Do you have a Japanese import car that won’t tune to local FM radio stations? It’s a well known fact that Japan uses a different public FM broadcast band to the rest of the world; 76 to 90 MHz instead of the usual 87.5 to 108 MHz CCIR band. Sure you can use a band expander but these suffer from a number of drawbacks, not to mention that the radio does not display the correct frequency of the station you are tuned to.

Here’s a guide on hacking your radio to convert it to natively tune across the CCIR band. This post is still a work in progress so I may update it from time to time and add more photos as I get the chance.

Background

Not all radios can be converted. Generally this guide applies more to OEM radios than aftermarket ones, as the latter are often developed specifically for the Japanese market.

OEM radios are generally designed to be sold in cars around the world, and I have often found that manufacturers stick with a common base design and modify it slightly to suit each local market.

What you need

Essentials

• Fine tipped temperature controlled soldering iron
• Fine solder
• Desoldering wick
• Fine enamelled copper wire
• Volt meter
• Capacitance tester
• Phillips #0 screwdriver (and other types as necessary)
• Working FM radio to use as a monitor
• 12-14v DC power supply, 1.5A minimum
• Suitable plug and harness to connect to the radio
• 4-8 ohm speaker
• FM or VHF antenna (or a long scrap of wire)

Also handy

• Tinned copper wire
• Ceramic or plastic tuning coil adjustment tool

For the elite

• Oscilloscope

Method

Remove the stereo from your car

This is pretty self-explanatory. If you are not sure about what to do, search Google as people in enthusiast forums often post instructions.

If you really get stuck, see your local car audio dealership.

Pull it apart

This can also be a bit tricky. In many radios I’ve come across you start with the top panel, followed by the front, then slowly work your way down. If you are unsure, take photos as you go and note where each screw goes.

Finding you way around

Locate the major components

Once the radio is open you need to identify the tuner module and microprocessor. Typically in a car stereo you will find a small number of chips; the microprocessor, an audio processing chip, a PLL for the tuner and perhaps a set of ICs to drive the CD mechanism. Often the microprocessor has the most pins. If you are not able to identify the chips, try searching for their part numbers in Google.

The tuner is usually a self-contained, well shielded unit soldered onto the main PCB. Most tuners are tuned by varying the voltage on a particular pin between ground and typically 8-9v, and many mark this pin as VT. If it is not labelled on the PCB then you can identify this pin by measuring the voltage swing whilst tuning the radio across the band. Mark it as it will be used later.

Also locate the Vcc pin of the tuner; if this is not clearly marked then look for a pin with a constant reading of 8-9v.

Set the area

Once you have identified the microprocessor, look around it for a set of resistors (often 0 Ohm) or jumpers. These may be on either or both sides of the PCB. Some older radios use diodes instead. Usually they will be accompanied by a set of unpopulated solder pads. If you are really lucky they may even be marked as Area 1 and Area 2. Usually Area 1 is for North America and Area 2 suits most other countries.

Usually each jumper resistor will have a matching set of unpopulated solder pads nearby. Each jumper will connect one of the microprocessor pins to either ground or Vcc (usually 5v) to select what mode or area the radio is intended to be used in. See the example photo below.

Start off by photographing or taking note of the original layout so you are able to restore the radio to its normal operation if you have no success.

Try desoldering the jumpers and moving them one at a time, then powering on the radio to see if the displayed FM frequency has changed. If the jumper does not have any noticable effect, move it back to its original location and try another one. Just be careful not to accidentally short the 5v rail to ground as you may permanently damage the radio.

Once you do identify the area jumper, also check that the AM tuner steps correctly as well; it will either be in 9 or 10 kHz steps. If it does not the chances are the FM band may step incorrectly for your region as well. Keep trying until you locate the jumper that suits where you live.

If you are successful in identifying the correct area jumper the radio will probably display 87.5MHz instead of 76MHz when first powered on. Connect an antenna and speaker. Try tuning the radio to a local station and see what happens. Chances are the radio will appear to tune fine on the display, but behind the scenes stay stuck on one frequency.

If it does work then you are in luck! Move on to the testing stage later in this article. If not, read on…

Hack the tuner

Provided you were successful with the above jumper switching it’s time to work on the tuner. This is usually a vertically mounted PCB protected by a metal shield.

Some quick tuner theory

Below is a schematic of a typical automotive FM tuner front-end circuit, this one based on the LA1175M manufactured by Sanyo. The details do vary quite a bit between models but the basic concept of operation is usually the same.

Car radios are usually based on a superheterodyne design. We will be working entirely on the front end which encompasses an RF amplifier, local oscillator, mixer and filter.

In the diagram above there are three tuned circuits formed using a varicap (AKA varactor) and fixed inductor.

As the varicaps behave like a voltage-controlled variable capacitor, the circuit is tuned by simply varying the voltage supplied to the varicaps (VT). Usually the tuning voltage is supplied from a PLL circuit located separately from the tuner module.

So in essence we have two ways of adjusting the frequency range of the tuner; by changing the inductance of the coil or replacing the varicaps with a type that has a different capacitance range to the original. The first is much easier so that’s where we will start.

Identify the FM section

Generally the tuner will have separate sections for tuning AM and FM. In my experience these are located at each end of the board. The quickest way to determine which end is which is to look up the IC part numbers in Google and work from there.

Mark the coils

Use a fine permanent marker to mark the position of the ferrite slug in each coil that features one. This can help you get it all back together if all goes wrong later.

Override the PLL

After tweaking the microprocessor the PLL will likely be struggling to tune the radio into the range it expects and therefore often holds the VT pin of the tuner at the highest possible voltage (about 8-9v) regardless of the frequency you select.

Disconnect the VT pin and connect it to the wiper (centre) of a 50k linear (B type) pot. Connect each end of the pot to ground and the tuner Vcc respectively as shown in the diagram.

From here you can use the pot to manually tune the radio across its entire band, completely bypassing the original radio controls. At this stage you might be able to pick up local stations near the lower end of the band.

Locate the oscillator coil

The easiest way to locate the oscillator coil is to tune the pot you just connected to about half way. Tune your monitor FM radio to local station near the middle of the band (e.g. between 96-100MHz).

Carefully move your finger near each of the coils on the tuner until you hear the same station as on the monitor radio. This coil is the oscillator. Adjust this coil by carefully turning the slug (if it is ferrite cored) or separating the windings (if it is air cored). This can be a big job as you may need to remove the tuner and shielding to access it.

If the coil is air cored but wound onto a plastic former (like the black one in the photo below), you will need to desolder the coil and remove some turns. Take note of the number of turns, winding direction and pin connections before proceeding. You may need to experiment a bit, so try removing a half turn at a time.

As you adjust this coil you should end up being able to tune across the entire local band using the pot. Once you start getting close, remove the pot, reconnect the VT pin and see if the radio will now tune correctly by itself. It will pay to check that it tunes across the entire band; some radios will still only tune about 16MHz wide.

If it does tune the entire band correctly, skip the next step. If it doesn’t appear to you may need to replace the varicaps.

Replace the varicaps

This is tricky as it is often difficult or impossible to determine what types of varicaps were already fitted. To identify the varicaps, look on the underside of the tuner PCB. Usually there will be two to four three-legged surface mount components. Two pins on one end will be connected across a nearby coil and the third pin will be connected (usually via a resistor) to the VT pin of the tuner module. The example below shows four varicaps identified.

Once you have identified the varicaps, replace them with something suitable. I’ve had quite good luck using SVC203 types with Sanyo tuner ICs (and in particular the Clarion 80-8028A tuner module) but the type you will need can vary widely.

To help gauge what type of replacement varicap to use, try removing one of the old ones and measuring it. It is likely that you will need to use a slightly lower value than the original and also use a component with a larger capacitance range.

This is very likely to be a trial and error affair so patience is a virtue. One thing for sure is that you will need to replace all of the varicaps simultaneously with identical types.

If you have had to remove the tuner module from the PCB, try temporarily soldering it to the underside of the PCB during testing.

Testing and adjusting

Once you are satisfied with the modification it’s time to test the radio. I’ve noticed that many Clarion and Sony radios can be operated fine without the CD or tape decks which makes testing much easier, however an Alpine model I tried refused to output any sound from the radio until the CD mechanism had been connected.

If the radio doesn’t work at all, double check that you haven’t missed any connections or accidentally created any solder bridges. Also remember that car tuners will not usually work unless you have some form of antenna connected.

Once the radio appears to work, try tuning it across the entire band and compare it with the monitor radio to see that all stations are being picked up. Also try scanning or seeking the radio across the band; if this fails to work you may need to adjust an additional coil.

Successful Conversions

Here’s some radios I’ve successfully converted with some more detailed instructions.

• McIntosh PF-2124I