Enigma-NG Maintenance Guide

Status: Draft Version: v.0.1.0 Associated Hardware Revision: Rev A Last Updated: 2026-05-16

1. Safety Procedures

• Safety Glow (Amber): If the external Amber LED is lit, the Supercapacitors are discharging (>5.1V). Do not open the machine.
• Residual Voltage Test: After the Amber LED extinguishes, use a multimeter on the 'SICHERHEITS-PROBE' (V+) and 'ERDE-PROBE' (GND) pads.
• Touch-Safe Threshold: Only begin work when the multimeter reads <2V.

RTC Battery Safety

The Controller board contains an RTC backup battery (ML2032/CR2032 coin cell).

⚠️ Battery Safety Warning: The RTC backup battery (ML2032/CR2032 coin cell) is a lithium cell. Do not short-circuit, incinerate, disassemble, or expose to temperatures above 60°C. Replace only with the same or equivalent approved type. Dispose of in accordance with local regulations.

• CR2032 (non-rechargeable): Standard fit. The BAT54 protection diode (D1) must remain in circuit.
• ML2032 (rechargeable): Only if D1 is removed and the Linux OS dtparam=rtc_bbat_vchg parameter is enabled. See design/Software/Linux_OS/ for software configuration.
• Service interval: >25 years under normal use. Battery replacement is a service-by-disassembly task - not field-replaceable in situ.

2. Internal Indicators

• LOGIK-BEREIT (Green): Located on the Power Module near the Controller dock edge. Indicates stable internal logic rails.

3. Power Module Fault Recovery

eFuse Latch-Off Recovery

The Power Module TPS25980 eFuse may latch OFF under the following fault conditions:

• Overvoltage (OV): Input > 16.9V (OVLO threshold).
• Overcurrent (OC): Output > 7A (ILIM threshold).
• Thermal (TCO F1): TCO opens at 72°C board temperature.

Recovery procedure:

1. Identify and resolve the root fault (e.g., faulty PSE port, overcurrent load, ambient overtemperature).
2. Remove all input sources (PoE cable, USB-C, battery).
3. Wait at least 3 seconds for the input bulk capacitors to fully discharge.
4. Re-apply a single known-good source.
5. The eFuse will re-enable automatically if the input voltage is within the UVLO-OVLO window and no fault condition is present.

⚠️ If the eFuse repeatedly latches, do not continue cycling power. Diagnose with a bench power supply and current meter before reconnecting the system.

4. Future Coupon Access

Any future bring-up or service probe access should be implemented on removable coupons rather than as permanent features on the production boards.

5. TPS25751 PD Profile Field Reprogramming

The TPS25751 (U4) on the Power Module reads its USB-C PD source profile (5V/5A, 25W) from the M24512-RDW6TP EEPROM (U18) at start-up. The profile stored in U18 can be updated in the field via the dual-purpose battery connector J4 (6-pin Molex Micro-Fit 3.0) on the PM board.

⚠️ Factory requirement: U18 must be programmed with the correct PD profile before the PM is installed into a system for the first time. An unprogrammed EEPROM will prevent the TPS25751 from negotiating a PD contract with the CM5, potentially causing CM5 throttling or failure to boot.

How J4 Dual-Purpose Switching Works

J4 carries both SmartBattery and TPS25751 programming traffic on pins 2 and 3, switched by the U19 dual SPDT I2C MUX (74LVC2G3157DP-Q10J). The active path is selected by PROG_EN_N on J4 pin 6:

PROG_EN_N state	J4 pin 6	U19 routing	Result
HIGH (normal)	NC on standard battery cable; 10 kΩ pull-up to 3V3_MAIN holds HIGH	J4 SMBUS_SCL/SDA → I2C-1	Normal SmartBattery operation
LOW (programming)	Programming cable shorts pin 6 to GND	J4 SMBUS_SCL/SDA → TPS25751 I2Ct (0x20)	EEPROM programming mode

A standard battery cable with pin 6 unconnected is completely unaffected.

J4 Connector Pinout (Molex Micro-Fit 3.0, 6-pin, 3.00 mm pitch)

Pin	Signal	Programming cable connection
1	VBATT+	Optional: bench supply V+ for standalone programming (see note below)
2	SMBUS_SCL	I²C adapter SCL
3	SMBUS_SDA	I²C adapter SDA
4	BATT_PRES_N	Leave unconnected
5	VBATT-	Optional: bench supply GND for standalone programming; also I²C adapter GND
6	PROG_EN_N	Short to GND (activates programming path via U19)

Standalone programming: The programming cable may supply power to the PM via pins 1 (VBATT+, 14.4 V nominal) and 5 (VBATT−/GND), allowing EEPROM programming without a running system or J1–J3 connected. When powered this way, the 5V bucks, LDO (U7), and 3V3_MAIN rail all come up normally, enabling U19 and TPS25751 to function.

I2Ct address: 0x20 (fixed by ADCIN1 = 3V3_MAIN, ADCIN2 = GND per TPS25751 datasheet §8.3.6 Table 8-6; see DEC-076).

Required Tools

⚠️ TODO: Software tool and programming cable specification to be confirmed. See .copilot/todos/tps25751-i2c-review.md for investigation notes.

• Software: TI USB-C Configuration Tool (TBD — download from ti.com for TPS25751/TPS25750EVM)
• Hardware: USB-to-I²C adapter compatible with the TI tool (TBD — candidate: Total Phase Aardvark or FT232H-based adapter)
• Cable: Custom 6-pin Micro-Fit 3.0 programming harness with pin 6 shorted to GND (TBD — full specification to be defined once software tool and adapter are confirmed)

Programming Procedure (Placeholder)

⚠️ TODO: Full programming procedure to be documented once tool and cable are confirmed.

1. Prepare the programming cable: 6-pin Micro-Fit 3.0 plug with pin 6 shorted to GND, I²C adapter wired to pins 2 (SCL) and 3 (SDA), GND reference on pin 5.
2. Power the PM board — either via J1–J3 (normal system connection) or via the programming cable itself (bench supply on pins 1 and 5, 14.4 V).
3. Connect the programming cable to J4. Pin 6 LOW → U19 switches SMBUS_SCL/SDA to TPS25751 I2Ct port.
4. Connect the I²C adapter to the host PC.
5. Launch the TI USB-C Configuration Tool on the connected PC.
6. Configure the desired PD source profile (5V/5A fixed source, no battery charger role).
7. Write the configuration to EEPROM via the tool — TPS25751 receives config over I2Ct (0x20) and writes it to U18 via I2Cc.
8. Disconnect the programming cable and refit a standard battery cable (pin 6 = NC → PROG_EN_N returns HIGH → U19 reverts to SmartBattery path).
9. Power-cycle the PM board and verify the CM5 USB-C port negotiates the correct PD contract.

Cross-reference: PM Design_Spec.md §5 (U4/U18/U19 description); DEC-076. Datasheet refs: TPS25751 §8.3.11 Tables 8-4/8-5; M24512 DS6520 §2.3/Table 3; 74LVC2G3157-Q100 Table 10.