K2 4401 TX problem...

[Steve Banks]

Hi Everyone,

The subject SN 4401 K2 belongs to a new ham, KC0TBO, who recently asked me
to complete and align it since he was moving out of state, and he needed a
hand with it.  The rig was essentially all finished along with its
accessories (KSB2, KAT2, KNB2, KIO2).  It appears to be very carefully
assembled and soldered.

Since I had just completed the A-to-B mods on my own K2 (SN1599), and had
also completed a KX1 (SN267), I gladly agreed to lend him a hand finishing
up his K2.  (My own K2's recent A-to-B upgrades posed a problem or two, as
did its original assembly, but they were minor compared to what I'm seeing
with SN 4401's TX problem.)

THE PROBLEM:  K2 4401's receiver and menu functions all seem to work FB.
CAL FIL, CAL PLL, CAL CUR, etc. all work exactly as expected.  However, the
rig REFUSES to transmit at less than 5.1A of total current draw (and 19.1
watts).  Its 40m TX alignment procedure (p. 75 of the Rev. F manual) fails
totally, since putting the subject K2 in TUNE simply pops 3A and 5A fuses
from my Rigrunner's 13 VDC supply rail where both of my own Elecraft rigs
usually reside.  That 5.1A TX current problem occurs irrespective of where
the K2 POWER control is set (full CCW at the moment).

Scott King and Gary Surrency at Elecraft have offered numerous helpful
suggestions, and several mailings of parts, in an effort to remedy this K2's
TX current draw problem.  What I've done is summarized below.  I hope one of
you will help light my lights before I send the rig off to Elecraft for
repair.  The past several weeks of trouble-shooting on my part have been
fruitless.

THINGS TRIED SO FAR:

1. ON THE RF BOARD"  As a first step, I carefully looked over and reflowed
the Low-Pass Filter toroids, assuming that an open- or short-circuit was
built in somewhere to the RF path to J4.  I found no such problem.  The
toroids all looked fine and reflowing their joints produced no difference in
the TX problem.  I also removed, rewound and reinstalled T1, T2, T3 and T4
at Gary's and Scott's suggestion, thinking that one or more of them had a
damaged winding.  I replaced Q7, Q8, Q11, and Q12, since the incessant 5.1 A
load only showed up in the TUNE mode when the 12V line is applied to the
Power Amplifier.  (I'm pretty sure it will also show up in any other
key-down situation.)

While Q7 and Q8 were removed I also measured the base bias on both of the FA
transistors, substituting a 10-ohm base-pad resistor as a "dummy-base-load,"
again at Gary's suggestion.  Both bias voltages were spot-on measuring 0.63
VDC each in TUNE.)  I'm satisfied now that Q7 and Q8 are not damaged.  I
also replaced C137 and C138 as possible gremlins just in case the TX base
bias had been way too high and was destroying Q7 and Q8.  RFC8 and RFC9 were
also replaced.  Again, no improvement was seen in the TX current problem.

2. ON THE DISPLAY BOARD: I replaced the POWER control pot, on a just-in-case
basis.  I also found and reflowed one or two LCD pins to correct an
intermittent segment on the display mode indicator...no big deal, but it was
easily fixed.

3. On the Control Board I reflowed a number of joints, thinking that maybe
the U6 socket, the MCU, or both, were damaged or open.  I replaced Q11,
thinking maybe it was damaged and failing to offer a proper ISENSE signal to
Pin 2 of the MCU.  But still no difference: 5.1A in the TUNE mode.

4. Both the 8V and 5V regulator outputs were measured.  Results were 8.01
and 4.98 VDC respectively.  The idling (DISPLAY) current in the RX mode
seems fine at 0.22ma with the S-meter in DOT and the LCD backlight turned
off.  That current increases only a few ma with the BAR mode set and the LCD
turned ON.  The BFO delivers a good range of bandwidth at 5.40 KHz.

Sorry for the bandwidth, but if any of you have any suggestions for where
else to look for the 5.1A TX current problem, I'd sure like to hear about
them, either on or off the reflector.

73,

Steve Banks
K0PQ
K2 S/N 1599
KX1 S/N 00267
(and temporary caretaker of K2 4401)










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[Stewart Baker]

Steve,

To me it looks like you have to break into the circuit to find out if the
control loop from VRFDET is working.

A suggestion would be to lift one end of C121 to stop drive to Q6,Q7 and Q8 and
prevent fuse popping. It should then be possible with a small DC voltage via a
pot to simulate the DC generated on the VRFDET line.

If you have a scope you can trace the RF back from Q5 and see why it does not
vary when either the VRFDET voltage or the power control is varied.

Hope this helps. Good luck.

73
Stewart G3RXQ

On Thu, 25 May 2006 10:25:56 -0600, Steve Banks wrote:

> Hi Everyone,
>
> The subject SN 4401 K2 belongs to a new ham, KC0TBO, who recently asked me
> to complete and align it since he was moving out of state, and he needed a
> hand with it.  The rig was essentially all finished along with its
> accessories (KSB2, KAT2, KNB2, KIO2).  It appears to be very carefully
> assembled and soldered.
>
> Since I had just completed the A-to-B mods on my own K2 (SN1599), and had
> also completed a KX1 (SN267), I gladly agreed to lend him a hand finishing
> up his K2.  (My own K2's recent A-to-B upgrades posed a problem or two, as
> did its original assembly, but they were minor compared to what I'm seeing
> with SN 4401's TX problem.)
>
> THE PROBLEM:  K2 4401's receiver and menu functions all seem to work FB.
> CAL FIL, CAL PLL, CAL CUR, etc. all work exactly as expected.  However, the
> rig REFUSES to transmit at less than 5.1A of total current draw (and 19.1
> watts).  Its 40m TX alignment procedure (p. 75 of the Rev. F manual) fails
> totally, since putting the subject K2 in TUNE simply pops 3A and 5A fuses
> from my Rigrunner's 13 VDC supply rail where both of my own Elecraft rigs
> usually reside.  That 5.1A TX current problem occurs irrespective of where
> the K2 POWER control is set (full CCW at the moment).
>
> Scott King and Gary Surrency at Elecraft have offered numerous helpful
> suggestions, and several mailings of parts, in an effort to remedy this K2's
> TX current draw problem.  What I've done is summarized below.  I hope one of
> you will help light my lights before I send the rig off to Elecraft for
> repair.  The past several weeks of trouble-shooting on my part have been
> fruitless.
>
> THINGS TRIED SO FAR:
>
> 1. ON THE RF BOARD"  As a first step, I carefully looked over and reflowed
> the Low-Pass Filter toroids, assuming that an open- or short-circuit was
> built in somewhere to the RF path to J4.  I found no such problem.  The
> toroids all looked fine and reflowing their joints produced no difference in
> the TX problem.  I also removed, rewound and reinstalled T1, T2, T3 and T4
> at Gary's and Scott's suggestion, thinking that one or more of them had a
> damaged winding.  I replaced Q7, Q8, Q11, and Q12, since the incessant 5.1 A
> load only showed up in the TUNE mode when the 12V line is applied to the
> Power Amplifier.  (I'm pretty sure it will also show up in any other
> key-down situation.)
>
> While Q7 and Q8 were removed I also measured the base bias on both of the FA
> transistors, substituting a 10-ohm base-pad resistor as a "dummy-base-load,"
> again at Gary's suggestion.  Both bias voltages were spot-on measuring 0.63
> VDC each in TUNE.)  I'm satisfied now that Q7 and Q8 are not damaged.  I
> also replaced C137 and C138 as possible gremlins just in case the TX base
> bias had been way too high and was destroying Q7 and Q8.  RFC8 and RFC9 were
> also replaced.  Again, no improvement was seen in the TX current problem.
>
> 2. ON THE DISPLAY BOARD: I replaced the POWER control pot, on a just-in-case
> basis.  I also found and reflowed one or two LCD pins to correct an
> intermittent segment on the display mode indicator...no big deal, but it was
> easily fixed.
>
> 3. On the Control Board I reflowed a number of joints, thinking that maybe
> the U6 socket, the MCU, or both, were damaged or open.  I replaced Q11,
> thinking maybe it was damaged and failing to offer a proper ISENSE signal to
> Pin 2 of the MCU.  But still no difference: 5.1A in the TUNE mode.
>
> 4. Both the 8V and 5V regulator outputs were measured.  Results were 8.01
> and 4.98 VDC respectively.  The idling (DISPLAY) current in the RX mode
> seems fine at 0.22ma with the S-meter in DOT and the LCD backlight turned
> off.  That current increases only a few ma with the BAR mode set and the LCD
> turned ON.  The BFO delivers a good range of bandwidth at 5.40 KHz.
>
> Sorry for the bandwidth, but if any of you have any suggestions for where
> else to look for the 5.1A TX current problem, I'd sure like to hear about
> them, either on or off the reflector.
>
> 73,
>
> Steve Banks
> K0PQ
> K2 S/N 1599
> KX1 S/N 00267
> (and temporary caretaker of K2 4401)
>
>
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[Don Wilhelm-3]

Steve,

If I understand correctly, this K2 is transmitting at full power no matter
where the power control pot is set.

This is one of the 2 more difficult areas to troubleshoot in the K2 because
it involves a loop (the other is the PLL/VCO area)

First thing I suggest putting a 20+ watt load on the K2, a 10 amp fuse in
the power supply line, and control transmit with a key rather than TUNE
because you can likely control transmit for shorter periods with a key -
keep the transmissions short while you are testing.

First let me explain the entire loop - The microprocessor knows the setting
of the power knob (if the display changes when the knob is rotated, then the
microprocessor has the proper information);  Starting at the other end, the
output power is returned to the microprocessor on the VRFDET line, and the
microprocessor then compares these two levels and attempts to control the
power out by adjusting V PWR out of the DAC a U8 pin 2 - this signal is
applied to the Keying Waveform shaping circuit U10A and Q8 on the control
board - the output from the Keying Waveshape circuits is the VALC signal
which is applied to the BFO injection into the transmit chain by RF Board
Q24 - the BFO injection level controls the power output.

So -- to troubleshoot, start with VRFDET - easiest way is first to check for
continuity from one end of RF Board R66 to pin 10 of Control Board P4 (the
resistance should be close to zero) - then check the resistance from P4 pin
10 to the microprocessor U6 pin 2 the resistance should be close to 820
ohms).

Next, monitor the voltage at U6 pin 2 during a quick transmit period - if
the RF detector (and its associated resistors) are intact and properly
functioning, you should have a healthy voltage at U6 pin 2 (likely 4 to 5
volts with full power output) - if you get that, VRFDET is OK and you need
to look elsewhere.  OTOH, if the VRFDET voltage is low check RF Board D9 and
its associated resistors for proper soldering, values, etc. (look at the
schematic to identify the components).

Looking elsewhere: the next thing is to check for the presence and level of
V PWR (U8 pin 2) and VALC (Q8 emitter) - if the power out is too high, then
these voltages should be small (the uP should be making them small to
reduced the power) - if they are large (3 to 5 volts), then the uP or DAC is
not doing its job properly, but most likely, the voltage will be correct at
V PWR.  The most likely failure between V PWR and VALC is something
associated with the Keying Waveshape circuit - Control Board U10A and Q8 and
the associated components.  Check especially the components soldered onto
the back of the Control Board (C45 and C46) to be certain they are in the
corect places.

If you find nothing wrong in the above checks, tell us what you found and
perhaps we can provide further guidance.

73,
Don W3FPR


-----Original Message-----

The subject SN 4401 K2 belongs to a new ham, KC0TBO, who recently asked me
to complete and align it since he was moving out of state, and he needed a
hand with it.  The rig was essentially all finished along with its
accessories (KSB2, KAT2, KNB2, KIO2).  It appears to be very carefully
assembled and soldered.

Since I had just completed the A-to-B mods on my own K2 (SN1599), and had
also completed a KX1 (SN267), I gladly agreed to lend him a hand finishing
up his K2.  (My own K2's recent A-to-B upgrades posed a problem or two, as
did its original assembly, but they were minor compared to what I'm seeing
with SN 4401's TX problem.)

THE PROBLEM:  K2 4401's receiver and menu functions all seem to work FB.
CAL FIL, CAL PLL, CAL CUR, etc. all work exactly as expected.  However, the
rig REFUSES to transmit at less than 5.1A of total current draw (and 19.1
watts).  Its 40m TX alignment procedure (p. 75 of the Rev. F manual) fails
totally, since putting the subject K2 in TUNE simply pops 3A and 5A fuses
from my Rigrunner's 13 VDC supply rail where both of my own Elecraft rigs
usually reside.  That 5.1A TX current problem occurs irrespective of where
the K2 POWER control is set (full CCW at the moment).

Scott King and Gary Surrency at Elecraft have offered numerous helpful
suggestions, and several mailings of parts, in an effort to remedy this K2's
TX current draw problem.  What I've done is summarized below.  I hope one of
you will help light my lights before I send the rig off to Elecraft for
repair.  The past several weeks of trouble-shooting on my part have been
fruitless.

THINGS TRIED SO FAR:

1. ON THE RF BOARD"  As a first step, I carefully looked over and reflowed
the Low-Pass Filter toroids, assuming that an open- or short-circuit was
built in somewhere to the RF path to J4.  I found no such problem.  The
toroids all looked fine and reflowing their joints produced no difference in
the TX problem.  I also removed, rewound and reinstalled T1, T2, T3 and T4
at Gary's and Scott's suggestion, thinking that one or more of them had a
damaged winding.  I replaced Q7, Q8, Q11, and Q12, since the incessant 5.1 A
load only showed up in the TUNE mode when the 12V line is applied to the
Power Amplifier.  (I'm pretty sure it will also show up in any other
key-down situation.)

While Q7 and Q8 were removed I also measured the base bias on both of the FA
transistors, substituting a 10-ohm base-pad resistor as a "dummy-base-load,"
again at Gary's suggestion.  Both bias voltages were spot-on measuring 0.63
VDC each in TUNE.)  I'm satisfied now that Q7 and Q8 are not damaged.  I
also replaced C137 and C138 as possible gremlins just in case the TX base
bias had been way too high and was destroying Q7 and Q8.  RFC8 and RFC9 were
also replaced.  Again, no improvement was seen in the TX current problem.

2. ON THE DISPLAY BOARD: I replaced the POWER control pot, on a just-in-case
basis.  I also found and reflowed one or two LCD pins to correct an
intermittent segment on the display mode indicator...no big deal, but it was
easily fixed.

3. On the Control Board I reflowed a number of joints, thinking that maybe
the U6 socket, the MCU, or both, were damaged or open.  I replaced Q11,
thinking maybe it was damaged and failing to offer a proper ISENSE signal to
Pin 2 of the MCU.  But still no difference: 5.1A in the TUNE mode.

4. Both the 8V and 5V regulator outputs were measured.  Results were 8.01
and 4.98 VDC respectively.  The idling (DISPLAY) current in the RX mode
seems fine at 0.22ma with the S-meter in DOT and the LCD backlight turned
off.  That current increases only a few ma with the BAR mode set and the LCD
turned ON.  The BFO delivers a good range of bandwidth at 5.40 KHz.

Sorry for the bandwidth, but if any of you have any suggestions for where
else to look for the 5.1A TX current problem, I'd sure like to hear about
them, either on or off the reflector.

73,

Steve Banks
K0PQ
K2 S/N 1599
KX1 S/N 00267
(and temporary caretaker of K2 4401)


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