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. 73 Bill, VE2WMA -----Original Message----- From: Don Wilhelm [mailto:w3...@embarqmail.com] Sent: Monday, January 27, 2014 2:58 PM To: William Moore; elecraft@mailman.qth.net Subject: Re: [Elecraft] [K2} K2-100 Test and Alignment Issues Bill, For the J3+ lead, I think the PA transistors may be producing that voltage in response to light shining on them. Shield the transistors from light and see if the voltage changes - if so, ignore it. As for the C1 adjustment - do the following steps in order. Preset R26 and R27 to about mid-range. If you want a closer setting, measure the resistance to ground from the center pin on the pot and set it close to 43k - you can measure from U5 pin 3 and pin 5 for easier access than the actual potentiometer. Balance the wattmeter by adjusting C1 - monitor the voltage at TP4 while sending 40 meter power through the wattmeter. You should be able to obtain a very near zero voltage if all is well. If you cannot obtain a very low voltage, there is a problem with one or more of the following: T4, D16, D17, R28, R29, C95 or C1. Check the windings of T4 first to be certain the correct leads are in the right holes and have been well stripped and tinned (if there is any question, rewind T4 with new wire). Then check the orientation of D16 and D17 against the parts placement diagram at the back of the manual. Be certain all the parts I mentioned are well soldered and there are no solder bridges. T4 does have a 3rd winding, and that is the red wire from the center of the SO-239 jack to the board for T4-6 and the bare wire from the center of the SO-239 to the board hole marked T4-5. Be certain the bare wire is not touching the shell of the SO-239 and was trimmed so it is not grounding against the heatsink. Once you have achieved the balance point for C1, do not change its position. Adjust R26 during a TUNE to indicate the same power on the K2 display as you read on your external wattmeter. Then adjust R27 to the same position as R26 unless you have a load which can produce a known SWR below 2.0:1, in which case you can use that load and adjust R27 until the K2 shows that known SWR. You can initially set R26 and R27 with the low power from the base K2 (do not connect the APP power cable). Later you may want to refine the R26 setting using 80 or 100 watts. Let us know how you make out. 73, Don W3FPR On 1/27/2014 2:02 PM, William Moore wrote: > I am now into the test and alignment phases of my just constructed > KPA-100 amplifier to be integrated into K2 #3842. Right from the start > of this phase, I have run headlong into a two issues I just can't figure out. > > I am constructing from the Revision G September 2010 manual. On the > page 47, the voltage test chart, all measurements are in accordance > with the ranges in the chart except for J3+ lead where instead of 0 > volts, I am reading a stable and consistent 0.044 volts; certainly not > a significant voltage but none the less, it is not zero as called for in the chart. > > The second issue is with reference to the C1 SWR Bridge Null > Adjustment described on page 48. Adjusting C1 varies the power output > reading on the K2 LCD but does not vary the SWR readout....... ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
