This Lovely Locally Assembled Amplifier Had Only A Minor Problem
This amplifier was brought by a customer as per recommendation of another. The complaint was that the Sub-woofer was not working and one channel of the 5.1 Surround speaker systems was not working. I made preliminary enquiries about the speakers used and advised the customer to check each and every one of them using a single 1.5V cell, as all the speakers are fixed on the walls in his house. (Method: Touch the speaker wires to the cell and listen whether any sound is coming from the speaker. A crude method. But advised him not to keep it pressed but do only a touch and go!)
I opened the set and did a cleaning to the extent possible. Let us have a look at the lovely lay out and assembly which I am sure you all would agree that can match international standard. Whoever has assembled it and gave it to the customer has indefinitely done a praiseworthy creditable job indeed!
1) Power supply section (60V, 25V and 12V) 2) Subwoofer amplifier using transistors. 3) Speaker Protection circuit 4) Five output perhaps using TDA2030 series. 5) Audio level LED display driver 6) The preamp and tone control circuits 7) 5V supply for the USB/FM module fit in the front. 8) USB/FM Module.
I connected six speakers of various kinds. Then tried using my signal injector to check whether all the outputs were working. This did not work for all channels, as these were adjusted to split the frequencies to give a surround effect. So, played music from a USB and checked. Except for the subwoofer output, everything else was working. Then by chance I noticed that it was getting cut off only at full volume of the independent control it had. Since I had applied lubrication on all connectors and controls after the preliminary cleaning, dust or dirt could not be the problem. As there was a pair of connections in the dual pot, out of which only one set was used, I shifted the connections to the other side, upon which the output was normal. I checked the frequencies at the output using my oscilloscope and here are the findings of the six output stages:
While it is a fact that these might vary according to the music, one thing was confirmed that outputs indeed were coming out. I could not take such an output feeding a standard signal, as these get cut off due to filters employed in the circuit.
So, what looked like a major problem got resolved by a simple shifting of connections and perhaps because of the cleaning and lubrication. I played the Amp for several hours before closing the cover and calling the customer to pick it.
He later informed me that one of the wires of the speaker was found broken and he rejoined it. He had confirmed that he checked each and every speaker by connecting it to different channels and vehemently denied any problems in the speakers! But customers are strange and we need to deal with them as they are!
Mission accomplished with splendor and satisfaction got easy admission to the collection bag!
I am adding some more pictures of each board for those who might find it interesting:
P.S: Forgot to mention that Amplifier boards and power supply boards were manufactured by my close friend in my town and I was amused to see these used very well by an unknown technician situated far away from where the customer bought this. I shared the photos with my friend too! (I did not remove the boards from the amp to take photos of the other sides as I did not want to disturb the cleanly laid out wires without any reasons for removing it!)
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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Waleed Rishmawi
July 12, 2025 at 3:18 pm
since it is a surround sound, every speaker on that system can be checked in the settings of that device. the amprilfier can produce hissing sound to adjust the sound level on every speaker connected to the device and based on that you can check if speakers are functional of not. it is a very ideal system check on almost every system I worked and repaired. thanks for the article and have a blessed day
Parasuraman S
July 12, 2025 at 5:45 pm
Thanks for the input and comments!
Yogesh Panchal
July 12, 2025 at 4:24 pm
Good Job! Sir
I am saying based on my past experience, if not required never try to disrupt any laying connection or deep cleaning in electronics.If any wire got out and if you do not know which cable is connected to which section it will become time consuming job.Sometimes you may have to pay the price for goodness.
Parasuraman S
July 12, 2025 at 5:46 pm
Yes, Yogesh Bai, very true! We have to be very careful in dealing with such sets. Thanks for your comments!
Albert van Bemmelen
July 12, 2025 at 7:27 pm
Your remark "I did not want to disturb the cleanly laid out wires without any reasons for removing it!" makes much sense and is exactly the way in how I would have left it! No reason to risk damaging a completely fine working audio system just to take some unnecessary photo of the solder side (lol)!
Parasuraman S
July 12, 2025 at 11:01 pm
Exactly, that's what we all feel when we such neatly laid out sets! Many thanks for your comments, dear Albert!
Mark J
July 13, 2025 at 2:27 am
Parasuraman another great repair. I always look forward to your articles.
Parasuraman S
July 13, 2025 at 9:42 am
Many thanks, dear Mark!
Imoudu. O
July 13, 2025 at 4:54 am
It's a piece of electronic art work that can be marketed around the world,and your camera added to its beauty.Thanks
Parasuraman S
July 13, 2025 at 9:45 am
Many thanks for your comments, dear Imoudu!
Humberto
July 15, 2025 at 12:24 am
Another repaired device for your satisfaction bag. Congratulations.
Parasuraman S
July 15, 2025 at 8:38 pm
Many thanks, dear Humberto!