Like I said, this device is spliced between the antenna input on the board and the aerials. It's that simple and there is no excuse not to do this on EVERY japan tuner. It's also way simpler than trying to retrofit a japan tuner to cover the U.S. bandwidth. Difficult even when parts were available. Now that almost every collectible box is obsolete and service manuals almost non-existent, the BEST solution.
Eric, what frequency shift model did you end up getting? Many folks don't know that they can be custom ordered with varying frequency shifts. Sometimes, these things don't even advertise the frequency shift. I would avoid those.
You are SOOOO lucky. Standard Japan broadcast is only 14mhz of bandwidth coverage (76 to 90mhz.). Because you are covering 72 to 90mhz, your radio has 18mhz bandwidth. That means if you obtained an 18mhz frequency shift model, you would get the entire US bandwidth with virtually zero overlap. That is important because frequency overlap could be the reason you are having some issues. In other words, if you have purchased a 12mhz frequency shift model, then tuning to 88 mhz on your radio dial would allow your radio to simultaneously receive 88 and 100mhz at the same time. As long as there are no competing stations on those 2 channels, you should be OK. However, if there are 2 stations, even if one is a weak station, you can have multipath and multistation receive issues which could prevent your tuner from "locking" onto the stereo signal. You may be able to alleviate this somewhat by incorporating a local/dx circuitry that is selectable from an external switch like they have on the Sanyo M9998. Look at the Sanyo M9998 circuit diagram for a sample of how to implement one into your existing tuner.
A COUPLE OTHER POSSIBILITIES REGARDING FAILURE TO LOCK STEREO SIGNAL:
(1) The difficulty in "locking" the stereo signal could be due to an attenuation of the received radio signal from incorporating the device. Perhaps a higher quality unit that does not attentuate the signal would work better OR perhaps consider adding an RF signal amplifier to the antenna system to compensate for the reduced input signal.
(2) Will the japan tuner receive in "odd" numbered increments or only "even?" What I mean is can you tune to 84.1 or 84.0 only? If you are only receiving in even numbered channels, then you may need to get another device that shifts the frequency by .1mhz. An analog system by definition is infinitely variable so theoretically an analog tuner can tune anyplace between the covered bandwidth. Digital is a sampling of analog and cuts the analog sample up into little bits. In the case of a normal tuner covering US frequencies, it would be 88.1, 88.3, 88.5, 88.7 etc. Since our normal radio broadcasts do not cover the even increments of 88.0, 88.2, 88.4, etc, there was never a need to program or sample those frequencies on U.S tuners. In any event, if your tuner is only covering the even increments, you'll need to get the band expander that supports the additional .1 increment shift.
(3) Voltage. These devices were designed to operate in automobiles, so you'll need at least 12volts but I believe they'll be most happy at 13.2 to 14 volts, the place where most vehicles operate at. If you spliced into a 12 volt regulated supply that was not designed for the additional load of the band expander, then the additional load could drag down the voltage of that circuit and perhaps affect the performance of the device, the tuner, or the boombox. Most tuner circuits require very precise voltage levels to operate properly. If your device is drawing power from a regulated supply on the tuner board, you may want to reconsider drawing that power from there and instead, take it from someplace else where exact voltage is not as critical. I don't know how many "cells" the Aiwa uses to power it but if it's a 10 cell box, then I personally would not hesitate to give it the full 15 volts.
Eric, what frequency shift model did you end up getting? Many folks don't know that they can be custom ordered with varying frequency shifts. Sometimes, these things don't even advertise the frequency shift. I would avoid those.
You are SOOOO lucky. Standard Japan broadcast is only 14mhz of bandwidth coverage (76 to 90mhz.). Because you are covering 72 to 90mhz, your radio has 18mhz bandwidth. That means if you obtained an 18mhz frequency shift model, you would get the entire US bandwidth with virtually zero overlap. That is important because frequency overlap could be the reason you are having some issues. In other words, if you have purchased a 12mhz frequency shift model, then tuning to 88 mhz on your radio dial would allow your radio to simultaneously receive 88 and 100mhz at the same time. As long as there are no competing stations on those 2 channels, you should be OK. However, if there are 2 stations, even if one is a weak station, you can have multipath and multistation receive issues which could prevent your tuner from "locking" onto the stereo signal. You may be able to alleviate this somewhat by incorporating a local/dx circuitry that is selectable from an external switch like they have on the Sanyo M9998. Look at the Sanyo M9998 circuit diagram for a sample of how to implement one into your existing tuner.
A COUPLE OTHER POSSIBILITIES REGARDING FAILURE TO LOCK STEREO SIGNAL:
(1) The difficulty in "locking" the stereo signal could be due to an attenuation of the received radio signal from incorporating the device. Perhaps a higher quality unit that does not attentuate the signal would work better OR perhaps consider adding an RF signal amplifier to the antenna system to compensate for the reduced input signal.
(2) Will the japan tuner receive in "odd" numbered increments or only "even?" What I mean is can you tune to 84.1 or 84.0 only? If you are only receiving in even numbered channels, then you may need to get another device that shifts the frequency by .1mhz. An analog system by definition is infinitely variable so theoretically an analog tuner can tune anyplace between the covered bandwidth. Digital is a sampling of analog and cuts the analog sample up into little bits. In the case of a normal tuner covering US frequencies, it would be 88.1, 88.3, 88.5, 88.7 etc. Since our normal radio broadcasts do not cover the even increments of 88.0, 88.2, 88.4, etc, there was never a need to program or sample those frequencies on U.S tuners. In any event, if your tuner is only covering the even increments, you'll need to get the band expander that supports the additional .1 increment shift.
(3) Voltage. These devices were designed to operate in automobiles, so you'll need at least 12volts but I believe they'll be most happy at 13.2 to 14 volts, the place where most vehicles operate at. If you spliced into a 12 volt regulated supply that was not designed for the additional load of the band expander, then the additional load could drag down the voltage of that circuit and perhaps affect the performance of the device, the tuner, or the boombox. Most tuner circuits require very precise voltage levels to operate properly. If your device is drawing power from a regulated supply on the tuner board, you may want to reconsider drawing that power from there and instead, take it from someplace else where exact voltage is not as critical. I don't know how many "cells" the Aiwa uses to power it but if it's a 10 cell box, then I personally would not hesitate to give it the full 15 volts.
