Multiple Problems Solved In National Two In One Model RXF9F
This set was brought by a new customer, as he heard about me from someone else. The complaint reported was that the radio became dead and it was lying unused for many months in the process of hunting for a technician who would attend to it, in the meanwhile of which they bought another radio. He wanted me to restore the radio and bring it back to proper working condition and was not keen on the tape section.
I briefed to him that I do not just do a symptomatic cure but would resort to a thorough reconditioning of the set top to bottom to the extent practically possible, which he was very glad to hear as that was what he learnt about me and my ways, the main reason for bringing it to me. I took up the case on my next free day, and did a thorough cleaning keeping it on the car porch verandah.
Brought the board to my service table and dismantled the tuner dial cord and graphic equalizer holding frame.
I gently removed the dial drum holding screw and slid it out of the gang and twisted it and held it in place with a clip.
That’s what you see in the second picture above. If we do not do this, the cord will slip out and it would be a real pain in the wrong place (LOL) to put it back in perfect synchronized alignment! There was wax covering in many places, which I removed using a small screw driver and then with liberal spray of CRC 2-26. I allowed the spray to sink in and melt the wax and then removed it using tissue paper. This is absolutely essential as we need to retouch the entire board and also remove all the electrolytic capacitors as a routine maintenance work and if the wax sediments are on the board it might cause dry solder problems. I noticed that the set had already undergone service and the transformer in it was not the original and was only just 500mA, 0-9V. The second picture on the top would show you that the set was supposed to be operated on 9V and the power consumption was 14W. So, there should have been a transformer of at-least 1.5A. I have the habit of keeping the customer informed with pictures and short videos and audio messages about the step by step progress being made. He told me that the set was inadvertently connected to 230V, when the setting was on 110V mode and the transformer burnt, during its first use! I told the customer that we would address the power requirement later after finishing all other works.
Proceeded with replacement of all electrolytic capacitors as most of it was way out of range in value and ESR and finished re-touching the board from one end to another. Then checked whether all the semiconductors on the board were ok. The radio was found not working in spite of all these exercises, though voltages to all stages and ICs were ok.
The circuit used one FM front end and one AM front end ICs, the IF outputs of both of which were fed to IC BA1332L, which was a demodulator. I looked through the datasheet of this IC to know the in/out pins of it. The IC was doing very interesting functions, which you can see from the following two extracts: (Please use cntrl+upward arrow to zoom)
The IF outputs from AM/FM ICs were fed to pin 2 & 3, which were fed to detector circuits to remove the carrier frequencies, then segregated to L & R channels for feeding to the audio amplifier section. Since both AM and FM were not working and the voltages to this IC were normal, I suspected failure of this IC and replaced it, upon which the radio started working very well. While I was getting audio in both the earphones when using Ambience mode, I did not notice then that one channel was silent. I came to know this only later while trying various modes on the selector switch, i.e., Mono, Stereo and Ambience. I took my Philips Signal Injector and started tracking from where was the left channel missing. There was one M51164AL IC used as the preamp. When I fed the signal to the outputs, only right channel was working. Left channel was not working both in the input and output. This is sometimes caused by the shorting of the IC. So, I removed this IC, upon which the signal was reaching from the output stage to both channels. So I replaced the IC, upon which both channels were ok. Let us have a look at the defective IC & its pin out:
But the outputs were much distorted and it was prominent in low frequency signals. After checking and replacing some of the suspected components in the amp area, I decided to replace the amp IC LA4555 and see. Though some of the distortions were solved, the low frequency problems were still there. Then I removed the graphic equalizer board and replaced all the fixed capacitors in it, upon which the output was far better. I was using the headphones all these while as trouble shooting was easier. Since the number of rectification works was increasing, I provided a two pin socket on the board as the power in wires were getting strained and cut. In the process of checking, I also noticed that the volume control pot was not good and it made intermittent contacts and sometimes the audio was missing. Any amount of cleaning did not make it ok. So I dismantled it and checked and found out that the tracks had problems:
As I had the same type with a different mounting, I removed its mounting and used this and fixed the pot upon which that got solved. Then I fit the board back in its place, providing yet another socket for motor DC supply, as I intended to make the tape mechanism working too in case it did not have any major problems. On connecting the speakers, I noticed that one channel was silent. I checked the speaker and found out that it was open! My hunting for a replacement did not succeed. So, I took both the speakers and went to a shop where they do the re-coning of the speakers. The work done was not satisfactory. So, I took the speakers along with two more similar speakers collected from a techie friend, which had torn cones, to a faraway place (around 30KMs from my home) after fixing a convenient time for the known guy who did only rework of speakers. I went by bus as the roads were all undergoing repair work and journey by car or two-wheeler was not advisable. I had to get down at a distance and walk for about a KM or more in scorching son, as I did not want to hire an Autorikshaw and increase the cost of repair work. Unfortunately, I forgot to take my cap too, as I was wearing helmet and driving my two wheeler for parking near the bus stand. I got the two speakers done and it was found ok on testing there. It took one full day of me to complete this errand apart from exposing to scorching sun and I felt tired after reaching home. I continued the work next day after finishing my hospital duty and on connecting the speakers; sadly the result was not satisfactory! I tried with various other speakers which I had which were also found not a perfect match. I consulted the guy who did the job and he told me it might be because of the impedance; i.e., the original speakers were having 3 Ohms, whereas 8 Ohms coils were used due to nonavailability of even 4 Ohms coil of the size required. So, some compromised should be accepted, was his suggestion.
Nevertheless, he told me to bring it back after the long vacation due to festivals in our place. Thus I undertook the travel once again like before after a gap of around 15 days. Though the speakers were tested to be working, he changed the coils with a different type and the cone papers once again. The speakers were tested once again for proper working and I carried it back home. This time, the output was much better though I could not say it was damn good at full volume and while using the graphic filters.
I forgot to mention that I got a 2A, 0-9V AC made by a local transformer manufacturer who ran the facility in his home. I fixed the transformer inside an adaptor box and cut the mains cord plug and directly soldered to the 9V AC output, leaving the inserting two pin jack on the other side intact. Then rewired the AC input in the power PCB to connect the 9V AC input to the rectifier diodes. So, instead of 230V in, 9V AC in was provided using the same socket. Took measurement of the place for label on the adaptor and made a computer printout. My printer was not working properly in spite of head cleaning and I let it be how it was. Let us have a look at these crazy arrangements:
Thus I had taken suitable measures to obviate the possible cause of distortion at full volume due to dropping power.
You all would agree that I did what best I could and there were limitations due to constraints beyond our control.
Next I took up the tape mechanism and cleaned it thoroughly and also lubricated all parts. The auto-reverse mechanism was very complex with several wheels required for its function. I replaced the broken belts and ensured that the wheels were all moving freely before connecting the motor to the board. On applying power, a portion of a broken gear wheel fell off sadly putting an end to my efforts to revive the tape section. As mentioned by me, I kept the customer updated with the progress made without any distortion of facts and he was a calm and cool customer.
The above pictures would show you how complex the mechanism was. Yet another wheel that handles the auto off control was also in a broken condition. These wheels are made of celluloid material and are very brittle and might break any time, especially when not in use for a prolonged time. Designers used this type of wheels in mechanisms during those days to reduce friction and noise. Anyhow, having abandoned the mechanism refurbishing work, I removed the belts and just tied the connectors and hid snugly behind it (I imagined what a dog does by sticking its tale to the groove, when it cannot bark or attack!) (LOL) and fixed the mechanism back.
I forgot to share the signal checkup made by me before fixing the board and here it is for the readers to view, which is an indication that there was nothing wrong in the signals passing through from the input to the output. The minor problems were indeed due to incompatible speakers!
The set was working well from line input and radio, provided we did not increase the volume fully and did adjust the graphic controls to the desired level. The radio was excellent and I felt very happy about it, as the complaint originally reported was about that. The customer was also very happy when I reported the outcome and shared the videos. He readily accepted the limitations understanding the practical difficulties and thanked me profusely for handling such a laborious work and even apologized for it. Such an understanding and supporting customer is a rarity nowadays!
Mission accomplished after a lot and lot of work done with intense satisfaction getting added to the bag without any hesitation. Here are the concluding pictures as usual:
P.S. Since the person who brought this set told me that it was used by his parents and his father was an ex-Army Man and all his brothers too served the Army, one of whom had to sacrifice his life while serving in the border, I decided not to collect any service charges but only recover the cost of components and other works done for repairing the set.
After all these are certain opportunities that we, civilians get to pay tribute to such men who guarded our country!
Don’t you all agree? Unfortunately, I was not financially sound enough to wave off the cost of components and other expenses incurred else I would have made it totally free! As I have not shared this part of my decision to him and wanted to put it across only during the time he comes for picking up the set, I hope and pray that he would agree to my gesture and accept my genuine offer! Here, the Army people are very strict and proud with their roles and do not generally accept gratifications of any kind from public! They dislike any sympathy in any form from anyone! I am keeping my fingers crossed, lest I should start biting the nails in anxiety! (LOL again)
This article was prepared for you by Parasuraman Subramanian from India. He is 76 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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Albert van Bemmelen
January 17, 2026 at 5:24 pm
This repair was quite an adventure you still managed to complete despite all unexpected complications. And happily also without any lasting consequences healthwise!
The shown ICs used in this radio cassette recorder are no doubt all Japanese circuits from a time that most consumer electronics all came from that country. I must have a quite a few of those used circuits laying around on spare part Sony boards.
Parasuraman S
January 18, 2026 at 9:46 am
Many thanks for your expert comments, dear Albert!
Mark J
January 18, 2026 at 1:38 am
Parasuraman anther great repair and restoration. Thank you for sharing.
Parasuraman S
January 18, 2026 at 9:46 am
Many thanks, dear Mark!
Jim
January 18, 2026 at 11:16 am
Great Job! .. saved another one!
Parasuraman S
January 18, 2026 at 3:53 pm
Thanks!
Muykit
January 19, 2026 at 1:25 pm
extra-ordinary !
Parasuraman S
January 19, 2026 at 8:12 pm
Many thanks!
Yogesh Panchal
January 19, 2026 at 3:40 pm
Good Job! Sir,
There's a unique joy in restoring antique device.
Parasuraman S
January 19, 2026 at 8:13 pm
Yes, inimitable and inexplicable! Thanks, dear Yogesh Bai!
MP
January 20, 2026 at 2:09 pm
Your technical skill level leaves little doubt that its riding high at the pedestle. You posses a high degree of human tolerance that manifests through perserverance of natures uncompromizing intolerable harsh conditions. Your limitless acts of kindness brings to the fore your caring attitude and enormous generousity that fill the soft spot of your heart as you relate with your clients. Your commited entire teachings as regards technical repairs, know no boundaries, they are plainly indiscriminative and an open window to immense learning opportunities. Gods blessings may be upon you.
Parasuraman S
January 20, 2026 at 8:11 pm
One cannot expect a better understandingly written appreciation from anyone else! Many, many thanks for your wishes and encouraging words! May God bless you too with long life, wealth, health and prosperity!
Waleed Rishmawi
January 20, 2026 at 8:51 pm
only you can do such professional work. thanks for sharing and have a blessed day
Parasuraman S
January 21, 2026 at 8:07 am
Many thanks, dear friend!