Al, first check the resistance with your DMM leads reversed. Some DMMs apply enough voltage that gates in the i.c.s start to conduct, giving you an abnormally low reading.
I trust you are using a DMM and not a VOM (like the old Simpsons, etc. - just about anything with a "wiggly needle" meter ;-) All of the older meters applied a dangerous amount of voltage to the circuit for today's solid state components. If you have access to a second DMM, try it and see what it says. Finally set your DMM for a fixed range that will let you see 100 Ohms rather than allowing it to "auto-range". The amount of voltage applied to the circuit varies with the range and that can produce strange results with some DMMs. U6 pin 8 on the RF board tests the 8V power bus for shorts. If you get the same results after reversing your DMM leads or (if possible) using another DMM, it's time to look for mistakes. That bus comes from voltage regulator U8 and serves Op Amp U6 (where you are checking), the VFO and the thermister board (see the schematic in your book K2 RF Board sheet 1 in Appendix A). It also passes through a choke to become bus 8A but that goes directly off the Control Board via J7, and at this point the Control Board should not be plugged in. Check for any problem (solder bridge, etc.) at the J7 connection to the board. Hopefully this will get you launched in the right direction. Our resident Guru who has built and serviced countless K2's is probably contesting or recuperating. I'm sure he'll pop up soon if you have more questions. I and many other "solder jockeys" here will be glad to fill in as best we can. Good luck! Ron AC7AC -----Original Message----- From: elecraft-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Al Gold Sent: Sunday, February 20, 2011 2:38 PM To: elecraft@mailman.qth.net Subject: [Elecraft] K2 RF Board Resistance Checks Hi All, I have a partially built K2 circa serial number 5000 and have completed Assembly Stage II of the RF Board. All of the resistance numbers are fine with the exception of U6 Pin 8 which reads 42.5 ohms and should be greater than 100 ohms. I have checked everything on the board visually for two days and checked the resistances of the resistors to no avail. No shorts, no cold solder joints, no unsoldered pins. I have seen in the archives where many people have had this same problem, but I have not found one with an actual solution to the problem. If there is anyone out there that has fixed their resistance problem on U6 can you please let me know what your solution was. Thanks and 73's, Allan KB1CLB ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
