27 POWERSUPPLYCRCUITS.3.6 Fault Fin

27 POWERSUPPLYCRCUITS.

3.6 Fault Finding Techniques and Typical Fault

Conditions

When a faulty power unit is returned for repair, the

fault has to be isolated to some particular portion of

the unit. The fault may lie in the transformer, the

rectifier, the filter section, or thegu1ator, and

measurement with a voltmeter will be necessary to

locate the fault.

However its probably best to start diagnosis with

a few rather obvious but often overlooked checks.

First measure the d.c. output voltage. If this is

zero, the next check should be on the mains input.

Is the mains supply reaching the transformer primary?

If it isn’t, there is the possibility of a faulty plug

(relatively simple to repairs), open circuit mains

wires, or a blown fuse. If the fuse i suspected always

test its continuity with an ohmmeter, never rely on

Just a visual Inspection It is also worth noting that

both the live and neutral wires may have a fuse in

circuit, so make sure bath are checked.

lithe fuse is blown it has done so because of some

fault condition and the fault must be cleared before

anew fuse is fitted. Resistance checks ‘(with’ the mains

unplugged!) must be used to locatštich a fault. Use

an ohmmeter to measure the resistance of the trans

former primary, the secondary, the rectifiers, and so

on. The winding resistance depends, of course, on

the size of the transformer. The primary resistance,

for a medium size transformer, should be low,

typically about 50 12. The secondary, usually supply.

ing a lower voltage, may have a resistance of only a

few ohms. Detecting shorted turns on a winding can

therefore be. quite’difficu1 Wherever possible com

pare the measured resistance with any available data

on the type of transformer being used. Another Use-

. ful check is to run the transformer off load and test

for overheating.

When using an ohmmeter take care to use the .

correct polarity for resistance checks where diodes,

electrolytic capacitors and transistors are presént. It

is all too easy to get misleading results, For example,

in Fig. 3.123 if the meter is used to measure the

. resistance of the ‘unstabffized line, the positive prod

(connected inside the meter to the positive plate of a’

battery) should be placed on the positive line and

:theñegative prod to earth. If the meter is reversed

there will be a low reištanee path through the

rectifiers and a leakage path through’ the’ capacitor.

Returning to the faulty power unit, Suppose how

ever that the fuse is intact, and that the mains is

‘reaching the primary. The, next Step is to measure the

secondaryaæ. voltage, the unstabijzedd.c. voltage

then the d.c. voltage in the regulator and so on, until

the fault is located. . ,

Table 3.1 lists some typical faults together with ‘

the associated symptoms, The faults are only a sample

of those which may occur. Locating a faulty com

ponent from a given set of symptoms will come with

practice and the following exercises are designed for

that purpose.

To regulator

Multmeter set

to ohms ronge

Red

Fig. 3.12 Using an ohmmeter to measure the resistance

across the unstabjljzed line

27 POWERSUPPLYCRCUITS.

3.6 Fault Finding Techniques and Typical Fault

Conditions

When a faulty power unit is returned for repair, the

fault has to be isolated to some particular portion of

the unit. The fault may lie in the transformer, the

rectifier, the filter section, or thegu1ator, and

measurement with a voltmeter will be necessary to

locate the fault.

However its probably best to start diagnosis with

a few rather obvious but often overlooked checks.

First measure the d.c. output voltage. If this is

zero, the next check should be on the mains input.

Is the mains supply reaching the transformer primary?

If it isn’t, there is the possibility of a faulty plug

(relatively simple to repairs), open circuit mains

wires, or a blown fuse. If the fuse i suspected always

test its continuity with an ohmmeter, never rely on

Just a visual Inspection It is also worth noting that

both the live and neutral wires may have a fuse in

circuit, so make sure bath are checked.

lithe fuse is blown it has done so because of some

fault condition and the fault must be cleared before

anew fuse is fitted. Resistance checks ‘(with’ the mains

unplugged!) must be used to locatštich a fault. Use

an ohmmeter to measure the resistance of the trans

former primary, the secondary, the rectifiers, and so

on. The winding resistance depends, of course, on

the size of the transformer. The primary resistance,

for a medium size transformer, should be low,

typically about 50 12. The secondary, usually supply.

ing a lower voltage, may have a resistance of only a

few ohms. Detecting shorted turns on a winding can

therefore be. quite’difficu1 Wherever possible com

pare the measured resistance with any available data

on the type of transformer being used. Another Use-

. ful check is to run the transformer off load and test

for overheating.

When using an ohmmeter take care to use the .

correct polarity for resistance checks where diodes,

electrolytic capacitors and transistors are presént. It

is all too easy to get misleading results, For example,

in Fig. 3.123 if the meter is used to measure the

. resistance of the ‘unstabffized line, the positive prod

(connected inside the meter to the positive plate of a’

battery) should be placed on the positive line and

:theñegative prod to earth. If the meter is reversed

there will be a low reištanee path through the

rectifiers and a leakage path through’ the’ capacitor.

Returning to the faulty power unit, Suppose how

ever that the fuse is intact, and that the mains is

‘reaching the primary. The, next Step is to measure the

secondaryaæ. voltage, the unstabijzedd.c. voltage

then the d.c. voltage in the regulator and so on, until

the fault is located. . ,

Table 3.1 lists some typical faults together with ‘

the associated symptoms, The faults are only a sample

of those which may occur. Locating a faulty com

ponent from a given set of symptoms will come with

practice and the following exercises are designed for

that purpose.

To regulator

Multmeter set

to ohms ronge

Red

Fig. 3.12 Using an ohmmeter to measure the resistance

across the unstabjljzed line

0/5000

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27 POWERSUPPLYCRCUITS.3.6 Fault Finding Techniques and Typical FaultConditionsWhen a faulty power unit is returned for repair, thefault has to be isolated to some particular portion ofthe unit. The fault may lie in the transformer, therectifier, the filter section, or thegu1ator, andmeasurement with a voltmeter will be necessary tolocate the fault.However its probably best to start diagnosis witha few rather obvious but often overlooked checks.First measure the d.c. output voltage. If this iszero, the next check should be on the mains input.Is the mains supply reaching the transformer primary?If it isn’t, there is the possibility of a faulty plug(relatively simple to repairs), open circuit mainswires, or a blown fuse. If the fuse i suspected alwaystest its continuity with an ohmmeter, never rely onJust a visual Inspection It is also worth noting thatboth the live and neutral wires may have a fuse incircuit, so make sure bath are checked.lithe fuse is blown it has done so because of somefault condition and the fault must be cleared beforeanew fuse is fitted. Resistance checks ‘(with’ the mainsunplugged!) must be used to locatštich a fault. Usean ohmmeter to measure the resistance of the transformer primary, the secondary, the rectifiers, and soon. The winding resistance depends, of course, onthe size of the transformer. The primary resistance,for a medium size transformer, should be low,typically about 50 12. The secondary, usually supply.ing a lower voltage, may have a resistance of only afew ohms. Detecting shorted turns on a winding cantherefore be. quite’difficu1 Wherever possible compare the measured resistance with any available dataon the type of transformer being used. Another Use-. ful check is to run the transformer off load and testfor overheating.When using an ohmmeter take care to use the .correct polarity for resistance checks where diodes,electrolytic capacitors and transistors are presént. Itis all too easy to get misleading results, For example,in Fig. 3.123 if the meter is used to measure the. resistance of the ‘unstabffized line, the positive prod(connected inside the meter to the positive plate of a’battery) should be placed on the positive line and:theñegative prod to earth. If the meter is reversedthere will be a low reištanee path through therectifiers and a leakage path through’ the’ capacitor.Returning to the faulty power unit, Suppose however that the fuse is intact, and that the mains is‘reaching the primary. The, next Step is to measure thesecondaryaæ. voltage, the unstabijzedd.c. voltagethen the d.c. voltage in the regulator and so on, untilthe fault is located. . ,Table 3.1 lists some typical faults together with ‘the associated symptoms, The faults are only a sampleof those which may occur. Locating a faulty component from a given set of symptoms will come withpractice and the following exercises are designed forthat purpose.To regulatorMultmeter setto ohms rongeRedFig. 3.12 Using an ohmmeter to measure the resistanceacross the unstabjljzed line

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27 POWERSUPPLYCRCUITS. 3.6 Teknik Deteksi Kesalahan dan Patahan Khas Kondisi Ketika unit daya rusak dikembalikan untuk perbaikan, kesalahan harus diisolasi untuk beberapa bagian tertentu dari unit. Kesalahan mungkin terletak pada transformator, yang rectifier, bagian filter, atau thegu1ator, dan pengukuran dengan voltmeter akan diperlukan untuk menemukan kesalahan. Namun yang mungkin terbaik untuk memulai diagnosis dengan beberapa pemeriksaan yang agak jelas tetapi sering diabaikan. Ukuran Pertama tegangan output dc. Jika ini adalah nol, cek berikutnya harus di input utama. Apakah pasokan listrik mencapai transformator primer? Jika tidak, ada kemungkinan plug rusak (relatif sederhana untuk perbaikan), terbuka sirkuit listrik kabel, atau sekering ditiup. Jika sekering i diduga selalu menguji kontinuitas dengan ohmmeter, tidak pernah mengandalkan Hanya Inspeksi visual yang Hal ini juga diperhatikan bahwa kedua kabel hidup dan netral mungkin memiliki sekering di sirkuit, jadi pastikan mandi diperiksa. Sekering lentur ditiup telah melakukannya karena beberapa kondisi kesalahan dan kesalahan harus dibersihkan sebelum lagi sekering dipasang. Cek Resistance '(dengan' listrik dicabut!) Harus digunakan untuk locatštich kesalahan. Gunakan ohmmeter untuk mengukur resistensi dari trans mantan primer, sekunder, rectifier, dan sebagainya pada. Berliku resistensi tergantung, tentu saja, pada ukuran transformator. Hambatan utama, untuk ukuran transformator menengah, harus rendah, biasanya sekitar 50 12. sekunder, biasanya pasokan. Ing tegangan yang lebih rendah, mungkin memiliki ketahanan hanya beberapa ohm. Mendeteksi bergantian korsleting pada berliku bisa karena itu menjadi. quite'difficu1 Sebisa mungkin com pare resistansi yang diukur dengan data yang tersedia pada jenis transformator yang digunakan. Lain digunakan-. cek ful adalah dengan menjalankan transformator off beban dan uji untuk overheating. Bila menggunakan ohmmeter berhati-hati untuk menggunakan. polaritas yang benar untuk pemeriksaan resistensi mana dioda, kapasitor elektrolit dan transistor yang hadir. Ini semua terlalu mudah untuk mendapatkan hasil yang menyesatkan, Misalnya, pada Gambar. 3,123 jika meter digunakan untuk mengukur. hambatan dari 'garis unstabffized, prod positif (terhubung dalam meter untuk plat positif dari' baterai) harus ditempatkan pada garis positif dan: theñegative prod ke bumi. Jika meter dibalik akan ada jalan reištanee rendah melalui rectifier dan jalur kebocoran melalui '' kapasitor. Kembali ke unit daya rusak, Misalkan bagaimana pernah bahwa sekering utuh, dan bahwa induk yang 'mencapai primer . The, Langkah berikutnya adalah untuk mengukur secondaryaæ. tegangan, unstabijzedd.c tersebut. tegangan maka tegangan dc di regulator dan seterusnya, sampai kesalahan berada. . , Tabel 3.1 daftar beberapa kesalahan khas bersama dengan 'gejala yang terkait, The kesalahan hanya sampel dari mereka yang mungkin terjadi. Menemukan com rusak ponent dari himpunan gejala akan datang dengan praktek dan latihan berikut ini dirancang untuk tujuan itu. Untuk regulator Multmeter mengatur untuk ohm Ronge Red Fig. 3.12 Menggunakan ohmmeter untuk mengukur resistensi di garis unstabjljzed

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