 22 did not permit these

measurements to be made.

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53
'1BS-114A (REV. 9-781

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS Tech Note 11092.Sov*t. Aca&iion No, 5. R^ciptEn!' s- AcossHiorj S©.

4. TITLE AND SUBTITLE

CHARACTERIZATION OF ELECTRICAL IGNITION

SOURCES WITHIN TELEVISION RECEIVERS

5. Publication D^te October 1979

S. Performins Organization Code

7. AUTHORiSi

George J. Rogers and David D. Evans

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

It, Project/Ta^c/WoA Ifert No.

A.

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS rSfreer, City, State, ZIP) U. S, Consumer Product Safety Commission

Washington, D.C. 2 02 07

13. Type of Report & Period Covered Final

14. ^on^mng Agstcy Code

15. SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, Fi PS Software Summary, is attached.

Ibi ABSTRACT (A 200~word or les3 factual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.) The ignition of television receivers initiated

by electrical failures in the circuitry was examined

by studying four receivers. They were: two black

and white portables, a color portable, and a color

console receiver. Selected locations within the

circuitry were stressed by introducing full or

partial short circuits to simulate the failure of

electronic components. The temperatures and increased

power dissipation generated by short-circuited

components were recorded. Although component temperatures greater than 500°C were achieved, no flaming

ignition sources were generated.

For comparative purposes the energy release rate

of the ignition source specified in the UL 1410 test

procedure was measured. Supplemental measurements on

the operating temperatures of chassis components under

varying ventilation conditions were also made.

17. KEY WORDS (six to fwe/ve entries,- alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Electrical failure; fire contairiirie;.t; ignition; television fire

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