OHAUS Defender D15HR, Service Manual

CHAPTER 2  DIAGNOSTIC GUIDE 

2.1 TROUBLESHOOTING 

This section of the manual provides guidelines for evaluating the condition and performance of a 
scale Base, and a standard troubleshooting methodology to follow. 

2.1.1  Checking Load Cells for Trouble 

1. 

Visual Check:

–  Remove the plastic shipping 

tabs from between the upper 
and lower Housings, if present. 

–  Clean the unit before evaluating 

any mechanical problems.  In 
some cases, debris may have 
accumulated inside the Base 
Housing.  Make sure there is no 
buildup of any foreign material. 

Figure 2-1.  Removing plastic shipping tabs. 

–  Examine the Base Housing for dents, bent Platform or signs of physical abuse 

that could cause the Base to malfunction.  Make sure that the proper Platform is 
supplied with the Base. Replace all damaged parts.  See Chapter 5 for parts 
identification. 

–  Remove the Platform from the Base.  Check that the Overload Stops are not 

touching the Top Plate.  (See Figure 5-1, Chapter 5.)  This would restrict 
movement, causing improper operation of the Base.  If the Overload Stops are 
improperly set, adjust them.  (See Section 3.3.) 

–  Check the metal surfaces of the Platform.  All surfaces should be parallel.   

If the platform is deformed, it should be replaced. 

–  Check the cables leading to the Load Cell for cuts, abrasions or other signs of 

excessive wear and tear. 

–  Check for a bent or twisted Load Cell:

Place the top surface and then each of 

the sides of the Load Cell on a flat surface, to see if it rests flat and even. A gap 
indicates a bent or twisted Load Cell. 

–  Examine the Load Cell for corrosion due to high humidity or exposure to 

chemicals. 

–  A Load Cell that is even slightly bent or corroded should be replaced. 

2. 

Perform a Resistance Test

, to determine if the Load Cell is severely damaged or a 

short circuit to the frame has occurred.  (See Chapter 4 for details.) 

3. 

Perform an Output Voltage Test

:

Measure the no load, 50% load and full load 

output.

The reading should meet the Load Cell specifications.  (See Chapter 4.) 

– 

The Load Cell output should be very close to linear over its capacity range.  

Defender™ H-Q-W Series Service Manual

2-1

Ohaus Corporation  www.ohaus.com