[Elecraft] [K2] KPA100 Troubleshooting - SWR high on low bands, Loss of power control

[Bill Coleman]

On Sep 1, 2012, at 9:02 PM, Don Wilhelm <w3fpr at embarqmail.com> wrote:

> Bill,
> 
> I am puzzled why a bad EL5146C would cause an INFO 080 problem. INFO 080 normally is the inability of the MCU to properly communicate with another firmware processor.  While it is entirely possible that the EL5146C was dragging down the output of the +5v regulator and causing the KPA100 firmware IC to fault, but I cannot tell from this distance.

Don, that was exactly the problem. The EL5146C had shorted internally, and was bringing the 78L05 to current limit at about 1 volt.

> As for your wattmeter problems, I suspect that the diodes D16 and D17 may be "half bad".  Yes, that is rare, but possible - they have been damaged enough to change their characteristics but not make them either open or shorted.
> 
> I would recommend arbitrarily replacing them and then try the wattmeter calibration again.
> For initial settings, adjust R26 to produce 43k ohms to ground as measured at U5 pin 5, and R27 to give 43k ohms as measured at U5 pin 3.
> 
> After that do the null adjustment and see what happens.

I have some 1N5711's on order from Mouser. Can I substitute plain silicon or germanium diodes as a temporary diagnostic tool? 1N914, 1N4148, 1N270, 1N4001, 1N4007 are some that I have on hand.