[Elecraft] K2 Saga continues

[Rich Haendel]

This is the continuing story of K2 S/N 4023.  High current ( 5.1 amps on =
all bands)=20
I decided to break the problem down into pieces.=20

1. Receive current all bands, CW mode,   0.22 amps

2. Driver Q6 disabled (disconnected the collector transformer T2, and =
disconnected RFC8 and RFC9 from the bias line coming from Q13 to ground =
so the finals have no bias, but the bases of the finals are at DC ground =
through RFC8 and RFC9.    Total TX current 0.4 amps.=20

3. Reconnected T2 to Q6, but did not connect the secondary terminals to =
the finals, instead I put a 47 ohm 2 watt resistor across T2 , terminals =
3 and 4.   Still no bias on finals.  Total TX current  0.6 amps. I noted =
RF signal on Q6 with my scope.=20

4. Reconnected the  bias for the finals, Q7 and Q8. Still have the 47 =
ohm load on the secondary of T2 as in 3 above.  (finals are not getting =
RF drive) Total TX current 0.64 amps.=20

5. Removed the 47 ohm load from T2, terminals 3 and 4 and connected T2 =
to the final amplifiers,  connected 50 ohm 20 watt load to the K2 RF =
connector. Total TX current 5.1 amps, TOO HIGH.=20

6. Disconnected T4, terminal 3 from going to the LP filters, instead =
connected T4 terminal 3 to a 50 ohm load.  Total TX current 1.8 to 1.9 =
amps tested on all bands.=20

7. Ran short to ground test on all band LP filters, all bands OK, ran =
coil open test on all coils, all coils test OK pad to pad on ckt board.=20
Checked continuity through relays, got 0.2 ohms from pins 4 to pins 7. =
Checked for short on RF connector, no short. checked for continuity from =
pins 4 through relays to 50 ohm load, saw 50 ohm RF load.=20

I did not play with RF detector circuit yet. Will try that next.=20

Anyone with some ideas.?

Rich Haendel W3ACO





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