[Elecraft] Re: K2 Communication Problems

[Don Wilhelm]

Mark,

FB on your readings.  If you have +1.4 volts on U1 pin 12, I would expect
pin 5 to be at +12 volts or above as you indicated ti actually was - BUT -
the thing that puzzles me is why you have only 1.4 volts out of the uP pin
25 when I would expect something closer to 5 volts.  You may want to check
the resistance of the internal TXD line to ground and try to find why this
line is being dragged down.

As for the RXD line, with the input pin from the computer floating (at J1
pin 3), the voltage at U1 pin 11 will not be well defined - it would
normally be either 5 volts or 0 volts (or close to those levels).  If you
connect +12 volts to J1 pin 3, you should see U1 pin 11 go to 0 volts, then
connect -12 volts (from U1 pin 8) to J1 pin 3 and you should see U1 pin 11
go to +5 volts (I may have the high and low states backwards, but in one
case you should have 5 volts and the other you should have 0 volts) - this
simple test indicates that the RXD signal is working through the MAX1406
level conversion IC.

To test TXD, you would have to disconnect the input to U1 pin 12 (you could
do this by removing one wire from the cable inside the K2 at the KIO2 end),
and alternately connect U1 pin 12 to ground and +5 volts while observing the
voltage on J1 pin 2 and seeing it switch from a positive voltage (about 12
volts) to a negative voltage ( between -5 and -12 volts).  If those
conditions are met, the MAX1406 is doing its job properly.

BTW, a Master Reset for this condition will accomplish nothing other than
loosing your filter settings and other data that is stored in the eeprom in
your K2 - so don't do that again for this problem.

Check that you still have PORT ON in the menu after the master reset.

73,
Don W3FPR

> -----Original Message-----
>
> This is for anyone who may be following my previous
> post on this problem.  I took some voltage
> measurements, and I am getting the following KIO2
> readings:
>
>  J1 pin 2= +12.7 Volts
>  U1 pin 11= 0 volts
>  U1 pin 12= +1.4 volts
>
> All other readings are pretty close to the table of
> voltages in the KIO2 manual p. 23.  The two U1
> readings above can be traced back to pins 25 & 26 of
> the MCU on the Control Board.  I have done a hard
> reset of the K2 and stillhave the same readings.  Do I
> have a flakey MCU?  Please help... anybody!!
>
> 73,
> Mark Baugh
> W5EZY
> Grenada MS
>
>