Game Boy Color: sound only from the speaker, or only from headphones

Three symptoms, one component

Sound only through headphones means the jack switch is stuck open, so the speaker is permanently disconnected. Sound from the speaker even with headphones plugged in means the switch is stuck closed and the amp is driving both loads at once, which will also sound thin and quiet. No sound at all means the amplifier itself or the amp supply is gone.

Test all three states before ordering anything: with no plug, with a plug partly inserted, and with a plug fully inserted. The behaviour at the halfway point tells you which contact is at fault.

Tracing the signal path

The amp is fed from the CPU through a coupling capacitor, and its output goes to the jack first and the speaker second. That order matters: if the jack is faulty, the speaker loses its feed even though the amp is working perfectly.

Inject a signal at the amp input with a signal tracer or simply touch the input pin with a finger while the volume is up. A hum from the speaker proves the amp and the supply are alive and pushes the fault back to the jack or the CPU.

1. Test with no plug, then with the plug fully in, then with the plug halfway. Write down what you hear in each state.
2. Measure continuity across the speaker terminals with the console off and no plug inserted. A healthy speaker reads 8 ohms plus or minus 20 percent.
3. Measure the amp supply pin. On a CGB-001 this is the 5 V rail from the DC-DC converter; if it reads low, the amp will be silent.
4. Touch the amp input pin with a finger while the console runs a game. A loud hum means the amp is fine and the fault is upstream.
5. Inspect the jack contacts under a loupe. Look for a bent spring contact or black sulphide deposits on the contact faces.

Jack, capacitor or amp

Clean the jack contacts first. A 3.5 mm cleaning plug with a drop of contact cleaner, inserted and removed ten times, fixes a surprising number of these. If the spring contact is bent, straighten it with a fine pick under magnification, or replace the jack if the plastic body has cracked.

If the amp is silent with a good supply and a good input signal, replace it. The CGB amp is a small surface-mount part. Coupling capacitors that have gone open will produce the same silence and are much easier to replace, so check them before touching the amp.

1. Clean the jack with a 3.5 mm cleaning plug and contact cleaner. Re-test all three states.
2. Replace the two output coupling capacitors if the speaker reads correct resistance but no signal reaches it.
3. If the amp output is dead with a known-good input, replace the amplifier IC. Use hot air at 300 °C with the board preheated.
4. Check the volume wheel for dead spots. On a CGB the wheel is a mechanical potentiometer and its track wears out before the amp does.
5. Test with the speaker at full volume and the headphones at half. Then test again with a cartridge that has stereo audio to catch a dead channel.