Unit Overview

Audi Symphony II — Front Panel View

The Audi Symphony II AUZ5Z4D CQ-EA1370LC (part number 8E0 035 195M) is a factory-installed head unit found in Audi A4, A6, and A3 models from the early-to-mid 2000s. This unit features an integrated CD player, AM/FM tuner, and a security pin-code system tied to the onboard EEPROM. When the unit loses power or is transplanted to another vehicle, the security code is required — locking technicians out of service operations.

This page provides the verified EEPROM S333 (93C66) firmware dump that allows qualified technicians to bypass the pin code lockout (code off) and restore full functionality.

Label & Sticker Identification

AUZ5Z4D CQ-EA1370LC — Rear Sticker Label Detail

Before proceeding with any firmware operation, always confirm the unit identity by matching the rear-label data against the specifications below. Mismatched firmware will result in a non-functional unit.

Technical Specifications

EEPROM Memory Index

EEPROM S333 (93C66) — Hex Dump Index Preview

The image above shows the hexadecimal index of the 93C66 EEPROM contents. The security code data resides in a specific address range within this 512-byte memory. The provided dump has the code bytes pre-cleared, setting the unit to a “code off” state upon write-back.

Known Issues — Audi Symphony II

Technicians commonly encounter the following faults with this model:

• CODE Lock / SAFE Mode: Unit displays “SAFE” after battery disconnect, incorrect code entries, or ECU reset. Three wrong attempts trigger a timed lockout.
• No Audio Output: Internal amplifier IC failure or cold solder joints on the output stage — often caused by thermal cycling.
• CD Read Errors / No Disc: Laser assembly degradation or worn spindle motor. Common after 10+ years of use.
• Display Pixel Loss: Segments of the LCD fade or disappear due to degraded ribbon cable bonding (flex connector).
• Intermittent Power Cycling: Faulty capacitors on the main power rail or corroded connector pins.
• EEPROM Corruption: Data corruption in the 93C66 due to voltage spikes, causing random safe-mode activation or incorrect station memory.
• Tuner Drift / Weak Reception: Front-end varicap diode degradation or damaged antenna amplifier input.

Diagnostic & Repair Protocol

Step 1 — Visual Inspection

1. Remove the unit from the dash using appropriate Audi release keys.
2. Inspect the rear connector for bent pins, corrosion, or heat damage.
3. Open the housing (4× Torx T10 screws) and examine the PCB for swollen capacitors, burn marks, or cracked solder joints.

Step 2 — EEPROM Identification & Removal

1. Locate the EEPROM IC marked S333 (equivalent: 93C66) on the main PCB — typically near the microcontroller.
2. Note the pin-1 orientation dot before desoldering.
3. Desolder using hot-air station at 280 °C with flux. Use Kapton tape to protect surrounding components.

Step 3 — Reading & Backup

1. Place the 93C66 into the RT809H programmer SOP8 adapter.
2. Select IC type: 93C66 (8-bit) in the RT809H software.
3. Read the chip and save the original dump as a backup file before any modification.

Step 4 — Writing Code-Off Firmware

1. Load the verified code-off dump file (downloaded below) into the programmer software.
2. Erase the chip, then write the new dump.
3. Perform a verify pass to confirm data integrity — must show 100% match.

Step 5 — Reassembly & Verification

1. Re-solder the EEPROM to the PCB, respecting pin-1 orientation.
2. Reassemble the housing and reconnect the unit to bench power supply (12 V, 3 A min).
3. Power on — the unit should boot directly without requesting a security code.
4. Test all functions: tuner, CD, display, audio output (all channels), and button inputs.

Video Reference

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