[Elecraft] KAT100 signal question

[Jack Brindle]

See notes and questions inside your comments...

On Jul 23, 2005, at 1:10 PM, BobConvers at aol.com wrote:

> This is a new KAT100, just completed and under test.  I have never  
> observed ANY relay action.

What makes you think the box is running at all? What is being  
displayed on the front panel, and does the K2 properly recognize the  
presence of the KAT100? Are there any bus error messages, or have you  
seen any? Also, why do you think the problem is isolated to the  
relays and isn't really seen elsewhere?
To put it another way, what _is_ working?

> RYLOAD remains at 2.25v and bounces a bit each time I adjust, say,   
> ANT1 to ANT2.

Like RYCK and RYDATA, RYLOAD should tend to sit at 0 or +5V. It is  
the slowest changing of the three signals. A voltage of 2.25 volts  
would indicate that it is very rapidly changing and your VOM is  
averaging it to that level, or something is incorrectly connected on  
the board. Again, maybe a bad solder joint, not soldered at all, OR,  
a solder splash causing a short from the RYLOAD line to a signal that  
is normally high (even +5V). If the RYLOAD signal is stuck at one  
level, then the shift registers cannot load the data from the  
controller, and would certainly not work.

> RYCK appears  steady at about zero; and 5Megs to ground with no power.
> U3-3 and U4-4 are always zero, also 5Megs to ground with no power.


> RYDATA (at both U1-17 and U2-3) is interesting - its action varies  
> according to setting of the K2 ATU menu.  When ATU is set to AUTO,  
> adjustment of ANT1 to ANT2 causes RYDATA to switch between zero and  
> 5v.  When ATU is set to C3, for example, RYDATA remains constant at  
> 5v with adjustment of ANT1 to ANT2 (bounces a bit when switching).   
> However, when I powered down, and back up again, I could not always  
> reproduce this exact behavior.
>
> After playing around, I reached an ATU menu condition where I could  
> see a five volt swing as I switched between ANT1 and ANT2.  I  
> looked for a similar swing at U2-18 and U3-3.  There was no  
> corresponding swing, always zero.  Am I correct that the finger of  
> suspicion is beginning to point at U2?

Not really. The evidence is getting stronger for a short between two  
conductors on the board. It is possible that one of the ICs is  
internally shorted causing the problem, but it is more likely that  
the problem is external to the chips. Go back and inspect the board  
with a good magnifying glass, and you might check your solder joints.  
Also, check the MCU (U1) to make sure that all pins are in the socket  
and that none got bent under when installing the chip. Bending pins  
when inserting chips into sockets is way too easy to do, especially  
for 40 pin devices. A bent pin could be shorting against another pin,  
causing conditions similar to what you described.


- Jack Brindle, W6FB
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