Massive Destruction Caused By Lightning In This NATIONAL RX-C47F TWO-IN-ONE
This set was brought by a regular customer residing in my area stating that it was lying with his relative in a faraway place and already attempted by someone there and given up. A few knobs, counter and a few screws were found missing on first observation. The old amplifier IC LA4143 along with three graphic equalizer knobs, one auto-reverse knob and a couple of screws were found wrapped by a piece of newspaper, which was inside the battery compartment.
The set was in dead condition. Little did I know what I would be seeing inside after opening! I accepted the set because of the fact that I was aware of the royalty, this set enjoyed during the halcyon days, as such sets were like kings and considered a luxurious possession. Of-course, the quality of the sound output was superb because of the circuit and speaker boom box. This set had auto reverse with repeat facility to play a tape. Anyhow, I opened the set and checked what the condition was inside. A couple of levers of the tape mechanism were missing. The mechanism fixing screws were missing. The reverse on/off switch was found hanging. The connectors of the mechanism were tied up. The inter-connecting wires between the mother board and graphic equalizer board were strained and showed it could break anytime. The DC power in wires were cut and left hanging. The dial needle holder was found cracked in two. Saw one carcass of a lizard. Let us have a look:
I dismantled the set fully and subjected it to thorough cleaning. Noticed fungi formation on the AC in socket and cleaned it thoroughly. Inserted the wire and applied power and found that the DC was coming in. Nevertheless I removed the transformer and primary power supply PCB. Cut the tracks of 110V & 120V and directly gave the AC in to 230V inputs marked on the PCB. Bypassed the battery and DC in connections, as these could cause intermittent or no contact problems. Shorted the two pins out of the three pins that are engaged when AC jack is inserted, as the contacts inside would be a trouble maker due to fungi. This is provided to cut of the External DC-in and Battery supply when the AC jack is inserted. I segregated the connections and made it direct as none use batteries and external DC adaptors for these types of sets. Checked and marked 0-15V AC on the Transformer and on the PCB for future reference. Put the unit back in its place after doing a thorough solder retouch.
Connected the DC wires to the main board and checked what was the condition. It was dead and the DC was getting loaded. So I checked the main board thoroughly and was shocked to see that many transistors were defective and the ground tracks were found cut in several places, which was a clear indication of lightning strike. On verification, I came to know that the customer was also not aware of it. I combed the board using lens and tracked the places where the ground connections were cut. I knew very well that many of the ICs would also have gone. Anyhow the first attempt was to bring back power supply working on the board. Here is a view of some of the damages found:
I used black wires and inter connected grounds. Then replaced all defective transistors, shorted Zener as well as signal diodes such as 5V, 7.5V, IN4148, C1740, C2001 & A564. Provided two sets of IN4148 diodes with anodes joined in place of two green three pin double diodes that looked like transistors {MA3V175D, MA3V176D (MA175WA, MA176WA) Switching diodes}, as these were open:
The power on led lit after doing these massive restorations. But the radio was silent. I used a headphone for checking purposes and applied signal on the volume control and found no output was coming. But it was ok at the inputs of the LA4143 IC. So, the set was getting back its life. Then replaced the AN7310 preamp IC, upon which one channel was working from the volume control level. Radio was still not working. Line in was working only on one channel. Sound output was poor, distorted and noisy when a signal was fed. Radio started working after I replaced all the three related ICs AN7220A (AM & IF AMP), BA1332L (Stereo demodulator), TA7358P (FM Front end). But the FM stations were not coming through. I suspected the band filter as it could get affected in lightning. I provided two 224 ceramic caps in series as replacement was not available.
The AM and FM stations could be tuned very well, though the sound output was still having problems and only one channel was working. The funny thing is that when a signal was fed to both the channels, the IC was waking up, but was silent on radio and line in signals from outside play back. I combed the tracks and components for any more problems that affected the right channel and could not find any. Then I knew that the new preamp IC AN7310 was defective. So ordered for a new one to a different shop and got it next day. Both channels started working after I replaced it.
After making sure that the set was getting back its life, I removed the almost breaking inter-connecting wires and provided jack and socket wiring in its place. I used heat-shrink sleeves on the side where the contacts were too close. Let us have a look:
As you can perhaps see from the second picture, I sliced the socket and connectors to make space for its proper seating as otherwise these two could not be fixed there. Unfortunately, I did not have a 12 pin connector. As for the interconnecting wires, I crimped male and female connectors and soldered these in place to make proper contact. I did this extra work to enable easy dismantling and troubleshooting not only for the present but in the future too if needed.
Replaced almost around 90 electrolytic capacitors and did a retouch of the two boards very well. The tape section was not used as levers were missing and it was really unfortunate that such a lovely set might have to live handicapped during the rest of its life due to negligent technicians! Applied power and found that the radio was dead again. Traced it to man-made shorts while retouching but overlooked even after scrutiny using a lens. Shorts were found in the band switch as well as the AM Oscillator coil output. Luckily the shorts were on the signal paths and not on voltage rails. The set worked perfectly well and I was amazed to see the performance! Listened to various channels by connecting the set to its original speakers and enjoyed the songs. Let us have a look at the external arrangement made for this:
Provided the missing screws and made a futile attempt to rejoin the cut tuner dial cord, wrapped the hanging tape reverse switch securely and taped it behind the mechanism. Fixed the mechanism with two screws. Rewired the Fine tuning control so as to enable easy removal of the front cabinet. Fixed the five long screws at the rear and sealed the screw holes with tape to prevent mud daubers building nests.
Blocked the empty holes in the front panel with tapes to prevent entry of curious visitors. Played the set tuning to various stations and tested it thoroughly while enjoying the songs and music that emanated from this lovely set.
Informed the customer to come and pick it up when I was satisfied with the test. I was of-course sharing photos and videos on every stage of progress made. Mission accomplished with greater satisfaction getting added to its collection!
I am sure you all will join me in my joy on this accomplishment! I know what you are looking for and here it is:
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
December 13, 2025 at 2:16 pm
You Still Got It Sir!
An incredible repair.
Parasuraman S
December 13, 2025 at 5:27 pm
Many thanks!
Albert van Bemmelen
December 13, 2025 at 6:44 pm
This is another fenomenal but also absurdly cumbersome restoration work you had to endure!
It for certain would have been scrapped for parts if you had not fixed it!