Unit does not power up

For the Eppendorf 5430, the intermittent startup and missing 5 V rail suggest a fault in the low-voltage power-supply section rather than the incoming 120 V supply. Check the electrolytic capacitors, startup components, regulator, and solder joints around the 5 V supply for deterioration or poor connections. Since the unit involves mains voltage, use the service manual or have a qualified technician perform live-voltage checks before replacing components.

Since you have 120 V reaching the main board but no 5 V output, the fault is likely in the board’s low-voltage power-supply section. The intermittent startup also points to a failing capacitor or another component in the startup/regulation circuit. Check the capacitors, rectifier, and regulator components for signs of failure, but use the Eppendorf 5430 service documentation for the correct test points and voltages. If the 5 V rail remains absent, board-level repair or replacement by a qualified technician would be the safest approach.

Unfortunately, I do not have access to the service manual or board schematics and Eppendorf is less than cooperative. However, based on the issues I have seen with the 5415, I took a stab in the dark and replaced the 2.2uf cap in the power supply circuit and it worked. The system starts right up now. Thank you!