Martel Electronics 235 - Manual (Page 84)

mA/V Module Service Information
The module contains a single 2AG 1/4A fuse in the milliamp output
circuitry. To determine if the fuse is blown, measure the voltage from
the milliamp positive (red) terminal to the volts negative (black)
terminal. A reading of 12V indicates that the fuse is good. To replace
the fuse, the module should be unplugged from the calibrator and
opened by removing the two screws in the case and separating the
halves.
The module is powered from the calibrator, therefore there are no
battery service requirements.
Service Information
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