National NN-V680W, Service Manual

Page: 18 / 44

7.1. Primary Latch Switch,
Secondary (Secondary Latch
Switch and Power Relay 1)
Interlocks.
1. Unplug the lead connectors to Power Relay 1 and verify
continuity of the power relay 1 1-2 terminals.
2. Unplug lead connectors to Primary Latch Switch and
Secondary Latch Switch.
3. Test the continuity of switches at door opened and closed
positions with ohm meter (low scale).
Normal continuity readings should be as follows.
7.2. Short Switch / Monitor Circuit
1. Unplug lead wires from H. V. Inverter primary terminals.
2. Connect test probes of ohm meter to the disconnected
leads which were connected to H. V. Inverter.
3. Test the continuity of short switch with door opened and
closed positions using lowest scale of the ohm meter.
Normal continuity readings should be as follows.
7.3. Magnetron (NEW H.V.)
Continuity checks can only indicate an open filament or a
shorted magnetron. To diagnose for an open filament or
shorted magnetron.
1. Isolate magnetron from the circuit by disconnecting the
leads.
2. A continuity check across magnetron filament terminals
should indicate one ohm or less.
3. A continuity check between each filament terminal and
magnetron case should read open.
7.4. Membrane key board
(Membrane switch assembly)
Check continuity between switch terminals, by tapping an
appropriate pad on the key board. The contacts assignment of
the respective pads on the key board is as shown in digital
programmer circuit.
7 COMPONENT TEST PROCEDURE
18
NN-V690P / NN-V690PS / NN-V680W / NN-V680WS