[Elecraft] KPA100 Power Malfunction

[Don Wilhelm]

Ed,

Lack of power control with the KPA100 installed normally points to a 
failure of the KPA100 wattmeter circuit.

Start with replacing the 1N5711 diodes D16 and D17.  It could also be 
that U5 and/or U6 are not performing properly.

If your KPA100 was working at one time and there is *any* possibility 
that you encountered a lightning surge, then D16 and D17 are the most 
likely suspects.

If it has not worked before, look at the soldering (especially U5 and 
U6, check all 6 leads of T4 for proper orientation and tinning - make 
certain the red wire goes through the center of T4 and the bare wire 
from the SO239 jack goes to hole #6.  There are a few other 
possibilities, but those should get you started on the right track.

The bottom line is that the base K2 is not getting a proper indication 
of power output from the KPA100 wattmeter and the base K2 develops full 
output because it thinks the power output is low - in other words, you 
do not have power control.  When you totally remove the amplifier and 
the power control is restored to normal, that indicates that the K2 
power control is functioning and the problem is in the KPA100 wattmeter.

73,
Don W3FPR

eKotz wrote:
> When the KPA100 is not installed, my K2/QRP operates normally.   
> However, with KPA100 installed I have no incremental power control and 
> no lit LEDs on the K2 S/RF meter.
> 
> The SWR is indicated to be 1:1 into an OHR RFL 100 Dummy Load.   "HiCur" 
> does flash on momentarily after switching to the 80 & 40 meter bands.
> I am using my straight key to key the K2... not TUNE.
> 
> First test on 40Mtr band:
> Both Hi Current and Lo Current Power Supplies on:
>    Requested power = .1 to 10w, power to dummy load = 20w
>    Requested power = 11 to 110w, power to load = 110w
> With only Lo Current Power Supply on:
>    Requested power = .1 to 15w, power to load = 10w
> I cycled DC power off/on:
>    Requested power = .1, power to load = .3w
>    Requested power = 10, power to load = 10
> I backed off requested power:
>    Requested power = .1, power to load = 10w
> I turned Hi Current Power Supply on:
> And raised requested power:
>    Requested power = 20w, power to load = 110w
> Then backed off again:
>    Requested power = 9.5w, power to load = 10w
> 
> Band                   Initial                 Power readings after I 
> raised
> (Mtr)                   Power               requested pwr past about 1w.
> (With Hi and Lo Current Power Supplies on:)
> 160-15                 0                      20, 110
> 12, 10                  0                        3, 25
> (With only the Lo Current Power Supply on:)
> 160-15                 0                      10, 10
> 12, 10                  0                         3, 3
> (The lower power readings read when =< 10W requested, the higher power 
> readings read when  > 10W requested and  the Initial Power is what I 
> read just after switching bands)
> 
> "HiCur" does flash on momentarily after switching bands.
> There are no INFO ### messages.
> 
> My equipment for this test: OHR WM-2 (QRP) and Heathkit HM-2140 (QRO) 
> watt meters and OHR RFL 100 and Heathkit Cantenna dummy loads.
> 
> The testing steps during the KPA100 build checked out properly.   I have 
> double checked the solder joints and reworked those that I thought might 
> have been questionable with no change in the (mis)behavior.   I don't 
> know if these findings are of any help to you... I would be glad to 
> supply whatever readings as I may be able.
> 
> Troubleshooting suggestions appreciated!
> 
> Thanks,
> Ed - AD7GR
> K2 #6050
> 
> _______________________________________________
> Elecraft mailing list
> Post to: Elecraft at mailman.qth.net
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft   
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
> 
>