Service Home 320V Power Supply (MMPS) - Troubleshooting Guide - CHC - TG0011
Last updated: 01/27/2026

320V Power Supply (MMPS) - Troubleshooting Guide - CHC

TG0011

Overview

The High Voltage Power Supply (MMPS - MINIMILL Power Supply) is the source of power for the servo amplifiers.

It operates with 3 phase 208Vac or 240Vac single phase power. It rectifies the incoming AC power and supplies 320-340Vdc to the servo amplifiers.

The High Voltage Power Supply also contains the regeneration circuit used for dynamic braking.

Types of 320V Power Supplies:
 
  1. 69-2000E  320V Power Supply (Terminal Strip) CHC 
  2. 32-5557 320V Power Supply (Molex Connectors) CHC / NGC
  3. 32-5566 320V Power Supply ( Terminal Strip) CHC / NGC
  4. 32-5566A 320V Power Supply (Terminal Strip with Fuse) CHC / NGC
    Important: Do not discharge the 32-5566A MMPS using a resistor, this will cause the fuse to blow.  Instead wait until the HV led light has turned off.

Electrical Safety

 DANGER: Working with the electrical services required for CNC machines is extremely hazardous and can result in serious injury or death.

Before connecting line wires to the CNC:

  • Turn off all power to the machine at the source.
  • Perform a Lockout-Tagout (LOTO) procedure to ensure the power remains off during service.
  • Verify that power has been disconnected by using an AC voltage detector on all incoming lines.

If you are uncertain about how to safely disconnect power or perform LOTO procedures:

  • Do not proceed.
  • Contact qualified personnel or obtain appropriate assistance before continuing.

Failure to follow these precautions may result in electrical shock, equipment damage, or fatal injury.

 Danger: Before beginning any work inside the control cabinet, verify that the High Voltage indicator light on the 320V Power Supply / Vector Drive has been off for a minimum of five (5) minutes. This waiting period ensures that residual voltage has dissipated and reduces the risk of electric shock.

Certain service procedures involve high-risk electrical components and may pose serious injury or fatality hazards. Technicians must not attempt any procedure unless they have a complete understanding of the steps involved and the associated risks.

If there is any uncertainty regarding a procedure, contact your Haas Factory Outlet (HFO) to arrange for a qualified service technician.

Symptom Table

Symptom Possible Cause Corrective Action
Alarm 648 DC BUS SHORTED Alarm 292 HIGH VOLTAGE POWER SUPPLY FAULT and Alarm 160 LOW INCOMING LINE VOLTAGE There is a problem with the DC Bus or the MMPS is shorted. Compare the measured DC voltage to the Diagnostic page.
Inspect the MMPS for short circuits
Alarm 292 HIGH VOLTAGE POWER SUPPLY FAULT and Alarm 647 REGEN LOAD SHORTED There is a problem with the REGEN or the MMPS is shorted. Measure the resistance across the REGEN load
Inspect the MMPS for short circuits
Alarm 292 HIGH VOLTAGE POWER SUPPLY FAULT and Alarm 119 Over Voltage and Alarm 650 DC Bus Over Voltage There is a problem with the REGEN or the MMPS is faulty. Measure the resistance across the REGEN load.
Incorrect DC Buss Voltage Display on the Gauge The incoming line voltage is low.  Measure the incoming line voltage and determine if is within specification.  For 480V machines check the transformer taps, to make sure they are set to the correct range.
The voltage monitor cable is not plugged in. Use the electrical diagrams to make sure the Vmonitor cable is connected.
The 320V power supply is not putting out the correct voltage signal. The 320V power supply will produce approximately 1VDC for every 100VAC.  If not the drive is defective. 

DC BUS

Corrective Action:

Diagnostic DC Voltage Check

  1. Press the [POWER ON] button.
  2. Measure the DC voltage between pins 1 and 2 of connector J4 on the MMPS.
  3. Compare the measured voltage with the DC VOLTAGE on the diagnostics page on the control. The readings must match +-2%.
  4. Press the [POWER OFF] button.
  5. Disconnect the DC Bus cables from connector J3 on the MMPS.
  6. Press the [POWER ON] button.
  7. Monitor the DC VOLTAGE on the diagnostics page of the control. If the readings do not match, the problem can be:
    • A bad connection on the cable that carries the voltage monitor signal to the controller PCBs. Make sure there is a tight connection on the J6 connector on the MMPS and the P17 connector on the CHC Maincon/Mocon.
    • A faulty MMPS if you have incorrect voltage at P17 on the Maincon/Mocon.
    • A faulty Maincon/Mocon PCB if you have the correct voltage on the cable at the P17 connector of the Maincon/Mocon. There is 0.01 VDC for every 1 VDC Bus. For example, 320 VDC must show 3.2VDC.

Low DC Buss caused by shorted Amplifiers Check

  1. Press the [POWER OFF] button.
  2. Disconnect the DC Bus cables from connector J3 on the MMPS.
  3. Press the [POWER ON] button.
  4. Monitor the DC VOLTAGE on the diagnostics page of the control.
    • If the DC Bus goes back to the nominal value, there is a short in one of the servo amplifiers. A low resistance or a short is a sign of a faulty servo amplifier.
    • If the readings match and the alarm continues, then the problem is a faulty MMPS.

Short Circuit Inspection

Corrective Action:

Inspect the MMPS. Disconnect all cables from the MMPS.

Bridge rectifier to chassis check.

  1. Set your meter to resistance mode (Ohms).
  2. Check terminals 1, 2, and 3 to chassis ground. If the reading does not show an open circuit (O.L) the MMPS is damaged.

Bridge rectifier to DC bus terminal check

  1. Set the meter in diode test mode.
  2. Put the black lead on J3 pin 2. With the red lead, check terminals 1, 2, and 3 of J1.
  3. Wait until the reading on your meter settles. If the meter does not show show an open circuit (O.L) the MMPS is damaged.
  4. Put the black lead on J3 pin 1. With the red lead, check terminals 1, 2 & 3 of J1.
  5. Wait until the reading on your meter settles. If the meter does not show show an open circuit (O.L) the MMPS is damaged.

REGEN Load Inspection

Corrective Action:

REGEN Load Check:

  1. Set the meter to resistance mode (Ohms).
  2. Disconnect the REGEN load from the MMPS from connector J5.
  3. Measure the resistance across the leads. The reading must be between 9.5 and 12.5 ohms. If the REGEN load is within specification, there can be a problem with the MMPS.
  4. Measure the resistance across pins 1 on J3 and pin 3 of J5 of the MMPS. A short is a sign of a faulty MMPS.

Electrical Diagrams

320V Power Supply Diagram (32-5566 / 32-5566A)

320V Power Supply Diagram (32-5557)

320V Power Supply Diagram (69-2000E)