I've been working on a Aiwa HS-J10. One problem is intermittent audio noise and cutout. Investigation led to a small black squarish component next to the earphone jack is broken off its solder mounts. There is another of these on the other side of the jack, and a third one nearby. I presume the jack was impacted and broke the thing beside it. This thing has defied my attempts to resolder it. There are no pins on the bottom. It is very hard material. What is this and is it vital for the unit, or could I just make a short between its contacts. If it is important, how can I solder it, or is there something I could install in its place? Circled in the photo. Earphone jack was next to it and is removed.
Those are L103, L104 and L105. The circled one seems to be L105, the one connecting 3.5mm jack's ground to the circuit ground. Those 1μH inductors have a reactance of 630Ω at 100Mhz, so at RF they act as 630Ω resistors. On the other hand at 10kHz reactance is 0.06Ω, so it's like they're not even there. Without L105, the jack's ground (which is supposed to act like FM antenna) will be grounded at RF, so no signal will get in the FM frontend. FM radio will probably still work to some degree, as the trace itself will act like an antenna and also has some of its own parasitic inductance, but reception won't be good. Since C157/C158 and C164/C165 are both short-circuits at RF, L103 and L104 are also needed since otherwise RF signal would go through the headphones voicecoil (which can be as low as 16Ω) directly to ground. Using these inductors, the antenna is pretty much floating from the rest of the circuit at RF frequencies. This configuration is used on any walkman that has FM radio and uses the headphone cable as antenna. To be noted though you don't necessarily need the inductors with ferrite core. SMD chip-type ones will also work.
Your expertise is greatly appreciated. Would any of these be suitable? I can get them locally, otherwise I have to order online. https://leeselectronic.com/en/search?controller=search&s=1uh+inductor
Without a datasheet can't tell. Apart from inductance, DC resistance (which should be low to not affect audio output impedance) and self-resonance frequency are also important. Above the self-resonance frequency, the inductor doesn't behave as an inductor anymore but as a capacitor. So we want this frequency to be above the frequency inductor is operating at. One example is this: www.digikey.com/en/products/detail/delta-electronics-components/0805CS-102EJFS/9764069 It has a self-resonance frequency of 280Mhz (way above 88-108Mhz in FM) and DC resistance of 80mΩ (which is nothing). Footprint is 0805 (2.29mm x 1.71mm), but it is possible an 1206 footprint (3.2mm x 1.5mm) will also work. In regard to the ones linked, first concern is footprint. In pictures they all look large compared to original ones.
Thank you. I've ordered a couple of the 0805 (in case I mess up one of them) and will update after installation.
Remarkably, the replacement inductors from Digikey took less than 2 days to arrive at my door. In the meantime I attempted to attach solder to the miniscule leads broken off and barely sticking out of the original inductor when it broke off its pads. Then I soldered it back in place. And crossed my fingers. I thought I had succeeded, but in testing the only radio reception I got were the artifact signals you described. So I set about installing a new inductor, not looking forward to the challenge to my soldering ability and my crude equipment, of the new inductor's even smaller form factor than the original. But I came across that, in removing the earphone jack to make room to work on the inductor, I had unsoldered two wires. And had neglected to resolder them before testing the reattachment of the original inductor. Fortunately I had taken a photo before I unsoldered them. With the wires reconnected, the radio seems to work fine. I poked around at the jack and inductor and could not induce malfunction. So my finicky soldering job must have worked. I glued the inductor to the side of the adjacent switch, for support in addition to the soldering. This also gives the inductor more clearance to the jack, in case movement of the jack originally broke the inductor off the board.
