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Electronic Repair Questions/Answers & Testimonials Part 11

By on August 29, 2008

I am a beginner to Electronic testing & repairing. The firm i work in is into Fingerprint based Security Systems and, Time Attendance & Access Control. I would like to know if one can test a CRYSTAL using a Digital Multimeter. If YES, please let me know how. I do not have an Oscilloscope for testing @ office.


Hi D.S,
If your digital meter have the frequency function and could measure up to many megahertz then you can test on the crystal. Not all DMM have the crystal testing function.


Hi JestineI have my Polaroid TV power supply blew sometime ago, Please can you be of help? or can I have replacement of this component T5AH/250. Thanks for your help and your email as well.



Hi Idowu,
That was a 5amp slow blow fuse and if possible get back the original value. if the fuse blow then there must be something that had shorted that had caused the fuse to blow. Check the bridge rectifier and if possible check all components in the power side like the power fet and also secondary diodes. If you did not check for the shorted components the new replacement fuse may blow again.


Good Afternoon,

Mr. Jestine Yong,

Today, while I am waiting for your ebook, I came across one unit Panasonic Colour Television Model No. TC-21S70K. It is a dead set, but I found out that capacitor C831 (220uf/50v) is very hot when touched after switch it on for a minute. Diode D835 (MA2560) is normal. What made it so hot? Which section need to be checked in priority. I have not go through it (checking the set) in details. I need your advice.

As for why the cap so hot? It could be the cap problem or corresponding components failure that had caused the cap to run hot. It could be the voltage across the cap has increased.


How do you tell the difference between a Voltage regulator and a transistor? They look about the same.

From the part number and board marking. Voltage regulator is an IC thus the board would mark as U or IC and for transistor the board marking is Q. General voltage regulator have the part number of 7805, 7809, 7905, 7912 and etc. Please take note that some manufacturers mark it as LM7805, 78L05 and etc.


hello jestine,
i havent read the report as yet but i have browsed through it.i had a back light problem. i tried a few things u suggested with no luck. i`ve rectified the problem by using an after market inverter to power it(the back light).when i get the chance i will read the report
thank-you regards, allan

Hi Allan,
That means is confirmed the inverter have problem! Please read my blog here and hope it could shed some light for you at


I always got view your website and I got learned many things from your website for troubleshooting monitor crt. I got question and need your advice..,I try to repair HP s7540 CRT Monitor 17″ with power on green blinking,I got checked and replaced a new transistor “C5929” and a few capacitor at power section,but still cannot solve the problem. I got try to remove “B+ Fet P8NS25” and power on, the monitor got display,no power blink and still good. I got try to replaced a new “B+ Fet P8NS25” and solder it back, but why the power on still blinking? help…

Hi Leo,
Thanks that you like my website. As for this Monitor model it has a common fault which is the:

SMPS primary winding partial shorted
B+ coil shorted
Flyback transformer primary winding shorted
shorted C5929 and
shorted B+ FET

Please check all the windings with a flyback tester or with a Blue Ring Tester. Hope this helps!

Few days later i got hi email:

Thank Q so much Jestine , your advice too accurate.
I checked
SMPS primary winding, Flyback transformer primary winding, C5929, B+ FET was good.., only the B+ coil was faulty and shorted. I replacing only the B+ coil and solve the monitor power blinking problem.


Hi Jestine, I want to buy The Flyback meter,A sencore Lc103 capacitor & inductor Analyzer, Peak electronic Atlas Component analyzer tester.please i want to know the price of each one. Thanks.

Hi T,

I do sell the flyback tester at
As for the sencore and peak atlas analyzer, you have to visit their website to ask about the price. You may visit and


Hi M,

Here are your questions and answers:

A person bring two monitors for repair. The first One is l.g studiowork 57v the problem is reduce in width while horizontal control works i have tested the B+ boost Circuit the B+ having 109v but still there is no effect checked all the component every thing is fine i think that the H/V oscillation ic may be faulty.

Yes the H/v oscillator IC may have problem but the B+ voltage is a little bit too high! Try trace back from the B+ fet gate signal to see if there are any components that is faulty. What is the high voltage measured at the anode of the CRT?

In the second benq 17inch monitor the display disappear after 10minutes in 1024×768 but putting the monitor on 800×600 the monitor work fine the monitor work only on 800×600.

Try check all of the e-caps first and if all are tested okay then chances is high the mainboard might have problem. It could be a data corrupted in the eeprom or in the MCU unit.


Hi mr yong

thank you a lot for this magnificent e-book i read the first chapter what talk about safety first. because i don’t have a time to read this book . really it’s small step but valuable things I’ve got it. I promise that i’ll try to read every word of this great book it’s first time i read book CONTAIN practical steps about every thing consist first steps to become professional in electronic repaire .

thanaks alot

have agreat day

b . m . h


Hi Gerald,

Here are your questions and answers:

I wish to inquire whether you have or sell any good mechatronics project books that i could use & implement in my teaching skills for the MLVK/SKM H-170-1/2 Industrial Manufacturing Asst.(Mechatronics) course. I would be most grateful if have/sell any practical lab/project books/publications which touches on the topics of electro-pneumatics, electro-hydraulics, PLCs(Mitsubishi), robotics. I find it hard to get those kinda books here in Kuching, Sarawak. Or, do you know of someone/vendors in Kuching, Sarawak selling the books?

Sorry Gerald, i do not have such book. Have you try

May i know what is the most suitable type of oscilloscope that service people use for repairing /debugging modern tv, dvds, high-end audio amps equipments? How much would it cost, it could blow a hole in my pocket…I have seen a fewsome at jalan pudu area, and wasn’t sure which to buy.

Getting a 100 Mhz analog scope is already adequate to repair lots of electronic equipment. If you get a 20 mhz you may end up have to upgrade it. Get the 100 Mhz scope so that you don’t need to upgrade again. To some that have the budget they may get a digital oscilloscope. As for the price, you have to check out from the seller as different brand have different pricing.

Thanks for any useful infos..

You are welcome!


hi mr yong

i need hep

i read some of u ebook and some of what about u said is some statement that the reader must have known about some electronic circuit to understand what explanation u written in the e-book and I’m ask help from somebody who REPAIRING in electronic circuit and i find them so stingy about help in just asmiple thing… i need help to kick him ace if u have any practical book that explained the electronic circuit without any help from any body i ‘ll be glad… yong let me honest with you im beginner in the electronic and i need help in practical thing with explanation not just theory…special i want to REPAIRING the monitors and lcd’s monitors and i read some reports about lcd monitor it’s looks like useful but if the book u write about monitors repairing will be effictive in practical repairing without any help from anybody .. if it is i’ll buy or not….. im waiting to receive the msg from u???????

Hi B,
Be familiar and strong in the testing electronic components first as this is the first rule in successful in repairing other electronic equipment. Once you have done in reading my ebook and have confident in testing electronic components then ask yourself as which electronic equipment you want to be in first be it in CRT Monitor, LCD Monitor, TV repair or etc. Learn one equipment one at a time to avoid confusion. If you are interested in the LCD Monitor repair then you can get this ebook and if you want to do Tv repair then you can get books about tv repair from



Unfortunately, my DMM doesnt have the FREQ function. I would like to know if simply by measuring the Voltage across the two XTAL pins, i can come to some conclusion. The PCB has a 32.768 KHz XTAL connected to the OSCI & OSCO pins of a RTC chip.

Voltage OSCI wrt GND = 1.0 V
Votlage OSCO wrt GND = 0.2 V

Hi D,
Sorry we can’t tell if it operate at the right frequency or not just by measuring the Crystal voltage.


I am repairing a panasonic tv set ,found there is a glass body diode p/n written vertically 2c8(actually don’t

whether it is 2c8 or 82c)shorted,I could not find its datasheet ,may I know it is a zener or a normal diode?


If it is written as 2c8 then it is a 2.8 zener diode and if it is written as 8c2 then it is a 8.2 volt zener diode.


Hi Jestine Yong,

I am staying in Johor Bahru. I think it could be difficult for me to attend the class. If you have any class in Johor Bahru. That would allow me to attend. For those electronic part in LCD monitor or power supply, is it very difficult to find the same model? Is the any age limit for learning electronic? I am 36 years old. Thanks for your reply. Sorry for any trouble caused.

Hi T,
We do help to book hotel for participants from other states. Nearby my place there is a 3 star hotel where i always book for students to stay. As for the lcd monitor or power supply, do you mean to find parts? or model? As for the parts, it depends and if it is a transistors, resistors, capacitors then it is quite easy to find in local market. If it is power IC (depends also in models) and if i can’t get from local supplier i would order it online. By the way it is not too old to learn about electronics. My oldest buyer who bought my ebook was 82 years old! There are also some in the mid seventies and mid sixties but all of them were from UK and USA.


I still got 1 more question need your advice, about the monitor samsung syncmaster793df 17″ sometimes got hiss sound like “eeeee…” when power on using the monitor. I try to find the answer but still cannot find it. Why sometimes monitor will coming up this hiss sound? and can this type of problem can be solve?

Try gently knock on the Monitor Flyback transformer and the SMPS ferrite core while the Monitor is running. If it quite down then pour some shellac onto the flyback ferrite core (with power off and let it dry for a day) and dip SMPS into shellac for a day and let it dry. If the sound still persist then direct replace the power IC and retest again. Try also to use the handle of the screw driver to knock on the mainboard. Hope this may work.


Hi Z,
I would like to ask sir about a voltage regulator is it ok 4.9 volts on its output when i measured it or it must be strict 5 volts. i desoldered the output pin and check the voltage and still 4.9 volts. Does the voltage regulator defective or there is an accuracy problem on my meter. but i doubt so.

I came across lots of LCD Monitor mainboard that was working fine even the voltage measured 4.85 Volt. It depends on what circuit you are working on. Some circuit are very sensitive and it must need an exact 5 volt in order to work properly. Try use another brand of voltage regulator.

Another i would like to ask is bipolar capacitor the same as polarized capacitor?

Please visit my other blog for the answer at

Thanks a lot sir.
You are welcome!


Hi J,

Here are your questions and answers:

1. common myths and reality in troubleshooting(say yesterday i tested a big capacitor using digital multimeter in resistance range.i recieved initially a low resistance which lead me to believe it is spoiled.But all of a sudden it started charging which left me confused.

To test big electrolytic capacitor you have to use ESR meter. Please visit my website at

I have stopped using ohm meter to test capacitor because it gave lots of confusing result.

2.While testing Fairchild Opto switch H22b1which is one side diode (which i checked) and other side darlington i am confusedshould the transistor give a very high resistance while i connect it across diode check? i got 1.6k.My friend argues it is blown. But i read in an article that darlington pair has low output impedance of 75 ohms or 1.6k.

Since i do not have this part with me thus i can’t provide you with an exact answer. Read my ebook at page 134 and you should be able to tell if the darlington transistor is good or bad.


I need to get 27 uf @ 375 volts DC how many Wet Tantalum capacitors i need to connect in series & what value ? the Max current value capacitor in markeet is is 125 VDC

Hi B,
Please visit this website to find out the calculation at


You had an article listed on the Compaq FP7317 17″ LCD monitor, but I couldn’t find it. I’ve got a Compaq FP7317 17″ LCD monitor. It seems to have some strange power “hiccup” problem. I power the monitor on. The power light stays green for a second, the screen flashes just briefly, then clicks back over to a dark screen with amber light. This occurs with a “hiccup” on the speakers.

Hi H,

Here is the link

By the way your problem could also be e-caps faulty-please check them too. Have a good day!


Respected Sir

First Thank You For your answer in benq monitor the snapper Cap Is damag and causing the display to shutdown at high resolution.But In lg monitor it is very hard to find the problem according to you advice i have checked the boost FET Volt( Drain=109v, Source=196v, Gate=192v, the no of Fet is j306)

FET Checked O.k tracing the gate componenet also o.k but still the same problem if you have

LG Studiowork 57m Circuit diagram then please tell me what should i do to solve this problem. Thank You

Hi M,
Have you check all the area in the pincushion/ horizontal size area? What about the modulation diode? Since it is using J306 then the B+ voltage is in good condition. By the way i do not have the schematic diagram-sorry.


Hi Jestine,

Really enjoyed your ebooks, I was also reading your blog and came across an
item you wrote were you said that although you did not have a spec sheet for
the 4600 you did for the 4532 FET which you used as a replacement.

I have a Samsung 173v monitor which shuts the lights off after about 3
seconds. I can see that 1 of the four fluorescent tubes does not light.
By swapping the tubes I can see that it is not the tubes fault so I assume
that the inverter cct for that tube is faulty and feedback to the inverter
ic is causing the unit to shut down.

This unit uses 4 of the 4600 FET’s but I am unsure how to test them as I do
not know the pinout and the unit shuts down so fast it is hard to get a live

Any idea’s



Hi D,
Glad that you like my ebooks! To trace them, look carefully at the pinouts of the ic and you could clearly see that it is actually 3 pins that are connected to circuit track. The rest of the pins are in parallel with other pins. Normally i test them with the help of Peak ATLAS Analyzer component tester. According to the data of the quite similar IC 4431, pin 1, 2 and 3 is source pin, pin 4 is gate and pin 5 to 8 is drain. I hope the 4600 IC have the same pin outs as the IC 4431. Hope this helps!


Dear Jestine,
Thank you for your reply. I am happy to learn from you.



Hi Abe,

how are the work internal principle of structure CRT & LCD display?

It is a big subject and you can try search from google for “How CRT Monitor Work” and “How LCD Monitor Work”.

1. I was face once a day Computer Monitor LED light the only on but noting display graphical image. what is that?
Is there any B+ voltage at the flyback? A missing signal to Horizontal output transistor also could cause no display (no high voltage) problem.

2. Some bady thanking me Monitor generate 11000V. is that the fact?

Depends on the size of Monitors. Bigger Monitors tends to generate higher voltage. A 14 and 15″ Monitor generate 24,000 volts.


Hi K,

I would love to advertise that I fix LCD monitors.What do you think?

Is good the profit margin is there.

My problem is that, on average how much would it cost to fix an lcd monitor?

Depends on problem and many percent of LCD Monitor problems were due to bad capacitors and dry joints. All these don’t cost must except that when you replace the backligh.

I how about charging a flat rate but that would all depend onhow much the parts cost.

In my company i’m charging flat rate for problem in the inverter and power. If i replace backlight or mainboard i will contact the customer first.

Tell me would this be a good business to get into?

Yes it is!

What do you think of my ideal to avertise to student that I repair pcs,and Macs and also LCD monitors.

Its a good idea if you are capable to handle all these equipment.

That is what I would like to do but is it feasible?? I really would like to tap into doing this but I need to know if ithis could work for me????????????????

Well it depends on how you run your business. Please read my article here


Hello Jestine,

Sorry to take too much time to conclude my reparing on my home 29″ TV Sets.

Finally the fault is due to no high voltage present on my TV set.

What I did is exchange the HOT and i able to bring my TV Sets alive for only a day and the next day dead again with no high voltage present.

For the HOT Spec is as following:

D1556 D1877

Vcbo = 1500V 1500V

Vceo = 1500V Replace with 800V

Ic = 6A 4A

Pc = 50W 50W

So can i suspect is due to the D1877 HOT not fullfill the original spec which unable to withstand more voltage and broken finally??? Please advice me once again.


Hi D,

Yes, the ampere is a bit low and you need to get a bigger one. Besides you need to check out other problems that could have cause the HOT to burnt at




  1. Ashutosh

    March 4, 2009 at 8:43 pm

    i need your help for reparing 15" lg sutdiowork crt monitor.problem is.. horizantal output transistor "C6810A" gose to short after few (5 to 10 ) minuts.display comes during this time.i got try to replece newone H/O transistorbut problem not solve.Also i got to try reples tested EHT,Yoke,CRT,and subtitude transistor but problem still not solve .powr supply voltage asho cheke it is normal.
    Hope for ur replay

  2. admin

    March 4, 2009 at 11:06 pm

    Hi Ashutosh,

    Try visit this link


  3. vishnu kumar vaishnav

    September 29, 2010 at 3:16 am

    hello sir
    I am vishnu kumar vaishnav I want know compaq 7540 CRTmonitor EHT transitor cofigration beacoue my monitor transitor has falt

  4. admin

    September 29, 2010 at 3:50 am

    HI Vishnu,

    What is the part number of the transistor?


  5. Vincent Perera

    December 3, 2010 at 2:40 pm

    Dear Sir,
    I purchased panasonic viera X series 37 T.V from Dubai before living the country.It purchase on 16.09.2010 and I taken it to Sri Lanka.Acording to the instruction I switched on.Then language appear on screen and after that country appeared.after that I press O.K Then Channel tuning start.After that all stop and T V came to stand by position.I tried several times and same thing happened.Now I need your help.How I can recover this broblem.Please help to me.

  6. admin

    December 4, 2010 at 12:47 pm

    HI Vincent,

    I have not seen this problem before. It could be the TV have problem. I suggest that you refer to any of the local distributor for more information.


  7. Masese

    December 6, 2010 at 10:24 am

    I have a question and need your advive.I tried to repair HP 7540 CRT Monitor 17″ with power on green, I got checked and replaced a new transistor “C5929″ ,then it worked for few hours and turned the screen blank while power still on. What could be the problem???. Please advice.

  8. admin

    December 6, 2010 at 12:45 pm

    HI Masese,

    Check the B+ coil because it may have burnt. Please visit this link too:


  9. Neeraj Sharma

    May 17, 2011 at 12:58 pm

    hello jestie,
    Please help me out...
    i tried to repair a compaq 17"monitor 7540, the problem is that power green remain constant and makes a sound clink clink from the relay, now when i desoldered the HFB pin of the EST the relay does not make any sound so i replaced the EST, but the problem remains the same....

  10. admin

    May 17, 2011 at 9:27 pm

    HI Neeraj,

    Try isolate the problem using the link below:

    It could be the power supply that can't withstand the current draw from the flyback.


  11. raju

    June 17, 2011 at 8:24 am

    7540 set -no eht no raster smps supllye ok output transister ok
    but no screen light

  12. admin

    June 17, 2011 at 9:26 pm

    Hi Raju,

    Does the HOT have base waveform? If no there will be no high voltage.


  13. Levis wanjala

    December 9, 2011 at 7:16 pm

    Hi sir,i av an airstar inverter,but it keeps burning the npn transistor after overheating,i replaced with 3205,50n06,z44,but they burnt and now it no longer produces AC bt burns even be4 switching,what might b the problem and the way 2 correct it

  14. Krishna Yogi

    October 13, 2012 at 12:24 am

    Hi sir, 
    I want to lean your ebook of Monitor Repairing, Can you halp me how to i can read your e book? 

    • Jestine Yong

      October 13, 2012 at 1:45 am

      Hi Krishna,

      I have sent an email to you.

    • Jestine Yong

      October 13, 2012 at 1:55 am

      Hi Krishna,

      Do you have other email because your email was bounced?


  15. kumar

    October 18, 2012 at 2:25 am

    i have a hp 7540 monitor,its working fine,but produse some noise in FBT.if i open the dos mode
    its getting noise. if i change the frequence 60 hz then no issue,tis working fine.
    what is the solution for this problem??

    • Jestine Yong

      October 19, 2012 at 9:35 am

      Hi Kumar,

      It could be flyback. try gently tap the flyback core to see if there is any changes or not.


  16. Ben

    August 16, 2014 at 6:05 am

    What is the model number of EHT of Compaq MV7540 monitor.
    All I could find written on the damaged sticker is:

    SAMPO 05B16
    # E159656 C
    FLO0261 A
    TFB**** A
    FE5B39CT FM1077

    The 3 or 4-digit number in place of **** can't be read as the sticker got scratched. And there's just a symbol instead of #, rest exactly like this.
    And on the body printed with grey:

    5Y11.B C
    And on the bar printed with black:


    I need help...

    • Jestine Yong

      August 16, 2014 at 4:31 pm

      Hi Ben,
      The best is to locate the schematic/service manual as this type of flyback can have few number and very confusing. It can be the TFBxxxxx or Sampo 05B16 OR even the FM1077.



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