Checking The Magnetron.5-4 - Furuno 1751 Operator's Manual

5. TROUBLESHOOTING
Checking the Magnetron
7) Poor sensitivity.
• Deteriorated magnetron (V801). Refer to "Checking the Magnetron" (below).
• Detuned MIC (U801).
8) Noise, marks and indications appear but no echo.
• Defective SPU Board (SPU-9046).
• Discontinuity of trigger line.
• Defective MD Board (MD-9052).
• Magnetron heater voltage not applied. Refer to page 6-20.
• Defective magnetron (V801). Refer to next section.
Checking the Magnetron
Fewer echoes appear on the screen when the magnetron has deteriorated. To determine
magnetron suitability, measure the magnetron current. An optional dummy load OP03-55
must be prepared for this measurement. For the location of parts, see Figures 5-2 thru 5-5.
Note that 'TOTAL ON TIME", the number of hours the radar has been operated, appears
on the INSTALLATION menu. See Figure 6-16 on page 6-16. Roughly speaking, the life of
the magnetron is approximately 3000 hours under normal usage.
1. Open the scanner upper housing and fix the stay. Connect the dununy load to circulator
HY801.
2. Connect a multimeter, set to 10 VDC range, to pins #1( +) and #2(-) of TP804 on the MD
Board (MD-9052) in the scanner unit.
3. Once turn off the radar system. Then, turn on DIP Switch SI #4 on the SPU Board inside
the display unit.
4. Operate the radar for transmission on short range, and turn downward auto return switch
SI once. This switch is located on the INTERFACE Board.
5. Confirm that the magnetron current (voltage) is 0.7 to 1.2 VDC.
6. Change the range setting to long range and confirm that the voltage is 1.2 to 1.4 VDC.
7. Turn SI downward once again to stop transmission.
8. Take off the dummy load and the multimeter, and close the scanner upper housing.
If the voltage is far out of the range specified above, the magnetron may be defective.
Be sure to tum off DIP Switch SI #4.
5-4