[Elecraft] K2/100 ATU

[Don Wilhelm]

John,

I suspect that the power scaling for the forward and reflected power 
signals is not working properly.
In high power (during a TUNE) the /FSCL and /RSCL signal go low which 
effectively grounds pins 4 and 2 of RP1 - that creates a voltage divider 
with R6 and R7 so the SWR calculation should be done the same for both 
low and high power.

These signals originate at U3 pin 7 (/FSCL) and pin 6 (/RSCL).  Check 
both with a DVM during a high power TUNE - they both should be near zero 
volts - if not, then U3 may be faulty.

If the voltage is OK during a TUNE, then check the soldering at RP1 pins 
1, 2, 3, and 4.  It is likely that there is an unsoldered (or poorly 
soldered) connection that has taken some time to develop enough 
oxidation to fail to conduct.

As an immediate work-around, turn the power down before doing a TUNE - 
the tuner settings remembered at low power should be the same setting 
that would be used for high power.

73,
Don W3FPR

John Chance-Read wrote:
> Recently I have been using an Orion 1 - I managed to get some nasty volts into it and blew the microprocessor - it has gone for repair back to your side of the world.
>
> I then got out my trusty K2/100 and ATU -  it was working Ok last time I used it - about a year ago.  The ATU now appears to be faulty.
>
> I had put into place current baluns and 10 rings on my 20 ft feeder - I think it should solve my problems with the Orion and I don't think it is the reason why the K2 ATU is faulty
>
> I have a  multi 9 band antenna which is below 3 : 1 on all bands except 20, 12, and 10 metres which are about 8 : 1 using a MFJ 207 
>
> The K2/100 without the ATU is OK on the 6 bands below 3:1, both on Low and High power. 
>
> With the ATU connected on LOW power it tunes all 9 of the bands to 1.1 : 1 except for 17 m which is 1.3 : 1 (a peculiararty with which I'm not concerned)
>
> On HIGH power the ATU tries to TUNE but is unsuccessful on ALL Bands - It indicates High Reflection and sticks in the TUNE position until I depress the button again - this might suggest I still have high voltages around the shack BUT
>
> With the K2/100 and ATU terminated in a quality 500W 50 ohm dummy load using an 18 inch long 50 ohm double sleeved co-ax,  the symtoms are the same - it will tune on LOW power but has exactly the same problems on HIGH in that it fails to tune (allthough it looks as if it tries) and ends up indicating High Reflection and the power is automatically reduced.  
>
> I am deaf so I cannot confirm that the relays are all working - but the fact that it successfully tunes on Low Power suggests all is OK
>
> Would appreciate some pointers as to were I should be looking from the experts on this rig.
>
>   
>