FAQ
TL;DR: One I2S line carries GSM-call audio; "audio data during cellular connection goes on the i2s line." If apps work but calls are silent, suspect a damaged CPU–audio codec–baseband link and seek board-level diagnosis. [Elektroda, RafalB, post #17134331]
Why it matters: This FAQ guides iPhone 6/7 users with call-only audio loss to fast, accurate hardware triage.
Quick Facts
- Typical symptom: apps (Siri, Voice Memos, Messenger) work; only GSM calls are silent; Wi‑Fi Calling works. [Elektroda, mtaton, post #17132216]
- GSM-call audio rides a single I2S link between CPU, audio codec, and baseband. [Elektroda, RafalB, post #17134331]
- Headsets (jack or Bluetooth) do not bypass this: apps work, GSM calls stay silent. [Elektroda, mtaton, post #17147108]
- Restoring and setting up as new did not resolve the issue. [Elektroda, mtaton, post #17134394]
- Common repair target: cracked audio codec/PCB joints ("codec audio and pcb" connections). [Elektroda, RafalB, post #17224448]
Why do my iPhone 6 microphone and speaker work in apps but not during GSM calls?
Apps and Siri use a different audio path than GSM calls. GSM-call audio travels on an I2S link between the CPU, audio codec, and baseband. A cracked joint or line break there kills call audio only. That leaves apps and voice recording unaffected. Board-level diagnosis should focus on that chain. [Elektroda, RafalB, post #17134331]
How can I quickly test whether this is a GSM-path issue?
Use simple isolation tests.
- Record in Voice Memos and try Siri; confirm both hear you.
- Place a normal GSM call; check if both sides hear nothing.
- Place a Wi‑Fi Calling call (e.g., T‑Mobile); verify audio works.
This pattern indicates a GSM audio-path fault, not an app issue. [Elektroda, mtaton, post #17132216]
Will restoring iOS or downgrading fix call audio silence?
A full restore and setup as new did not change the symptom. Calls stayed silent, while apps kept working. That outcome points away from iOS or settings. Focus on hardware diagnosis rather than downgrading attempts. [Elektroda, mtaton, post #17134394]
Do wired or Bluetooth headsets help or bypass the issue?
Testing showed no improvement with headsets. Headphone jack and Bluetooth worked in apps. During GSM calls, both directions remained silent. Headsets do not bypass the failing GSM-call path in this scenario. [Elektroda, mtaton, post #17147108]
What exactly is the hardware path for GSM-call audio on iPhone 6?
GSM-call audio runs over an I2S link from the processor to the baseband via the audio codec. As one technician put it, "audio data during the cellular connection (GSM) goes ... on the i2s line." Damage along this chain mutes calls while apps keep working. [Elektroda, RafalB, post #17134331]
Should I replace the microphone flex or dock connector first?
In call-only failures, a mic flex swap may not help. One user replaced the microphone tape, yet callers still could not hear them. Apps like Voice Memos still worked. This points to a board-level GSM audio path issue instead. [Elektroda, JadwigaTopaz, post #17760674]
I’m on iPhone 7/7 Plus—could it be the same root cause?
On iPhone 7/7 Plus, technicians often find audio codec/PCB joint failures. An expert notes, "The most common problem here is codec audio and pcb - broken connections with the system." Expect board-level repair if calls are silent but apps work. [Elektroda, RafalB, post #17224448]
Why does Wi‑Fi Calling work while normal calls are silent?
In the reported case, GSM-call audio success was 0%, while apps and Wi‑Fi Calling worked 100%. This split helps isolate the fault to the cellular call path. Use Wi‑Fi Calling as a diagnostic step when available. [Elektroda, mtaton, post #17132216]
What if I can hear callers, but they can’t hear me?
That indicates an uplink-only failure during calls. One user could hear the interlocutor, but the interlocutor could not hear them. They had already replaced the microphone tape. Suspect the GSM uplink path or codec joints on the board. [Elektroda, JadwigaTopaz, post #17760674]
Should I try a headset test first?
Yes. A headset test is a quick isolation step. If headsets fail during GSM calls, it strengthens the board-path suspicion. Run this check early to save time on parts swaps. [Elektroda, el_danone, post #17146607]
Can carrier Wi‑Fi Calling help confirm the fault?
Yes. Test with a carrier that supports Wi‑Fi Calling to compare paths. A user suggested trying an Orange SIM to verify behavior. Working Wi‑Fi Calling with silent GSM calls supports a GSM-path fault. [Elektroda, unr3al2, post #17762622]
Is this a software issue or hardware fault?
Technicians in the thread pointed away from software causes. One response states, "it's not the software's fault" and suggests hardware replacement. Use software tests only to document the pattern, then pursue board-level checks. [Elektroda, proelektronics1, post #17139630]
What should I ask a repair shop to check specifically?
Ask for inspection of the CPU–audio codec–baseband audio path. Mention the I2S link that carries GSM-call audio. Request rework of cracked joints or line repair if faults are found. [Elektroda, RafalB, post #17134331]
Is there a temporary workaround to make calls?
Yes. Use Wi‑Fi Calling if your carrier supports it. Alternatively, place calls through VoIP apps like Messenger or WhatsApp. Those worked while GSM calls were silent in the reported case. [Elektroda, mtaton, post #17132216]
