Re: [Elecraft] K2 RF Board Resistance Checks
David, I was over simplifying when I said voltage. Voltage is important but current plays a huge role too. My DMM's (4 of them, one a Fluke) produce less than 0.6V except on the lowest resistance range. On the highest resistance ranges the voltage is 0.2 V or a bit less. On the lowest resistance range, the voltage increases to over a volt, but it's current limited to less than 1 mA. That's where the d'Arsonval meter movements have trouble. Even the venerable Simpsons need more current to operate the meter mechanism than is safe for the circuit under test with most modern electronics. Junctions will start to turn on at somewhere between 0.2 and 0.6 VDC, depending upon the silicon material used. That's why the readings can be changed greatly by the orientation of the test leads. Ron AC7AC -Original Message- From: David Christ [mailto:radio...@mchsi.com] Sent: Monday, February 21, 2011 2:15 PM To: Ron D'Eau Claire; elecraft@mailman.qth.net Subject: Re: [Elecraft] K2 RF Board Resistance Checks What is the maximum safe voltage? It must be less than 1.5 v as that is what the Simpson and Triplett VOMs use in their lower ranges, but how much less? David K0LUM At 3:47 PM -0800 2/20/11, Ron D'Eau Claire wrote: 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 Good luck! Ron AC7AC __ 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
Re: [Elecraft] K2 RF Board Resistance Checks
What is the maximum safe voltage? It must be less than 1.5 v as that is what the Simpson and Triplett VOMs use in their lower ranges, but how much less? David K0LUM At 3:47 PM -0800 2/20/11, Ron D'Eau Claire wrote: 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 Good luck! Ron AC7AC __ 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
Re: [Elecraft] K2 RF Board Resistance Checks
David, If the voltage is over 0.6 volts, and is applied to the base of a transistor (assuming the emitter is grounded), the transistor will conduct. So my answer it less than 0.6 volts. OTOH, if the voltage is less than 0.3 volts, you will not be able to make diode forward conduction tests with the ohmmeter (those meters will usually have a diode test setting). 73, Don W3FPR On 2/21/2011 5:15 PM, David Christ wrote: What is the maximum safe voltage? It must be less than 1.5 v as that is what the Simpson and Triplett VOMs use in their lower ranges, but how much less? David K0LUM At 3:47 PM -0800 2/20/11, Ron D'Eau Claire wrote: 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 Good luck! Ron AC7AC __ 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
Re: [Elecraft] K2 RF Board Resistance Checks
Al, The first thing to try is reversing your meter leads. Often ohmmeters use a higher voltage which can make some solid state devices conduct. Is the Control Board plugged into the RF Board? If so, remove it and remeasure. Is U8 oriented correctly? How about Q18 and Q19? Check the values of R15 (33 ohms) and R9 (100k ohms) If it still is low, tell us what you found with those checks and ask again. 73, Don W3FPR On 2/20/2011 5:37 PM, Al Gold wrote: 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. __ 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
Re: [Elecraft] K2 RF Board Resistance Checks
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
Re: [Elecraft] K2 RF Board resistance checks - not in spec
I also found pins 29 and 30 (dot/dash) on U6 on the Control Board to have higher than spec resistance, 96.7k and 96.5k respectively. They should be 70-90k. Weird. Steve, KC8QVO -- View this message in context: http://elecraft.365791.n2.nabble.com/K2-RF-Board-resistance-checks-not-in-spec-tp5091997p5095619.html Sent from the [K2] mailing list archive at Nabble.com. __ 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
Re: [Elecraft] K2 RF Board resistance checks - not in spec
Steve, Those resistance readings are too low, and you will have to find the cause. What I believe is happening is that the low resistance on the paddle connections is triggering the circuits to go into a transmit state - and if that happens, the buttons do not work nor will the encoder change frequency. Do you have anything plugged into the key jack? If so, remove it and remeasure. Did you make the measurement after the RF Board and the Control Board had been connected? If so, then those readings are intended to be done on the RF Board alone. If still low, check for solder bridges - check RF Board J8 pins 17 and 18 carefully. If there is a large deposit of solder, wich away the excess. As a last resort, lift one end of R1 and R2 and remeasure the resistance both at the key jack and at J8 pins 17 and 18 - both should be greater than 1 megohm. If the key jack is low, you may have a defective key jack, but if J8 pins 17 and 18 are low, you have a short to another circuit somewhere. Again, examine the soldering carefully. Solder sufficient to only fill the thru-plated hole is all that is necessary. If you have a pile of solder much more than that, wick most all of it away, it is certain to cause trouble. Please understand that I have no idea at this time about your soldering skills (no insult intended), but too much solder and not enough heat are common builder problems - the solder must flow out onto the solder pad and the lead, and excess solder will mask a bad connection. Adjust the soldering station temperature so you can produce a good flow of molten solder in 2 to 3 seconds. 73, Don W3FPR Steve KC8QVO wrote: Here are my out-of-spec measurements. Any ideas? R1 = 96.4k R2 = 96.5k Both should be 1M. Everthing else in the list checks out (well above the lower spec limit). At this point the rig powers up and gives me the 201 message, switches to ELECrAFt, then 7100.00c but the buttons and knobs don't work (the next step is to push the display button to see what the voltage reading is, switch back to VFO, and spin the VFO knob to observe the frequency change - neither the display button or the VFO knob do anything). Steve, KC8QVO __ 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
