What the 4152 alarm means

The main-circuit power relay was detected welded (contacts stuck closed) after a power system overcurrent event; the controller cannot safely disconnect motor power. This fault appears in a large share of our Epson RC90 / RC700 (EPSON RC+) service tickets, and the first round of on-site checks usually finds the source.

Most common causes

  • Overcurrent event welded the relay contacts
  • Repeated e-stop under heavy load
  • Aging relay
  • Short downstream that the relay interrupted
Field note: Most of the time the problem is the first item on the list, so ruling it out saves you half the time.

Step-by-step field fix

  1. Power down completely and verify with a meter that motor power is actually off
  2. Find and clear the overcurrent cause (short, seized motor, drive fault)
  3. The controller must be replaced (main-circuit relay is internal) — do not keep running with a welded power relay
  4. Inspect downstream wiring for damage from the overcurrent
  5. After replacement, run a full E-stop functional test
Safety first: For EPSON 4152, this alarm family involves the DC bus, which sits at several hundred volts and stays charged for minutes after power-off - touching terminals is a shock hazard. On site you may not carry out the first step yourself: Power down completely and verify with a meter that motor power is actually off. Beyond that it is the DC bus and power stage work - leave it to a professional. On EPSON 4152: checking incoming voltage at the disconnect and looking at breakers and fuses is fine to do yourself; opening the cabinet to touch bus terminals or pulling power modules needs a qualified electrician.

How we diagnose drive alarms on site

EPSON 4152 belongs to the drive & power stage family. On EPSON 4152 the failing stage is drive units integrated in the controller cabinet, per axis on the RC700-A / RC90-B and the RC series - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading EPSON 4152 at the EPSON RC+ error list and controller front-panel indicators; codes segment as 4xxx / 5xxx / 9xxx.

The chain involved in EPSON 4152 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

Overcurrent event welded the relay contacts is common on EPSON 4152, but look at the duty cycle: Cells with high-inertia loads or frequent start-stop cycles return far more regenerative energy than a plain transfer cell, and the braking resistor lives in a hot cycle that shortens its life. When we suspect this family we ask what changed: if the takt was raised recently or a heavier fixture went on, the alarm cluster usually lines up with that process change. Replacing the resistor alone will not fix it - the chopper rating and resistor wattage have to be re-checked against the new duty.

Field notes on this page cover EPSON 4152 (Relay Welding Error of Main Circuit); written by the Henghuan repair team, updated 2026-10-01.

Not sure? Don't force it — contact an engineer

Send the alarm code, the robot model and a description of what was happening at the alarm. Our engineers handle EPSON 4152 every day, and remote diagnosis by phone/video is free.

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Related Drive & Power Stage alarms

4154 — Regeneration Resistor Overtemperature 5040 — Motor Torque Output Failure — High Power State 5048 — Overvoltage of Main Power Circuit 5049 — Overcurrent of Motor Driver 5054 — Motor Overload (Duty)
Same family: this code belongs to the Drive & power stage alarms family - the page collects all Drive & power stage-family codes we have handled, with the common inspection order and spares.
Other brands: we also keep field-fix libraries for Nachi · Omron · ESTUN and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the EPSON 4152 alarm mean?

The main-circuit power relay was detected welded (contacts stuck closed) after a power system overcurrent event; the controller cannot safely disconnect motor power. This fault appears in a large share of our Epson RC90 / RC700 (EPSON RC+) service tickets, and the first round of on-site checks usually finds the source. EPSON 4152 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Overcurrent event welded the relay contacts".

QCan I clear a EPSON 4152 alarm myself?

Whether EPSON 4152 clears on its own depends on the outcome of "Power down completely and verify with a meter that motor power is actually off". Finish the flow with "After replacement, run a full E-stop functional test" to confirm EPSON 4152 - do not skip it. If that step is clean, the second most frequent cause on EPSON 4152 is "Repeated e-stop under heavy load". If EPSON 4152 returns after two clears, or the checks point at Overcurrent event welded the relay contacts, stop the cell and call a professional robot repair engineer.

QFor drive/power alarms like EPSON 4152, what spares do you bring on site?

The commonest causes we see on EPSON 4152 are "Overcurrent event welded the relay contacts, Repeated e-stop under heavy load, Aging relay", so we stock the van against those. For EPSON 4152 specifically, we stock the van along the energy chain: braking resistors, bus capacitors, input fuses, drive-board supply parts and the common power modules for the brand. For EPSON 4152, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what EPSON 4152 shows on the EPSON RC+ error list and controller front-panel indicators; codes segment as 4xxx / 5xxx / 9xxx and what the machine was doing - phone or video triage is free.

The content on EPSON 4152 was written by Henghuan Robotics service engineers from hands-on repair experience. Alarm descriptions are our own reference summary and may differ by controller or software version — defer to Epson documentation, or contact us to confirm. Henghuan is an independent service provider with no affiliation or endorsement by Epson.