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Electronic Repair Questions/Answers and Testmonials- Part 60

By on August 2, 2010

Greetings from the USA! I just wanted to say I’ve never seen a more comprehensive electronics repair site on the internet – your site is WONDERFUL!





Hi dear Mr.Yong;

I’m repairing a capacitance meter. I found an item on the PCB, which is marked in red-circle in these pictures.. please tell me what is it ? is it a capacitor or a crystal ?(please see two pics )

Thanks for all the guidelines you gave me !!

best regards!!


HI Kushan,

Generally it is a crystal but some manufacturers may design a capacitor that have similar shape. If you have a capacitance meter or a scope then you can find out the different.





Hi Jestine

I think it is a switch mode , because it is in a welding machine that works on both AC and DC mode (toggle a switch). The welding machine is very old (+15 years) , and there is not even spare parts for the make anymore . All the relays and switches in the machine works , but we are struggling to get the amperage for the machine to weld .

Best regards


HI Craig,
I have not repair such machine before thus i do not know what type of transformer it is using. Assuming it is a switch mode transofrmer then what you need to do is to check the primary winding of the transformer with BLUE RING Tester. Is there any welding forum that you can post the question because i believe there should be someone be able to answer that question.






Hi Andrew,

My HP 1502 LCD Monitor is blank screen but green LED stays on.

Before the LCD Monitor went into such condition, it was blank screen and moving the screen backward or moved the power code would restore it. It seems to suffer from dry-solder joints. I checked for dry joints and changed the capacitors with 5 rated 470micF 25V [C926, C924, C929, C930, C932] and 2 rated 1,000micF 25V [C922 & C925]. Originally capacitors at C926, C924, C929, C930, C932 are found to be fixed with 1000 microF 16V (I bought the Monitor 2nd Hand from a Computer Repair Shop).

You should replace the 1000uf with the original value because 470uf would be too low.

Kindly advise me on the following matters:-

1) When I check the voltage at VCC Pin 9 of IC TL1451ACN, there is no voltage. So how to trigger the sign from the Main Board to switch on the Start Circuit? 2) From your article, you wrote “In order to let the 12 volt to flow through the transistor and reach the vcc pin of the ic, first, a ‘on’ signal must be sent from the main board to trigger the transistor.” Now I have checked all capacitors and transistors and resistors except the ICs.

The signal is coming from MCU in the mainboard when the MCU is receiving a good and stable voltage. If there is no signal from the MCU then the MCU may have problem.

I had de-soldered the IC 833Z near the IC TL1451ACN and when I resoldered it, the Part Number is not cleared and I had soldered it with wrong polarity. When I switched on the LCD for testing, there is white screen but no OSD. I changed it back to original polarity now. Is this IC Part which seems to read as 833Z on your Board Diagram but mine seem to read as BE432C or 8F432C or BF432 which are not traceable on internet. Kindly advise if this IC can be easily burnt or not?

I’m not sure about the IC because i do not have the complete schematic for this Monitor. In your case, the most important is the On signal  (about 2 to 5 volt) to trigger the start circuit so that the supply voltage can be applied to the inverter IC.





ok gracias.
por que las fuentes SMPS, actuales, en especial las de los  TV LCD de 32 pulgadas, tiene mayor cantidad de componentes y son mas complejas de entender,y dificiles de reparar, la pregunta es como hace ud, para ir aislando y probando hasta encontrar la falla. gracias espero



Hola Luis,

En primer lugar usted necesita para comprobar si hay alguna potencia de salida de la SMPS. A veces no poder LED no significa que el SMPS no es bueno porque el problema está en el MCU placa base. Debe probar la salida con un voltímetro de corriente continua.

En segundo lugar-Si usted tiene que confirmar el lado SMPS principal es el problema que usted tiene dos opciones:

1) realizar pruebas de tensión en la tapa grande y IC de potencia para comprobar si hay oferta o no.

2) Controlar todos los componentes del lado del primario. Sin embargo, su prueba de los componentes electrónicos de habilidad tiene que ser bueno en el control de esos componentes. Si todos los componentes de verificación para estar bien después dirigir a sustituir el IC de potencia y vuelva a probar.

Con este método se puede resolver por lo menos más del 90% del problema de alimentación.






Dear Justine,


Greetings from Dinkar Patel!

I need your support to buy  Insulation Meter/Tester to repair TV as well as Computer and other household gadgets. Also I request you to suggest whether I should go for Analog or Digital Insulation Meter. I have following choice to buy (Please refer Attached file)


HI Dinkar,

Since i do not have a digital insulation tester thus i can’t give any comment on that. However, i completed a review on a transistor tester that can check the insulation of a capacitor it is cheap too. Please visit this website to check this out:





hi jestine…

i have a 21″ sanyo colour i found out my tv had no red colour.the rest of that still ok…i sus pect something wrong on small board behind the tube.what do you reckon?

thanks for the help.




Yes check that small board and compare the signal with Blue and Green circuit. Any differences is the clue for you to trace on that point till you locate the fault.





Dear Jestine,

I am Rajesh Nair from India, i am a regular reader of electronics articles of yours for the past 3 yrs.
Sir,as i have been in the electronic industry for the past 12 yrs now i want to expand my business with chip level repairs.
For that i will require BGA machine for higher end repairing ,
In india the BGA machines prices are very high so i would like to import it from China for a best deal ,So i request you,can you pls share me the BGA machine best and cheap prices or the Manufacturer Addresses in China so that i can go ahead for it.
Pls reply.


HI Rajesh,

Thanks for your email. Since I’m not from China and do not have contact on the BGA machine locally thus i can’t provide any info for you. I suggest that you search from the internet and email them your requirement.

Have a good day!





Dear Sir


How are you? I am fine.

I want to know that, how a Uninterruptible Power Supply (UPS)  provide uninterruptible power that another power system can not do?

Please Explain.






HI Salim

Thanks for your email. I suggest that you visit this link below:





Hi Jerald,

hi jestine  how r u and u r family,

Fine thank you.

i have started repairing small stuff with ofcourse u r help, i have one query about the IC TDA7381 where the pins have the initials of P-GND, S-GND, AC-GND, NOW THIS IC IS USED IN CAR MP3 PLAYER EHICH HAS GONE DEAD SO I WANT TO KNOW WEATHER ALL THESE GROUNDS R THE SAME

It depends on the equipment design but generally is all the same. You can confirm it by using ohm meter to measure the continuity  between the 3 pins and if there is low ohm reading then they are connected.


I suggest that you visit this link to understand the pin out:

so that you will know pin to check on the VCC. The ic diagram did not mention about the negative voltage of the car battery thus your meter black probe connect to the player casing and the red probe to the vcc pin and read the voltage.




Hi Jestine,

Your recommendation is great!
I was able to repair my TV by using one your recommendation below.
Big thanks for the help.

Thanks again






HI Yong,


I am repairing a remote control ceiling fan , the motor can’t run smoothly.

I found one capacitor written 1.5uF +/- 5% ,if check with multimeter read 921nF and checked with blue esr read 1.5 esr ohm ,the esr value is less than the values shown,is this cap ok?

921nf is definitely out. As for using the esr meter to test i suggest that you compare the value with a good one because my side here do not have same cap value to compare.

And found another cap written 0.68k 500V,just to confirm is it 0.68uF or 680nF ?


0.68uf and 680nf is actually the same value except one is in microfarad and the other on is nanofarad.





Dear Sir,




Sir, Please help me with my UPS after I change the battery the unit does not work and did not display indication of power output.

I have not record the placement of battery. I thought it was only easy yet it doesn’t function.

I try to connect the battery in parallel no effect, I try to connect in series but spark along the terminal was observe, indicating a short circuit.


Any suggestion from you is highly appreciated.



Thank you!


Very truly yours, 


Felix Selorio


Hi Felix,

First you need to replace with the same spec of batteries and second thing is to check the connection fuse and the fuse in the mainboard for open circuit.






Hi Jestine ,

I trust you are well ,we fix pcb for the Hewlett Packard printers

Where can I buy a BGA smd station (reflow) at a fair price ,it must heat
from the bottom and top

Regards ,




Since my place does not sell BGA machine thus i suggest that you visit this website:





HI Aliou,

i need to test a transformer of UPS who have many output winding( many color of output).

This would be tough if you do not have the schematic as it contains lots of output. I suggest that you power On the UPS and randomly test the AC output at the secondary side. If you get few different AC voltages then you will know that the transformer is working.






these interviews are great, it seems like i myself is taking with them, i just loved this months newsletters. i have got a great motivation. thank you sir you are doing a great job, thank you once again and go on and on and on.






Thank you for the information.

The Sony TV, I mentioned, happened to have a defective LCD screen.So I’m told by Sony service…Is there a way of testing LCD screens ?

With the CRT monitors it’s easy, but I don’t know how to test LCD screens.

Have a nice day.


HI Krut,

At this moment there is no way to test the LCD screen except to connect it back to the system and test. This most probably due to too many signals need to be connected between the mainboard and the lcd screen.





HI Bunu,

Hi Jestine,how is your work?.

Fine thank you.

I’ve changed my e-mail from yahoo,because its difficult to log in (maybe its network problem).

I guess you need to resubscribe again at:

because i can’t manually add your email into my database.

Jestine ,I have a Toshiba laptop,15″ Wide dark-screen.It had a back-light problem.I managed to fix this problem (invetor-board).The sreen is now coming bright,but it has a red display.May you help me on how to fix this problem.Thank you so much,have a great day,Happymore.If you are online,we may do an instant chart,thanks.

Red display can be from weak lamp, loose connection between the mainboard to lcd panel or problem with lcd panel.





HI Nicholas,

Love your books!


Trying to understand a capacitor code.

I have a very small blue film capacitor with the markings “.1 M”

Is this the same as a capacitor with a marking of “104”.

Yes it is the same because the manufacturer already converted the value.

How do I know the voltage or a replacement for the.1 M?

Thanks in advance for your help!

If it is very small then the voltage is a 50 volt capacitor. A written would indicate 1 ,2 or 3 KV.





HI Dean,

Good day sir,

Good day!

I have a problem with a Hanns G lcd monitor, model # JW199d. At first the power light would come on green then go to amber signaling no signal from the cpu, I changed a few caps and now the light stays on. However, the screen lights up for approximately 2 seconds then goes dark. Shining a flashlight on the screen reveals that there is actually display images on the screen. What could you suggest the problem could be? it uses two separate circuits for the lights and I’m thinking it would be odd that they both go out at the same time. What are your thoughts?

Most probably one of the back light have problem that had caused the monitor to shutdown. You may need a good backlight to compare.





HI Andrew,

I need some clarification from you on the following matters related to the same LCD monitor with blank screen and LED stays green.

1) There are 2 resistors rated 4.3 Ohms 2W which are very hot to touch maybe 80 deg Celsius and one of them has the covering slightly cracked. Capacitor 1000uF 25V is also very hot to touch. maybe 80deg Celsius. Are these normal?

I suppose it to be abnormal because usually resistor won’t run that hot. I suggest that you check all the surrounding components.

2) The voltages are the CN102 connector from Inverter Board 715L1034-1A to Mainboard 715L1066 are as follows:-

Pin    Voltage        Pin      Voltage
2         1.4V            1           0 V
4         5.0V           3           5.0V
6         0 V               5          0 V
8         3.4V           7           3.4V
10       0.1V           9           0.1V
12     13.0V           11         13.0V

I compare with other similar 17’CPT inverter the voltages will be 1.8V, 3.3V and 12V. I suspect the Power Board is not producing enough power for the main board and it could be the reason why there is no Signal On to trigger the Start Circuit at the Inverter Board. Do you think so?

It can be the power supply or the mainboard itself have problem that draining down the voltages.

3) The voltages for the 2 Ics at the inverter board are as follows:-

IC1084 33CM
IN     +5.2V
OUT   3.4V
ADJ     0V

This has the correct output.

IN      5.0V
OUT   0.1V
ADJ    0V

This IC most probably have problem

There are 2 resistors and 1 cap damn hot are located at IC2. Is this IC faulty? If I removed this IC2, then IC1 will not have OUT voltage at 3.4V. So is this IC faulty? Is there any Replacement part for this AIC1084?

The back number is the crucial one. 33 means output 3.3 volt. Sorry i have no source where to get one. You may need to salvage from junk monitors or make one using LM317T IC or even order it from the internet.

4) If TL1451AC PWM is faulty will Pin 9 vcc shows 12.0V? At present there is no voltage at Pin 9.

There is no supply voltage because no signal to trigger the start circuit.



Hi jestineyong,I ‘ve  got a viewsonic VG800 which is abt 6 yrs old,it powers on & shows no input signal & goes to standby mode after 3-5 secs.,that is the backlight still working ,could it be the inverter board or logic board problem ,the power supply is OK,can it be repaired ?THKS  for yr recommendation 4 how to solve>>>..


HI Philip,

First you need to make sure the power supply is producing good and stable voltage. Next check that there is no dry joints in the high voltage transformers and if all tested okay then check the backlight. You need good backlight for comparison.





HI Jean,

First I want to Thank you so much to answer so fast my question (if it’s you?)

Yes it is me Jestine.

…hahaha!!….I’ m a guy from Montreal,  Quebec, Canada…..

Nice to know you.

When I repair a piece of equipment i’m trying to learn in the same time…of course this tv could go in the garbage if you know what I mean….but by this I’m in a learning process……Many Thanks again….Yes I have some power on the B+ and the HOT base…..first the board  around the flyback is craking (old) and there is a connection of small whire going to the neck board…..these connections on the main board near the FB (gonig to the “H” on the neck board)  where broken after repair the bord….the lamp fired again ……


now the problem I get is…degaussing….I change the posistor no success…check the coil OK….try the degauss with big magnet no success…Any clues…only if you have time to answer…..

If after using external degausser and still can’t remove the color patches in then the internal tube structure  (most probably the shadow mask had collapsed. You can’t repair this kind of problem. However, sometimes a dry joints problem in the vertical output IC may cause this  kind of problem too.

Have a good day!





Hi Jestine,

The meter is working fine up to now, managed to find bad caps which have been read good by the capacitance meter.
Jestine I want to fix probe to the meter but can you please advise me of the maximum length it should be.
It will be easier to test caps in circuit.




HI Guilly,

30cm will be good . If too long the result that you get will vary and unstable .





hie jestine i have this crt tv that when switched on takes too long to show screen what is the  likely cause of this fault.


Hi Felix,

The the heater and the G2 voltage is normal then suspect a weak pc tube.





HI Boby,

Could you please help me with these repair problems:

1. Have a TV “21” inch, forgot model and brand. When ‘on’ the power,
it powers on but blinks and does not power on with no display. Specify
which section or parts could be faulty.

You may need to visit this website to isolate the problem:

2. Have a CRT monitor, NEC brand. When ‘on’ the power, it powers on ok
with good display, but stays for some time and then it starts to roll
down and raps up the screen to the very bottom of the screen and stays
there leaving the screen all black or blank. Please help.

please check the supply voltage and dry joints in the vertical output IC.





Hi jestine naraen here i have a LCD TV make LG MODEL MT-42PM10B and the fault is that it power and play for 3hours and lost its image after .

what i notice is that on i after having switched the set for abt 2hrs and i power on the set it work normally

so it would be highly appreciated if you can guide me


thanking you in advance




HI Nareen,

Make sure the supply voltages from the SMPS are good and stable. It may be dry joints in the high voltage transformer or weak back light.





Hi Jestine
Good day to you and hope you are good. I have a query for you and hope
you help me. I have a DOSS SA-30 PA amplifier that was reported faulty.
The main power transformer was cooked.It has a center tapped secondary
for 24V-0-24V. Can i use a transformer with an isolated secondary, i.e.
0-24V and 0-24V?They use only one fullwave bridge rectifier. and two
filters in series.
Hope to hear from you


Hi Koniel,

Theoretically it will work but i guess you need to try it out. You can’t get the part that’s why use use two transformers?





Good day Sir Jestine….. I have a question what parts or components if the horizontal size can’t adjust?



HI Sio,

It can be bad caps, shorted modulation diode or even bad pincushion transistor.




Hi Justine,


I am studying the above books and will communicate with you as soon as I’m done with them.

However,for a start, I would like to heartily say thanks and congratulations for the inspiring book : THE ART OF SUCCESS IN ELECTRONIC SERVICING. The time and DEDICATION which you have put into this book is really remarkable and is very beneficial to those of us interested in electronics.It is clear as crystal that you had the interest of the student at heart when you wrote this book.


Thanks again until next time.







Hi Jestine,     hows doin  well l have Question for you     when l turn on the tv he just  flush a one time and  then no more but have sound no picture .     TV  s JNC  LCD  20 inch   could you pls let me know how l repair this tv .     and fine out the problems.     Regards     James



Make sure the output voltages from the SMPS are good and stable, no bulged e-caps and check for dry joints in the high voltage transformer pins. If all tested good then suspect one of the backlight have problem.





HI Exodus,

hello Jestine Young

thanks very much for the great advice to prefer 100Mhz  than 60Mhz oscilloscope

which was part of life saving.

You are welcome!

Sir, now advice on the specification on the Isolation Transformer, how many  WATTS will do.

1KVA is equivalent to about 600 watt. Assuming if you are repairing only LCD Monitors (consumption less than 100 watts-depends on sizes) then you need a 150 watt transformer which is about 250VA. It all depends on the equipment you are dealing with. The higher watt the better but it is more expensive.

Have a good day!








Hi Jerald,

Sorry i do not have info on this. If you have the schematic then one may know if it can be converted to using 12 vdc supply. Assuming if you do not have schematic then you may need to see how many output voltages does this DVD have. If it use 12 volt and 5 volt then you can use a 12 volt dc power supply and a 7805 voltage regulator circuit to power up the mainboard and the motors.

Have  a good day!





HI Noorishkandar,

Macam mana kita nak tahu mana satu pin secondary transformer yang output dia 6.4VDC ?

Kena ukur dgn multimeter.

Saya dah cuba trace dari pin connector 6.4VDC tapi tak jumpa line yang menuju ke secondary output pin transformer.Any tips yang Encik Jestine dapat membantu saya.

Kamu kena trace dari SMPS output dgn menggunakan multimeter set ke DC voltage. Ia mempunyai 4 ataupun 5 output voltage. Salah satu pastinya adalah 6.4 volt.

Sekiranya ada gambar rajah litar 6.4VDC  dari secondary output pin transformer ke heater mungkin dapat membantu.

Maaf saya tiada schematic tersebut.






HI Roger,

sir ,good day,the led is color red,when i on the tv ,its blinking,,i already check the 3 trans,at crt socket,off board,its ok,but i didnt try to check the voltage of 3 trans,maybe i try tonight,,i already measure all tagging at the board secondary voltage at secondary side,are all ok,except the 185v,its read only 156v,i already replace one resistor 11ohms,but its reads 32ohms.but the problem is there,the sound tik tik tik is also there,i already replace total of 3 components,but still not work,i already check all components at crt socket level,but all are ok,my analysis is,something that block the signal..maybe bcos,of the horinzontal lines from top to bottom,i check already the yoke coil,its read low resistance.range times 1.i scan all the ic using my hands,at the top,i sense warm,but except the system ic that very cold,you know sir,this trouble maybe challenge my passion,perseverance and my determination to enter the world of electronics a beginner,but im happy what im doing now sir,bcos you are still there to guide me….thanks for that sir…

Red led could mean the system IC is not functioning. Make sure the system IC is getting good supply voltage and the crystal at the side have sinewave. Horizontal Yoke coils can’t be check with ohmmeter because it can be misleading. You need a blue ring tester. However for vetical yoke coils you can use ohm meter to test it. Have you try to use this method to isolate the problem?

Actually this kind of problem you will learn more as compare to just replace the fuse.

Have a good day!





HI San,

I received the meter today..thanks.

You are welcome!

Regarding the usage, can you brief me how to use the ESR meter to check for shorted component on a circuit board without removing the component? I read through some notes and it say the value will increase if there is problem with the board component.. how do I check and what is the value to look for?

Turn on the meter by pressing the black button. Now short the probes and press the button another time to reset the microcontroller IC. Once done you can check any electrolytic capacitor onboard. You can test it either ways using the probes. In the beginning you have to refer to the chart that i have given you. For example if you are measuring a 22uf 250 volt, according to the chart it is 3 esr ohm. That means the value that you get from check the cap has to be lower than 3 ohm. If you get 5 or 6 ohm that means the cap have problem. If you get 1.2 ohm, the cap is good. If you get 3 ohm (marginal cap) i suggest that you still replace it because the cap may breakdown after 3 to 6 months time.

In other words, the bad cap ESR value will increase when it has problem.

Assuming it’s a transistor problem, can the meter detect it?

This meter is for checking only e-caps and for transistor you need to use an ohmmeter.

I am dealing mostly with LCD and Printers repair..

Noted. LCD Monitor have lots of caps problem.

Have a good day!






These days I am still finding the potential customers. I go to the large corporation / bank/ institution myself, but more than 80% said that they don’t even bother about bad monitor because they directly return the bad set to the supplier/ vendor and some of them said that they use the lend system, so whenever problem occurs they just return it and get new replacement.

In these condition, how could I get the big potential customer. Do you ever have this kind of problem.

Once your company established there will be no problem in getting big customers. The reason for that is because they wanted to see your company profile-how long you have been in the business, how many staff you have and etc. As for us we don’t like to deal with big corporation (in my country). Usually their payment is very long. Sometimes it may take up to 120 days!!!!! I’m not saying all big customers is like that but generally most of them are. Because of this the company cash flow will be in bad shape. You need to pay workers, rental, buy parts and etc.

Do you think it is feasible to directly find the bad set from the supplier/ vendor?

I’m rather dealing with small vendors like computer shops and sole proprietor (running the business from home). Their payment are fast and sometimes pay you cash too. Although the volume was not big at least you got the money to roll. Since you have the knowledge you can actually try other field instead of computer like CCTV, ALARM, TELEVISION and etc. Get your local yellow pages and try to call if they need any one that can help solve their electronics problem.

If you have other question please do email me again.






Hi Jestine
Ok..I got that part you explain to me..thanks.. but when I try to measure a non polarize cap..value 7C104J (250V) , I got the reading of 12 esr…  is this correct? The capacitance reading is 96.3nF….   based on the Blue ESR chart.. cap <5ufd is above 50esr …. mean this cap is bad?




HI Jon,

This meter is designed to test only on electrolytic capacitor and not non polarized cap. However, form my own Rand D i found that you can use to test on non polarized cap but the value has to be from .1 uf and above. When you test on the non polarized cap you can’t follow that chart. You have to make your own chart by comparing with a good .1uf cap.

Here is a chart for electrolytic capacitor:





Hi Jestine ,

I’ve sent you a pictures of my tv to see what it looks like exactly , look to the head of the people how they big and there is a black bold line in the botton of the picture , please take a look to the attached pictures.



Hi Bassem,

Thanks for the photos. I’m very sure the problem is in the vertical section. Have you check all the components in that section especially the resistor value and capacitor. If all check to be okay then i suggest that you directly replace the cap and retest because I’m afraid there are caps that breakdown when under load or even the vertical yoke coil have problem.




Good day or good evening,

I spent the whole afternoon today July 31 to sail on your wonderful blog electronics.

Sailed from this July until November 2009. Because many new interesting issues related to electronics, not left me time to read everything.

As soon as possible I’ll visit all the previous pages.

God bless you and your family for the excellent work that is put on the internet.


Praia – Cape Verde





  1. anuraganimax

    August 8, 2010 at 11:44 am

    Hi Mr Yong
    I wish to test a transformer present in a UPS(standby power supply type). I'm getting confused with so many pins it has. Any advice?

  2. admin

    August 9, 2010 at 7:15 am

    Hi Arunaga,

    For UPS you need the schematic diagram to guide you to find out the winding. You are right UPS transformer is a bit complicated because it consist lots of windings.


  3. Azahar

    March 1, 2011 at 1:43 am

    Saya ada masalah dengan power board.Masalahnya ialah tentang Pin 1 hinnga 11 pada board model(715L1039-1-LV).Boleh Jestine
    terang kan pin (gnd,5V,12v,on/off,ADj dan DIM).

    mohon bantuan,

  4. admin

    March 1, 2011 at 8:52 am

    HI Azahar,

    gnd adalah bumi, 5 volt untuk IC, 12 v untuk inverter circuit, on/off untuk control supply ke inverter ic, adj dan DIM untuk keterangan.



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