Wednesday, November 19, 2014

21 inch LG Super slim Television dead


A friend of mine referred to me a client who wanted her TV checked by a technician. I usually carry with me a small digital meter and a screw driver because most of my job are done in a freelance kind of setup.

This is because i have another full time job very different from electronics repair which i do as an hobby and also my plan B.

My friend it is good to have plan B in this life because even if you are employed one can be retrenched or loss your job but no one can sack you from using your hands(talents).

For this particular  day i forgot to pack these tools of trade. So after the request i almost gave the lady the following day appointment but since she wanted to have her TV back due to high demand by the children,i inquired from her if she has a screw driver in her house and promised me that her husband is a computer guru and therefore he has all manner of screw driver sets in her house.

With that i decided to attend her  case on the same day. When i reached on site, true to her words she went into one of the rooms and she came out with a bunch of screw driver(all sizes) and i pulled out which i thought was best for the job.

Before opening the TV she connected me to her husband via cell phone for some briefing.The husband told me he suspect the switch because some times the tv had problem to power on when the power button is pressed.

I took that information seriously and to confirm the switch is okay or not i pressed it till home and still nothing  happened on the screen.

I pulled my voltage tester stick and it lighted when brought near the tv. This confirmed to me that the tv is getting powered and therefore there could be something else blocking the power.

So i undressed the TV and took with  me the motherboard to my workshop for further testing.
When the lady was packing the board into a plastic bag, i heard her scream and told me that she got a shock from the board but i didn't take her very serious.

Back to my workshop, i pulled my meter and tested across the main capacitor(220uF/400V) and to my surprise i got 242 Vdc just hanging there.


Then i remembered her words of getting a shock, with that i realized how lucky she was because if she could have touched directly across the two pins of this capacitor it could have been a different story all together.

Lucky was i too for packing it in a polythene bag (poor conductor of electricity) otherwise i could also be in trouble, thank God non of the above happened.

After discharging this capacitor using the series bulb, i started to troubleshoot it.


Because the complain was set dead, i started scanning the primary side of the power supply and looking at the power switch it reminded me of another TV of the same model which had a intermittent  switch problem.

I pressed the power ON switch and clicked how they do when fully engaged but testing across the neutral line of the switch i noticed the switch was open and because i had such an experience i just soldered a jump wire between the two pins of the switch.



I thought the problem is now solved but to my surprise the TV has no voltage on the secondary side.
So i decided to test components on the primary side, just by coincidence i started with the capacitor which filter the Vcc pin voltage supply to the control ic which was rated 22uF/50V.



I was doing this from the bottom side of the TV board and when i tested across this capacitor my ESR meter registered an abnormal ESR reading as you can see here.



For your information a capacitor with ESR of 5 ohms can completely cripple a whole 47 inch LCD tv and here we are talking  91.80 ohms.

To be sure i was testing the correct component i decided to solder it out of the circuit completely and test it again and truly my fears were confirmed as you can see here.



I salvaged another capacitor from the junk and after testing and finding it to be in good health condition i replaced it.



I applied power again to the board and this time i got a voltage at the secondary side and i concluded that the issue is now fully solved.

I went back to the owner the following day and after re-assembling the board back to the tube the tv came back to life.

  

Advice:
I strongly advice technician to be on lookout for this kind of switch because even if it is switched off still there is power on the live line all the way to the main capacitor but no return, therefore if you touch on this line by coincidence assuming the power switch is off then you will provide a very good ground and hence get electrocuted

This also explains why the voltage tester pen was lighting when brought near the TV.



Humphrey Kimathi

Author CRT Television troubleshooting guide



 For more information about this book click the book cover.

Thank you guys

Stay safe



Wednesday, November 5, 2014

My new eBook “CRT television troubleshooting guide”



After five years blogging and interacting with many technicians across the world doing electronics repair majoring in CRT television and listening to their most pressing issues on their line of repair I have compiled a book which will demystify CRT television repair forever.

The book addresses over 18 common CRT TV problems and how to solve them with ease.




Stay safe

Humphrey

Saturday, October 18, 2014

Need help in troubleshooting CRT Television problem

Dear Sir,
My Name is Yogesh, I am from INDIA.
I am one of your fans and I regularly visit your Blog for technological update.

Sir recently I came across the CRT TV Problem that there is intermittent fluctuation on the screen and picture shaking vertically (maybe overloading).

I have opened the TV and found China make kit with
Toshiba IC.8893CRNG7D65.

I need your help to troubleshoot the problem sir,
can you help me if possible.

Thanking you-Yogesh

Monday, September 8, 2014

Blog follower from Philippines want to know a few things about CRT television repair

Master,

Good morning, I read your article recently: the Understanding of CRT television critical voltage test points...

I was confused a little bit about the word B+ ...I want to clarify this because as a newbie in the field of electronics, safety first is my goal when rendering my services to others...

My question is this: all transformers “s.m.p.s transformer, drive transformer, and the fly-back” are producing a B+, right?

Transformers do not produce any voltage Alex, they just transform (change)

For example they can step down or step up the voltage/current.

But remember you cannot have the two (current and voltage) being increased or decreased at the same time.

Take for example the transformer used in your radio rated 240VAC to 12VAC.

The 240VAC is stepped down to 12VAC, in this case we will have the voltage decreased but the current will increase and that is why you see the output wires of most step down transformers are thicker than the primary side because of this high current.

For drive transformer this is also step down transformer but in case of drive transformer they are basically used to match impedance.

Here are the list of primary power supply is composed of : 1 Fuse, 1 surge limiter,1 main capacitor,bridge retifier < 4 diode> 1 smps transformer, 2resistors in series ,1 posistor1 ,3 ceramic capacitor, 1 degaussing pin, 1 power pin, many jumper line, 4 signal diode...Secondary output supply is composed of 4
diodes that is carrying a dc voltages taken from smps transformer, filter capacitor ranging to 160v, 100v, 50v,25v,16v and 10v,, right?

Sure Alex, this is a good description of common power supply components found in switch mode power supply (S.M.P.S)

But I have a comment on your remark on the secondary diodes…since the output of any transformer is AC current, that is why we have the secondary output diodes which are used to change(rectify) this AC back to DC current.

The diode only manage to rectify the AC signal into Pulsating Direct Current, this is still not clean enough to be used by the circuits and that is why capacitors comes in handy to smooth this pulsating DC into clean DC ready for use by other circuits.



About horizontal driver series is composed of: 1 driver transformer, 1 driver transistor, driver resistor and the final destination is the HOT Transistor ...Now master my question is where can I find the B+ among the electronics components mentioned above?

The best place get this B+ is at the positive leg of the Capacitor you mentioned earlier rated 160V, whenever you see a capacitor on the circuit and want to guess the voltage on that line it is filtering just consider the working voltage of the capacitor used to filter that line…if it is rated 160V just divide that by 2 and you get 80V…so expect the voltage on the line to be between 80-100, this is just a rough estimate of what to expect thought.

Another good point of getting this B+ is the middle leg (collector) of the HOT transistor.



About R-red, G-green, B-blue cathode pins, at sight , how can we know the RGB cathode pins points? In this regards we need to be accurate pointing pins because the printed layout of all PC board is not the same.

Usually these are labeled like KG, KR, KB and should not be a big issue here Alex.


I am planning to buy a book CRT television repair course thus I am worried1… the pictures you Have shown is not the same with the unit I am repairing...like for example the picture of pins Fly-back transformer, page 6 of understanding the CRT television critical voltage test points, the B+ is away from the fly-back transformer, it should be the pin of fly-back transformer has a B+. How come the two points has a B+...I am confused...Please show to me the B+ points.

In electronics Alex, what is important is to get the basic concept and then you can apply the same to any other TV model which shows up at your workbench.

Having said that let me say that I have written my book from the technician work bench point of view and you can confirm that from testimonies of satisfied customers who bought this book.



Anyway,,,I am worried to buy a book because it did not show the complete details or picture of B+.

Oh! Alex, this means you status in electronics repair will remain stagnant and this is not a very good report unless you want to change your career to something else.

All the best my friend.

Thank you Master.

Alex Ancheta L.I.B
Purchaser

Philippines

Thursday, September 4, 2014

introducing a new ebook on LCD and LED television repair

For those of you who are in LCD and LED Television repair and want to sharpen your skills on the same, this book is definitely a good companion on you workbench.

The eBook is written by a renowned LCD's/LED's expert Mr Kent Liew from Malaysia

For more info about the book click the book cover below.



See you on the other side



Saturday, August 16, 2014

A question on how to identify Surface Mount Component

A customer and a friend of mine Mr.Wilson from Malawi who lives in Pretoria, South Africa wanted to know how to identify Surface Mount Component

Hie Mr. Kimathi,

In the first place I want to appreciate you for extraordinary knowledge I have gained from your CRT TV repair eBook.

It’s so clear that even somebody who doesn’t know anything concerning electronics can manage to at least fix a TV with this book at hand.

The issue now is, I am looking for the book which can help me with the Surface Mounted Components like Diodes, Transistors etc, as I am struggling to identify and test many of components from LCD TVs and monitors that’s why I have decided to ask you about your Basic Electronics Course eBook.

I am ready to purchase it as soon as I get this information from you.

Hope to hear from you soon.

May God Almighty continue to bless you and reveal more to you in Jesus name
Kindly,

Wilson.

  
Hi Wilson,
Thanks for your feedback and glad to hear that you have found my eBook valuable companion at your work bench.God bless you too my brother.

Regarding my basic electronics eBook, I have not written about smd components but when it come to testing, the method is the same only that smd are small in size...

What you require maybe is just how to identify them and you can easily Google “how to identify smd components" and I am sure you will get a lot of info for free on the internet.

Again if you have an android phone, go to Google play and download an application called "electroDroid" this is very good even for other components also

Regards Humphrey

Tuesday, August 5, 2014

Another great way to test for remote control without presence of the appliance

A friend of mine and an electronics repairer from Fiji islands sends me this report on how to test a remote control.



While I was playing with one remote control of my DVD player, I was thinking the sensor is just a LED, but why it cannot light when we press the buttons.

I brought it close to my eyes and was trying to view the lightening of that LED.

Hopefully in some remotes we can see a little blink if LED, but as far as I have seen in remotes which are produced nowadays are hard to view the light of the LED with our naked eyes.

Interpretation:
May be the signal light is so tiny that we cannot see it with our naked eyes.

I thought to use my mobile phone camera to magnify the signal light and see if it is visible.

I was so happy, actually to see the LED lightening while watching it though the camera.

Here are the pictures I took:







It can be perorated that ,if a remote is not working it will not have its LED lightened when you press the buttons.TRY THIS OUT WITH A GOOD REMOTE AT HOME

So all my repairer friends there is a very good tester for remotes, which is always in your pockets (Our mobile phones with cameras).

After reading this article I decided to do the same test using my tablet and the result were the same (positive) as you can see the pictures below



This article is prepared by Atish Chand, a repairer from Fiji Islands