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Electronic Repair Questions/Answers and Testmonials- Part 59

By on July 19, 2010

Hi Jestine,

Just want to thank you for your ability to explain things at a basic level.Your books have been a tremendous help to me,again thanks.



Hi Jestine 

I’m just retired and thought I would do something I always wanted to: have the ability to repair electronic stuff.  Wow this book has given me a whole new interest.  Superb.

With every blessing and success





How can i differentiate between SCR/TRIAC from transistors.


HI Moses,

Look at the part number and find the spec.





HI Cahyono,

Dear Mr. Jestine Yong. I have comp. monitor 17″ and need you to help me by answer my question. The facts are: 1. All output regulator tensions are ok (5v, 6,3v, 50v,etc) 2. G2 is 400v 3. The crt filament is ok (I can see the heating light at the neck) 4. pilot lamp in front of the unit isn’t blinking (stay on) 5. PS relay indicates the unit works 6. no display on the screen (stay dark) 7. I adjust the screen and focus VR at the fbt but it doesn’t work the question is why the screen stay dark??? thanks before, and hope you will answer me immediately. bye…

I guess you may need to check the G1 voltage. It should have about -10 to – 70vdc and if you get more than -100vdc then the display will become dark.





HI Kim,

Your book is great for novices like me, and wonderful to be able to pin point any damaged component.


I bought it because I was searching for a way to test transistors… I have an adapter board for my programmer, but basically the adapter board is the programmer itself. It’s intended for use with motorola mcu’s

I borrowed this to a friend of mine and he said he accidently forgot to separate the wires when he tried to read internal eeprom of a 912 mcu. Being a novice I thought perhaps the relays was malfunctioning, because they dont operate like they should, but after I changed the relays it’s still the same so I am thinking maybe one of the transistors feed the relays so maybe thats where the problem is..

as the 912 processor only needs +5v, gnd, bkd(bdm) and reset I am assuming he could have short circuited the 12v and gnd. The adapter doesnt operate the relays properly so it gives error.

Since you have replaced the relays only those components in the yellow box that you can check (please refer to the photo). Chances is slim if those components have problem because it is the big IC that triggers the transistors to turn on the relay. Try check those components in the yellow box first and if all are okay then susepct the ICs.

Have a good day!





can i share a problem with you about a computer monitor? I’ve been at it even before i started contacting you. that’s the reason why i tried researching in the internet about the monitor’s problem.
It’s a samsung 15″ magic monitor. i don’t have the model make right now. anyway, the monitor just went blank. but when i turn up the SCREEN (voltage?) the display comes up & i have to tune it down again just to make it right. the display will only last for a few minutes then it goes blank again. plus, i noticed the display ‘flashes’ like you’re blinking really fast while looking at the monitor display. i noticed that when i turn up the screen just a little. turning it nearly to the full will stop the flashing. then i turn it down again so i can have a normal display. then there’s the display also in windows. whenever i open a window the whole display bulges in the middle, especially when the display is in white. the desktop wallpaper returns to it’s normal size when i close any window.
the flyback’s good (due to the presence of HV), checked the transistors, SMPS section seems to be fine. the monitor goes blank but it still has HV. what else…i’m at a dead end with this.
this problem has kept me baffled since! but i like the challenge. though i’m not good in troubleshooting since i’m really new to this.
i’ll appreciate it very very much if you can help.


Hi Rene,

When the monitor suddenly  blank i suggest that you check the g2 and the G1 voltage. Make sure both voltages remain stable and if there is changes then suspect the line have problem. Check the voltage with analog meter which is faster then reading from multimeter.





Hey Jestine,

Good to hear from you. I just received in my shop my new LST01 Inverter/CCFL tester. It works pretty go. I have one question for you I have on my bench an IBM 9417-HB7 with U202 and U203 blown. They are the inverter driver FETS. The power supply/inverter board is made by Samsung model number IP-35135C. I cant make out the numbers on the FETS because they are burnt. Would you happen to know the part numbers? I found the Samsung power supply for sale on Ebay for $47.50. Thank you for your time and get back to me when you get a chance.




HI Richard,

Thanks for the email but sorry i do not have the schematic and the monitor with me thus i do not know the part number otherwise i would have open up the monitor and look for the part number. I’m not sure what type the board is using. It can be 4411, 4410 and etc. Some of the IC could have one p-channel fet, one n-channel fet and some may have the p and the n-channel together.







Hi Jestine,


Good Day to you!


I really need your help,, I would like to ask you if where could i buy lcd screen..for my LG flatron W1642ST..I already sent this to LG but they said the warranty is already void, bcoz they found some corrosion inside due to water spill they said. The problem of my lcd screen is there is a black spot on the lower left side of the screen, as big as quarter dollar coin.


tnx a lot.


HI Glenn,

Sorry i have no info where to buy lcd screen. The lcd screen is very expensive and usually customer choose not to repair it. Try email Luca at info(at) to see if he has the screen or not.





hi mr jestine.


my computer power supply has a problem and after some minutes work, 5 v output voltage is rised

up to 5.3,5.8,…, and finaly 6.3v and cause my usb mouse become defective.


what is problem in the power supply?


what components have been defective in most probably?


thanks a lot.


HI Saeed,

If this power supply have optoisolator circuit then check this circuit especially the resistor for high ohm. If all tested to be okay which include the filter caps then the secondary side toroidal inductor may have problem.





HI Moshej,

I have now bought your book LCD Monitor Repairs (I first bought the Testing Electronic Components) in order to fix my LCD monitor.

Thanks for the support.

My problem is the Gigabyte LCD Monitor (I bought it about 7 yrs ago) whose ‘power on’ led is flashing rapidly & there are built in speakers that are making a rapid ticking sound.

My first guess is blown caps (see pic 2)…is the cap in focus (in centre of pic) what you would call ‘blown’?  (the one behind it is similar).

I can’t see the different. if the top cap have a small hum we call it as bulged caps.

But my real purpose in this email is to identify certain sections and components…

In pic 3…

  1.  there is a black covered component LI TAI 0612 (CC-000331) can you tell me what that is?

Those are coils to remove ac ripple in dc line.

In pic1…

  1. any idea what those 2 rectangular green components are next to the input cable?

Those are non polar caps for filtering the interference in power line.

  1. The cables to the back lamps are in the top left & right, there is a little black transformer next to what looks like a bigger transformer….why would each back lamp have 2 transformers?

The big one is to generate the high voltage and for the small one if I’m not mistaken it is for feedback purposes.

  1. The big yellow object with hi-pot written on it I presume is another step-up transformer…why would they have this transformer as well as the other transformers? And is that the SMPS transformer?

It is a step down transformer so that you can get a lwer voltage of 12 and 5 volt dc. The other two yellow transformers are high voltage transformer for backlights.

  1. The group of caps in bottom right…what part of the circuit are they? (output power filters)? And if so what are they filtering?

Yes they are output filter caps for removing ripples in the output line.

Finally, would I do any harm if I connect this board on its own to the 220V mains and then commence testing? Or is it likely that the board will shutdown almost immediately due to there not being the correct draw-down?

You can connect the ac 220 volt to the board provided that it is connected to the mainboard because the power board sometimes need a mainboard in order to work.






I’m new in repair electronic, but I understand electronic circuit a little bit. Now, since my job include repair a printing/industrial electronic card. Could your book help me?And I want to know about your course.


HI Roy,

Thanks for the email. May i know where are you from? because at the moment we no longer taking in international participants. Some cards are quite hard to repair due to the unavailability of spare parts. My Testing Electronic Components ebook is the first step understand how to test electronic components. Once you are good in testing electronic components in fact you can perform the repair job on any electronic equipment. The ebook comes with my support too just in case if you have problem in troubleshooting it. Could you send a photo of the card for me to see?

Have a good day!





Hi Jestine


I am repairing a control board and found an eprom faulty , if  i buy a new eprom to replace it ,don’t know whether it works or not ? Pls advice ,many thanks!




HI Yong,

It will not work because inside do not have a program. You need to find the program and program it then only it will work.





HI Dong,

hi mr.yong, thanks for your ebook it helps me a lot,,

You are welcome!

,i have some question for you , i repair atx power supply for desk top pc the problem is the power fet is shorted at the same time the diode in single package 2 leg and the resistor 0.56 ohms i think this is a current sense resistor if im not get mistake,

Yes it is a current sense resistor.

is this current sense resistor a very sensitive can i replace it to another value?

You have to replace with the same value.

coz its hissing sound from the trnasformer when i plug it in. can you please send me secret info about how to repair atx power supply. thanks a lot.


Hissing sound can be something shorted in the secondary side that had cause the transformer to have sound. Bad filter cap, and shorted ic at the secondary side could cause this problem.

Have a good day!





HI Billy,

I appreciate your prompt attention, nevertheless it would be better if you give examples on how is it that u use the tester on the switch mode transformer, B+ coil, flyback primary winding and horizontal yoke coil.
Ilustrations are alot better.

Testing B+ coil and horizontal yoke coil (blue and red wire) is direct. just poke in the meter probes either ways and you should get at least 4 readings and above for B+ coil and 6 readings and above for horizontal yoke coil.

For testing flyback primary winding coil please visit this link:

For testing the smps primary winding, trace from the positive pin of the big filter capacitor (make sure you discharge first) that lead to one of the smps transformer pin. The next pin trace from the drain pin of power fet. It will lead you to another pin. So both the pins are the smps primary winding pins.






buenas Sr Yong, yo siempre he tenido problemas en las fuentes SMPS, que el lado secundario da voltajes oscilantes de salida bajos, pero ud. dice que esto es debido a que, el circuito de muestreo u otra falla en el lado secundario, hace que la fuente se apague, o entre en el modo oscilante, osea que el modo oscilante se produce, debido a una falla en los secundarios, pero nunca en el lado primario, debido a que el circuito primario esta oscilando , por favor corrijame en esto . u orienteme. gracias



Hola Luis,

Hay alguna traducción que no entiendo sin embargo aquí están mis sugerencias

Hay muchas razones por la tensión de salida será baja:

1) las tapas de filtro mal
2) componentes en corto en el secundario.
3) ohmios de alta resistencia en el sentido actual en el lado primario.
4) parcialmente SMPS cortocircuito del transformador devanado primario.

Le sugiero que revise todas estas primer circuito.





Dear Sir,

In LG 500G Monitor there is no display and even indicator is not glowing. SMPS output voltages are ok. In command IC VDD voltage is 5.1v Reset pin 4.3v crystal pin voltage 2.2 and 2.5v. I suspect it is a command ic problem but it is not easily available and costly too. Is there any method in your view to make sure the command ic fault. When i press any button, crystal pin voltage is not changing. Waiting for your prompt reply.

Thanking you

Gopal Sharma


Hi Gopal,

Since the CPU is getting the right voltage and the crystal are good then suspect that it is bad. It is difficult to test this type of ic because it has lots of pins and functions in it. Since the LED signal is coming from the CPU and the LED does not light then suspect the ic problem. By the way it will be difficult to find such ic.






HI Bailing,

This monitor was said to smoke by the owner, but don’t know where is the location. After checking I found J6810 HOT faulty ( red probe on base, black probe on C&E, the pointer of analog multimeter set to x1 flick a little bit ). According to the owner this HOT had been replaced by another repairman, and I could see it because he was using a fake HOT ( rough top surface ). After replacing the HOTand some capacitors, I tried to power it on, power led was green, no display and got the following result:


RK, GK, BK voltage is OK
Heater is only 4.14 V, and the filament was not glowing

There is supply because the smps is working but you may need to check the heater why it is low. It couold be bad e-caps along the line.

G1 is not stable
G2 is missing ( around 70 mV )

Low or zero voltage means the flyback is not energizing.

And then I disconnected the G2 cable from CRT board, took voltage measurement again, got same result ( voltage still missing ). Would this mean the FBT is faulty?

Probably yes and no. It could be missing either B+ voltage or signal to base of HOT.

Could a FBT smoke?

Usually it will arc and not will not produce smoke.

From your experience what is the minimum voltage to the heater to make it glow?

at least 5.5 volt and above but normal voltage is 6.3 volt.

What is the common pin cushion transistor besides D2058. Is the newer model use the MOSFET?

B649A, D669A and etc. Very rare crt monitor use mosfet unless it have different circuit.

Could we test a picture tube is OK with multimeter ( without giving high voltage )?

No you can’t you need a crt rejuvenator.






HI Nooriskandar,

Hai Justine..bagaimana kita nak check nilai volt yang keluar dari pin 7 h/v oscillator tda4858 IC menggunakan multimeter?

Connect probe hitam ke cold ground dan probe merah ke pin 7.

2.Dimanakah saya boleh dapatkan penerangan bagaimana crt monitor bekerja?Maksud saya seperti dari primary power supply pergi ke secondary supply and then dari secondary supply kebahagian mana supply ataupun signal tu pergi?Lebih kurang dari power supply,bahagian display dan crt board.

Sila masuk laman web ini:





greetings sir!
i think that’s it, that the negative voltage is high. i measured nearly 70-80 volts. i thought that’s low. and the display is dim. not too dim but dim. my problem is i don’t know where the heck i need to troubleshoot it. that’s the funny part. haha!
from the G1 socket i saw a disc capacitor much like that of the G2 but brown & a bit thin. a 1 watt resistor, some more resistor, zenner, ordinary diode, the capacitor i told you about with the collector leg connected to the G1 line, another resistor, big diode, then the pin of the flyback. from all of that i don’t know where else to look. at this point i’m guessing. it’s frustrating since i don’t know the principle operation of the G1 voltage.
thanks for the info. i know i can rely on you sir! i’ll look around some more & see if i can lower the voltage.
thanks again! more power!


HI Rene,

When you adjust the brightness function in the front panel the negative voltage should change and if it is constant then there must be something that had gone wrong. The negative voltage came from one of the flyback pin. This negative voltage is connected to a brightness circuit where the monitor CPU  (assuming the monitor is a digital monitor) could control it. If the CPU or the eeprom data had corrupted it could cause the voltage to be stagnant.





HI Bailing,

I found something interesting, the other repairman had replaced the pin cushion transistor with N-ch Mosfet, causing no display and no G2 voltage ( see the photo ). After replacing with D2058, the monitor works but the display is small and cannot be widened, also there is pin cushion problem. What a pity is that I don’t know the exact type of the original pin cushion transistor. What is causing this screen to be small, do you think? ( see photo )

It could be not using original transistor or the surrounding components have problem.

Now I got these voltage measurements:
G1   -72 V
G2   168 V
Heater  5.82 V
The supply of horizontal driver transformer is only about 7.8 V. This should be 12 V, shouldn’t it? I had replaced many e-caps, check transistor for leakage, resoldering dry joint but didn’t help.
What is causing this supply voltage too low?

Check for shorted horizontal driver transformer primary winding or even shorted h.driver transistor. Try remove the transformer and see if the voltage will rise.

Should I replace D2058 with another type, what type?

Yes you should try on other type. Try D2012 AND D1589.

By the way, from your experience what is causing a supply voltage too low, except for the high ESR e-cap?

It could be the supply voltage itself have problem that can’t sustain the load draw or any components along the line that are leaky.







I had been quite selfish all this time.  I had been receiving newsletters and articles from you but never bothered to respond or even drop an appreciative message.  I am an “electronic junkie” or simply a hobbyist.  I love to read articles about electronics and I do some repairs at home.  Your articles and newsletters contain a lot of helpful tips that hugely assist anyone dabbling in electronics.  Pls continue to do so — generously share your knowledge to others.

No problem and as long as you enjoying the newsletter I’m already glad.

When I have the money I will get your book on LCD Repair.  Big thanks.

Thanks for the support!





Hi Hussein,

my story similar yours but a bit different . i am studying software engneering in acodemy and i am working in a IT site of a company. story begin in one month ago when i was searching ram in cabinet .accidently i saw some pc power supplys that dust was over them.i desied that repair them then i begun studying in electronic componet and searched internet how can i know what is a componet and how can test them in circut. there was sites that tell you what is a component and how test them when they are not in circut.but i want know how can test them in board.because soldernig and unsoldering is time consuminig.

Certain components you can test on board like electrolytic capacitors, fuse, small coil and etc. But for semiconductor like diodes, transistors, resistors , non capacitors and etc you need to check on board. Even i have to solder it out and test  it off board for accuracy purposes.

oneday i saw a video from you in youtube site that you was testing a capacitor and i amazed. you done the testing very quick. i follow links until reached to your site and because of you i am learning some consept. i know this is not enough . i must hardly read and exprence some fact. by the way thank you so much

You are welcome!






Hi Jestine,

Ihave  aphillips Wsrceen older type TV but excellent picture-the children use this for games-becuase of temporay loss of remote control they have been using the power switch direct and you know kids treat things-anyway the red light goes to orange then blinking red-whereas before it went from red-orange to green-can this be the relay not switching the power to normal operations?

appreciate your comments.





Hi Peter,

Yes it can be the relay or signal that is missing that trigger the relay. That means you may need to trace from the relay to the driver transistor and see if there is any voltage at the base when the tv power button is pressed. If the relay is working then it could be parts faulty in the main power supply. Make sure that the power ic in the main power supply is receiving voltage.




Hi Tarmuzi,


one year has run to contacted you, my planning is changing, we still work on field and dont know have more time stay in workshop.

Time flies.

at the spare time I try to fix the battery pack of Garmin GPS 296, found the one cell of lithium battery is flat (voltage zerro) replaced to battery cells check the output when measure at the negative point and positive point no output(should be 7,4 volts) but when measured at data point witht positive point the voltage is shown 7,4 volts DC.We tried to replaced the IC1 (attached the drawing) but no shop in Glodok Jakarta to sell the SMD IC I am request. What I need your help is:

1. what component with mark ZD1( code L2 in part) and ZD2(code A2 in part).

From this link :

A2 is a 5.1 volt zener diode and L2 IS A 9.1 VOLT zener diode.

2. How to get the IC SMD with order small qty or you have the sabtitude data for that types 

    a. S-8232 Battery protection IC for 2 serial cell pack

    b. DS2438 Smart battery Monitor

    c. Si9410BDY N Channel 30V (D-S) MOSFET

Sorry no info on this. I suggest that you try to search from RS component website to see if they sell these link of parts or not. Or even visit this link of electronic suppliers:






Hi Jestine i am a gas engineer in UK i get boiler pcb to replace because gone faulty one problem i need advise with is when power is turned on without demand relay energises for fan in your experiance what componant can cause this problem relay checked is ok.    THANKS


HI Auranzaib,

You need to check the relay signal. This signal may be comes from CPU to trigger a small transistor. When this transistor triggers, the relay will function. That means the base of transistor should have at least few volts in order for the relay to work.





HI Wadi,


 How you doing? i hope you doing fine.

I’m fine thank you.


I  have 2 question regarding the troubleshoot.


1. I have repaired 1 lcd monitor Model Dell 17inch. The simptom is when power on the display is white color. I suspected the video ic faulty. My question is where can i easly to find the replacement? The video ic part no. is GM2621-LF (Dual input LCD controller for entry level applications).

White display is usually due to bad lcd panel (assuming you have check that the power supply voltages are good and stable in the lcd panel). Sorry i have no info about this IC.


2. The LCD projector simptom is when i power on, there have power and light, but when around 6 second the projector suddenly turn off, the fan is not running when power on. So my question is do you have any idea about this problem?


Since I’m not into this repair field thus i have no direct answer for you-sorry. Anyway, you may open up the projector and check to see if the supply voltages good or bad. A too high output voltages can cause any device to shutdown. Check the lamp too because in LCD Monitor, if the lamp have problem it will shutdown in few seconds.





Hi Jestine

Just a snippet; since starting to carry out component level repair about 6 months ago (inspired by your books) on LCD monitors, motherboards, laptops and desktop SMPS, I have kept every faulty component I have replaced. The result is as follows:

Electrolytic capacitors 33  (20 of which are the infamous  Hermai). 32 of them show clear bulging; all measure incorrect capacitance (usually low) and high ESR.
SMPS power diodes 4 – all open circuit
SMPS inrush resistors 2 – all open circuit
SMPS power IC 1 – dead
SMPS power FET 7 – all dead
SM resistor 3 – all open circuit

SM capacitor 1 – burnt & open circuit
Axial resistor 1 – burnt & open circuit
Laptop power jacks 8 – all failed to “make” reliably

Sometimes the failed components were probably secondary failures due to (say) a power diode failing – I have kept no record of these. Sometimes the fault has appeared to be due to an IC with lots of legs – I have made no attempt to replace these. There were a number of dry joints, particularly in laptop power circuits, but I did not keep a record of these either.

From your experience, does this seem more or less typical – i.e. electrolytic capacitors are the commonest source of failure?

All the best



Hi Gerry,

You are right- e-caps have the highest failure most probably due to heat and quality problems.

Have a good day!







Now I use the D1589 as the pin cushion transistor, and the monitor works perfectly ( see the photo ).Thanks, you’re really second to none! I haven’t tried the D2012 because I see in the datasheet, it is not for switching circuit. Now the monitor is drawing 0.2 A AC, and I’m still monitoring it.

You are welcome-if it continues to draw 0.2 amp then it should not have problem.

It’s interesting to note that the heater voltage is still 5.72 V and the voltage supply for the horizontal driver transformer is still around 8 V ( see the photo ), but the monitor works normally. What do you think about this?

Many designs the output voltages is determined by the setting of the VR in the primary circuit. That means if you increase the VR all the output voltages will be increased which include the heater and the vcc of the h.driver transformer. A too high output voltages will put stress on the HOT. Since this monitor is running ok (make sure to test on few resolutions) then i guess the voltages should be acceptable.






How are you? Quick question Ive been using your LCD monitor repair guide and you show how to get into the factory mode for the Samsung 510N. Ive been using your service code to get into the factory service mode on these Samsung 740N to check the panel hours after I complete a repair. I have one monitor on my bench now that came in with the complaint of distorted video. The Auto adjustment is locked. It wont let me do an image reset or color reset. I don’t see nothing in the service mode that would lock the auto adjustment. I guess somebody got into the menu and was able to lock it out but I just haven’t found it yet. Let me know if you know how to unlock the auto adjustment. Thank you for your help and time.



HI Rich,

I’m fine thank you. Many times the auto lock problem was cause by bad MCU program and not the service mode setting. Philip LCD Monitor is just one of the example and since i do not have the MCU thus i can’t repair it.

If you have other question please do email me again.

Have a good day!





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