Modifying BPL M9903-Two-In-One To House USB Unit In Place Of Tape
This two-in-one of BPL make was brought to me for servicing stating that the sound was intermittent and there were a lot of crackling noises. Working on a set made by BPL, in which I worked for almost 20 years, brought nostalgic memories and I was all in excitement!
As the customer was not interested in the Cassette Tape section to be restored, I suggested adding a USB input in its place, which he readily appreciated and accepted.
As usual, my work began with thorough cleaning after dismantling the whole set.
Replaced all the electrolytic capacitors on both the boards (the amplifier and tuner), and also the volume control.
Since the AC transformer was defective, replaced it with a suitable one and provided a 7808 regulator IC as this set required 7.5V DC.
Fixed a 7805 IC too on the same transformer for providing power supply to the USB module. 7808 was fixed on the side and 7805 on top of the TX (Transformer)
Removed the preamp IC and related components and also the protruding parts of the Tape Mechanism, and also the play wheels, to accommodate the USB Module. Removed the eject door, took it to a shop, where they do cutting of plastic parts for electrical fittings. Requested him to cut the eject door to mount the USB module from the front. He did a professional job, as usual.
Fixed the module on the door, wired its 5V power supply and stereo outputs to the preamp output tracks (Pin holes pierced – see picture below) of the removed IC, M51164AL. As I had routed the power supply through the on/off leaf switch of Tape Mechanism, it made things easy, as the customer can either use its own Tuner or opt for USB/FM pressing any of the Play/FF/REW buttons of the Mechanism, after selecting the function switch to Tape.
Switched on and checked and found the set to be working perfectly. I put all the parts removed for the sake of USB in a cover and taped it inside the Battery Compartment for future use, in case the customer wants to restore the Tape Mechanism. Here are the pictures of set working in USB Mode and the parts replaced (bundled inside a cover) and useful parts stored in the battery compartment:
You will notice from the above picture that the USB module was placed in such a way not to block any of the original symbols of the set! The customer reported that his entire family, especially the grand-children were very happy and amused to use this old set, with new features, which included blue tooth connection to their Android Phones! Satisfaction bag bulged further with one more added to it!
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/track-served-as-a-fuse-to-save-crt-tv-from-lightning/
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Albert van Bemmelen
April 2, 2020 at 1:31 pm
You did another time consuming job and made the audio device even better by adding the Bluetooth option!
I take it that the used 7805 and 7808 regulators are capable in delivering the needed power for the amplifier as they only deliver about 1A at 5V and 8V at max if decently cooled. (I understand that you used the copper housing of the transformer for this?).
Gassan Ali
April 2, 2020 at 9:58 pm
Nice work! I want to learn more about radio communication sets that are used in vehicles and vessels. Is there any resource that you recommend? I sometimes have to deal with such equipment at my job. Since these devices are rarely used outside of their specific areas, it's kind of difficult get the right type of learning resources.
Parasuraman S
April 4, 2020 at 6:07 pm
Basically Radios are same. The frequency range (Band) is changed to suit the requirement. Some frequencies circuits are classified and are used only by security forces. These are not available to the public. Moreover, trying to probe or know them is itself an offence! Whatever it may be, it is for our own good that it is that way!
Parasuraman S
April 3, 2020 at 6:03 am
Yes. The current drawn is well within the limitations. Transformer housing does help to dissipate whatever little heat developed! Many thanks for your comments!
Mark
April 2, 2020 at 4:47 pm
Well done Parasuraman!
Another detailed repair. Good thinking outside of the box.
Parasuraman S
April 3, 2020 at 6:04 am
Many thanks!
Robert Calk Jr.
April 2, 2020 at 6:17 pm
Good job, Parasuraman! Nice upgrade to the radio.
Parasuraman S
April 3, 2020 at 6:04 am
Many thanks!
Alena Patterson
April 3, 2020 at 5:13 am
Wow, you are amazing! Love reading your repairs.
Parasuraman S
April 4, 2020 at 6:02 pm
Many thanks! It is my pleasure too!
Lazarus
April 11, 2020 at 5:34 pm
Thanks, for showing the modification to USB, job well done!! I have worked for GE semiconductor div. as a M.Eng. took care of all Auto IC assembly equipment, so also all Utilities equipment. I hv basically studied Radio Eng. but never repaired Radios, as I was full time in Industry. I needed much needed direction like yours, to modify radios amps.,as I hv retired, n much interested in working at home. Even though I hv lot other hobbies of repairing mo-bikes etc. Tks once again to you!!
Parasuraman S
April 11, 2020 at 8:42 pm
Many thanks! Glad to note your interest in antique electronic devices apart from your other hobbies. All the best to you. (It is better to keep ourselves fully busy after retirement, in order to keep our brains active)
Humberto
April 15, 2020 at 10:42 am
Well done.
Parasuraman S
June 13, 2020 at 11:27 pm
Many thanks!
cipriano olivar
August 14, 2020 at 8:34 pm
me gusto muchas gracias hermano.
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I liked it thank you very much brother.
Parasuraman S
May 27, 2023 at 8:12 am
Many thanks for your comments!
Pranav
June 18, 2021 at 6:50 pm
Sir, I have a national Panasonic's RQ565D with me. Its radio (MW,SW1 and SW2) radio is not making any sound. The tape is working fine with full sound. But when switching to radio, no sound is coming at all. Need your help sir.
Parasuraman S
May 27, 2023 at 8:14 am
Please try to download the schematic or service manual from net. The common causes are the function switch and fungi attack on board. Resistor open cases are also found.