Saturday, March 26, 2011

Akira Television Dead



First I checked the status of the fuse and surge limiter. The fuse passed the test with flying colors and the surge limiter did not make-it was Gone according to my resistance test meter.

Now whenever you find the fuse or the Surge limiter gone as I have said it before, let me repeat it for those who are new in my class Please never replace any of these two components without checking the cause why they had to blow unless you want to keep the manufacturer of these two safety components in the business by buying their products.

click  picture to view  bigger version

Therefore if you find the fuse or surge limiter has gone suspect a heavy short on the primary power supply components. On the high list of suspect is the chopper transistor- So I went straight to this transistor and sure it was dead short collector-emitter junction.

I replaced the chopper transistor and the surge limiter and because I still suspected some more short on the supply I put the television on using the series current limiter bulb.( Those who have already bought my CRT TV repair course  e-book  knows how valuable this small gadget is in terms of saving your new replaced components from shorting immediately after replacement).

click picture to view big version

On power ON the series bulb never lit, I checked the voltage at the collector of the chopper transistor and was present, around 300 vdc but none at the base.

If you find no Voltage at the base two things may have happened.

1. Either there is an open component on the start-up path usually the start-up resistor or dry joints or even circuit broken.

2. There is a shorted component at the base of chopper transistor which is taking the chopper transistor base directly to the ground. See diagram Transistor 2SC3807 or capacitor across this transistor


Click photo to view bigger version

In most cases it is the transistor which gets shorted and therefore starts by testing the condition of this transistor c3807 and finally the cap517.

You can even lift up the middle leg of this transistor c3807 and if you can now get some voltage at the base of chopper transistor (v513) then you can conclude that this transistor c3807 is shorted.

In my case I set the meter on the diode test (continuity) and tested between the two legs of capacitor c517 and the meter buzzer rang indicating to me that there is a shorted component across that path.

I removed one leg of capacitor c517 off the circuit and still I had a short reading on the meter. Finally I removed transistor v512 (c3807) and the short disappeared indicating to me that this transistor was also shorted.

I replaced the transistor and powered the set and the power supply was restored.

But still there was a problem because the TV was coming up and down. I was still using the series bulb and whenever the Television was shutting down the bulbs were very bright indicating some problem on the secondary side.

Then I decided to tap the set a bit on the side with my hands to see if there were any dry joints remaining but nothing happened.

Then I decided to tap the CRT neck board circuit with the back of the screw driver and I noticed the screen kept on changing. I checked it keenly and I noticed a lot of dry joints there too.

So what has this to do with the narrow screen? This is because the RGB amplifier voltage source is coming directly from the primary supply and hence a problem on the neck board circuit can even cause the power supply to drop or even block it completely.

So a Technician who is ignorant of how that Television work may spend up to two weeks looking for a faulty components on the power supply whereas the problem is at far end on the small CRT neck board circuit and end up being frustrated enough to send the Television back to the owner with the very unpleasant word to the Customer” Not able to repair due to lack of spare parts”

After re soldering the CRT neck board the screen was now full width and there was sound but no picture…..To be continued…..

Wishing you all the best Guys

Let meet in our next class





Saturday, March 19, 2011

How to use an oscilloscope



In my CRT Television repair course eBook that I have just released to the market I have tried as much as possible using common test equipment like multi meter which every technician can afford on his work bench but with the option of advancing to other advanced like oscilloscope down the Road.

But from the feedback I have received it seems many Tech out there already have oscilloscope and would like to be advised how to use this equipment to get best results.


One thing I must emphasis is that most of the faults in electronics hardly require the use of oscilloscope but if you have one that is definitely an added advantage.

While trying to figure out how best I can help a young technician on how to use an oscilloscope I remembered my former school, radio and electronics school of Australia where we used to have a supplementary downloads for students and in this article I believe you too can gain from this valuable information. And being an old student It is my pleasure to introduce you to this great source of information.
For more information of the xyz of oscilloscope please click on the file below.


And for a small video on the same topic kindly click the link below.


A word of advice also goes to Techs who maybe have not done basic electronics, let me use an example of the horizontal circuit of CRT television, when we talk of horizontal circuit we are referring to a set of individual components with work together to make a horizontal circuit.


So the Basic factor is the Component. It is very important for a technician to be able to test individual components fast and without struggling and for this I strongly recommend a book on Basic electronics.

I have read several books on electronics and the latest one was testing electronics components by Jestine Yong. I am telling you guys this book is more than enough for any tech (beginner or advanced)


The book shows you how to test any component under planet earth (electronically speaking) and has many bonuses and numerous short cut on how to test and troubleshoot equipment up to component level.
For more information on this book click the link below.


With that gentlemen thank you for attending and being keen in this class

Let meet in the next lesson

Humphrey Kimathi

Author CRT Television repair course.






Thursday, March 17, 2011

How to Search for Television or I.C datasheet From the Internet

I have Received several emails from users asking me to assist them with service manuals and ic data sheets, for that reason i think maybe there are many out there with the same problem and hence in this article i am sharing briefly how you can get data sheet of almost any component from the net.

 


The best place to start with is google search engine, just open a blank google page and you will get the page like one shown above.

Insert the Television model or the ic reference (you can add data sheet or pdf for better filter) and click search...you will get many result and you can narrow down to what you think reflect almost exactly what you want.

Also sometimes if you don't get the result by using the model number  you can use the chassis Number of that television and there you go.

Also consider visiting this site for a variety of Television service manual for almost all models.

 


Thank you guys
See you in the next class







Saturday, March 12, 2011

Replacing CRT television power supply with the universal power supply


Sometimes if you are in CRT television repair you may encounter power supply failure that is too complicated or expensive to repair.

In this video you will be shown how to replace the Television power supply with the universal power supply available cheaply in most market.

Click here…

http://www.youtube.com/watch?v=rh21GpGPFSM

Friday, March 4, 2011

Television with intermittent picture repaired remotely


I Received this email from one of my keen follower a couple of weeks ago from London.

Hi Humtech
Complement of the season hope you and your family are enjoying a wonderful new year so far, i have this problem with this TV set when i turn it on i see picture for about 15 minutes and the  picture slowly go away but i am still getting sound, what do you think the problem is. Could it be the video IC?

My reply
Hi *****
 That sounds like the heater problem but not video....  Re-solder all the pins on the Line output transformer (fbt), then go up to the CRT neck board and Re-solder all the CRT socket pins.
 In conclusion I don’t expect you to use any spare parts....just use the solder and the solder gun.  If it doesn’t work send me the model and or circuit diagram of this tv...

Feedback


Hi humtech
Complement of the season to you, just to let you know the TV is working fine after I did what you said..THANKS.

 Conclusion by Humphrey

1. Most intermittent problems in electronics are caused by dry joints or loose connection;

2. Most of the problems in electronics have simple solutions and therefore never assume the worst unless you have enough facts to support your suspicion.

3.Usually any Television more than  Five(5) years need some fresh solder on the Chopper transformer pins and surrounding components, the flyback pins and the CRT neck components/Socket pins as First Aid even before you start troubleshooting.