Powermatic 3520A Inverter problems

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My guess is some of the power supply capacitors have gone bad. They provide the "oomph" needed under load, and all electrolytic capacitors degrade over time.

Does the following help?
https://www.docgreenwoodturner.com/pmcontrol1.html

For reference, here's how you test capacitors:

• Multimeter (with capacitance measurement, if possible)

• ESR meter (optional but highly recommended for in-depth testing)

• Power supply (for leakage testing, if applicable)

• Oscilloscope (optional, for advanced testing in-circuit)

• Screwdriver/soldering iron (if removing the capacitor from a circuit)

• What to Look For: Check for physical signs of failure:
  

  • Bulging or domed top (indicates internal pressure from gas buildup).

  • Leaking electrolyte (brownish or crusty residue).

  • Cracked or damaged casing.

• Conclusion: If you see any of these, the capacitor is likely bad and should be replaced without further testing.

• Note: This works best for detecting a short or open circuit, not subtle out-of-spec issues. Remove the capacitor from the circuit first to avoid interference.

• Steps:
  

  1. Set your multimeter to continuity mode or resistance (ohms) mode.

  2. Discharge the capacitor by shorting its leads with a resistor (e.g., 1kΩ) or insulated tool to avoid damaging the meter or shocking yourself.

  3. Touch the multimeter probes to the capacitor leads (polarity doesn’t matter for this initial test).

  4. Observe the reading:
     

     • Immediate beep or very low resistance (e.g., <10Ω): The capacitor is shorted and bad.

     • Infinite resistance (open circuit): Could indicate a failed capacitor (open), but electrolytic capacitors should show some charging behavior (see next test).

• Limitation: This doesn’t test capacitance or ESR.

• How It Works: A good electrolytic capacitor will charge up when connected to a multimeter in resistance mode, causing the resistance reading to increase over time.

• Steps:
  

  1. Discharge the capacitor fully.

  2. Set the multimeter to a high resistance range (e.g., 20MΩ).

  3. Connect the probes, respecting polarity (positive to positive lead, negative to negative lead—electrolytic caps are polarized).

  4. Watch the reading:
     

     • Good Capacitor: Resistance starts low and gradually increases to infinity (or very high) as it charges.

     • Bad Capacitor: Resistance stays low (leaky/short) or instantly jumps to infinity (open).

• Limitation: This is qualitative and doesn’t measure actual capacitance or ESR.

• Steps:
  

  1. Discharge the capacitor.

  2. Set the multimeter to capacitance mode.

  3. Connect the probes (mind polarity).

  4. Compare the reading to the capacitor’s rated value (e.g., 100µF, 220µF).

• What to Expect:
  

  • Good Capacitor: Reading should be within ±10-20% of the rated capacitance (tolerance varies by capacitor).

  • Bad Capacitor: Significantly lower capacitance (e.g., 10µF when rated for 100µF) or no reading at all.

• Note: Some cheap multimeters struggle with large electrolytic capacitors or may not detect subtle degradation.

• Why ESR Matters: Equivalent Series Resistance increases as a capacitor degrades, reducing its ability to filter or store charge effectively.

• Steps:
  

  1. Discharge the capacitor.

  2. Connect the ESR meter probes (some meters don’t require polarity).

  3. Measure the ESR and compare it to typical values for that capacitor type/size (charts are available online or in meter manuals).

• What to Expect:
  

  • Good Capacitor: ESR is low (e.g., <1Ω for large caps, <5Ω for smaller ones, depending on specs).

  • Bad Capacitor: ESR is significantly higher than expected.

• Advantage: Can often be done in-circuit if the meter is designed for it.

• Why: Electrolytic capacitors can develop internal leakage current, causing them to fail in high-precision circuits.

• Steps:
  

  1. Discharge the capacitor.

  2. Apply a DC voltage (below the capacitor’s rated voltage, e.g., 10V for a 16V cap) using a power supply with a series resistor (e.g., 100kΩ).

  3. Measure the voltage drop across the resistor with a multimeter to calculate leakage current (I = V/R).

• What to Expect:
  

  • Good Capacitor: Very low leakage (microamps, depending on size).

  • Bad Capacitor: High leakage current (milliamps or more).

• Caution: Other components can interfere, so this is less reliable.

• Steps:
  

  • Use an ESR meter designed for in-circuit testing.

  • Or, use an oscilloscope to check ripple voltage across the capacitor in a working circuit—excessive ripple suggests failure.

• Signs of Failure: High ESR, low capacitance effect, or erratic circuit behavior.

• Safety: Always discharge the capacitor before handling or testing to avoid shocks, especially with large ones.

• Replacement: If you’re unsure and the capacitor is old or suspect, replacing it is often easier than exhaustive testing, especially in critical circuits.

• Context: If it’s in a device showing symptoms (e.g., power supply hum, instability), combine these tests with troubleshooting the system.

If this sounds complicated, it can be if not familiar with the the terms and using mult-meters, o-scopes. etc. In the real world, most just follow the replacement step above, as it's more cost efficient (all this troubleshooting takes time), and it replaces a component that is doomed to fail because of age with a new one.

Added later 16 min 33 s:

Moving this to the Turning forum...