Fixing my K2 - a repairathon

Somewhen in 2019, I realized a malfunction of my –until then for years flawlessly working- K2/KAT2 + KPA100/KAT100 combo: the rig control had stopped working, and, more severe, the power control (in ssb) seemed to be defective. The KPA made way too much output, therefore my power supply went into protect.

At the same time, I noticed that our club-IC7300 –also located at my station- didn’t communicate anymore with my log program. Hm…?

By trobleshooting the IC-7300 things became clear: it appeared, that most probably a lightning stroke had occured nearby – part of the USB input had „disappeared“: a smd choke had vanished to nothing, and burning marks were clearly visible on the pcb.

So my K2 obviously suffered from the same problem. –The web research made no hope for a quick solution. I tried to track the fault down to a certain module of the K2 by disintegrating and testing part for part against a known-good K2 (borrowed from a friend). –What turned out to be a reasonable, but no real good idea….

Finally, I was optimistic heavin‘ found the culprit: the co-processor on the ssb-module KSB2 seemed to be partially dead, on pin2 (ALC) there was no life anymore. „Fine!“ I thougt. „That was a quick fix!“. Ordering a sparepart from elecraft, my work seemed to be done by now.

When I replaced the defective processor with the new one, things got strange: I re-assembled the rig, but when testing, I found that the fault still persists! –Hours and hours later, I found out that the trouble manifests in an erratic ALC reading; when switching the display from showing the rf output to alc, the alc (in ssb) always shows heavy reaction, 7 or 8 bars always lighted up on transmit.  

From that point on, things even got worse: Now, the borrowed K2 seemed to suffer the same fault! Right after I tried its ssb-module in my K2… WTF!?

At that time, I decided to concentrate my efforts on my own K2 first. I tried to understand the ALC circuit (thanks to the work of Joerg Bartels DK7JB on https://www.bartelsos.de/empfaengerprojekte/experimente-am-k2-mit-baumappe - in German language, p.181ff). Getting more and more desperate, I replaced almost any semiconductor etc. pp. Thanks to Farnell, parts arrived in 24h… Final result: nil.

Once more thinking of a (again) defective processor on the ssb module, I asked my friend Mike DK3CJ for his co-pro from his second KSB2 – and voila! My basic K2 found back to full life again.

Being shure now, that I might have fried both co-pros (mine and from my friends first K2) by false handling etc. (inserting in the opposite direction..?), I ordered two new spare KSB2-controllers.

More than 4 weeks later (thanks to USPS – yes, that USPS, which got in trouble during the last elections…) my mailman finally delivered a package from California. Thankfully, at least he forgot to withheld the import dues :-/

Installing the new processor, things went on exactly like months before. The basic K2 seemed to be healthy again. –Knowing, that the schottky diodes for the power/swr-measurement in the KAT2 are prone to failiure by static I decided to replace them at that time. Afterwards I successfully did the alignment procedure for the swr and power measurement according to the manual.

I put all together (K2, KANT2 and KIOB2) and made a final test.

Guess what happened…

Ohhhhh no…. The nasty, by now, well-known fault (heavy ALC reaction), came up again!!

Some moments later I realized: „ooops, I did it again…!“ –Yes, I fried the next co-pro, next 50 bucks burnt. –But why!? 

Now, it came to my mind, that I always looked at the different modules seperately – but never at the complete K2 at once! So my new assumtion was, that something „outside“ the basic K2 every time killed the ssb co-pro!

For verification of my new hypothesis I disconnected my K2 from anything outside, installed the second of the two ordered processors, and, crossing fingers, tongue at the right angle, switched on the rig – the error was gone, the K2 worked! Conclusio: something on the KAT2 or the KIO2 kills, when attached, the processor.

With this assumption, I measured all the voltages at the processor socket – with and without KAT2 and KIO2 attached. And, at the end, it turned out, that when the I/O-module KIOB2 was attached, I measured a voltage level of 12V at pin 2 (ALC...) at the co-pro socket! This is, of course, WAY BEYOND the allowed voltage level of any processor i/o pin.

What had happened? –Well, the 12V is power supply for the I/O-board, coming from control pcb. At this point I started a visual inspection oft he KIO2.

And than it caught my eye.

Pins 7 and 8 of a 10-pin header had become shorted by a soldering tin connection, thin as a hair! Probably by electric arc, tin had gone molted, resulting in this short. Pin 7 is the ALC-line, and pin 8...well, make an educated guess ;-).. Pin 8 is 12V. BINGO!

Thinking backwards, this explains all. First, there was this short caused by arcing. Original co-pro killed. Then I destroyed the next co-pros every time I assembled the K2 and attached the faulty KIO2 again. Arghhh…-

Some lessons to be learned:

Always look to a faulty system in general! Never assume anything that is not clearly and undoubtly proven. –Never rely on USPS first class mail when you need parts fast. Use at least USPS International priority shipping or UPS, no matter what it costs…

Some weeks later, final replacements for the ssb-board controllers have arrived and the second K2 has been completed again. After complete alignment, both transceivers work fine again, giving me the fun of making some very nice contacts again. Yippie! -But, there was one more issue I had to deal with: when trying to connect my log program (UCX-Log, highly recommended!) to the trx, nothing happend...  Again, I made a false assumption; thinking of a defective MAX1406 (TTL<>RS-232), I replaced the IC (the two chockes in the rx/tx line were fine, so I thought this must be the only option). Nothing happened - I missed a tiny choke in the ground connection, which was faulty...