Rakentelu Foorumi

Hi Jarno,

Do not operate the rig at high power at all, or at QRP levels for more than a few seconds until this problem is solved, or you may damage the PA transistors in the K2 or the KPA100.


First remove both the KAT100 (if you have that option too), and the KPA100 to see if the basic K2 is OK.

If the antenna was left connected when there was a thunderstorm nearby, lightning can damage the 1N5711 diodes in the KAT100 and/or KPA100 SWR sensors. Your big windstorm and the spark likely caused the damage. Please be sure to disconnect the antenna and the power supply if you will not be using the rig and if there is a chance of storms in the area. Try to use a DC grounded antenna too. Lightning protection and antistatic devices on the feedine or antenna just cannot protect 100% against damage.

If the diodes are OK, there should be about 98-100K ohms between their cathodes and ground when tested with an ohmmeter. You can do this at the side of the trimmer pots that connect to the diodes too. Connect the postive ohmmeter lead to the cathode, and the negative lead to a ground point on the tuner.

Then, if your meter has a diode test funtion, there should be about 0.38 to 0.40VDC of diode drop across the 1N5711 diodes, with the + lead to anode, - lead to the cathode.

If the diodes are damaged, it is easier to remove them without damaging the PCB by clipping one lead. You will need to remove the hex spacers, the screws in Q1-Q4, the 3 screws across the rear panel that go into the heat sink, and unsolder the wires to the speaker at its terminals. When the heat sink is taken off, use care to not damage or lose the thermal pads on Q1-Q4. The thermal pads on Q1, Q2 may be reused as long as most of the black coating remains in place, and the pads are reinstalled in their original positions.

If you do not have any 1N5711 diodes and cannot get them locally, 1N34A or similar diodes may be used temporarily. But do order the correct resistors when possible. Order by sending an email to parts@elecraft.com, and get a few spares in case you need them in the future.

When done with the repairs, check to see if the alignment and calibration of the null cap, FWD and REFL cal pots still check out OK. You must be able to get a low SWR null voltage at TP4 of about 10 millivolt or less when a good 50 ohm dummy load is connected to the antenna jack as directly as possible. Redo the FWD and REFL cal pot settings if necessary, using an external wattmeter to calibrate FWD pot R25, and then set REFL pot R26 to about the same setting.



Note that the mounting screws in PA transistors Q1, Q2 may need to be retightened after the rig is operated for a short time, and after the PA heat sink has cooled down. Do not overtighten the screws in Q3, Q4 however, or you may crack and damage their plastic case.

Never transmit with the heat sink left off of the K2 or the KPA100, or the PA transistors will be damaged.

--
73, Gary AB7MY
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gary@elecraft.com
Elecraft Technical Support

Poistin diodit ja edelleen ohmit ei näytä niinkuin pitäisi.
Diodien poiston jälkeen:
D17 85,5 kohm
D16 90,7 kohm