MEASURING RESISTANCE
SECTION FOUR
Turn a circuit
off before measuring resistance.
If any voltage
is present, the value of resistance will be incorrect.
In most cases
you cannot measure a component while it is in-circuit. This is because the
meter is actually measuring a voltage across a component and calling it a"
resistance."The voltage comes from the battery inside the meter. If any
other voltage is present, the meter will produce a false reading.
If you are
measuring the resistance of a component while still "in circuit,"
(with the power off) the reading will be lower than the true reading
Measuring
resistance
Measuring
resistance of a heater (via the leads)
Measuring
the resistance of a piece of resistance-wire
Measuring
the resistance of a resistor
Do
not measure the "Resistance of a Battery"
1. Do not
measure the "resistance of a battery." The resistance of a battery
(called the internal impedance) is not measured as shown in the diagrams above.
It is measured by creating a current-flow and measuring the voltage across the
battery. Placing a multimeter set to resistance
(across a battery) will destroy the meter.
2. Do not try to
measure the resistance of any voltage or any "supply."
Resistance is
measured in OHMs.
The resistance
of a 1cm x 1cm bar, one meter long is 1 ohm.
If the bar is
thinner, the resistance is higher. If the bar is longer, the resistance is higher.
If the material l of the bar is changed, the resistance is higher.
When carbon is
mixed with other elements, its resistance increases and this knowledge is used
to make RESISTORS.
Resistors have
RESISTANCE and the main purpose of a resistor is to reduce the CURRENT FLOW.
It's a bit like
standing on a hose. The flow reduces.
When current
flow is reduced, the output voltage is also reduced and that why the water does
not spray up so high. Resistors are simple devices but they produce many different
effects in a circuit.
A resistor of
nearly pure carbon may be 1 ohm, but when non-conducting "impurities"
are added, the same-size resistor may be 100 ohms, 1,000 ohms or 1 million
ohms.
Circuits use
values of less than 1 ohm to more than 22million ohms.
Resistors are
identified on a circuit with numbers and letters to show the exact value of
resistance - such as 1k 2k2 4M7
The letter (omega
- a Greek symbol) is used to identify the word "Ohm. "but this symbol
is not a variable on some word-processors, so the letter "R" is used.
The letter
"E" is also sometimes used and both mean "Ohms."
A one-ohm
resistor is written "1R" or "1E." It can also be written
"1R0" or "1E0."
A resistor of
one-tenth of an ohm is written "0R1" or "0E1." The letter takes the place of the decimal
point.
10 ohms = 10R
100 ohms = 100R
1,000 ohms = 1k
(k= kilo = one thousand)
10,000 ohms =
10k
100,000 ohms =
100k
1,000,000 ohms =
1M (M = MEG = one million)
The size of a
resistor has nothing to do with its resistance. The size determines the wattage
of the resistor - how much heat it can dissipate without getting too hot.
Every resistor
is identified by color bands on the body, but when the resistor is a surface-mount
device, numbers are used and sometimes letters.
You MUST learn
the colour code for resistors and the following table shows all the
colours for the
most common resistors from 1/10th of an ohm to 22 Meg ohms for resistors with 5% and 10%
tolerance.
If 3rd band is
gold, divide by 10
If 3rd band is
silver, Divide by 100(to get 0.22ohms etc
PICTURE 19
Reading
4-band resistors
The most
"common" type of resistor has 4 bands and is called the 10% resistor.
It now has a tolerance of 5% but is still called the "10% type" as
the colours increase by 20%so that a resistor can be 10% higher or 10% lower
than a particular value and all there resistors produced in a batch can be
used.
The first 3
bands produce the resistance and the fourth band is the "tolerance"
band.
Gold = 5%
(Silver =10% but
no modern resistors are 10%!! - they are 5% 2% or 1%)
RESISTORS
LESS THAN 10 OHMS
When the third
band is gold, it indicates the value of the "colors" must be
divided by
10.
Gold = "divide
by 10" to get values 1R0 to 8R2
When the third
band is silver, it indicates the value of the "colors" must be
divided by
100. (Remember:
more letters in the word "silver" thus the divisor is "a larger division.")
Silver = "divide
by 100" to get values R1 to R82e.g: 0R1 = 0.1 ohm 0R22 = point 22 ohms
See 4th Column
above for examples.
The letters
"R, k and M" take the place of a decimal point.
e.g:
1R0 = 1
ohm, 2R2 = 2 point 2 ohms, 22R = 22 ohms, 2k2 = 2,200 ohms 100k = 100,000 ohms
2M2 =
2,200,000 ohms
HOW
TO REMEMBER THE COLOUR CODE:
Each colour has
a "number" (or divisor) corresponding to it.
Most of the
colours are in the same order as in the spectrum. You can see the spectrum in a
rainbow. It is: ROY G BIV and the
colours for resistors are in the same sequence.
Black, Brown -
colour of increasing temperature, Red, Orange, Yellow, Green
Blue
(indigo- that
part of the spectrum between blue and violet) violet, gray, white
Colour value
No of zero's
Silver-2 divide
by 100, Gold-1 divide by 10, Black 0 No zeros, Brown 1 0
Red 2 00, Orange
3,000 or k, Yellow 4 0,000, Green 5
00,000, Blue 6M
Violet 7, Gray 8, White 9
Here are some
common ways to remember the colour code:
Bad Beer Rots
Our Young Guts, But Vodka Goes Well
Bright Boys Rave
Over Young Girls But Violet Gets Wed
Bad Boys Rave
Over Young Girls But Violet Gets Wed with Gold and Silver.
Reading 5-band
resistors:
5-band resistors
are easy to read if you remember two simple points. The first three bands
provide the digits in the answer and the 4th band supplies the number of zero's.
Reading
"STANDARD VALUES"
(on 5-band
resistors)
5-band resistors
are also made in "Standard Values" but will have different colours
to4-band "common" resistors - and will be confusing if you are just
starting out. For instance, a 47k 5% resistor with 4-bands will be:
yellow-purple-orange-gold. For a 47k
1% resistor the
colours will be yellow-purple-black-red-brown. The brown colour band represents
1%.
The first two
colour-bands for a STANDARD VALUE or "common value" in 1% or 5%will
be the SAME. These two bands provide the digits in the answer.
It's the 3rd
band for a 5% resistor that is expanded into two bands in a 1% resistor.
But it's easy to
follow.
For a standard
value, the 3rd band in a 1% resistor is BLACK. This represents a ZERO in the
answer. (For 5-band resistors BLACK represents a ZERO when in the third band.
This is
different to 4-band resistors where black represents the word OHMS! If thethird
band is BROWN, the answer will be 1).
So the 4th band
has to represent one-less ZERO and is one colour UP THE COLOUR CHART! In other words the 3rd and 4th bands
(combined) on a 1% resistor produces the same number of zero's as the 3rd band
on a 5% resistor!
Resistors come
in a range of values and the two most common are the E12 and E24series. The E12
series comes in twelve values for each decade. The E24 series come in
twenty-four values per decade.
E12 series - 10,
12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82
E24 series - 10,
11, 12, 13, 15, 16, 18, 20, 22, 24, 27, 30, 33, 36, 39, 43, 47, 51, 56, 62, 68,
75, 82,
91
Here is the
complete list of 1% 1/4watt resistors from:
CIRCUIT SPECIALISTS.
The following
list covers 10 ohms (10R) to 1M. To buy 1% resistors from Circuit Specialists,
click:
10R 121R
806R 3k83 7k15
14k7 39k2 121k
12R1 150R 825R 3k92 7k5 15k
40k2 147k
15R 182R
909R 4k02 7k87
15k84 4k2 150k
18R2 200R
1k0 4k22 71k5 16k9
46k4 182k
22R1 221R
1k21 4k64 8k06 17k4 47k
200k
27R4 240R
1k5 4k75 8k25
17k8 47k5 212k
30R1 249R
1k82 4k7 8k45
18k2 49k9 221k
33R2 274R
2k4 k87 8k66 20k 51k1
226k
36R5 301R
2k21 4k99 8k87
22k1 53k6 249k
39R2 332R
2k 25k11 9k09
22k6 56k2 274k
47R5 348R
2k43 5k23 9k31 23k7
61k 9 301k
49R9 392R
2k49 5k36 9k53
24k9 68k1 332k
51R1 402R
2k67 5k49 9k76
27k 4 6 9k8 357k
56R2 475R
2k74 5k62 10k 29k4 75k0
392k
68R1 499R
3k01 5k76 11k3
0k1 82k5 475k
75R 565R
3k32 5k9 12k
33k2 90k 487k
82R5 604R
3k48 6k04 12k1
34k8 90k9 499k
90R9 681R
3k57 6k19 12k4
36k5 95k3 562k
100R 750R
3k74 6k81 13k
38k3 100k 604k
1M
Here is the list
of 1% resistors from suppliers (such as Farnell):
1R0 13R
68R 360R 1k8 9k1 47k
240k
1R2 15R
75R 390R 2k0 10k 51k
270k
1R5 16R
82R 430R 2k2 11k 56k
300k
2R2 18R 91R
470R 2k 412k 62k
330k
2R7 20R
100R 510R 2k7 13k 68k
360k
3R3 22R
110R 560R 3k 15k 75k
390k
3R9 24R
120R 620R 3k3 16k 82k
430k
4R7 27R
130R 680R 3k6 18k 91k
470k
5R6 30R
150R 750R 3k9 20k 100k
510k
6R2 33R
160R 820R 4k3 22k 110k
560k
6R8 36R
180R 910R 4k7 24k 120k
620k
7R5 39R
200R 1k 5k1 27k
130k 680k
8R2 43R
220R 1k1 5k6
30k 150k 750k
9R1 47R
240R 1k2 6k2
33k 160k 820k
10R 51R
270R 1k3 6k8
36k 180k 910k
11R 56R
300R 1k5 7k5
39k 200k 1M
12R 62R
330R 1k6 8k2
43k 220k
Surface Mount Resistors
4-Digit Surface Mount Resistor on a PC Board
3-Digit
Surface Mount Resistor on a PC Board
The photo above
shows surface mount resistors on a circui t board. The components that are not marked are capacitors
(capacitors are NEVER marked).
All the SM
resistors in the above photos conform to a 3-digit or 4-digit code. But there are a number of codes, and the
4-digit code caters for high tolerance resistors, so it's getting very complicated.
Here is a basic 3-digit SM resistor
The first two
digits represent the two digits in the answer. The third digit represents the number of zero's you must place
after the two digits. The answer will be OHMS.
For example: 334
i s written 33 0 000. This is written 330,000 ohms. The comma can
be replaced by
the letter "k". The final answer is: 330k.
222 = 22 00 =
2,200 = 2k2
473 = 47
000 = 47,000 = 47k
474 = 47 0000 =
470,000 = 470k
105 = 10 00000 =
1,000,000 = 1M = one million ohms
There is one
trick you have t o remember. Resistances less than 100 ohms are written:
100, 220, 470.
These are 10 and NO zero's = 10 ohms = 10R
or 22 and no
zero's = 22R or 47 and no zero's = 47R.
Sometimes the resistor is marked: 10, 22 and 47 to prevent a mistake.
Remember
:
R = ohms
k = kilo ohms =
1,000 ohms
M = Meg =
1,000,000 ohms
The 3 letters
(R, k and M) are put in place of the decimal point. This way you cannot make a mistake when reading a value
of resistance.
THE COMPLETE RANGE OF SM RESISTOR
MARKINGS
Click to see the
complete range of SM resistor markings for 3-digit code:
Click to see the
complete range of SM resistor markings for 4-digit code:
0000 is a value
on a surface-mount resistor. It is a zero-ohm
LINK
!
Resistances less
than 10 ohms have 'R' to indicate the position of the decimal point.
Here are some examples
Three Digit Examples
330 is 33 ohms - not 330 ohms
221 is 220 ohms
683 is 68 000 ohms, or 68k
105 is 1 000 000 ohms, or
1M
8R2 is 8.2 ohms
Four Digit Examples
1000 is 100 ohms - not 1000 ohms
4992 is 49 900 ohms, or 49k
1623 is 162 000 ohms, or
162k
0R56 or R56 is 0.56 ohms
A new coding
system ha s appeared on 1% types. This is known as the EIA-96 marking method. It consists of a
three-character code. The first two digits signify the 3 significant digit s of the resistor
value, using the lookup table below. The third character- a letter - signifies
the multiplier.
code value code value code value
code value code value code value
01
100 17 147 33 215 49 316 65 464 81 681
02
102 18 150 34 221 50 324 66 475 82 698
03
105 19 154 35 226 51 332 67 487 83 715
04
107 20 158 36 232 52 340 68 499 84 732
05
110 21 162 37 237 53 348 69 511 85 750
06
113 22 165 38 243 54 357 70 523 86 768
07
115 23 169 39 249 55 365 71 536 87 787
08
118 24 174 40 255 56 374 72 549 88 806
09
121 25 178 41 261 57 383 73 562 89 825
10 124 26 182
42 267 58 392 74 576 90 845
11 127 27 187 43 274 59 402 75 590 91 866
12 130 28 191 44 280 60 412 76 604 92 887
13 133 29 196 45 287 61 422 77 619 93 909
14 137 30 200 46 294 62 432 78 634 94 931
15 140 31 205 47 301 63 442 79 649 95 953
16 143 32 210 48 309 64 453 80 665 96 976
The multiplier letters are as follows:
Letter mult
F 100000
E 10000
D 1000
C 100
Letter mult
B 10
A 1
X or S 0.1
Y or R 0.01
22A is a 165 ohm resistor, 68C is a 49900 ohm (49k9) and 43E a 2740000 (2M74).
This marking
scheme applies to 1% resistors only. A similar arrangement can be used for
2% and 5% tolerance types. The multiplier letters are identical to 1% ones, but occur before the number code and the following code is used:
2% 5%
Code value code value
code value code value
01 100 13 330 25 100 37 330
02 110 14 360 26 110 38 360
03 120 15 390 27 120 39 390
04 130 16 430 28 130 40 430
05 150 17 470 29 150 41 470
06 160 18 510 30 160 42 510
07 180 19 560 31 180 43 560
08 200 20 620 32 200 44 620
09 220 21 680 33 220 45 680
10 240 22 750 34 240 46 750
11 270 23 820 35 270 47 820
12 300 24 910 36 300 48 910
With this
arrangement,C31 is 5%, 18000 ohm (18k), and D18 is 510000 ohms (510k) 2% tolerance.
Always check
with an ohm-meter (a multimeter) to make sure.
Chip
resistors come in the following styles and ratings:
Style: 0402, 0603, 0805, 1206, 1210, 2010, 2512, 3616, 4022
Power Rating: 0402(1/16W), 0603(1/10W), 0805(1/8W), 1206(1/4W), 1210(1/3W), 2010(3/4W), 2512(1W), 3616(2W), 4022(3W)
Tolerance: 0.1%, 0.5%, 1%, 5%
Temperature Coefficient: 25ppm 50ppm 100ppm.
EIA
marking code for surface mount (SMD) resistors
01S = 1R 01R
= 10R
01A = 100R 01B = 1k 01C
= 10k
01D = 100k 01E = 1M 01F
= 10M
02S = 1R02 02R
= 10R2
02A = 102R 02B = 1k02 02C
= 10k2
02D = 102k 02E = 1M02
03S = 1R05 03R
= 10R5
03A = 105R 03B = 1k05 03C
= 10k5
03D = 105k 03E = 1M05 18F = 15M
04S = 1R07 04R
= 10R7
04A = 107R 04B = 1k07 04C
= 10k7
04D = 107k 04E = 1M07
05S = 1R1 05R
= 11R
05A = 110R 05B = 1k1 05C
= 11k
05D = 110k 05E = 1M1 30F
= 20M
06S = 1R13 06R
= 11R3
06A = 113R 06B = 1k13 06C
= 11k3
06D = 113k 06E = 1M13
07S = 1R15 07R
= 11R5
07A = 115R 07B = 1k15 07C
= 11k5
07D = 115k 07E = 1M15
08S = 1R18 08R
= 11R8
08A = 118R 08B = 1k18 08C
= 11k8
08D = 118k 08E = 1M18
09S = 1R21 09R
= 12R1
09A = 121R 09B = 1k21 09C
= 12k1
09D = 121k 09E = 1M21
10S = 1R24 10R
= 12R4
10A = 124R 10B = 1k24 10C
= 12k4
10D = 124k 10E = 1M24
11S = 1R27 11R
= 12R7
11A = 127R 11B =
1k27
11C = 12k7 11D = 127k 11E
= 1M27
12S = 1R3 12R
= 13R
12A = 130R 12B = 1k3 12C
= 13k
12D = 130k 12E = 1M3
13S = 1R33 13R
= 13R3
13A = 133R 13B = 1k33 13C
= 13k3
13D = 133k 13E = 1M33
14S = 1R37 14R
= 13R7
14A = 137R 14B = 1k37 14C
= 13k7
14D = 137k 14E = 1M37
15S = 1R4 15R
= 14R
15A = 140R 15B = 1k4 15C
= 14k
15D = 140k 15E = 1M4
16S = 1R43 16R
= 14R3
16A = 143R 16B = 1k43 16C = 14k3 16D = 143k 16E
= 1M43
17S = 1R47 17R
= 14R7
17A = 147R 17B = 1k47 17C
= 14k7
17D = 147k 17E = 1M47
18S = 1R5 18R
= 15R
18A = 150R 18B = 1k5 18C
= 15k
18D = 15k 18E = 1M5
19S = 1R54 19R
= 15R4
19A = 154R 19B = 1k54 19C
= 15k4
19D = 154k 19E = 1M54
20S = 1R58 20R
= 15R8
20A = 158R 20B = 1k58 20C
= 15k8
20D = 158k 20E = 1M58
21S = 1R62 21R
= 16R2
21A = 162R 21B = 1k62 21C
= 16k2
21D = 162k 21E = 1M62
22S = 1R65 22R
= 16R5
22A = 165R 22B = 1k65 22C
= 16k5
22D = 165k 22E = 1M65
23S = 1R69 23R
= 16R9
23A = 169R 23B = 1k69 23C
= 16k9
23D = 169k 23E = 1M69
24S = 1R74 24R
= 17R4
24A = 174R 24B = 1k74 24C
= 17k4
24D = 174k 24E = 1M74
25S = 1R78 25R
= 17R8
25A = 178R 25B = 1k78 25C
= 17k8
25D = 178k 25E = 1M78
26S = 1R82 26R
= 18R2
26A = 182R 26B = 1k82 26C
= 18k2
26D = 182k 26E = 1M82
27S = 1R87 27R
= 18R7
27A = 187R 27B = 1k87 27C
= 18k7
27D = 187k 27E = 1M87
28S = 1R91 28R
= 19R1
28A = 191R 28B = 1k91 28C
= 19k1 28D = 191k 28E
= 1M91
29S = 1R96 29R
= 19R6
29A = 196R 29B = 1k96 29C
= 19k6
29D = 196k 29E = 1M96
30S = 2R0 30R
= 20R0
30A = 200R 30B =
2k0
30C = 20k0 30D =
200k
30E = 2M0
31S = 2R05 31R
= 20R5
31A = 205R 31B = 2k05 31C
= 20k5
31D = 205k 31E = 2M05
32S = 2R10 32R
= 21R0
32A = 210R 32B = 2k10 32C
= 21k0
32D = 210k 32E = 2M10
33S = 2R15 33R
= 21R5
33A = 215R 33B = 2k15 33C
= 21k5
33D = 215k 33E = 2M15
34S = 2R21 34R
= 22R1
34A = 221R 34B = 2k21 34C
= 22k1
34D = 221k 34E = 2M21
35S = 2R26 35R
= 22R6
35A = 226R 35B = 2k26 35C
= 22k6
35D = 226k 35E = 2M26
36S = 2R32 36R
= 23R2
36A = 232R 36B = 2k32 36C
= 23k2
36D = 232k 36E = 2M32
37S = 2R37 37R
= 23R7
37A = 237R 37B = 2k37 37C
= 23k7 37D = 237k 37E
= 2M37
38S = 2R43 38R
= 24R3
38A = 243R 38B = 2k43 38C
= 24k3
38D = 243k 38E
= 2M43
39S = 2R49 39R
= 24R9
39A = 249R 39B = 2k49 39C
= 24k9
39D = 249k 39E = 2M49
40S = 2R55 40R
= 25R5
40A = 255R 40B = 2k55 40C
= 25k5
40D = 255k 40E = 2M55
41S = 2R61 41R
= 26R1
41A = 261R 41B = 2k61 41C
= 26k1
41D = 261k 41E = 2M61
42S = 2R67 42R
= 26R7
42A = 267R 42B = 2k67 42C
= 26k7
42D = 267k 42E = 2M67
43S = 2R74 43R
= 27R4
43A = 274R 43B =
2k74
43C = 27k4 43D = 274k 43E
= 2M74
44S = 2R80 44R
= 28R0
44A = 280R 44B = 2k80 44C
= 28k0
44D = 280k 44E = 2M80
45S = 2R87 45R = 28R7 45A = 287R 45B
= 2k87
45C = 28k7 45D = 287k 45E
= 2M87
46S = 2R94 46R
= 29R4
46A = 294R 46B = 2k94 46C
= 29k4
46D = 294k 46E = 2M94
47S = 3R01 47R
= 30R1
47A = 301R 47B = 3k01 47C
= 30k1
47D = 301k 47E = 3M01
48S = 3R09 48R
= 30R9
48A = 309R 48B = 3k09 48C
= 30k9
48D = 309k 48E = 3M09
49S = 3R16 49R
= 31R6
49A = 316R 49B = 3k16 49C
= 31k6
49D = 316k 49E = 3M16
50S = 3R24 50R
= 32R4
50A = 324R 50B = 3k24 50C
= 32k4
50D = 324k 50E = 3M24
51S = 3R32 51R
= 33R2
51A = 332R 51B = 3k32 51C
= 33k2
51D = 332k 51E = 3M32
52S = 3R4 52R
= 34R0
52A = 340R 52B = 3k4 52C
= 34k0
52D = 340k 52E = 3M4
53S = 3R48 53R
= 34R8
53A = 348R 53B = 3k48 53C
= 34k8
53D = 348k 53E = 3M48
54S = 3R57 54R
= 35R7
54A = 357R 54B = 3k57 54C
= 35k7
54D = 357k 54E = 3M57
55S = 3R65 55R
= 36R5
55A = 365R 55B = 3k65 55C
= 36k5
55D = 365k 55E = 3M65
56S = 3R74 56R
= 37R4
56A = 374R 56B = 3k74 56C
= 37k4
56D = 374k 56E = 3M74
57S = 3R83 57R
= 38R3
57A = 383R 57B = 3k83 57C
= 38k3
57D = 383k 57E = 3M83
58S = 3R92 58R
= 39R2
58A = 392R 58B = 3k92 58C
= 39k2
58D = 392k 58E = 3M92
59S = 4R02 59R
= 40R2
59A = 402R 59B = 4k02 59C
= 40k2
59D = 402k 59E = 4M02
60S = 4R12 60R
= 41R2
60A = 412R 60B = 4k12 60C
= 41k2
60D = 412k 60E = 4M12
61S = 4R22 61R
= 42R2
61A = 422R 61B = 4k22 61C
= 42k2
61D = 422k 61E = 4M22
62S = 4R32 62R
= 43R2
62A = 432R 62B = 4k32 62C
= 43k2
62D = 432k 62E = 4M32
63S = 4R42 63R
= 44R2
63A = 442R 63B = 4k42 63C
= 44k2
63D = 442k 63E = 4M42
64S = 4R53 64R = 45R3 64A = 453R 64B
= 4k53
64C = 45k3 64D = 453k 64E
= 4M53
65S = 4R64 65R
= 46R4
65A = 464R 65B = 4k64 65C
= 46k4
65D = 464k 65E = 4M64
66S = 4R75 66R
= 47R5
66A = 475R 66B = 4k75 66C
= 47k5
66D = 475k 66E = 4M75
67S = 4R87 67R
= 48R7
67A = 487R 67B = 4k87 67C
= 48k7
67D = 487k 67E = 4M87
68S = 4R99 68R
= 49R9
68A = 499R 68B = 4k99 68C
= 49k9
68D = 499k 68E = 4M99
69S = 5R11 69R
= 51R1
69A = 511R 69B = 5k11 69C
= 51k1
69D = 511k 69E = 5M11
70S = 5R23 70R
= 52R3
70A = 523R 70B = 5k23 70C
= 52k3
70D = 523k 70E = 5M23
71S = 5R36 71R
= 53R6
71A = 536R 71B = 5k36 71C
= 53k6
71D = 536k 71E = 5M36
72S = 5R49 72R
= 54R9 72A = 549R 72B
= 5k49
72C = 54k9 72D = 549k 72E
= 5M49
73S = 5R62 73R
= 56R2
73A = 562R 73B = 5k62 73C
= 56k2
73D = 562k 73E = 5M62
74S = 5R76 74R
= 57R6
74A = 576R 74B = 5k76 74C
= 57k6
74D = 576k 74E = 5M76
75S = 5R9 75R
= 59R0
75A = 590R 75B = 5k9 75C
= 59k0
75D = 590k 75E = 5M9
76S = 6R04 76R
= 60R4
76A = 604R 76B = 6k04 76C
= 60k4
76D = 604k 76E = 6M04
77S = 6R19 77R
= 61R9 77A = 619R 77B
= 6k19
77C = 61k9 77D = 619k 77E
= 6M19
78S = 6R34 78R
= 63R4
78A = 634R 78B = 6k34 78C
= 63k4
78D = 634k 78E = 6M34
79S = 6R49 79R
= 64R9
79A = 649R 79B = 6k49 79C
= 64k9
79D = 649k 79E = 6M49
80S = 6R65 80R
= 66R5
80A = 665R 80B = 6k65 80C
= 66k5
80D = 665k 80E = 6M65
81S = 6R81 81R
= 68R1
81A = 681R 81B = 6k81 81C
= 68k1
81D = 681k 81E = 6M81
82S = 6R98 82R
= 69R8
82A = 698R 82B = 6k98 82C
= 69k8
82D = 698k 82E = 6M98
83S = 7R15 83R
= 71R5
83A = 715R 83B = 7k15 83C
= 71k5
83D = 715k 83E = 7M15
84S = 7R32 84R
= 73R2
84A = 732R 84B = 7k32 84C
= 73k2
84D = 732k 84E = 7M32
85S = 7R5 85R
= 75R0
85A = 750R 85B = 7k5 85C
= 75k0
85D = 750k 85E = 7M5
86S = 7R68 86R
= 76R8
86A = 768R 86B = 7k68 86C
= 76k8
86D = 768k 86E = 7M68
87S = 7R87 87R
= 78R7
87A = 787R 87B = 7k87 87C
= 78k7
87D = 787k 87E = 7M87
88S = 8R06 88R
= 80R6 88A = 806R 88B
= 8k06
88C = 80k6 88D = 806k 88E
= 8M06
89S = 8R25 89R
= 82R5
89A = 825R 89B = 8k25 89C
= 82k5
89D = 825k 89E = 8M25
90S = 8R45 90R
= 84R5
90A = 845R 90B = 8k45 90C
= 84k5
90D = 845k 90E = 8M45
91S = 8R66 91R
= 86R6
91A = 866R 91B = 8k66 91C
= 86k6
91D = 866k 91E = 8M66
92S = 8R87 92R
= 88R7
92A = 887R 92B = 8k87 92C
= 88k7 92D = 887k 92E
= 8M87
93S = 9R09 93R
= 90R9
93A = 909R 93B = 9k09 93C = 90k9 93D = 909k 93E
= 9M09
94S = 9R31 94R
= 93R1
94A = 931R 94B = 9k31 94C
= 93k1
94D = 931k 94E = 9M31
95S = 9R53 95R
= 95R3
95A = 953R 95B = 9k53 95C
= 95k3
95D = 953k 95E = 9M53
96S = 9R76 96R
= 97R6
96A = 976R 96B = 9k76 96C
= 97k6
96D = 976k 96E = 9M76
If you want an accurate RESISTANCE measurement, remove the resistor from
the circuit and use a Digital meter
SURFACE
MOUNT COMPONENTS - PACKS
Talking
Electronics has pack s of components for the repairman. The following packs are
available:
SURFACE
MOUNT RESISTOR PACK consists of 1 off each standard value
10 ohms to 1M
& 2M2 (60 resistors) $14.20 including pack and post
SURFACE
MOUNT CAPACITOR PACK consists of: 2 - 10p 5 - 47p 5 - 100p 5 -
470p 5 - 1n 5 - 10n
5 - 22n 5 - 100n
5 - 1u 16v
electrolytic 5 - 10u 16v electrolytic (40 components)
$23.80 including pack and post
SURFACE
MOUNT DIODE PACK consists of: 5 - 1N 4148 (marked as "A6")
$10.00 including pack and post
SURFACE
MOUNT TRANSISTOR PACK consists of: 5 - BC 848 (marked as "1K") NPN 5 - BC858 PNP $10.00 including pack and post
CREATING
ANY VALUE OF RESISTANCE
Any value of
resistance can be created by connecting two resistors in PARALLEL or SERIES.
You can also
create a higher wattage resistor by connecting them in SERIES OR
PARALLEL.
We are only
going to cove r two EQUAL VALUE resistors in SERIES or in PARALLEL.
If you want to
create a "Special Value," simply connect two resistors and read the value with a Digital Meter. Keep
changing the values until you get the required value.
We are not going
into series or Parallel formulae. You
can easily find a value with a
multimeter.
TWO
EQUAL-VALUE RESISTORS IN SERIES
Two equal-value
resistors IN SERIES creates a value of DOUBLE. You simply ADD the values.
This can be done
with any to two values as shown. Three equal-value resistors in series is three times the value
TWO
EQUAL-VALUE RESISTORS IN PARALLEL
Two equal-value
resistors I N PARALLEL creates a value of HALF. Three equal-value resistors in parallel is equal to one-third the
value.
If you want a
particular value and it is not available, here is a chart.
Use 2 resistors
in series or parallel as shown:
Required Value R1 Series/ Parallel R2 Actual value
10 4R7
S 4R7
9R4
12 10
S 2R2 12R2
15 22
P 47 14R9
18 22 P
100 18R
22 10
S 12 22
27 22
S 4R7
26R7
33 22 S 10 32R
39 220 P
47 38R7
47 22 S 27 49
56 47 S 10 57
68 33 S 33 66
82 27 S 56 83
There are other
ways to combine 2 resistors in parallel or series to get a particular value. The examples above are just
one way. 4R7 = 4.7 ohms
TESTING
A RESISTOR
To check the
value of a resistor, it should be removed from the circuit. The surrounding
components can affect the
reading and make it lower.
Resistors VERY RARELY change value, but if it is
overheated or damaged, the resistance can
increase. You can take the reading of a resistor
"in-circuit" in one direction then the other, as the surrounding components may have
diodes and this will alter the reading.
You can also
test a resistor by feeling its temperature-rise. It is getting too hot if you
cannot hold your finger on it (some "metal film" resistors are designed to
tolerate quite high temperatures).
TESTING
AN "AC" RESISTOR
There is no such
thing as an "AC" resistor. Resistors are just "resistors"
and they can be in AC circuits or DC circuits. Resistors
can be given names such as "Safety Resistor" "Ballast Resistor"
"LOAD
Resistor" "Feed Resistor" "Dropper Resistor" or
"Supply Resistor." These are jus t normal resistors with a normal resistance
- except a "Safety Resistor."
A safety
resistor is made of a flame-proof material such as metal-oxide-film and not carbon-composition.
It is designed to "burn out" when too much current flows BUT NOT
CATCH FIRE.
It is a
low-value resistor and has a voltage-drop across it but this is not
intentional. The voltage-drop is to create a "heating-effect" to burn out the resistor. In all
the other types of resistor, the voltage-
drop is intentional.
A Ballast
resistor is a normal resistor and can be called a Power resistor, Dropper
resistor, Supply resistor or Feed resistor. It is designed to reduce the voltage from one
source and deliver a lower voltage. It is a form of:
"in-line" resistor.
A Load Resistor
is generally connected across the output of a circuit and turns the energy it receives, into heat.
RESISTOR
NETWORKS
To reduce the
number of resistors in a circuit, some engineers use a set of identical
resistors in a package called a Single-In-Line (SIL) resistor network. It is
made with many resistors of the same value, all in one package. One end of each resistor is connected all the
other resistors and this is the common pin, identified as pin 1 and has a dot on the package.
These packages
are very reliable but to make sure all the resistors are as stated, you need to locate pin 1. All values will be
identical when referenced to this pin
RESISTOR
NETWORKS
Some resistor
networks have a "4S" printed on the component. The 4S indicates the
package contains 4
independent resistors that are not wired together inside. The housing has eight
leads as shown in the
second image.
Independent
resistors have an even number of pins and measuring between each pair will
produce identical
values. Resistance between any pair will indicate leakage and may be a fault
TESTING
A POSISTOR
A Posistor is a
resistor t hat connects in series with the degaussing coil around the picture tube or Monitor.
When cold, it
has a very low resistance and a large current flows when the monitor or TV is
switched on. This current heats up the Posistor and the resistance increases.
This causes the
current to decrease and any magnetism in the shadow mask is removed. The
posistor can one
or two elements and it is kept warm so the resistance remains high. Many
Posistors have a
second element inside the case that connects directly to the supply to keep the
Positive
Temperature Coefficient resistor high so that the current through the
degaussing coil falls to almost zero. This constant heat eventually destroys the package.
The heavy
current that flows when a set is turned ON also causes the posistor to crack
and break and this results
in poor purity on the screen - as the shadow mask gradually becomes magnetic..
Posistors have
different resistance values from different manufacturers and must be replaced
with an identical type.
They can be
checked for very low resistance when c old but any loose pieces ins ide the
case will indicate a
damaged component.
A
"BURNT" RESISTOR - normally and technically called a "burnt-out" resistor.
The resistance
of a "burnt" resistor can sometimes be determined by scraping away the outer coating - if the resistor
has a spiral of resistance-material. You may be able to find a spot where the spiral has
been damaged
Clean the
"spot" (burnt section of the spiral) very carefully and make sure you
can get a good contact
with the spiral and the tip of your probe. Measure from one lead of the resistor to the end of the damaged
spiral. Then measure from the other lead to the other end of the spiral.
Add the two
values and you have an approximate value for the resistor. You can add a small amount for the damaged
section.
This process
works very well for damaged wire-wound resistors. They can be pulled apart and each section of the
resistance-wire (nichrome wire) measured and added to get the full resistance.
There is another
way to determine the value of a damaged resistor.
Get a set of
resistors of the same wattage as the damaged component and start with a high value. It's handy to know if
the resistor is in the range: 10ohm to 100ohms or 1k to 10k etc, but this is not essential.
Start with a
very high value and turn the circuit ON. You can perform voltage tests and if you know the expected output
voltage, decrease the resistance until this voltage is obtained.
If you do not
know the expected voltage, keep reducing the value of resistance until the circuit works as designed.
This is the best
advice in a situation where you do not know the value of a resistor.
There is a third
way to determine the value and this requires measuring the voltage drop across the resistor and the current-flow.
By multiplying the two you will get a wattage and this must be less than the wattage of the resistor being
replaced.
TESTING
POTENTIOMETERS (variable resistors)
To check the
value of a variable resistor, it should be removed from circuit or at least 2 legs should be removed. A Rheostat
is a variable resistor using only one end and the middle connected to a circuit.
The resistance
between the two outside pins is the value marked on the component and the centre leg will change from
nearly zero to the full resistance as the shaft is rotated.
"Pots"
generally suffer from "crackle" when turned and this can be fixed by
spraying up the shaft and into the pot via the shaft with a tube fixed to a can of
"spray-lubricant" (contact cleaner).
"Pre-set
pots" and "trim pots" are miniature versions of a potentiometer
and they are all tested the same.
FOCUS
POTS
Focus pots quite
often get a spot of dirt where the wiper touches the track. Cleaning with spray fixes the bad focus but if
the pot is leaking to chassis from inside the pot (due to the high voltage on the terminals) simply remove
it from the chassis and leave it floating (this will restore the high voltage to the picture tube) or
you can use one from an old chassis
MAKING
YOUR OWN RESISTOR, CAPACITOR, INDUCTOR, or DIODE
Quite often you
will not have the exact value of resistance or capacitance for a repair.
We have already
covered placing resistors and capacitors in parallel and series:
Resistors
in Parallel and/or Series
Capacitors
in Parallel and/or Series
Here are some
extras:
RESISTORS
Two 1k 0.5watt
resistors in parallel produces a 470R 1watt resistor.
Two 1k 0.5watt
resistors in series produces a 2k 1watt resistor.
CAPACITORS
Two 100n 100v
capacitors in series produces a 50n capacitor @200v
INDUCTORS
: Two inductors
in series -
ADD THE VALUES
DIODES
: Two 1Amp 400v diodes in series produces a
1Amp 800v diode
Two 1Amp 400v
diodes in parallel produces a 2Amp 400v diode
ZENER DIODES:
Zener diodes can
be connected in series to get a higher voltage.
Two 12v zener
diodes in series produces a 24v zener.
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