Open Head Testing
The SI-20KA has a switch that allows it to take readings at high, or even zero AMPs. This allows the user to achieve a '0.0.0' on the Ammeter. To do this, the mag unit needs to be on standby with nothing clamped between the heads, and front panel selector is on the 'Contacts' position. Then push the 'Mag' button 10 times. The final digit should read as zero, or, '0.0.0'.
If the final digit change from zero to some other value, i.e., 0.0.1 (10 AMPs), then there is a short from headstock to frame.