Hi Guys,
As a last resort I am appealing to the "Elecraft collective" to
see if I can get help with this problem.
I have a K1 that has been going great for years , but during a band filter
change it was fired up without the ATU replaced and it fried the output
transistor and D19.(also damaged T4 which has been re-wound....and double
checked since)
I replaced both the output transistor and D19 and it "sort of " went for a
while then decided to die on transmit completely.
I replaced the driver.....no change... Then I started looking with my very
limited quality "scope". I appear to be getting drive through the Transmit
mixer OK, and the buffer stage appears to giving me a 10x increase in drive
level. The signal looks OK until I get to point "TR1" at the junctions of D5
and D14 where it goes into the BPF. There is not much drive appearing at
point "TR2" ....certainly not enough to get the driver excited enough to
work
This problem is common to each band on two different 2 x Band boards, so I
have to presume they are OK.
Because the level drops at point "BPF" on the cct diagram, I immediately
thought there was a problem in the T-R switching circuit.The diodes tested
OK , but to make sure I removed all diodes and they did indeed test fine, so
did the resistances associated with them. Q4 appeared to be doing it's job
OK but I swapped it out for a new one....replaced all the diodes. OP1 still
showed on transmit....nothing on the power meter.
I then decided it might be a lack of drive earlier on so replaced Q5
...still no change....from memory there was about 6v being applied to the
Drain of Q5 from the MCU.
I might be wrong, but I expected to see about the same outputs from the
Mixer/Osc chips U7 and U8.....they are pretty much the same.
The set receives just fine...another reason not to suspect the BPF's. If I
listen to the weak signal that *is* produced, I can peak all the filters on
it while listening to the signal on another receiver.
So...where does one look from here? What is a very basic transmitter circuit
has me bluffed at present...luckily I have little hair left to pull out. Any
Ideas???
Regards.....Ron ZL1TW
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