Hi Gasant,

1)      Does the transformer supply the  Drain leg of Fet with power

The drain is just like a switch controlled by the gate and the supply is coming from the transformer.

2)      Does the Drain leg of the Fet make the run dc circuit.

Run dc ac signal source is from one of the output of the secondary winding in primary side. The primary winding have to be energized in order to get the ac signal source from the secondary winding.

3)      Does the run dc circuit connect to VFB leg of PWM.

It depends on the design. Some have the run dc output connect to the vfb pin and to some it have just only a resistor or preset to determine the error amplifier in the ic.

4)      What IS  RT/CT

RT (oscillator charging current) and CT (oscillator timing capacitor) determines both oscillator frequency and maximum duty cycle

5)      What is ISENSE (is it to control current in ic)

I sense is current sense. if there is too much current draw it will shutdown the generator from producing output.

6)      What is REF

is also Vref (voltage reference output) and could provide 5volt  to external circuity. This line usually have a 0.01uf or larger cap cap shorted to ground to provide best stability

7)      What is comp

Comp is compensation.  This is used to provide an accurate average current limit in the internal voltage amplifier of the ic.

Thank you



hie how are you i have a problem with sva tv problem is the 27vdc supply to vertical ic which now comes from the line output transformer which is very low 7vdc can it be the transformer

Hi Bonolo,

try trace backward to see, it could be a bad e-cap or a leaky diode. If all check to be good then replace the flyback transformer.



Dear Jestine,

Few days back I have bought a Blue ESR tester as dismantle package and I soldered all components. But at the time of switch ON the meter it shows first LED (from LHS) & both 7-segment display marked 0 0 and switch OFF can not done, only I can OFF the tester by disconnect battery. Since it is a costly item and I bought out side of my state, so please help me.


HI Amitava,

There must be some thing that have connected wrongly. First make sure the transistor (3904 and 3906 ) did not connect wrongly and make sure also the resistors value are properly installed.




What are the voltages that are normally produced from the secondary output

of the SMPS. Most of the books i have read they don’t tell about the output values.

I’m using a 220V ac in my area.


Hi Simon,

It depends on the power supply spec it self. All equipment power supply produce different voltages and you need to check it out yourself by measuring the cathode side of the secondary output diodes.



HI Anand,

Jestine, what is the difference between a plasma, lcd and a led t.v ?




Hope this helps.



I just purchased your E-book and am very pleased with it. I have a question in regards to the above monitor. I have an intermittent problem, the monitor works fine until it goes into standby. After PC wake it does not detect input signal. Powers up but just detects for a quick second then nothing. Any suggestions as to start looking?

Thank you

Hi Mike,

First make sure the output voltages from the power supply are good and stable. Make sure no bulged e-caps too. If the voltages are good even in the mainboard then most likely the mainboard MCU have problem. If the MCU programs run it can cause lots of weird symptom which include the intermittent problem you have just described.




I look at the

Peak Atlas DCA55 Meter Tester New Free Shipping Semiconductor Analyser

This is listed on EBay for 89USD which is good price. I understand the device will give me the ‘details’ of the component, but will it tell me if the component is bad?? or does it just give details/description of part.  Would you condider the device a valuable addition to electroinc tool bag?



Hi Bart,

If the component have problem yes the meter will tell you about it. I have this meter but rarely use it unless if i do not know what type of components that I’m checking. Some part number are funny and i need to use this meter to tell me what type of component it is. But again if the components is bad this meter would not tell you what type of component it is.



HI Patrick,

I’m really enjoying your newsletters and I’m studying your eBook, Testing Electronic Componets, LCD Monitor Repair and Free Bonus books.

Thanks for the support.

But, I don’t have skill to find defected componets yet. I know I need more study and pratice.
So, if you have time to help me to find problem of my router it would be very thankful.

I have a Linksys e1000 wireless router by Cisco. Problem is…. when I plug power on it only LED lights on 4 LAN Ports and Internet LAN Port. But I don’t plug any LAN Cable on them. And there is no LED light at Power and Wireless. I just open the cover to find any bad capacitors or burt componets top and bottom but I don’t see any physical damaged ones.

The first thing is to make sure the ICs is getting good supply voltage. In fact I have opened up a router before and there was not much components can be tested because most of the functions are control by the ICs. If one of these ICs have problem then we can’t do much about it because in the market hard to find such ICs.

By the way, use your finger and touch too to see which ic is totally cold or extra hot. Those ICs have problem.



Hi, first I have a problem: I have to change the Q801, is a 2sk2750, I made a mistake in the smps. When I change this component, say me: how many volts should I espect from the g2 of the crt? How can I measure it (I have no high voltages measurement instruments)?.
Shortly, I have to solve the problem of Q801 (is a problem to find it or a substitute), and then I can do other tests. Thank you for your help, if you can say me how to measure the g2 voltage, and if I have to take extra care (besides the fact that is high voltage). When I solve the smps little problem I’ll say you.


The first thing, make sure the power supply give good and stable output voltages. Next there must have at least a 110vdc B+ to the flyback pin. The HOT base also should have a pulse so that the flyback will energized. Once the flyback is energized you will get heater voltage, g2 voltage and the 24kvdc high voltage. The g2 should have about 250 to 300vdc. No g2 voltage means no display.


HI Said,

1. Hot ground and Cold ground: u indicated this in smps it is the lcd monitor smps or its is the ATX power supply of cpu.

i. How can i recognized the Hot/cold ground points in power supplies.What is the identification marks of that points from which i easily understand that this is that points.

It can apply to any equipment that is using smps. Hot ground is the big fat capacitor negative pin in power primary side. Cold ground is the earth ground or negative pin of the secondary filer capacitor.

ii. what is the purose ot that points.

It is the nature of the smps design because it has primary and secondary side.  Primary side is HOT ground and secondary side is cold ground.



Hi Jestine,

This lcd monitor can only display a brief moment and then display disappears, as in the video attached ( with signal ). I had checked all the 4 ccfls are good, supply voltages 5V & 13.8V are stable and the EN signal 3.3V is also stable.

To make certain, I checked with external ccfls, and the problem is the same as you could see in the video. Do you know why 2 of the ccfls are brighter than the other two ( only lit halfway along the length of the ccfls and very dim ). According to the chinese technician the problem is one of the high voltage trafo develops short circuit, but after checking with the ring tester the two high voltage trafo are both good.

Please advise how to troubleshoot this problem further.


HI Boling,

Probably one of the transformer have problem. Compare the ohm reading between the transformer and botht should have the same ohm reading (secondary winding). Sometimes blue ring tester could check ok but the resistance out causing the display to shutdown. Check also the ballast cap and make sure the capacitance is within range.



HI Nichole,

Thank you very much for the articles you sent…Its quiet great knowing you are extending your unselfish help in sharing your expertise in the field of electronics. Another bunch of ideas that I am really appreciative of.

You are welcome!

I had witnessed how you and some of your contributors would make effort to share their knowledge and expertise in the field of electronic technology.

On my part, I had planned a couple of times to have the knowledge practiced in actual but I am a bit hesitant to try things out due to some of this:

1. Since most of the electronic gadgets nowadays uses surface mount devices, How would you purchase to obtain for this parts?

(considering here in the Philippines, specifically in my place, surface mount devices would normally not available)

Most of the SMD parts i remove it from junk board and used conventional spare parts. If you wish to buy smd components you can visit these three website:




2. Are you still using the conventional type of soldering iron or resort to a heat regulated one?

I’m still using the conventional type hakko 981 dual mode. I’m already used to it so i would not change at this moment.

3. Is it ok if by chance of non availability of smd parts, have the defective parts be replaced with a converntional spare parts of the similar values? How do you react to situations like this?

Yes you can try it and I have tried many times and almost 90% it can work.



please, i need your quick help, i can’t know how can i test crystal oscillator using a personal scope hps5?

and when i test it should i connect power to the board or not?


You should power on the equipment. I’m not sure what range your scope can test. If the crystal is 20 MHZ and your scope is 10 mhz then you can’t test it. Just set to AC and play around with the volt/time division till you see a sinewave.



hi jestine how r u.hope u r fine.yesterday my friend brought a laptop charger circuit board.it has uc3842A pwm ic.but some one has removed its fet.so i am thinking to place k2645 .if is there any better fet than this pls inform me .thank you.

Hi Rohit,

Yes you can use K2645 which is already good enough.



Jestine Yong works as an Electronics Repair Lecturer in Kuala Lumpur Malaysia and his training website is http://www.NoahtechElectronicsTraining.com. You can check out his repair blog at http://www.JestineYong.com