[Elecraft] [K2] K2-100 Test and Alignment Issues

[Don Wilhelm]

Bill,

Regarding T4, there is one other possibility that I did not mention 
before.  If the direction of the windings is not as shown in the manual, 
it will work "backwards" which may be what you are observing.

As for the minimum voltage of 1.4 volts, that is WAY too high.  The 
bridge should null to less than 14 millivolts with 15 or 20 watts 
flowing through it.

You could do a sanity check on it by attempting to null the bridge by 
monitoring the DC voltage at U5 pin 3 rather than U5 pin 1.  The voltage 
on U5 pin 1 should be the same as at pin 3 if U5 is working OK.
If you still have a high voltage at U5 pin 3, then try doing the balance 
(nulling) while monitoring U5 pin 5.  If you can obtain a null at U5 pin 
5, then for certain T4 is wound in the wrong direction.

73,
Don W3FPR

On 1/30/2014 4:39 PM, William Moore wrote:
> Don and John,
>
> Thank you so much for coming to my aid with these baffling (to me) problems.
> I have undertaken both your suggestions but still, unfortunately, no joy.
>
> The J3+ issue The J3+ lead now gives a voltage reading of -0.225 volts while
> covering the PA transistors with a thick cardboard and a mostly darkened
> room. I can also confirm, absolutely, that no 13.8 volt current has ever
> passed through J3 or the Aux 12 volt line to the K2.
>
> The Wattmeter issue. I reset R26 and 27 to 43K and tried once again to
> balance the wattmeter with C1. Twisting C1 with a plastic handled screw
> driver, I got the voltage at Test Point 4 down to 1.4 volts but I am not
> sure if that is what you mean by "close to 0.0 volts". At the same time,
> glancing at the K2 LCD it still shows a 9.9::1 swr and the watt meter on my
> Kenwood AT-200 antenna tuner bypassed to a dummy load indicates the K2 is
> pumping out a full 15 watts. Varying C1 while looking only at the K2 LCD, I
> can get 1.0::1 SWR but the power out on the LCD registers 0.1 watts while
> the AT-200 wattmeter says the K2 is still pushing 15 watts to the dummy
> load. Varying C1 does not change the 15 watt output on the KAT200 watt
> metre. It always remains at a constant 15 watts.
>
> I then disassembled the KPA-100 circuit board from the heatsink. I checked
> that all the components you listed were the correct values and oriented
> properly i.e., D16 and D17. I checked the solder joints until my eyes
> crossed with a lamp having a magnifying lens in the centre of the
> fluorescent bulb. I found no solder bridges, unsoldered leads or poorly
> soldered solder pads.  I thinks John's problem that he referred to in his
> post was a solder bridge between R24 and R26 but I found this junction was
> clean of any hint of a solder bridge. I found no protruding grounding leads
> anywhere. I am quite sure but, not absolutely sure, that T4 is wound (12
> turns twisted wire counted inside the core), wired and soldered correctly
> with no leads shorting. The T4 solder pads are full with bright silvery
> solder, no craters and the solder flows through the holes to the top of the
> circuit board.
>
> The only variable that I can see left is to pull T4, rewind and reinstall.
> However, before I do this, is there any other measurements, checks or
> procedures that I have overlooked or new ones that can be suggested?
>
> My career background is in the field of business and economics so I kind of
> feel like I am an auto mechanic trying to diagnose and perform surgery on a
> complex cardiology problem. That is to say, I really appreciate your help.
>
>