[Elecraft] KPA100 U6 voltage issue

[Don Wilhelm]

Cathy,

Are you saying that with the KPA100 connected to the base K2, you have 
17 volts on U6 pin 6, but with it still connected to the base K2, you 
have a lower voltage at RF board D9?  Check the voltage at both ends of 
RF board R66 -  If the highest voltage there does not match the reading 
at KPA100 U6 pin 6, there is a discontinuity somewhere.
I can't think of any way you could actually have 17 volts on U6 pin 6 - 
maybe 12 volts or even up to 15, but that is a strange voltage.
During receive that voltage should be very close to zero.
First make certain all the pins on U6 are soldered.
Then measure U6 pin 7 and pin 8.  Both should be at 5 volts.
If you really have 17 volts (actually anything more than 5 volts) at U6 
pin 6, there is no way that U6 could be generating that voltage. It has 
to be coming from a source outside U6 (although the 17 volts may have 
damaged U6).

Check the KPA100 carefully with a magnifier for solder bridges, 
especially on the pins of P1 (12CTRL is adjacent to VRFDET).
Check the orientation of diodes D1 thru D8 - especially D6 - all the 
cathodes should point in the same direction.

Do you have the ribbon cable oriented in the proper direction - from P1, 
the cable should extend over the front edge of the KPA100 - it it is the 
other way around, swap the ends of the cable with each other.

If you have the KSB2 option or the K60XV option installed, try removing 
both those options and check again.  Other than the MCU and D9 in the 
base K2, those are the only places you will find the VRFDET line.

73,
Don W3FPR

On 6/27/2015 2:10 PM, Catherine James wrote:
> I recently began building a just-purchased KPA100 kit for my K2 #5191.  All was well until I reached the voltage checkpoints on page 26.
>
> U5 pin 1 is 0.8 volts (not 0 to 0.1)
> U5 pin 7 is 0.9 V (not 0 to 0.1)
> U6 pin 6 is 17 volts (not 0 to 0.5)
> I am much more concerned about U6, but perhaps the U5 voltages give you more information.
>
> The K2 appears to work fine with the partially built KPA100 disconnected. Voltages on D9 of the K2 RF board (my proxy for V RFDET) are much lower than 17 volts (kpa100 not connected) so the high voltage appears to come from the KPA100, not the K2.
>
> I have the KSB2 installed, but haven't explored that its voltages, and haven't tested whether it still works following the "17 volt incident".
>
> I don't see any obvious solder bridges on the KPA100.
>
> Where would voltages near 17 volts normally be found on the KPA100 board?
>