[K2] Erratic power control with base cw K2

[Alastair Couper]

I have a base K2 sn 1056, with a to b mods, including cw shaping mod, and  
the latest firmware. I have removed all options to ease troubleshooting.  
Turning the power control gives erratic power output, varying widely and  
randomly as I turn the control. If I turn the power control to max, then  
power is also max, but other positions are random. This happens on all  
bands, into 50 ohm load, and also using the antenna tuner option. Max  
power out is normal at about 15w, more or less. The rig works in all other  
aspects. Power supply shows 13.0 to 13.5 while transmitting.

The display info smoothly follows the effects of turning the knob while  
receiving, so the info is making it into the CPU, and the pot is OK. If I  
push TUNE, then the power output level at the watt meter adjusts as I turn  
the control. But the level shown on the watt meter is quite variable with  
regards to the control setting. If I leave the control at half, one push  
of the TUNE will give 15w, and the next push will give 2w. Also the watt  
meter reading jumps to max intermittently as I turn the control back and  
forth from zero to max.

The voltage from VRFDET is making it back to pin 2 of the CPU, and it's  
value reflects the level that I see at the output on the watt meter at  
R66. The voltage at VPWR is erratic when turning the power control, as is  
the voltage at VALC, but those two voltages seem to be about equal, as  
best I can measure. (No scope). The VALC at R98 on the RF board is the  
same as at Q8 on the control board, so that signal is making it. As I turn  
the control in TUNE, I see from around ~.4 volts to ~1.2 volt at 15 watts  
out. Higher voltage on VALC does make more output power, so that potion is  
OK.

If I plug in the KSB2 board, then on SSB I can get what is apparently  
normal smooth power control, but the problem is still there in CW. Initial  
keying sometimes give HiCur readings. So the loop on CW is not working for  
some reason, and I am open to further suggestions.

I have been reading posts about R98, which is at 270 ohms. Not sure if  
that applies here.

tnx,

Al NH7O
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[Don Wilhelm-4]

  Al,

Try it with regular keying - say a string of dots.  The LED bargraph is
a good indicator of the instantaneous power output up to 10 watts - 1
bar per watt.

The power control is intentionally more "sluggish" in TUNE than in
normal keying as an assist to those who use a manual tuner.

The resolution on the 8 bit DAC controlling the VPWR level will produce
about a +/- 0.5 watt variation from the power level that is set.

Moving the power control during a TUNE may produce some slightly erratic
power level changes because there is a lot going on when you turn that knob.

What I am suggesting is that there may be no problem at all - check with
normal CW keying.

73,
Don W3FPR

On 6/27/2011 4:05 AM, Alastair Couper wrote:
> I have a base K2 sn 1056, with a to b mods, including cw shaping mod, and
> the latest firmware. I have removed all options to ease troubleshooting.
> Turning the power control gives erratic power output, varying widely and
> randomly as I turn the control. If I turn the power control to max, then
> power is also max, but other positions are random. This happens on all
> bands, into 50 ohm load, and also using the antenna tuner option. Max
> power out is normal at about 15w, more or less. The rig works in all other
> aspects. Power supply shows 13.0 to 13.5 while transmitting.
>
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[Alastair Couper]

> What I am suggesting is that there may be no problem at all - check with  
> normal CW keying.
>

It's the same in cw as in tune. I can't reliably set the power at any  
place but max. For sure, definitely not normal operation.
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[Don Wilhelm-4]

  Al,

Do you have the KAT2 installed? - you said a "base K2", but some use
that term for any K2/10 without consideration for the options.

If you have the KAT2, disconnect it and run it into a good 50 ohm dummy
load to see if the condition still exists.

If it works smoothly without the KAT2 and badly with the KAT2 installed,
there is something erratic in the KAT2 wattmeter circuit - I would
arbitrarily replace the wattmeter diodes.

Be aware that a bad cable between the K2 and the dummy load could cause
that kind of erratic behavior.  The K2 must properly sense the actual
output power and feed it back to the MCU so that a comparison with the
requested power can be done.

It is also possible that something is awry in the firmware chip.  If you
do not have success, the next thing to try is to write down all the menu
settings (including your filter settings) and do a master reset (hold
the 4, 5, and 6 buttons down while turning on the power).  Yes, you will
have to reenter those menu settings, but it can straighten out problems
that seem to exhibit erratic behavior.  Try removing and re-seating the
MCU before attempting the master reset - any oxidation on the IC pins
should be wiped clean by the re-seating process.

On 6/27/2011 12:09 PM, Alastair Couper wrote:
>
>> What I am suggesting is that there may be no problem at all - check
>> with normal CW keying.
>>
>
> It's the same in cw as in tune. I can't reliably set the power at any
> place but max. For sure, definitely not normal operation.
>
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[Alastair Couper]

Further testing here. I tried  changing the control board MCU to the  
previous firmware version, and no change, so that is ruled out. But... I  
do notice that my keying wave form is not right. The rise time is very  
slow, about 50ms, the falling time is about right. And the keying sounds  
like it, very mushy. So there is something in that circuit, with the  
keying bandwidth mod installed, that has changed.  Probing further...

--
ac
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[Alastair Couper]

That was it. The previous owner had put in the wrong cap in the cw  
bandwidth mod (.047uf instead of .01uf) and that made all the difference.  
Key waveform now good, and power control is stable.

Thanks for the great support effort. It makes all the difference, knowing  
that there is no problem so arcane and buried that it can't be fixed,  
unlike the newer rigs. I certainly learned a bit more about the K2, which  
was the point of all this.

Al NH7O

> Further testing here. I tried  changing the control board MCU to the
> previous firmware version, and no change, so that is ruled out. But...
> I do notice that my keying wave form is not right. The rise time is very
> slow, about 50ms, the falling time is about right. And the keying sounds
> like it, very mushy. So there is something in that circuit, with the
> keying bandwidth mod installed, that has changed.  Probing further...
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[Don Wilhelm-4]

  Al,

With the keying waveshape mod installed, you must use MCU 2.04p/KIO 1.09
or later.  Reverting to an earlier firmware level will cause distorted
keying waveshapes.

In addition to the parts on the Control Board, check RF board C111 (2.2
uF) as well as C168, R98, D36 and R99.

73,
Don W3FPR

On 6/29/2011 12:37 AM, Alastair Couper wrote:
> Further testing here. I tried  changing the control board MCU to the
> previous firmware version, and no change, so that is ruled out. But... I
> do notice that my keying wave form is not right. The rise time is very
> slow, about 50ms, the falling time is about right. And the keying sounds
> like it, very mushy. So there is something in that circuit, with the
> keying bandwidth mod installed, that has changed.  Probing further...
>
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