Just to follow up on this for anyone who might be searching the archives, the problem was traced to the power supply. It was undersized and wasn't what everyone remembered it as being, and after being pulled out from under the desk it turned out to be an Astron 20, rather than an Astron 35.
On Mon, 2 Apr 2012, Don Wilhelm wrote: > Hisashi, > > The current indicated by tapping the DISPLAY button is the current drawn by > the base K2, and not the current into the KPA100. Your 2.5 amp current at 10 > watts is normal, as is the drop in current as you go into the KPA100 "is on" > stage because at low KPA100 power levels, the base K2 does not have to drive > the KPA100 very hard. > > I would suggest starting with the DC Diode voltage measurements - use the > values in the new KPA100 manual rather than your printed one - the chart in > your old manual is no longer good. > > Make certain the HV bias supply voltage stays "up to par" during transmit. > > If you have a 'scope, observe the RF output carefully with an eye on the > time-base of the 'scope so you can try to determine the frequency (even if > relevant) of good transmission vs. the frequency when it begins to draw more > current. If it is oscillating, determining the approximate frequency of > oscillation can be helpful. > > This is not an easy thing to troubleshoot, I wish you luck. > > 73, > Don W3FPR > > > On 4/2/2012 9:39 PM, Hisashi T Fujinaka wrote: >> I just installed the KPA100UPKT about a month ago. >> >> Just to be clear, as I turn up the power, the internal metering shows >> 1.5A while the external metering shows the current increasing as the >> power increases. >> >> I'll check the voltages around the diodes and the HV bias supply to >> begin with. Thanks for the pointers. >> >> On Mon, 2 Apr 2012, Don Wilhelm wrote: >> >>> Hisashi, >>> >>> OK, so that sounds like the KPA100 may be oscillating. First things to >>> check >>> are the diodes in the T/R switch, the high voltage bias supply (check >>> during >>> transmit too) and the operation of Q6 and Q7. >>> >>> Is this the newer KPA100 design with blue toroid cores at L16 and RFC1? >>> If >>> not, you will want to install KPA100UPKT, it was designed to combat an >>> oscillation tendency. >>> >>> 73, >>> Don W3FPR >>> >>> On 4/2/2012 8:19 PM, Hisashi T Fujinaka wrote: >>>> After getting the suggestions from Eric and you, I looked at the >>>> metering I have already. >>>> >>>> I don't think it's the SWR bridge because the power reading matches the >>>> wattmeter on my MFJ-1788. It steadily increases and looks about the same >>>> as what the K2 shows. >>>> >>>> However, the voltage/current meter I get to from the DISPLAY button is >>>> odd. As I turn up the power before the KPA100 kicks in, I get an >>>> increasing current up to 2.5. Then the current reading drops to 1.5 and >>>> stays there. The metering of my power supply shows increasing current >>>> and everything resets itself when it gets ~15-20A. >>>> >>>> Time to look for the schematics, but any suggestions would be >>>> appreciated. >>>> >>>> On Mon, 2 Apr 2012, Don Wilhelm wrote: >>>> >>>>> Hisashi, >>>>> >>>>> If by "reset" you mean the power turns off, you are most likely seeing >>>>> the >>>>> internal resettable fuse trip. >>>>> Normally you would see a HiCur message too. >>>>> Usual causes for that behavior are either that the KPA100 wattmeter >>>>> diodes >>>>> have been damaged or you have a damaged PA transistor in the base K2. >>>>> >>>>> Check the actual output power -- >>>>> Connect an external wattmeter between the KPA100 and a dummy load then >>>>> set >>>>> the K2 power knob to about 30 watts. set to CW and hold the key down >>>>> long >>>>> enough to read the external wattmeter. If it shows full power output >>>>> (greater than 100 watts), you have a problem with the wattmeter in the >>>>> KPA100 >>>>> - most likely bad diodes at D16 and D17. >>>>> >>>>> 73, >>>>> Don W3FPR >>>>> >>>>> >>>>> On 4/2/2012 11:37 AM, Hisashi T Fujinaka wrote: >>>>>> OK, it's S/N 4355 with all the latest mods and it used to just reset >>>>>> when I got on 15M phone. Now it's resetting on 30M CW while I'm trying >>>>>> to work DX so it's bugging me. :) >>>>>> >>>>>> Besides the standard checking for 10-year-old cold solder joints, is >>>>>> there anything else to check right away? >>>>>> > -- Hisashi T Fujinaka - ht...@twofifty.com BSEE(6/86) + BSChem(3/95) + BAEnglish(8/95) + MSCS(8/03) + $2.50 = latte ______________________________________________________________ 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
