Floor Scraper Won't Start, Won't Move or Keeps Tripping

Most scrapers that seem dead aren't. On a ride-on it's usually a safety interlock, the breaker or the battery plugs. On a walk-behind it's usually the extension cord, a tripped overload or a worn switch. Work through the easy checks before you open anything. This guide uses the National 5700 ride-on, 6280 Commander and 550 walk-behind machines as examples, and references their manuals.^[1][2][3] Check the manual for your model.

Walk-behinds: start with the power supply

An undersized or overlong extension cord starves the motor. It causes no-starts, stalls and tripped breakers. The manuals size cords by supply voltage, total cord length and the machine's maximum amp draw. Here are the rows for a 13A machine on 120V, the 6280 Commander's full-load rating:^[1]

Count every cord in the run, not just the last one. For other machines, look up the amp draw on the nameplate or in the manual and use the full table. A poor-quality outlet can also blow fuses and breakers.^[2] Move to a different outlet or a better circuit.

Walk-behind won't start

Once the cord and outlet check out, work down this list.

Always put the ON/OFF switch in the OFF position before plugging the machine in.^[1]

Motor hums but the machine doesn't run, or breakers keep blowing

On the 6280 Commander, there are three likely causes.^[1]

• Failed isolators. Remove the wheels and bottom cover to inspect them.
• Failed capacitors. Replace them as needed. The 6280 uses a run capacitor (6280-151A) and a start capacitor (6280-151B).
• Dirty motor start switch contacts. Remove the fan cover and fan, then clean the start switch points with an emery board or cloth.

Walk-behind runs but won't move

If the motor runs, the problem is in the drive or the controls.

• Speed control set too slow. Turn the knob counterclockwise until the machine moves forward.
• Wheels not in engage mode. Install the wheel pins.^[1]
• Broken belt or chain. Remove the wheels and bottom cover to inspect, then repair or replace.
• Control handle mechanism failure. Inspect it, then repair or replace.

Rattling, or the motor heating up

The isolators are rubber vibration mounts between the base and the body. The 6280 base uses seven of them (405950, which replaces 70810).^[1]

• Worn isolators and loose fasteners both cause rattling.^[2]
• On the 6280, a hot motor can mean a binding motor shaft. Inspect the isolators, the cutting head bearing and the eccentric.^[1]
• The 6280 schedule calls for inspecting and replacing the isolators and the cutting head bearing every 1,000 hours.^[1]

1. Remove the wheels one at a time and take out the bottom cover bolt behind each wheel.
2. Remove the bottom cover and inspect the isolators from the side for damage or wear.
3. To replace them, remove the side slide weights, side weights and front weight. Loosen the seven socket head cap screws, using locking pliers to grip each isolator.
4. Replace each isolator. Use red threadlocker on the cap screw threads.^[1]

Ride-on won't start

The 5700 has three safety interlocks (seat switch, e-stop and breaker), so check them first, in this order:^[3]

1. Operator properly seated. The seat switch keeps the machine from running without someone in the seat.
2. E-stop twisted up to the "POWER ON" position.
3. 70A circuit breaker in the ON position.
4. 48V blue battery plugs fully connected.
5. Green start button pressed firmly. A partial press may not engage.
6. Wire harness connected.
7. Batteries charged. See Ride-on scraper batteries.

If all of that checks out, the start switch, e-stop contacts, relay or breaker may have failed. Never use the power button or key to control speed; cycling the on/off switch wears out the electrical components early.^[3]

Ride-on runs short or shuts down

Short runs usually point to the battery side.

• The low-voltage alarm sounds at 44V on the 5700, and the machine shuts down at 43.5V. Stop and recharge when it sounds.^[3]
• Shorter runtime than before: check that the charger is charging (it has an indicator LED), that the blue plugs are fully installed, and that the motor fan cover isn't plugged. Blow it out after every job.^[3]

References

1. National 6280 Commander operating and service manual (401891 Rev K)
2. National 550 operating and service manual (401862 Rev J)
3. National 5700 operating and service manual (401809 Rev P)
4. OSHA: Control of Hazardous Energy (Lockout/Tagout)
5. OSHA 29 CFR 1926.417, 1926.404, 1926.416

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