[Elecraft] RS232 KPA 100 Problems

[Don Wilhelm]

Andrew,

Check the base K2 first.
First of all, if your K2 is less than SN 3000, you must have the 
sidetone source mod on the Control Board.  It is easy to check - if that 
mod is installed, there will be a wire to P4 pin 1 that you can see 
without removing the Control Board.
Next, check to see if you have sidetone on that K2 - the sidetone source 
must be U8-4.
Also be certain PORT is set to ON in the secondary menu.

Having finished those preliminaries, it is time to drag out the 'scope, 
but first you need some signal source at the RS-232 connection.  It is 
easiest if you use a software application that continuously polls the K2 
in an attempt to connect.  I have the N2PK software which continuously 
tries until it is closed.  HRD tries to connect for a bit and then gives 
up, so your 'scoping time is limited to the time the application tries 
to connect.

What should you see - on the MAX1406 chip pin 6 you should see the input 
RXD signal coming from the computer.  It should swing between more than 
3.5 volts positive to more negative than 3.5 volts.
If that is present, then the input signal is getting to the chip - if 
not, check the inductor RFC7 or the computer cable.
That RXD input signal should result in a signal out of U4 at pin 11 
which has the dame data pattern and swings from 0 volts to +5 volts.  
That same signal should get to the K2 control Board U6 pin 26.

OK, that is the received data part.  Upon receiving data, the transmit 
data should be generated by Control Board U6 and come out at pin 25 with 
a voltage swing between zero and +5 volts.
That signal should make its way to KPA100 U4 pin 12.
The MAX1406 converts the levels to RS-232 and the TXD signal should come 
out of U4 pin 5 with both a negative and positive voltage swing - goes 
through  RFC6 and should be sent on to the computer.

So now you know the 'full story' - good luck with the 'scoping.

73,
Don W3FPR

Andrew UK wrote:
> Hi,
>
> After 3 years I decided to use my RS232 interface, however it does not work,
> I measured the voltages and only had -1 volt on pin 8!!! I thought the Max
> 1406 maybe faulty so change it and also fitted an ic socket, still -1 volt
> and -2.5 with the ic removed. fault traced to C38 it was cracked! replacing
> this I now have -12 Volts. However still no comms. I am using the correct
> elecraft lead.
>
> PC works with an FT847 using a null modem lead so the PC serial port is
> working.
>
> can anyone (Help Don)  give me some guidence to fault find, if I scoped TXD
> going in to the Max 1406 what should I expect?
>
> 73's
>
> Andrew
>   
>