21-inch CRT Samsung Television Model CS21C512CL Come In Dead Now Repaired!
I received this television from a client who wanted it checked, I asked him a brief history of the problem and told me they shut the TV using remote control to say a word of prayer before having the dinner and that was the end, never woke up again.
He also mentioned that I was the second person to open it having been to another technician about a year ago. Since I was busy I decided to schedule it the following day expecting an easy fix since dead equipment are easy to repair according to my past experience.
The following day I began to work on it but before opening it I applied the power to confirm what the client said and noted the television was dead as a dodo. Upon opening the set, I went straight to the safety components and to begin with, I tested the main fuse and according to my meter it passed the exam with flying colors.
This made me to change the tactic of approach and decided to use my series lamp current limiter and do some live voltage testing.
I started with the voltage across the main capacitor and I noted it was fluctuating very fast between 280 to 310 Vdc. Just when I was figuring out where next to attack, with the power off and disconnected from the board, I turned the board the other side and while doing it I incidentally touched across the main capacitor and got a nasty shock but I survived.
Besides learning my lesson from the shock, I concluded that the power has no output on the secondary side because these television discharge via the secondary side that is why you see the power ON led taking time to go out since it is also hooked to the secondary side. I removed the HOT transistor from the circuit and applied the power again and tested B+ voltage and still got zero volt output.
With this I concluded the problem is still on the primary side and I tested every component on the primary side and all were found okay. With this I decided to directly replace the control I.C which in this case was STR W6753. I did it and noted there was output but very low, less than 10 volts, Also I could hear some low noise like the control IC was trying to start then shutdown. Like I said I had already re-installed the HOT transistor because I figured the problem was only the control IC but I was wrong again.
I decided to focus on the secondary side and noted the HOT transistor area is darkened and this prompted to test with a meter set to diode mode between the collector and emitter pin and found it was okay, No beep.
I decided to use my sense of touch and upon touching it immediately after power off noted the transistor was very hot, I decided to subject it to further test using my multi components tester and this is what I got.
The transistor is reading a resistor?, for the output transistor since it has base-emitter resistor I was expecting at least two diode results like the one below.
The reason the meter is confused is due to base emitter resistor like I said and that is why it is not able to pick it as a transistor.
If you remember in basic electronics, we learnt that testing a transistor using a meter you consider the transistor like two diodes connected back to back like as shown below, picked from my basic electronics course book sold here.
I replaced the HOT transistor and was sure I have got the final culprit and after applying the power I noted the television was not generating the HV voltage, I tested the B+ and noted it was stable and decided to concentrate on the horizontal drive circuit, first I tested the Horizontal drive filter capacitor using my tester and I was not happy with the results as you can see here below.
A good capacitor value 47uF/100v should have an ESR reading of less than (1) one ohm and this is reading 13 Ohms.
Kindly note that the capacitance is within the range 45.87uF and that I why I advise techs never to trust capacitance test for good capacitor, ESR test is the way to go!
I replaced the capacitor and again applied the power and still no HV voltage was generated, I even begin suspecting the fly-back transformer but after testing it with my homemade fly-back tester I found its okay. You can easily make one here.
I decided to do some voltage testing around the horizontal drive circuit and testing on the horizontal drive transformer I noted only one pin has voltage and I was expecting two pins with voltage and the other two without voltage.
I removed the small transformer from the circuit and testing across same side pins did not get reading on one side and upon close observation I noted the small wire broken as you can see below.
Getting this part from the shop is practically impossible and I though this is the end of my effort, later I figured the idea of salvaging from a junk television of the same model and I was lucky I got one.
I did not mention that the first time I opened this television I noted the connector to the degaussing coil was not connected and decided to connect it via my series lamp current limiter and noted the bulb was too bright like the sun and with this I concluded the posistor was shorted and that is why the previous technician decided to leave it hanging.
I replaced it and now the series bulb was bright and then low and concluded the circuit is now okay and working well. I again applied the power and this is what I saw.
Later I called the owner with the success story and he pointed to me that the television had a problem of spots on the screen since last time it was taken to the previous tech and asked if possible I should check on that issue also. I assured him the issue is now sorted out and was very happy.
Thank you friends
Humphrey Kimathi is from Nairobi Kenya and the author of:
1) Lcd-Led television repair guide
3) CRT Television repair course and
4) Basic Electronics course.
He is also a blogger at Electronicsrepairmadeasy.com
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Albert van Bemmelen
June 16, 2020 at 6:50 pm
Interesting article with useful DIY info on making a Fly-back tv transformer tester. Building one is easy but I understand that the link about the k7205 tester is in fact the predecessor of the today's Blue Ring tester, which I already got. I won't be needing it for testing Fly-back transformers much anymore though because that technology is almost gone these days with the last existing crt tv sets.
Humphrey Mndaka
June 16, 2020 at 9:22 pm
Well put Albert,
Regards Humphrey
Paris Azis
June 17, 2020 at 6:07 pm
Hey Albert
Just think about how many times you need to know if a coil is in good condition (without even a single turn shorted) and you will understand how much you still need this tester on your bench.
I have also built one for myself and find it indispensable for our job. Just because it tests any coil wound on a core! Now use your imagination!
Just in order to give you an example: last week a good friend of mine came by having with him a dismantled Makita saw.
He told me that their official servicing technician, where he brought the machine in the first place, told him:"just look at its coils!The machine is burned out".
Then he came to me and asked me if I only could test its stator and rotor for shorts. I replied that of course I could do that. He left it to me because he was in a hurry. If he could wait for 5 minutes more, he would had it back with the answer that nothing was wrong with the machine.
Anyway he got the answer next day.
I tested successfully both its stator (in a second!) and its armature in less than 5 minutes, testing its coils one after the other.
The stator could light up only the 3 red leds, while the rotor could light up the first yellow led, along with the first 3 red ones.
This tester tests any cored coil without any doubt.
I also had a happy feedback from my friend Nikos. He called me on the phone saying "listen to this noise and tell me what it can be from" and then started the saw...
Just use your imagination about its uses!
Parasuraman S
June 16, 2020 at 9:49 pm
Excellent and a fruitful hunting effort like that of a tiger! Many thanks for sharing very valuable information and methods to do troubleshooting!
Humphrey Mndaka
June 17, 2020 at 5:24 pm
Thank you sir for your feedback.
Regards Humphrey
el shaddy
June 21, 2020 at 8:07 pm
Dear Parasuraman , you used to write like humphrey. Nowadays your articles are like short notes lol... please go back to your original style.
thanks
Humberto
June 17, 2020 at 11:01 am
Very professionaly explained your repair in the article. Congrats.
Humphrey Mndaka
June 17, 2020 at 5:25 pm
Thanks and welcome my friend Humberto.
Regards Humphrey
Paris Azis
June 17, 2020 at 6:10 pm
Good job, Humphrey.
Humphrey Mndaka
June 17, 2020 at 9:29 pm
Thank you sir Paris.
Regards Humphrey
Charles Johannes
June 19, 2020 at 7:34 am
Thanks fo the info
Gary Gemmell
June 19, 2020 at 9:53 am
Quality repairs there Humphrey always enjoy your articles well laid out and explained!
el shaddy
June 21, 2020 at 8:03 pm
Always liked your style of writting , very Articulate and simple to digest. Thanks
Christian
July 26, 2021 at 7:58 pm
Hello sir what is the number of the 21inche Samsung ultraslim flyback number