Bad Diode SB3100 Found In Samsung LCD Monitor
This Samsung LCD Monitor model 632NW belongs to a technician friend of mine, who shifted his line and confined only to servicing Washing Machine, AC Control Boards, and Microwave Ovens etc.
This is a monitor he uses to view and select songs from his USB/DVD player. It became dead and he opened and tried to troubleshoot without paying much attention. He replaced the PWM IC and also the opto-coupler, as he did not see any output. But it remained same in spite of that. That’s how he decided to refer it to me, though a little more probing could have solved the case, exposing his aversion towards other devices than what he concentrated.
As he had already opened the set, and done a preliminary cleaning, my job was made simple. I discharged the tank capacitor and removed the SMPS board from its metal casing. Observed for any bulgy capacitors, even though I know he would have checked it himself. Used my Ring Tester and checked the primary of the SMPS Tx and it showed short. Then I checked the secondary for any shorted components. Yes, there indeed was! The Diode SB3100 was dead short. This is a 3A, 100V SCHOTTKY BARRIER RECTIFIER diode.
As I was not having this diode with me, I replaced it with SR360, which is a 3A 60V diode, just to check. The output was coming, but the voltages were less. 3.7V in place of 5 and 11.7 in place of 14. So, probed for any defective components, including ESR checking of all caps. As I could not find any, I did a dry solder patch-up on the board, including retouching the IC pins. Gave power and noticed that the outputs were perfect. So, connected the board to the mother board and LCD panel and powered it on. It was working perfectly.
Informed my friend, who brought the diode, which I replaced on the board. As he mentioned about some width problem in the display, connected it to my computer and took snaps and send it to him, reassuring that there was nothing wrong. Here are a few pictures of various stages: (The mirror you see is a broken rear view mirror of my old car, which I use for such purposes!)
A job completed without much complications, and got added to my ‘satisfaction bag’!
This article was prepared for you by Parasuraman Subramanian from India. He is 69 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/fake-batteries-found-in-xiaomi-power-bank-t10-4/
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Robert Calk Jr.
October 16, 2018 at 12:44 pm
Good job, Parasuraman. The correct testers make troubleshooting much easier.
Albert van Bemmelen
October 16, 2018 at 1:51 pm
Another real pro repair job in the 'satisfaction bag' Parasuraman!
Steve
October 16, 2018 at 10:45 pm
Nice job well done.
suranga Electronics
October 17, 2018 at 12:29 am
Good Job Mr-Parasuraman!
Humberto
October 17, 2018 at 1:04 am
Great repair, as usual in you, Mr. Parasuraman. Congratulations.
beh
October 17, 2018 at 1:27 am
Great repair thanks for report.
Henrique J. G. Ulbrich
October 17, 2018 at 1:50 am
Very good, Parasuraman. The use of your old car mirror is another example of "nothing is wasted, everything is transformed". Greetings.
Simmons Troy J.
October 18, 2018 at 9:21 am
Hi Parasuraman,
You mentioned that you checked the primary side of transformer and it showed shorted. Would that not indicate that there is a problem on the primary side? Maybe you meant to say you checked the secondary side of the transformer and it showed a short therefore you would search for a shorted component. Please clarify for a novice like me.
Really enjoy reading your articles. Learning so much. Thank you for your time & contributions.
Parasuraman S
November 10, 2018 at 5:42 pm
Checking the primary of an SMPS transformer with a Blue Ring Tester will show shorts in either primary or mostly secondary. Please search for Jestine Yong's guidance for use of Blue Ring Tester.