FBT Found Failed In Samsung CRT TV + Tips And Tricks For Troubleshooting CRT TVs
MAKE AND MODEL: Samsung CRT TV Model # CS21C370FL
COMPLAINT REPORTED: Dead
TROUBLESHOOTING AND RECTIFICATION DONE: Opened, dismantled the board after discharging the anode and cleaned the inside and board thoroughly. Looked for any visible damage to any of the components. Did not find any. Did the ring test on the SMPS, which showed healthy. Same was on the FBT too. Disconnected the B+ rail to the FBT, connected a 100W Bulb as load, switched on. The B+ was normal and steady. The Horizontal Output Transistor (HOT) was ok on checking. An LED remained LIT when connected to Base and Emitter of HOT, indicating that the Horizontal oscillation was taking place. Looked for any defective diodes on the secondary of the FBT, did not find any. Reconnected the B+ rail to FBT, loaded the board to CRT and switched on. Set did not work and the B+ dropped indicating a short in the FBT. Discharged the anode and tank capacitor for any residual high voltages. Disconnected the PCB and removed the FBT. Connected one end of the primary that goes to the Collector of the HOT, to ground, and applied the B+ to the other pin. Voltage dropped, indicating that there indeed is a short within the FBT. As mentioned in yet another article, this is a sure method to check the condition of the FBT. If the voltage does not drop, we have to give a 40 to 60W Bulb Load to its secondary that goes to RGB supply on the CRT Board. If the voltage drops, then also the FBT is defective for sure. Another method is to check the current drawn by FBT, by measuring it on the point where B+ enters the FBT primary. If the current is beyond 150mA to 250mA, the FBT or its secondary loads (if checked without removing the FBT from the board) is defective. Better to go for a change. Even if there is a leak in the HOT or its surrounding components, more current will be drawn. Another tip is to provide heat zinc to the HOT (that has no heat zinc) whenever we change FBT as the replacements available in the market are not having good quality and might draw a little more current resulting in overheating of HOT. (These are certain tips and tricks that can be useful to new comers).
Obtained a replacement matching its number, fit the FBT and checked that the TV was working. After dismantling the PCB once again, did my routine maintenance of replacing all the electrolytic capacitors on the board and re-touching all the solder joints on main board and CRT PCB. Rechecked all the electrolytic capacitors to ensure that these were fit correctly following the polarity marked, before soldering the caps and cutting the leads. (This is a tip to the new comers. This is very essential so as to avoid a human error and possible damages when power is applied) Then cleaned the board thoroughly using IPA, to clean the residual flux that can cause problems later due to formation of capacitance. Reconnected the board, switched on, and I was thrilled to see the result. But I noticed that there were slight gaps on both sides. When I checked with my techie friends, one of them wanted me to check whether the button magnet on any of the PIN AMP coils was missing. He said that usually there will be an additional magnet and sometimes this could fall off when we do cleaning using blower and/or brush. That was exactly the case in this TV. I picked up one from a discarded board, from the top of the horizontal coil and put it on the PIN AMP coil of this TV. The width became perfect. (This is yet another tip for those who are doing servicing of CRT TV. Before jumping to adjusting the width by entering service mode, we should ensure this is checked first) Mission accomplished and satisfaction added, along with new lessons learnt!
For the sake of new comers and those who are interested in learning further on CRT TV service, kindly buy these books and see the links: (1) https://jestineyong.com/crt-tv-repair-ebook/ (2) https://jestineyong.com/crt-television-troubleshooting-guide/ (3) https://www.repairfaq.org/sam/crtfaq.htm (4) http://www.electronicrepairguide.com/high-voltage-circuit.html
Here Are Some Pictures:
This article was prepared for you by Parasuraman Subramanian from India. He is 70 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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You may check on his previous repair article below:
https://jestineyong.com/ic-failure-in-philips-radio-dl167/
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Albert van Bemmelen
September 19, 2020 at 6:41 pm
I have to say that you did another fantastic job but reading that pagewide and very long text without photos inbetween all given information, is like others previously mentioned quite tiresome to read. And mainly just because I do not repair any crt tv's these days you have to forgive me for not reading it. Nevertheless I value it and of course it is added to my Jestine Yong repair article databank!
Parasuraman S
September 19, 2020 at 10:34 pm
Many Thanks! That is the reason I am giving a brief description on the photos. That will give an idea, I hope!
Henrique J. G. Ulbrich
September 19, 2020 at 10:57 pm
Once again a complete job and a good report. The problem with putting a heat sink in this case is that (unless mounted isolated) it becomes a large area, with short-circuit risk.
You din´t mentioned your satisfaction bag anymore!!!!
Parasuraman S
September 20, 2020 at 8:49 am
Heat zinc: Yes, it was provided isolated and grounded too, to avoid any possible problems. (The transistor is with plastic coating, no metal ground plate.
Yes, satisfaction got added to the same bag! (LOL)
babu ms
September 19, 2020 at 10:59 pm
Sir,
I am beginner and studying crt tv repair written by Humphery kimathi.Your article to check fbt is very very fantastic and more useful information is given,gained knowledge very much.I am getting confident that I can do repair crt tv by reading your articles.
Thanking you.
Parasuraman S
September 20, 2020 at 8:52 am
The idea of releasing such articles in this blog by Jestine Yong is for budding technicians like you. Glad to note that the article was found useful. Many thanks for your comments!
Randika Jayasekara
September 20, 2020 at 3:39 pm
Sir,
Could you please advice, when checking FBT from outside of the PCB, how do we keep that HV CRT cap in a safe manner.
Parasuraman S
September 22, 2020 at 11:01 am
In the method that I have explained, Horizontal output transistor is not connected. So the oscillation is not taking place. Hence there is no High Voltage production. So it is safe!
Waleed Rishmawi
September 20, 2020 at 8:27 pm
Good job on the repair again. Photos helps a lot but sometimes long details without photos get very distracting. Love the repair though
Parasuraman S
September 22, 2020 at 11:05 am
Many thanks! This method is found very useful to many! Moreover it is easy to compile and publish!
Carlo Alberto Birocco
September 22, 2020 at 4:49 am
It's a very interesting article. I like this exaustive text and the detailed pictures. Very, very nice!
Parasuraman S
September 22, 2020 at 11:06 am
Many thanks for your support!
Yogesh Panchal
September 22, 2020 at 3:23 pm
Few year Back replacing the EHT in TV is Seasonal Business in India Because of the rainy days...Never imagined to HOT check the EHT out of the circuit...nice
Article.......Sir one more request to please make article with stage wise Photos that will make article more interesting.
Parasuraman S
September 22, 2020 at 3:34 pm
Many thanks. Let me see, after finishing the already prepared articles!
Amin
October 11, 2020 at 11:03 pm
Hi,I have a grundic 28 inch crt tv
The tv set has sound but no picture
Several technician couldn't fix the problem, i live in iran
Please help how to troubleshoot the tv
Thank you
Amin
October 13, 2020 at 4:23 pm
Hi, anybody here answer my question
Tb has sound but no picture.
Thank you.