[Elecraft] KAT100 - Reluctant to come on, K2 often displays "not inst"

[Bill Coleman]

OK, a final follow-up on this.

Since the 12CTRL signal resulted in 5V power at the regulator immediately, I racked by brain trying to figure out why The KAT100 would fail to light the LEDs for seconds, sometimes tens of seconds.

I decided the problem might have to do with the U1 clock. I put a scope probe on pins 13 and 14 of U1. While the KAT100 fails, these pins would float up to about 1 volt. When it worked, these pins would be at 0 volts, because the chip is sleeping! (the oscillator doesn’t run while the chip sleeps, to save battery power) So, it looked very much like the oscillator wasn’t starting reliably at power-on.

I hit the Z1 resonator with a heat gun, with no immediate effect. Later I nudged Z1 with a screwdriver, and the KAT100 suddenly came to life. Not sure if I had a bad device, or just a bad solder connection, I re-flowed the solder connections to Z1 and to pins 12-14 of U1, where they connect.

This seemed to work. I let everything cool down overnight, and checked it again in the morning. Oddly, the K2 was giving Info 080 and the KAT100 was failing again! I didn’t have time to diagnose.

Today, however, the K2 powered right up, and the KAT100 snapped to attention, both working flawlessly.

At the moment, I’m going to declare the mystery as being solved, and ignore the transient Info 080 issue. If it crops up again, I think I will replace Z1 on the KAT100. 

> On Aug 21, 2018, at 4:23 PM, Don Wilhelm <donwilh at embarqmail.com> wrote:
> 
> Bill,
> 
> The AUXBUS is NOT at fault.
> The parts to concentrate on are shown in the lower left corner of sheet 2 of the KAT100 manual.  Something there is not working reliably.  My first guess would be Q2, but it could be something else associated.
> 
> That entire powering circuit is controlled only by the 12CTRL signal from the K2.
> 
> 73,
> Don W3FPR
> 
> On 8/19/2018 9:32 PM, Bill Coleman wrote:
>> OK. I could use a little more help with this issue.
>> 
>> Let’s re-cap where we are.
>> 
>> Issue:
>> 
>> KAT100 doesn’t always turn on right away. When it does this, it may or may not switch low/high power LEDs when the power control is rotated. Pressing Ant 1/2 or Tune, the K2 will indicate “not inst”. Sometimes it will power up just fine.
>> 
>> Observations:
>> 
>> - If powered on incorrectly, the KAT100 never “recovers” — if the K2 doesn’t see the KAT100 at power up, it never discovers it.
>> 
>> - Generally fails when unit is cold / not used in a while, will eventually work if turned and left on for several hours, then switched off and back on.
>> 
>> - KAT100 is receiving power before the K2 is switched on. When the K2 is switched on the 12CTRL line on J3 pin 8 comes up immediately, and the 5V output from U8 does as well. So, power is immediately available when the K2 is switched on
>> 
>> - When the KAT100 works, the ANT 1/2 and Low / High Power LEDs light immediately on power-on.
>> 
>> - When the KAT100 fails, the ANT 1/2 and Low / High Power LEDs stay dark for a second or so, sometimes a few seconds
>> 
>> - AUXBUS transitions are coming in on J3 pin 6 and make it all the way to U1 Pin 40.
>> 
>> - I have two different interconnect cables. One is a three-way cable built exactly to the KAT100 specs, complete with jackscrews. The other is a simple two-way cable that connects Pin 1 and Pin 6-9 straight through with no jackscrews. Failure occurs with either cable.
>> 
>> - I have reseated the U1 chip in its socket with no change in behavior.
>> 
>> My current working theory is that there’s something in the KAT100 that prevents the U1 chip from resetting quickly. If it comes up immediately, the LEDs light and the K2 catches the unit during initialization. If its sleepy and doesn’t come up right away, it misses the opportunity to initialize and the K2 doesn’t know it is there. I think the antenna tuner and the low/high power indication are done in two separate initialization steps, because sometimes the KAT100 will respond to turning the power knob, and sometimes it won’t when the Ant 1/2 / Tune always responds with “not inst”.
>> 
>> Nothing else in the K2 apparently suffers from any AUXBUS failures, all the other units - SSB, NB, DSP, KPA100 always come up right away. This makes me think the issue isn’t with the K2, but perhaps with the KAT100 alone.
>> 
>> Anyone have suggestions? I’d really like to make my K2/100 with KAT100 a reliable rig again. I don’t want to have to power it up a day before I want to use it.
>> 
> 

Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
            -- Wilbur Wright, 1901