CMM1000 Troubleshooting Guide

Rev. 3 – Dec. 15, 2000

Note:  This guideline is intended to supplement normal service practice with respect to the CMM1000 Cordless Lawnmower.  Prior to performing the actions listed below, please ensure that the mower has been fully inspected for obvious damage or faults.  

CAUTION:	The batteries in the CMM1000 lawnmower contain significant energy, which can generate arcing and/or heating if shorted.  When servicing the unit, keep wiring, metal components, and tools away from the battery terminals.

CAUTION: 	The foam blocks surrounding the batteries are an integral part of the battery containment system.  IT IS IMPERATIVE THAT THE FOAM BLOCKS ARE MAINTAINED IN GOOD CONDITION AND ARE PROPERLY INSTALLED AFTER SERVICE.

General Service Note:

Evidence of the following items can have significant impact on run time and cutting performance:

•	Dull, unbalanced, chipped, bent, or incorrect blade
•	Motor friction which may be caused by stack rub (usually misalignment of motor end cap or insulator ring), misaligned or corroded bearings, fractured or chipped magnets, or other foreign material in the motor
•	Damaged axles or height adjust system which may cause rear end blade drag when mowing  

If any of these issues are found, the problem(s) should be corrected and the mower re-evaluated (except when poor overall condition does not justify refurbishing).

Quick Check for Run Time Complaint:

If the customer indicated complaint is related to short run time, there may be nothing wrong with the mower.  Typically spring or wet conditions result in shorter run time and/or less area of cut due to higher power consumption.   This is normal.  However, in order to rule out blade or charging problems quickly, perform the following quick check.

•	Inspect mower for damage, foreign material build-up in deck, and for damaged, worn, or unbalanced blade.  If blade is not in good shape, replace with a new one before continuing.
•	Carefully rotate blade to check motor.  If blade does not rotate freely or a rubbing or grinding noise is heard, proceed to step 5 “Motor Problems” before continuing.  If blade rotates freely, continue to next step.
•	Plug transformer into wall outlet and then into mower.  If either red or green LED illuminates, transformer is OK, and charging circuit is probably OK.  
•	Leave transformer connected until green LED illuminates, then proceed to step 3 “Run Time Test”

DETAILED TROUBLESHOOTING PROCEDURE

1. Transformer:

The transformer has a 26 VAC nominal AC output voltage with the transformer plugged into the AC mains.

1.	Measure the voltage across the two OUTSIDE pins on the three pin connector. 
2.	The voltage should measure 26 to 30 VAC depending on mains voltage.	

2. Charger:

The charger is a 2 step charger. There are 2 voltage levels output by the charger
A properly working charger connected to a discharged battery will have the red LED illuminated. The red LED is illuminated whenever the battery is drawing more than 0.3  amps of current from the charger.  At this point, the charger is in the bulk charge mode. 

•	The bulk charge voltage  (charging step 1) is set to 29.3 to 29.8V DC when the red LED is illuminated. The actual voltage measured across the battery can be lower than this (as there is current flowing).  The voltage measured across the battery terminals may be anywhere in the range of 19 to 29.8 volts when the red LED is illuminated.

2. CHARGER (cont’d):

As the battery becomes fully charged, the charging current tapers down because the battery can’t accept any more charge current. The CMM1000 charger senses this drop in current and switches the charger to the float voltage (step 2). 

•	The float charge voltage is 27.3 to 27.9V DC with the green LED illuminated .The voltage measured at the battery terminals should be very close to this as there is very little current flowing into the battery (less than 0.3 Amps).

These voltages are measured during the complete battery charge cycle at a temperature of 75’ F.

An “all seems well” service check can be accomplished as follows.   If attached, first disconnect the charger transformer from the charger connector.

1.	To disconnect the charger from the battery circuit, locate the two1/4 inch fast-on (spade) connectors on the component side of the charger.
2.	Carefully lever the connectors off of the terminals with a flat bladed screwdriver. 
3.	Connect a DC voltmeter to the exposed terminals (the negative terminal is closest to the edge of the board).	
4.	Connect the powered transformer to the charger, observe that green LED is illuminated - the open circuit measured voltage should be 27.3 to 28.0 volts.
5.	The bulk voltage measurement requires approximately 300 milliamps of current to flow through the charger to illuminate the red LED.  To accomplish this, either connect an 80 to 90 ohm, 5 watt or greater resistor across the charger terminals or re-connect the battery to the charger. If the red LED illuminates then the charger is outputting a current. The charger has changed from the float to the bulk mode indicating the charger is OK

NOTE: It is possible to measure a voltage anywhere from 19 to 29.7 volts DC with a battery connected and the red LED illuminated. The charging current determines which LED is illuminated and the state of charge of the battery determines what the terminal voltage is. With a battery connected and the green LED illuminated the battery voltage should be between the 27.3 to 28 volts.
If this is the case then the charger is OK. The CMM1000 is a low current charger and charge times of up to 24 hours are not uncommon.

3. Run Time/Battery Capacity

1.	To determine the battery capacity in the CMM1000, it is necessary to run the mower and measure the time it takes to discharge the batteries. Ensure that the battery is fully charged (green LED illuminated). Remove charger transformer from mower.
2.	Check to make sure the blade is securely fastened and that there are no obstructions under the deck. Blade should be in good shape and properly balanced - if not, replace blade with a new one.
3.	Start the mower and secure the bail handle, so the mower can run continuously. Write down the start time of test. Allow the mower to run until the meter on the mower indicates on the black line between the green and yellow areas on the meter (approx. 20.5 V). Note the time and shut mower off. 
4.	If the mower run time is 50 minutes or greater then battery is O.K.  Recharge mower batteries. 
•	If run time is less than 50 minutes but more than 30 minutes, charger is likely OK and batteries are faulty.  Replace batteries, recharge, and re-test.
•	If run time is less than 30 minutes, run a detailed check of transformer (step 1) and charger circuit (step 2).

4) No-Run/No Stop/Key Issues

THE CMM1000 KEY OPERATION IS A ROBUST MECHANICAL INTERLOCK AND DOES NOT INTERFACE WITH ANY DIRECT ELECTRICAL CONNECTIONS.  IN THE EVENT OF CABLE DAMAGE, THE KEY MAY NOT FUNCTION AS INTENDED.  FOLLOW THE STEPS BELOW TO EVALUATE.  

The CMM1000 is equipped with a cable-activated switch under the shroud (on the electronic module) and a bail and lever control on the handlebar. The key actually traps one end of a pivoting lever providing mechanical interlock for switch activation.

Cable Problems:

The most common problem with the switching mechanism is a result of a damaged or corroded cable and/or conduit (the outer sheath).  Typical modes of failure include:

•	Inability or significant difficulty when installing the key.
•	A mower which will start but will not shut off when the bail is released.  In this case, the mower will usually shut off when the key is pulled.

4) No-Run/No Stop/Key Issues (cont’d):

Troubleshooting Procedure:
BEFORE PROCEEDING, ENSURE HANDS AND FEET ARE CLEAR OF THE MOWER AND THE UNDERSIDE OF THE MOWER DECK IS CLEAR OF DEBRIS.

1.	Try inserting key.  If key is not fully insertable, or takes significant effort, proceed to step 2.  If key inserts smoothly, pull bail handle and firmly push lever forward until it snaps into the on position.  If mower doesn’t start, proceed to Section 5 - Module/Battery/Motor Problems.  If mower starts, release bail.  If mower stops, repeat procedure several times.  If mower starts and stops properly, switch and cable assembly are OK.   If mower doesn’t stop when bail is released, pull key.  If mower stops, proceed to step 2. If mower doesn’t stop, allow battery to run down or cut red or black battery lead.  Lower switch is faulty - Replace module and cable.
2.	Check that bail operates smoothly and returns to home position when released.  If OK, proceed to step 3.  If not, check for bail or upper control system damage or contamination. 
3.	Visually inspect the conduit (outer cable cover), especially on mowers which have been return shipped without the proper packaging.  Conduit with kinks, sharp bends, or tears in the vinyl coating should be replaced.
4.	Without inserting key, pull the bail and then move the start lever on the handlebar to it’s full forward position.  The lever should make an audible “click” and then return to the “home” position when released. If the lever does not move smoothly, the cable probably needs to be replaced.  The mower should not start since the key is not installed.
5.	Release the bail.  There should be a distinct snapping sound as the cable and switch return.
6.	Insert key.  If the key does not easily enter the keyhole, visually inspect keyhole.  You should be able to see the full end of the lever.  (If available, look at a known “good” mower first for comparison).  If only a part or none of the lever is visible, it is very likely that the cable is not returning properly and requires replacement.  By not allowing key entry, this design feature prevents the user from operating the machine with a damaged cable.  If this fault is found, replace the cable assembly only - the switch and module are usually OK.
If unsure of correct cable operation, remove the top shroud.  Look for corrosion on the cable where it exits from the conduit.  If corroded, replace. Inspect that the cable is correctly installed and the return spring in the proper position (over the cable between the duck-bill on the switch and the nest on the cable attachment spring).   Ensure that the upper control lever and bail are in the home position and that the key is not installed.  Using your finger(s), grasp the switch lever where the cable is attached and try to pull the cable out further.   If the cable pulls further out, the key will probably now fit in properly.  This indicates that the cable is not returning freely.  Replace the cable.

5.  Module/Battery Problems:

FOR THE FOLLOWING CHECKS, KEEP HANDS AND FEET CLEAR OF DECK IN CASE UNIT STARTS.  AS AN ADDED SAFETY FEATURE, REMOVE BLADE AT THIS TIME   

If upper control switch and cable system appear to be working correctly, but the motor does not start, insert the key, pull bail handle, engage upper switch lever, and perform the following checks:

1.	Measure the battery voltage with a DC voltmeter. (Positive battery lead is the lead connected to the circuit breaker, Negative battery lead is connected to the bolt on the corner of the switch board.)  Attach meter to these two measurement points and, with key installed and bail pulled, engage upper switch lever. If no voltage then the battery is faulty.  If battery voltage drops below 19 volts, the battery or motor is faulty.  Check motor.  If motor OK, battery is faulty.
2.	If battery voltage does not vary then move positive meter lead to the other stud on the circuit breaker. If no battery voltage present then circuit breaker is faulty.  If battery voltage is present on other side of circuit breaker, but the motor does not run and the battery voltage does nor vary, then check voltage across motor brushboxes.  If voltage is present, check the motor and motor/brush interface.  Replace motor or brushes as required. .  If voltage is not present at the brushbox and all procedures above have been performed, the switch is likely faulty.  Replace the electronic module.

6.  MOTOR

Note:  If motor shaft does not rotate freely, check for evidence of severe blade impact.  Inspect blade (large chips, rubs, or bends), lower insulator washer (is it twisted with respect to the blade?), motor shaft (bends), and top end cap (cracked or broken).  Motor damage is often the result of customer induced sudden impact.

Locked Rotor:

If the motor shaft does not turn freely, disassemble motor and inspect.  If magnets are broken and laminations have apparent damage, replace motor.  If magnet(s) are broken or foreign material blocks rotation, but armature appears OK, replace magnet/flux ring or remove foreign material and re-assemble.

6.  MOTOR (cont’d):

Armature Rub:

If the motor shaft rotates freely but a rubbing or scraping noise is heard and/or felt, the motor alignment may have shifted causing armature rub.  It may be possible to correct with the following procedure:

1.	Loosen the nuts on the motor bolts until there is some play in the motor end cap (52).  
2.	Try to shift magnet ring (53) back and forth within insulator (54).  If there is more than approximately 0.010” play between the magnet ring and insulator, replace the insulator with a new one before proceeding with step 3.
3.	Carefully align end cap on magnet ring, ensure motor bolts are as vertical as possible, and gradually tighten motor bolt nuts a little at a time on each side until torqued to spec. (15-18 in-lb.)
4.	Rotate and check for armature rub.  If rub persists, repeat alignment procedure.  If unsuccessful a second time, replace motor.

Motor Brushes:

The brushes in the CMM1000 have very long life.  On rare occasions, one may “hang-up” in the brush box, causing intermittent starts, humming, or no-run.  This can usually be corrected by disassembling, cleaning and replacing the brush assembly.  

If the brushes look burnt or worn without evidence of significant hours of use (typically 250 - 300 hours), check for other problems, which may cause high currents such as very dull or unbalanced blade, motor alignment, bent armature shaft, bad bearing/bushing, or armature rub.  Replace brushes and correct other issues as required.