This article was prepared for you by Parasuraman Subramanian from India. The reason for not working even after replacing the IC by my friend perhaps indicates duplicate ICs! Here are a few more pictures: Satisfaction got added to its collection as usual. I took videos and pictures and sent it to him through Whatsapp. This time it started picking up stations! (I also replaced one electrolytic cap in the AM area also, which my friend had overlooked.) So, refit the board and allowed it to run for a few minutes before keeping it aside for pick up by my friend. So, fit the coil A in place of coil B in its own case. Then opened the coil of this board (call this B) and studied the connections. I looked for an Oscillator coil from my old collection and removed one and opened it (let us call this coil as A). Then my suspicion was on the Oscillator Coil. I replaced the crystal once again and also the IC (removing it from a Sony salvaged board that I had) with the same result. I downloaded the datasheet and took print out of a Radio circuit using the IC CXA1238S and studied the circuit thoroughly for any faulty component. On checking by applying power (9V DC) directly to the filter cap, I confirmed that though the hissing noise was there, it was not picking up any stations. He brought only this portion as I declined to add one more set to my already packed service room. He bought a new IC and put it in with the same result. He tried replacing the crystal, and then replaced all the electrolytic caps, and also retouched the dry solder. you could also skip the scope and sig-gen and just use an RTL SDR to measure with, but use a capacitor to isolate the RTL's antenna input, as there are often DC levels present in the radio.This board was brought to me by one of my technician friends stating that the FM was not picking up any stations though the AM was working. with the sig gen set to 200khz deviation (if the sig gen doesn't have a deviation meter, you can use an RTL-SDR to measure it), and the y axis gain adjusted to take up the whole 10 divisions across, you now have a way of measuring the bandwidth. you can use sine wave modulation if you are adjusting the RF and IF, but for measuring, you want a linear sweep) driving the X axis, and the output of the probe driving the Y, axis. the scope is used in XY mode with the modulating audio (preferably triangle wave audio. you would use an RF demodulator probe (consists of a germanium diode voltage doubler and a BNC cable) connected at the input of the radio's FM demodulator, and the sweep generator connected to the antenna input of the radio. If you have access to an FM signal generator and a oscope you can measure the actual selectivity of the receiver. Initially it was only the audio ceramic filters you had to change, plus the notch filter on the video - but with the advent of SAW filters for the main IF you had to replace that as well, as it was sharp enough to reduce the audio carrier. SAW did replace transformers in TV IF circuits, due to their complex nature, but radio IF's (and the audio IF in those TV's) used ceramic filters as they did everything required, and are probably cheaperĪs far as TV's go, I modified a LOT of grey imports (with 5.5MHz audio IF instead of 6MHz) over the years - in fact I modified them both ways (imports and exports). However, for practical purposes, Ceramic filters and SAW are the same thing anyway. I never even considered IF transformers, although I thought ceramic filters rather than SAW - I've no idea if SAW's were used in later radios?, but ceramic filters replaced IF transformers a great many years ago. Neither did I, which was why I said 'perhaps' - as it could be a difference between the two radios, one with a tuned frontend, and one without.
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