IMPORTANT!!! Please, do not use an analog multimeter for testing resistance unless it is specifically designed for solid state. You didn't say so, but many meters, including those that use a simple 1.5 volt battery for the Ohms tests, can destroy a great deal of the solid state components in your K2!!
The older ohms scales were not current-limited, which means that if you hook up the meter to measure resistance across a transistor junction that is forward-biased, it will often destroy the transistor. That's true of discrete transistors or one of the gates in the many integrated circuits used in your K2. Voltage measurements with such meters may be off too, although it wouldn't produce the sort of errors you saw on AC here. Before the modern DMM's became popular, most lower-cost meters drew significant current from the circuit under test to operate the needle. In high impedance circuits where only tiny currents are flowing, the readings such a meter may give you can be grossly wrong, because the meter itself is loading the circuit. Back then, only more expensive "vacuum-tube voltmeters" provided a sufficiently high input impedance for such measurements. Nowadays, almost any DMM will provide an input impedance in the 10 meghom range, which is pretty standard now. That's high enough for decent accuracy in almost any circuits we'll encounter in our rigs. Old Vacuum Tube Voltmeters (VTVM's) provided an input impedance in that range too, so if you use one of those you will likely get good readings everywhere. But, even the higher-priced VTVM's often used a simple 1.5 volt battery in a fairly high-current ohms measuring circuit that would destroy most transistors and integrated circuits. The only safe way to measure resistance in the K2 is with a meter specifically designed for measuring resistances in solid state circuits. Even then, you may notice your resistance readings vary widely. The minimum values are picked as value above that which any rig will show. You may find too that the resistance will change radically when you reverse the leads, since that will cause any solid state junctions in the circuit to switch on or off. So you resistance measurements are fine and I suspect the voltage measurements is indicating something wrong with the measurement setup rather than the K2 since it seems to be working fine. Ron AC7AC -----Original Message----- Hello. Hot on the heels of my previous report, here comes the next one relating to the first test phase. Executive summary: it works! Unit came up with E10 as expected, display brightness and timeout setting are ok and led shines pretty brightly. Digging a little deeper, however, there are a few details on which I'd like to hear your opinions: -page 26, resistance checks: quite a few of those that had to be greater than 10k gave an infinite reading (U1 pin 2, 6, 7, 9-12 and 15; U3 pin 1 and 8) and some of those that should have been greater than 1k were indeed greater, only very much so! (e.g., U1 pin 4 was 140k). Is that normal? -page 28, ac voltage checks: I'm getting readings in excess of 20V (yes, volts instead of millivolts!). A cursory reexhamination of the boards confirms capacitors' polarities are correct and solder joints appear to be fine (i.e., not always beautiful looking, but reasonably good considering I'm It may be worth mentioning that my friend Nicola IZ4FTB and I were using an AMM (yes, one of those old-fashioned cutie things with the fancy swinging needle ;-) whose battery really should be replaced, fast! Next week, we'll get a DMM and repeat the tests before proceeding further, but in the meanwhile I'd like to hear your thoughts on these issues, especially considering that the little rig that could apparently does and quite fine, thank you! 8-) B73, Andrea. P.S.: pictures will soon appear on my website. _______________________________________________ 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
