A Lovely USB Radio Model Voyager VBR651BT Restored After A Severe AC Voltage Surge
This USB Radio Blue Tooth set was brought to me by a friend of mine with the complaint that the Charging red light was on when connected to the Mains, but nothing worked. I opened the Radio as soon as he left, keeping aside another work that was occupying my work table, as I liked to work on Radios, especially when they are so cute like this.
Let us have a look at the inside of this set: (The red LED was directly connected to the AC input through a resistor and that is why it was found lit) (I forgot to mention that this had built-in battery & a torch light too with a separate on/off switch)
From the last two pictures, at-least some of you would have noticed a 1000uF/16V cap burst. My checking brought out following defective components: 5.1 Zener diode short, 1117 5.0V IC burst and the Bridge rectifier short.
I replaced all the defective components and also the rest of the electrolytic caps on the board. As an exact replacement of the three legged 1117 series regulator with an output of 5 V was not available, I used a 7805 SMD regulator and fixed it adjusting the position to have the first pin for input, centre pin for ground and third pin for output. In this circuit, the 1st pin was not used for adjusting the voltage and was directly grounded. I also did not have same size bridge rectifier.
So I bent the leads to fix it in the same place. Though the fixing looks clumsy, the purpose was served, as the set came back to life and started working in all modes; i.e., FM/AM/USB/Blue Tooth. (And light too, once battery got sufficiently charged)
After testing the set in all modes for a few hours, I fixed it back and carried it in my car and delivered it to his home on my return from my hospital duty.
Mission accomplished with intense satisfaction getting added to the bag. Let us now look at the toll as conclusion of this article:
This article was prepared for you by Parasuraman Subramanian from India. He is 74 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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Tayo
September 28, 2024 at 12:21 pm
I would have never thought to use the 7805 and rerouting the leads as you did.
That's why you're the Maestro!
Well played
Parasuraman S
September 28, 2024 at 3:47 pm
Many thanks for your comments, dear Tayo! I could use the 7805 as the adjust pin was not used. If it was used, I might have had to go for exact replacement.
Albert van Bemmelen
September 28, 2024 at 2:42 pm
The AMS1117 regulator exists in many voltage output versions. Even in the adjustable output version. I suppose that the reason for not being able to get one of those is lack of available online ordering options in your country. Luckily you still were able to find a 7805 regulator in SMD size. Those are the ones I myself hardly have in stock being the 78L05 types.
Parasuraman S
September 28, 2024 at 5:04 pm
AMS1117 is available for ordering online and we may get even in local market. I have bought these subsequently and stocked it. Thanks for your keen observatory comments, dear Albert!
Yogesh Panchal
September 28, 2024 at 3:31 pm
Excellent Repair!Sir
Parasuraman S
September 28, 2024 at 5:08 pm
Thanks, Yogesh Bai!
Waleed Rishmawi
September 28, 2024 at 4:27 pm
the master of modification and of the replacement of capacitors..LOL. I always enjoy your articles full of challanges and news things to learn. keep up the good work and have a blessed dsay
Parasuraman S
September 28, 2024 at 5:36 pm
Thanks, dear friend for your continued encouraging comments!
Steve Johnson
September 28, 2024 at 10:40 pm
I want to be like you but am struggling to understand how to systematically diagnose the problems. Thank you for your articles.
Parasuraman S
September 29, 2024 at 2:44 pm
Please develop and encourage the internal push to solve problems and then your own mind would suggest ways. It always depends on our intensity to resolve an issue. All the best, dear! Jestine Yong has published a few basic books which were found very useful. I suggest you buy them. All are gems! Kindly visit 'repairing e-store' in this blog!
Mark J
September 29, 2024 at 3:24 am
Parasuraman Good job on the repair.
Parasuraman S
September 29, 2024 at 2:52 pm
Thanks, dear Mark!
Parasuraman S
September 29, 2024 at 2:52 pm
Thanks, dear Mark!
Imoudu.O
September 30, 2024 at 5:21 am
I do wonder how you use to know the voltage rating of burnt or damaged zener diode on board, most often its not written on them.Pls i want to know.Thanks for sharing sir.
Parasuraman S
October 1, 2024 at 10:01 pm
Take help of the circuit of the IC or the set itself. Ascertain whether the zener diode is used as a protection or regulation. Try to obtain info from your techie friends. These are some that come to my mind now! All the best!