After I got started with good hints from Don and Jack, Gary helped me nail it. Turned out to be bad U2, which I probably zapped with static when installing it.
Symptoms (on a KAT100, new, under construction) were no operation of ANY relay, although the front panel LEDs lit up correctly when switching between ANT1/ANT2 and adjusting power on the K2. A major clue was the 2.5 volts measured on U2, pin 12 (RYLOAD), which as Jack pointed out was not a valid logic level. It should have been zero. At Gary's suggestion, I removed the processor U1 (carefully, using an anti-static wrist strap), bent pin 15 of U1 straight out horizontally, and re-inserted U1 so that pin 15 was no longer connecting the processor to RYLOAD. Voltage on pin 12 of U2 jumped to 4.1 volts, so U1 was OK, trying to pull RYLOAD down - something else was pulling it high. I re-inspected the board with a magnifier and even took some macro digital photos and blew them way up on the computer screen so the pads of U1 and U2 were as big as postcards (I KNEW those 5 megapixels would come in handy). There were no shorts or solder splashes, although left-over rosin looks really gross at that magnification! This meant it was probably one of the 6B595s U2, U3, or U4. I ordered a new 6B595 and asked Lisa and the folks at Elecraft to get it to me overnight to Maryland, which they did. OK, it's probably one of the three 6B595s U2, U3, or U4 - but which one? Gary suggested I check and and see if one of the 6B595s was warmer than the others. I let things run for about 15 minutes and checked - all were cool. NOW what? Then I realized I had forgotten to bend pin 15 of U1 back to its normal position, so U1 hadn't been soaking up electrons, trying to get RYLOAD to ground. I re-inserted U1 in its normal configuration and after only a couple of minutes, U2 was noticeably warmer than the other two chips. I clipped the 20 leads of U2 and fired up the Hakko desoldering pump that people on the list had spoken highly of. Quickly, all 20 holes were sucked clean and the leads fell out, didn't even have to use solder wick. I popped in the new 6B595, fired things up and - klackety klack - SUCCESS! It took a while but, with lots of help, I found the problem and learned a lot in the process. I'm really proud to be part of the great Elecraft community! 73, Bob, WO3E _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
