Don't Miss

Electronics Repair Questions/Answers and Testimonials -Part 71

By Jestine Yong on January 11, 2011

Hi Jestine Yong

I’m Jannie from South Africa. You are really a Blessing to me. When I bought
your e-books last year I didn’t know what to do with my life! I was
struggling within myself. Then I bought more of your e-books and I have read
them, and I know that I must do repairs because I love electronics! Have a
great 2011. God Bless

Regards Jannie

=======================

Hi,Jestine

I am pleased to extend my thanks and appreciation to you for the various repair newsletters that you send to me over the passed few months, since I got in contact with you. Those repair newsletters have improved my understanding in the field of Electronics to the extend that I am able to repaired and solved electronic equipment problems on my own.

Thanks for your time,

Have a very good day

PETER S

==============================

hi sir this is edmond i purchased your bok testing electronic components, and electronic repair articles. i have been studying an electronics technicians course online now on and off for roughly 5years now. i have honestly found your books alot more informative in testing components,troubleshooting,repair etc,a lot more useful than my whole course.i have found it has given me alot more confidence intesting and repair.i am know pretty confident in tackling almost every repair that icome across.i look forward togetting more information as soon as ican.thank you very much,awesome info the best service money can buy. thanks again for fabulous tutorials,happy new year and god bless you and your family! Cheers

==============================

HI Stephane,

After having been busy doing maintenance and administration tasks on other PCs, I finally managed to have time to get back on this “learning” project. And, I have good news. I can say, at last: EUREKA! The motherboard is running!

Congratulation!

As you suggested in your last reply, I replaced the missing (and unknown) SMD resistor with a 1k ohm resistor. Unfortunately, with this resistor, the motherboard still refused to start. Then, I tried a 2.2k ohm with no more luck. Finally, I tried a 5.1k ohm (because I did not have any 4.7k ohm on hand). Even with this one, the motherboard remained completely silent. But, after each SMD resistor change, I tested the power supply’s PS-ON pin’s voltage and I observed that every time I increased the SMD resistor’s value (ohm), the PS-ON pin’s voltage also increased. Since the voltage of the PS-ON pin should normally be at (or near) 0 volt (when the power is applied to a fully functional motherboard), I said to myself that maybe I’m going the wrong way. So, I made a 180 degree turn and replaced the 5.1k ohm resistor with a 0k ohm (a simple jumper). Then, I applied power to the motherboard and BAM! The motherboard emerged from its sleep with all the fans running and the HDD spinning. The motherboard is finally back to life!

Wow! that was fantastic. This shows that never if one never give up, many things can be done.

At that point, I checked the voltage of each power supply’s connector’s pin and all voltages (3.3V, 5V, and 12V) are as expected. Then, I connected a monitor to see if there is any boot problem or error messages, but it doesn’t. It even boots into Windows without any complains. But, I did not stopped there. Since I received my brand new PC-Diag’s FlipPOST card, I used it to see if the BIOS can communicate (without any problems) with the hardware… and it does. The FlipPOST card reported NO ERROR.

Noted.

Now, to be very sure that everything is hunky-dory with this motherboard, I performed the following tests:

– Stress tested the CPU/Northbridge/RAM with MPrime (on Linux) and Prime95 (on Windows).

– Stress tested the CPU/Northbridge/RAM/Southbridge/IDE Bus/HDD’s system-file with Bonnie++ and Iozone (on Linux), using single and multiple files, different files’ sizes, and different data blocks’ sizes.

All tests returned NO ERROR. So, I think that I can conclude that the motherboard is, not only back to life, but in full health.

Lastly, about the PC-Diag’s FlipPOST card, I tested it on several fully functional PCs that I have here. Unfortunately, right now, I have no problematic motherboards on hand. As expected, it returned the BIOS’ POST codes in real time while the PC was booting. In all cases, the card returned the “boot loader call” code, such as: “00” or “FF” (depending on the BIOS). Also, it has two HEX-LCD: one displaying the current POST code and the other displaying the previous POST code. When the POST finished, you can browse (backward and forward) through the POST codes sequence with the help of a “S1” and “S2” button. The card also have a series of 7 LEDs that show the state of the System Pulse (SYS), System Clock (CLK), BIOS Input/Output Write (IOW), Oscillator/Frame Cycle (OSC/FRAME), Reset (RST), BIOS Memory Read/Initiator (BIOS/IRDY), and the Data Transfer (DATA) buses’ signals. It also have the standard 4 voltage LEDs for the 3.3V, 5V, +12V and -12V state. So, despite the fact that I tested it on fully functional PCs only, the card seems to perform really well. Consequently, I can say that it is a very good investment (thanks to you).

Thanks for the review!

I whish to conclude this message (and close this thread) with a million thanks to you. Your precious help, commitment (for the time you spent reading my messages and writing back answers) and your kindness (for the sharing of your knowledge) are all the reasons why I succeeded in this “learning” project. I have learned lots of new skills, such as: how to correctly interpret ESR and OHM results, how to solder an SMD resistor, etc. Furthermore, my friend is now the happiest guy in the world, knowing that he will be able to use his newly revived motherboard for his file server project.

So again, many thanks to you.

You are welcome and your passion has really drove you through!

All the best!

Jestine

==============================

HI ND,

Recently I received a 21″ Akira color TV with no power…..when I open and checked the power section and I found out that the HOT and the power regulator strf 6656 shorted and some of the surrounding components….resistor and capacitor,so I replaced both HOT and regulator and also some of the surrounding components.I connect the power thru a bulb and switch it ON,unfotunately that the bulb blinking and the b+ present also blink.I checked the surrounding components again and found OK.Attached the video of the blinking bulb for your info and need your help.

Power blinking after the replacement of components doesn’t mean that the power supply have problem. It could be the current not enough flowing to the power circuit due to the light bulb. If your meter could measure the secondary side and it has dc voltages then you can remove the light bulb and place the fuse and power on. Hope that the full power can be obtained.

Have a good day!

Jestine

===================================

Hi Nsimba,

Further to my request, I want to know how can I find the bad capaitors in my TV plasma PD-42p2a. They are many capacitors I should I know wich one are bad.? Do I neede to remove all of them on the board to test them or I can test them whilst in the board.

First you need to know what is the complaint of the tv then you move on to the suspected section. From there you can start to check the capacitor. If it is an electrolytic capacitor, you can check it on board with ESR meter and if it is non polarity capacitor you have to check it off board.

Jestine
http://www.JestineYong.com

=================================

Hi Jestine,

Yes I can measure the DC voltage the b+ seem to be a bit high… flickering from 140 to 160 Vdc.I never come thru with this kind of problem before,ok I’ll to put the fuse and turn it ON and see what happening and thanks for your tip and support.
ESR meter and a fbt tester is a must for a technician to have,it make me faster to check the capacitor with high esr.

Thanks

===============================

sir good morning, I am repairing AKAI LCD TV Mod.# LCT32AE who’s the trouble is dead power supply, I found thermistor colored green / letter M at the body, located at the bottom of chopper transformer,when i test it i read 950K ohms.Now the question is, is it really 950K ohms or it is off value? If that is good what is the possible defective of this TV? Thank you very much sir.

Hi Ed,

If you really have confirmed that the component was a thermistor, the ohm value should be about 5 to 10 ohm and it can’t be 950k ohm.

Jestine

=============================

Hi Thomas,

I have purchased LCD Monitor repair books recently,

Thanks for the support!

and now I had some issues with HP LCD Monitor 17″ backlight problem, all the monitors are after 5 seconds backlight is getting off, can you explain what could be the problem?

already checked as per your repair manual.

Please find the below all models HP Monitors

HP L1740 – 4 Units

HP L1702 – 3 Units

HP L1706 – 2 units

Waiting for your reply and help to repair the above 9 monitors

There are few reasons as to why the display will shutdown after few seconds:

1) bad or bulged filter cap at the power supply secondary side. You need to test it with esr meter and if you do not have this meter, you can directly replace and retest the monitor.

2) Dry joints in the high voltage transformer. The dry joints sometime can be too tiny and you can’t see it with bare eyes. Just directly resolder the high voltage transformer pins and retest.

3) One of the backlight have problem. Replace one by one the backlight and power on. If the monitor did not shutdown then you know that the backlight have problem. Since you have so many lcd monitor, you can use a good backlight to test on the suspected lcd monitor.

4) Bad high voltage transformer-you can compare the Ohm reading of the top and bottom high voltage transformer. An open winding in the high voltage transformer could cause the display to shut down.

5) Bad Mainboard- If the MCU in the mainboard have problem, it will not send an on signal to the start circuit. If the start circuit do not work, the inverter ic will not get the supply voltage. If no supply voltage, the inverter will not produce a waveform to energize the high voltage transformer. If the high voltage transformer don’t work then there will be no backlight.

Jestine

==================================

HI Simon,

I bought your SMPS book a couple of weeks ago and am currently reading it.
It’s very interesting, many of the techniques I have already used over the
years, but some are new to me.

Thanks for the support!

I have one question though.
Whenever you talk about measuring resistance you say there should be “One
Reading” and shouldn’t be “Two Readings”.

What do you mean by “One Reading” and “Two Readings”?
If I measure a resistance, how could there ever be two readings?

Okay, lets take diode for example. A good diode when you test it with an analog meter the meter will show one reading in either way. If a diode is shorted it will show two readings in either way.

Jestine

==============================

Hello Mr.Jestine, the first saya akan menyampaikan sedikit pengalaman;saya pernah memperbaiki power supply CPU yang menggunakan IC UC 3842, tegangan output tak stabil,saya coba replace IC tersebut dengan yang baru,apa yang terjadi malahan tak ada output tegangan.dari pengalaman tersebut saya mau tanya apakah ada IC UC 3842 yang baru tetapi tak bisa pakai? penasaran saya ganti lagi dengan yang baru tetapi hasilnya sama tak ada output voltage.akhirnya saya kembalikan dengan IC semula,hasilnya keluar voltnya sama dengan kerusakan awal yaitu tak stabil. saya mohon tanggapan dari Mr. Master.trimakasih.

Hi Anci,

Ya kadang kala IC berkemungkinan rosak ataupun ic bukan dari jenama yang sama. Saya pernah tukar motorola UC3842 ic yang baru dgn Sg Thompson tetapi ia tak berfungsi. Bila saya guna balik kilang yang asal ic itu berfungsi.

Jestine

===============================

Hi jestine!
Happy New year! May it be a blessed one!
I have just received a Matsui 1408T television as a gift! Its not very old!
Problem is, when I switch on, there is a thin blue line horizontally accross the screen! I don’t have a schematic.
Any ideas as to what the cause of this could be?
Much appreciated!
Riaan
P.S: downloaded your latest Ebook! Great stuff!
Sent from my BlackBerry® wireless device

HI Riaan,

Check the vertical ic for dry joints. Make sure the vertical IC is getting supply voltage. If there is no dry joints and have good supply voltage then directly replace the vertical output ic and retest.

Happy New Year!

Jestine

==============================

HI Manjit,

At the moment I am repairing a dell monitor.
Can you put me on the right path?
The problem is when switched from cold works for approx 15 mins. After this
the LCD goes off. The Green status of the main switch stays green. If I
switch off main switch on the monitor the displays comes on for 20 seconds
and then goes off. If I switch off and let it get cold then it will remain
on for 15 mins. The monitor is dell model E173 FPb.
Can you also where I can get a diagram for this?

It can be caused by bad filter cap (bulged cap), dry joints in the high voltage transformer and one of the backlight have problem. A bad Backlight is very common in LCD Monitor. As for the diagram, sorry i don’t have the diagram.

Jestine
http://www.JestineYong.com

==============================

Hi Suman,

i have a lcd with no power problem, but some time it
on automatically,what should be the problem.

It can be the mainboard problem or the power switch.

in this lcd i check backlight transformer but i can’t any
voltage(red probe on backlight socket and black on cold ground with ac
1000v AC).on voltage regulator i found 1.5 to 2 v(mm niddle moving
forward and back). in this board the power ic is Q621600 . but i
cant found on internet this ic (please tell me VCC pin please).the
invter ic is TL494C but on net this is not also
available(please tell VCC PIN).

For your information no power problem not necessary must be the power supply problem. Since the power led is coming from the main board thus it can be the main board problem. What you need to do now is to check if there is any output voltages from the power supply. If totally no voltage then check all components in the primary side. If there is output voltages then suspect the mainboard have problem.

For TL494 PIN 12 IS THE VCC:

http://pdf1.alldatasheet.com/datasheet-pdf/view/5775/MOTOROLA/TL494.html

Sorry i do not have the Q621600 datasheet.

Jestine

============================

HI Jun,

Sorry i’ve got a terrible influenza and been in bed for less than 2weeks but thank God i’m back to my repair shop.

Good to hear that you have recovered.

With regards to my recent problem i can only measure one 5 volts to cold ground.I can feel you are perfectly right saying a signal from the mainboard is needed to activate or to power up the main power supply .My big problem now is where or what particular part in the mainboard a signal trigger will come from. You were asking me what the dc voltage going to power ic is.Well if i am not mistaken when i measure directly to the big filter capacitor it is more than 250V going to mosfet.I noticed there were 3 optoisolator in the right lower side two of them have 5 volts at pin 1 and two but the one in the middle doesnt have supply.At the left upper side of the power board were two optoisolator both have supply in pin 1 and 2.Jestine please help me solve this challenging kind of trouble,,,,Thanks

It depends on the power supply design. Some design where the cpu will send an on signal to trigger a transistor and this transistor will cause a relay to conduct. When the relay conduct ac supply could flow to the main power supply section thus power up the whole tv. Another design where the cpu will send a signal to the optoisolator and when this optoisolator conduct, it will somehow trigger the primary side circuit causing the main power supply to give full output power.

If the cpu have problem ( not sending signal) or the relay or the optoisolator circuit have problem thus the set will always be in the stand by mode.

Jestine

====================================

hi jestine wish you a very happy new year I have a problem for 15″crt moniter
HOUT is ST2310FX sort condition here the part is not available so,
kindly inform
me for equallent number for the above transistor .[FBT IS 79C554-1]
can i put c5928

Hi Sara,

You can try to get the part from this link:

http://parts.digikey.com/1/parts/1002690-trans-npn-1500v-12a-isowatt218fx-st2310fx.html

I always encourage repairer to use original part number. You may need to test all the equivalent number. If the monitor HOT is hot then it can’t be used as replacement and you need to use another part number.

Jestine

==================================

HI Abbas,

You need power up the voltage regulator to test it because you can’t just test it with an ohmmeter. You need to find out the spec of the voltage regulator and then apply the voltage to the ic. From there you can test the output voltage with your dc voltmeter. Positive regulator apply positive voltage and vice versa.

Jestine

HI Abbas,

Jestine

============================

TV Khind< problem got 3 line at upper side screen (blue,red & green), refer picture i attach.

Hi Shamsul,
Try adjust the convergence board on top of the tv and if still the same, you may need to direct replace the vertical output ic and retest.

Jestine

===========================

Hi Sir Jestine, I solved my problem I find the bad diode near the vertical ic. my view sonic monitor is back to a good display thank you very much sir to teach me how to troubleshoot the vertical problem.

Sio

============================

Who makes the best multimeters in Japan: Sanwa, Yokogawa, Hioki or Kyoritsu?

I was thinking to buy Yokogawa TY720, you probably have more expirience with these companies..

Thanks,

Djoko

Canada

Hi Djoko,

I have not use yokogawa and Hioki before thus i can’t give any comment on the meters. As for the Sanwa and Kyoritsu i prefer Sanwa. There was one time when i used kyoritsu analog multimeter and the selector broke after only few months of using it.

Jestine

==========================

Hi Ming,

happy new year,

Thanks and same to you too.

in your ebooks, you always mention that use the hot ground when measuring the circuits in the primary side of the power supply. i know that the hot ground is the negative side of the primary filter.besides this negative side of the primary filter, what other hot ground we can also use ?

There is only one hot ground in the primary side of power supply. The negative pin of filter capacitor have circuit traces to other part thus you not necessary have to connect the back probe to the negative pin. You can connect it to any component pin that have connection with the negative pin of the big filter cap.

also, are start up resistors always SMD resistors located on the bottom of the start up circuits? thank you for your explaination. have a good day.

If you are repairing lcd monitor then most likely the start up resistors are SMD. Start up resistors can be SMD or carbon film resistors.

Jestine

==========================

Likes

(0)Dislikes

(0)

14 Comments

Kapil

January 24, 2011 at 2:15 am

Hi justin Wish you a happy new year. I have a problem with samsung 45bn crt monitor,when i switch on the monitor power led blink and it goes off but when I open the 5 volt supply track from the regulator ic 7805 the power led remains on
please give me the solution.

Likes(0)Dislikes(0)

Reply
admin

January 24, 2011 at 9:46 am

HI Kapil,

It could be the flyback transformer shorted. Please visit this link.

http://www.electronicrepairguide.com/testing-flyback-transformer.html

Jestine

Likes(0)Dislikes(0)

Reply
Amir Mukhtar

February 2, 2011 at 7:46 am

Dear Sir,
My name is Amir Mukhtar. I have been working in repair electronics fields for more than 18 years. I am very inspired from your expertise and tips.
Sir, your information which you been provide is very valuable and worthfull for all repair persons and readers. I appreciate your support and expert opinions.
Although, I am alrounder in my field but i learn many things daily in routine repairing in my office as well my part time electronic repair workshop, where i provide repair services to the karachites (pakistan).
thanks you for your work and expert opinions.

regards
Amir Mukhtar

Likes(0)Dislikes(0)

Reply
admin

February 2, 2011 at 9:27 am

HI Amir,

Thanks!

Jestine

Likes(0)Dislikes(0)

Reply
Baxter

February 22, 2011 at 4:30 pm

hello sir
i have Hp L1706 TFT main board with a burnt transistor. the transistor burnt beyond recognition that am failing to find the right replacement. it is located near two capacitors,10microF & 22microF. i suppose its the biggest transistor comparing to others.Help me to know the type of that transistor or its equivalent. it is labeled Q203. thank you in advance.

Likes(0)Dislikes(0)

Reply
admin

February 23, 2011 at 8:42 am

Hi Baxter,

Since i do not have this monitor in my workshop at current moment thus i could not find the number for you-sorry.

Jestine

Likes(0)Dislikes(0)

Reply
Larry PHenneger

July 18, 2011 at 9:26 am

What is "dry joint on the analogue devices IC "?

Likes(0)Dislikes(0)

Reply
admin

July 18, 2011 at 9:07 pm

HI Larry,\

Dry joints means loose contact between the pin and the solder. When fresh solder is applied there will be no more dry joints.

Jestine

Likes(0)Dislikes(0)

Reply
george

July 8, 2012 at 9:56 am

hi jestine
my problem is I have a tv matsui model IT is okay but It can only receive uk signals is there a way I can change the tuner so as to receive stations in kenya.I have overheard that there is a way in which u can do so.
I also have another tv jvc in timer mode and not at standby mode at times it switches on but after a shortwhile say five minutes it gets into timer mode.

Likes(0)Dislikes(0)

Reply
- Jestine Yong
  
  July 11, 2012 at 5:31 am
  
  Hi George,
  
  Sorry i do not have info about the modification of the tuner. AS for the timer mode it can be the programs in eeprom or even the mcu have problem. Before that, is all the output voltages from the power supply good and stable?
  
  Jestine
  
  Likes(0)Dislikes(0)
  
  Reply
george

August 9, 2012 at 8:27 am

hi jestine, tell me the outputs of an str f6654 since i have 300v at pin 3 and 4v at pin 4 the rest pins have nothing but at the flyback transformer i can get 20v which is very low to switch the tv i'm suspecting the str to be faulty please help me how i can solve this problems again i have a panasonic tv displaying a sharp horizontal line i have changed the vertical ic la7837 but sill in vain i suspect now the processor an 5192k-b could it be the problem.

Likes(0)Dislikes(0)

Reply
- Jestine Yong
  
  August 10, 2012 at 8:30 pm
  
  Hi george,
  
  What is the complaint of the first tv? Is there any good output voltages from the power supply? The second unit is you need to chekc the supply voltage to the vertical output ic. If there is supply then direct replace the vertical ic and retest.
  
  Jestine
  
  Likes(0)Dislikes(0)
  
  Reply
george

August 11, 2012 at 7:59 am

i have an lg crt tv no picture but audio is present once i connect the antenna but there is a rainbow present at the at the tube i suspected the tube and changed it but still no picture but audio present the tv is displaying on the tube but with a rainbow what could be the problem?

Likes(0)Dislikes(0)

Reply
- Jestine Yong
  
  August 14, 2012 at 2:19 am
  
  Hi geroge,
  
  Could you send to me the picture at jestineyong(at)electronicrepairguide.com . (at) means @
  
  Jestine
  
  Likes(0)Dislikes(0)
  
  Reply