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 but 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 test-point 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.

Warning, please note:

I found that Q15 will fail IF an unregulated AC/DC adapter is used and IF there simultaneously is a poor connection in the battery-holder. The voltage from the AC/DC adapter may peak to 16 volt and kill Q15

 Good Luck, de SM7DLK, updated 2020-01-31

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