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SMD Regulator IC Found Open In OLSENMARK OMR1239

By Jestine Yong on September 12, 2020

MAKE AND MODEL: OLSENMARK MODEL OMR 1239 USB RADIO

COMPLAINT REPORTED: DEAD

TROUBLESHOOTING AND RECTIFICATION DONE: Opened, dismantled and cleaned the set thoroughly. Applied power externally to check upto which stage the power was reaching. Noticed that it was reaching to pin one of SMD regulator IC which had a marking ‘54FK.’ Searched the web and came to know that it was a 2.8V regulator IC. As this part was not available in the market, I replaced it with AMS1117 – 2.5V SMD IC. As the positions of the pins were different, drilled three holes on the board where 54BK was, and fit the AMS1117 from the top, ensuring that the input, ground and output was in position.

Powered the set again and noticed that the Radio and USB were working very well. The point .3V difference did not matter at all! (It struck me now while writing this article that I could have added a diode to the ground to boost .5V in the output!) Did patch up of all the solder joints on the boards after replacing all the electrolytic capacitors as a routine preventive maintenance. Assembled the boards back and let it run for many hours using all its functions and ensured that it was working very well. Mission accomplished and satisfaction got added!

HERE ARE A FEW 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/micro-switch-found-short-in-sony-car-stereo/

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Radio Repair

13 Comments

Yogesh Panchal

September 12, 2020 at 2:08 pm

well done! Sir

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- Parasuraman S
  
  September 12, 2020 at 5:48 pm
  
  Many thanks!
  
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Waleed Rishmawi

September 12, 2020 at 2:10 pm

Splendid work from a pro.

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- Parasuraman S
  
  September 13, 2020 at 7:26 am
  
  Many thanks!
  
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Albert van Bemmelen

September 12, 2020 at 2:32 pm

Nice job in finding a replacement regulator chip Parasuraman! But I guess you had no time to order a better fitted AMS1117-3V regulator, because you probably know that they come in different voltages? Click here

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- Albert van Bemmelen
  
  September 12, 2020 at 3:29 pm
  
  Although only the AMS1117 3V3 does exists I see your point in using the lower 2.5V regulator. But you also could have used the AMS1117-ADJ to exactly make the 2.8V output voltage here needed. See this small circuit here
  
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  - Albert van Bemmelen
    
    September 12, 2020 at 3:40 pm
    
    I found this datasheet from ON semiconductor that may be very helpful if the AMS1117-ADJ is needed and apparently is giving more information compared to that of other manufacturers: https://www.onsemi.com/pub/Collateral/NCP1117-D.PDF
    
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    - Albert van Bemmelen
      
      September 12, 2020 at 3:44 pm
      
      Above mentioned datasheet also says that the AMS1117-2.85V exists which could be an option?
      
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- Parasuraman S
  
  September 13, 2020 at 7:30 am
  
  Many thanks! I have seen all your comments below. Special thanks for the efforts taken to throw more light on the regulator. All combinations are not easily available in this part of the town. I have to manage with what is available. That is the situation many times. I am aware of the variations of 1117 and have seen this in use in LCD/LED TVs and several other uControllers. Nevertheless, the information shared by you is very valuable, indeed! Once again many thanks!
  
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Albert van Bemmelen

September 12, 2020 at 5:45 pm

In case needed that 2.85V regulator is sold here

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- Parasuraman S
  
  September 13, 2020 at 7:32 am
  
  Import from China is temporarily stopped. I am a registered user and have been buying things from there. It takes around 30 to 45 days to get anything by speed post. All courier services are very expensive.
  
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Parasuraman S

September 12, 2020 at 5:50 pm

Many thanks!

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Imoudu

September 14, 2020 at 5:13 am

Pls explain the diode pins
(k&A) connection to voltage regulator.

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