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MFJ-269 Antenna Analyzer.
A solution to the 27.9v problem.

 

This short article is intended to help others who experience the same problem I had with my MFJ-269 Antenna Analyzer.

 - When the unit is switched ON, an internal test is carried out and the battery supply voltage is shown on the display. If the display shows 27.9v  there will also be other problems like.

  •  Give incorrect readings on lower frequencies

  •  No function on higher frequencies

  • High battery consumption

 The problem is caused by a defect driver/buffer transistor (Q15), which is located on the main board.

Remove the main cover and battery box. Locate testpoint T6 on the main board. This is the output from transistor Q15 (BFR106). The voltage at this point should be around 4 volt. If the voltage is higher, around 8 volt, the transistor Q15 is defect. Since the problem with BFR106 seems widely spread the BFR540 was selected as replacement. The BFR540 is higher rated, 20 volt and 120 mA.

Replace the transistor and become a happy user again.

The voltage at T6 should be approx. 4 volt. When Q15 is defect the voltage instead will be around 8 volt. This will cause 100mA to pass resistor R59 below. When Q15 is removed also check that R59 is Ok, value should be 82 ohm.
This is the main board and the location of Q15.

 Good Luck, de SM7DLK, 2007-11-03

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