Restoration And Modification OF Panasonic RX-CS730 Two In One
This set was brought to me by a boy doing his post-graduation in Marketing, with a request that it be restored to working condition and a USB/FM/Bluetooth module fixed in place of cassette player. Evidently this set has been lying in the attic and a sudden interest brought it out for the present generation to revive it and return to the halcyon days and nostalgic childhood, adding latest technology!
Well, I love to do such restoration work and I kept aside all other work and took it up immediately. As usual, I opened and dismantled the set to find tons of dust as expected. One speaker was found replaced by crude looking rectangular one in the past repairs on the set. Following picture of the other speaker, which I opened for cleaning would give you an idea of what I would have found in the rest of the inside:
After thorough cleaning of inside and wiping the inside well to the extent accessible by cloth and brushes, I brought the PCBs for retouching and replacement of all electrolytic capacitors. Found a lot of dry solders, with a few leads of components dislodged from the PCB. After finishing this work, I cleaned the PCBs thoroughly using IPA. Then located the tape head pre-amp IC and disconnected its power supply, inputs and outputs. For connecting the following USB/FM/Bluetooth module, I needed 5V supply, ground, FM antenna in and then wire the Left and Right channel outputs to the inputs of the AMP, i.e., at the outputs of tape preamp IC, which I had isolated. The IC number was BS3313L, pin details of which are given below (Please use cntrl+scroll to zoom out/in):
Pins 5 & 9 were inputs, while 1 and 12 were outputs. The VCC was given to pin 8. I scraped the tracks of all these pins in order to deactivate its function and also to arrest random pick-up from the tape head, as the leaf switch of play/FF & REW was to be used for 5V supply to the module. The mechanism had a connector giving in 12V for the motor; two wires for the leaf switch (in and out) with a ground wire. I used the same connection by isolating it from the motor. The 7805 regulator IC with a further 220/25uF smoothing capacitor at the output of the IC was fit on the mechanism, screwing it well to dissipate possible heat.
Then tapped the Antenna connection from the board through a 0.01 cap, L & R channel inputs and ground. Made a hole on the cassette door for a panel mount of the USB MP3 module. Inserted it and fixed it with two self-thread black screws. Inter connected the power supply and output wires.
Then inserted the connectors in the appropriate places. Rechecked and applied power, keeping the play button pressed. Was very glad to see the USB lighting up.
I noticed that the headphone jack was having something was obstructing and I could not take it out. So I removed it and dismantled it to find a broken pencil tip inside!
Then turned my attention to the FM Radio of the set (not that of the module.) As I am experienced enough to know that the 10.7M crystals would normally be the cause, and from the crystals what we get from the market, only 2 or 3 will be working out of 20, I fixed a three pin socket, cutting it away from a six pin IC socket.
Then checked the crystals one by one. Out of 29 pieces I checked, only 6 were working well, six were weak, and 17 nos got rejected! Even out of the six, only one was excellent!
After ensuring that FM was working very well, I replaced the two speakers and provided two tweeters in place of defective diaphragm type one that it had. Then played the set for a long time, before fixing it back and then rechecked it and found it to be working very well. Then I polished the cabinet and made it shine like new.
The output was so good that the boy was rejoiced to get back his favorite childhood day set in perfect working condition with new features added! He even went to the extent of making a short video of all stages that I had shared with him, with the title ‘nothing is impossible!’
Mission accomplished with a great satisfaction of a job well done, promptly adding it to the collection.
This article was prepared for you by Parasuraman Subramanian from India. He is 72 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 article on Restored A CCTV Power Supply With A Perfect Output
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Albert van Bemmelen
June 17, 2023 at 12:52 pm
Impressive BS3313L Tape preamp to bluetooth MP3 player modification!
Never knew that only one out of so many 10.7 MHz FM crystals in the market would qualify to function as if amplifier.
Still the term 'leaf' switch you used is completely unknown to me and Google didn't make it any clearer.
Henrique J. G. Ulbrich
June 17, 2023 at 10:45 pm
Dear Albert, as I know, a leaf switch is a switch driven by a lever (blade, foil). This blade has multiple simultaneous functions: it conducts the movement for the switch actuation, is part of the electric contact itself, and actuates as the return spring of the switch. Some kinds of microswitches, instead of being driven directly by the actuation button integrated on the component, are actuated through a lever additionally mounted in the microswitch body. This lever receives the movement and presses the actuating button in the microswitch. A known example of this variant are limit switches.
Parasuraman S
June 18, 2023 at 9:50 am
Good explanation! Thanks!
Lee
June 27, 2023 at 9:03 am
You also find leaf switch's in Pinball machine flipper button's.
Parasuraman S
June 28, 2023 at 8:17 am
Yes, these are found many mechanically operated circuits!
Parasuraman S
June 17, 2023 at 2:48 pm
Kindly see the image in the following link to know what is a leaf switch
These type of switches are common in wherever mechanical switches are employed like a tape recorder. There might be many in some mechanisms. Even solenoid controlled switches are in use. Many thanks for your expert comments and observations.
Albert van Bemmelen
June 17, 2023 at 3:37 pm
Thanks for clearing that up Parasuraman!
Google previously mentioned => "Leaf switches are popular devices used in data centers to aggregate traffic from server nodes and then connect to the core of the network, consisting of spine switches. In this model, there are only two tiers of switches between the servers and the core network."
And that of course couldn't be it.
Parasuraman S
June 17, 2023 at 9:11 pm
Many thanks, dear!
Waleed Rishmawi
June 17, 2023 at 4:58 pm
you actually did not repair the device, you revived it as it was dead and no it has a new soul. thanks for sharing your success and keep up the good work. i never done this kind of job before but I look foward to doing such task soon. have a blessed day
Parasuraman S
June 17, 2023 at 9:13 pm
Taking up such rejuvenation work revives our zest and enthusiasm in our ever revitalizing challenging jobs! Many thanks for your comments, dear friend!
Hollis LuQuette
June 18, 2023 at 3:18 am
Well done Mon Ami , I searched you tube for that video and I couldn't find it , if it's on you tube , I would like to have the link please .....
Parasuraman S
June 18, 2023 at 9:52 am
Sorry, I could not follow as to what you are referring to!
Yogesh Panchal
June 25, 2023 at 12:33 am
Good Job! Sir
Parasuraman S
June 26, 2023 at 9:34 am
Many thanks, dear Yogesh!