Sharp SH-920 Instruction Manual page 67

No. Defects Causes
The electro magnetic chuck is
defective.
P.67 OF 70
Remedy
switch is defect.
3. Repair or replace with
new switch
1. Check 2 wires of the
chuck, it must be in short
circuit "OΩ". If not, it
indicates the chuck is
broken. Please repair it.
2. Check each wire with
chuck body (earth), it
must be ∞ Ω. Otherwise,
it means the "insulation" is
bad; dry the coil and
improve its insulation.