I've found the problem. Gary at Elecraft told me that VFRDET (pin 2 of the control board processor) is pulled low, and should be close to 0 volts when in receive - if it's not, the processor will not assert RX. After a couple email exchanges with him, I found that when I had inserted the IC into the socket, pin 1 bent over and shorted with pin 2. Straightening the pin and reinserting the IC solved the problem.
My thanks to Gary, and now I can finish my radio! VRFDET input pin 2 of > the 18C452 is allowed to float, it will not assert the RX pin 28 to 5V > and the 8R line for the RX will remain off. On Mon, 2004-06-14 at 23:34, Brian Mury wrote: > Not sure if my previous email made it to the list - I haven't seen it > yet, and I've had other emails not make it (while some just take a > really long time to show up). > > Anyway, one more bit of data to add. In my previous email I said: > > If I short Q2's collector and emitter to force 8R to 8V, or short Q4's > > source and drain to turn Q2 on and make 8R go to 8V, then the S meter > > starts acting normally, but I get no audio out - so I may have more than > > one problem. /MUTE maybe? I tried monitoring /MUTE with my scope, but > > putting a scope probe on that pin mutes the audio when the receive is on > > - the scope appears to be loading the circuit somehow. Floating pin? > > If I short Q2's collector and emitter, and pull /MUTE high (5V), then > the S meter works *and* I get audio, so it looks like a problem with > both RX and /MUTE not getting asserted properly. > > Once more, any ideas anyone has would be appreciated - I don't know > *why* RX and /MUTE are behaving incorrectly. > > On Mon, 2004-06-14 at 23:28, Brian Mury wrote: > > No replies to this one yet, but I have spent a bit of time looking over > > the schematic and poking around with my DMM & scope. Here's what I've > > found so far: > > > > TX (RD4 on the control board MCU) is normally low, 8T is 0 volts. When > > transmitting, TX goes high, Q3 turns on Q1 and 8T becomes 8 volts. > > > > RX (RD5 on the control board MCU) is normally low, 8R is 0 volts. When > > going into one of the CAL menu items or the ATU menu item, or between CW > > elements when transmitting (see my original message below), RX goes > > high, Q4 turns on Q2 and 8R becomes 8 volts. > > > > I haven't found a description of any of these signals anywhere, but it > > looks like TX and RX are MCU outputs; that TX should be high and 8T > > should be 8V when transmitting; and that RX should be high and 8R should > > be 8V when receiving. Is this correct? > > > > If I short Q2's collector and emitter to force 8R to 8V, or short Q4's > > source and drain to turn Q2 on and make 8R go to 8V, then the S meter > > starts acting normally, but I get no audio out - so I may have more than > > one problem. /MUTE maybe? I tried monitoring /MUTE with my scope, but > > putting a scope probe on that pin mutes the audio when the receive is on > > - the scope appears to be loading the circuit somehow. Floating pin? > > > > Assuming TX and RX are indeed MCU outputs, and that RX does get asserted > > under certain conditions, does this point to a bad MCU? Since RX *does* > > get asserted, I would suspect that it's *not* an issue of something > > pulling it low that shouldn't be. > > > > Any ideas? > > > > > > On Mon, 2004-06-14 at 07:20, Brian Mury wrote: > > > I've just completed part 2 of my K2 RF board. I seem to have a problem > > > on receive. I get no audio, and the S meter is reading maximum. If I > > > select any of the CAL menu items or the ATU menu item, the receiver and > > > S meter work normally. As soon as I exit the menu, it goes back to no > > > audio and the S meter reading max. I can also receive between elements > > > when keying. > > > > > > Anyone have any ideas what to check? -- 73, Brian VE7NGR _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net http://mailman.qth.net/mailman/listinfo/elecraft You must subscribe to post. Subscriber Info (Addr. Change, Unsub etc): http://mailman.qth.net/subscribers.htm Elecraft page: http://www.elecraft.com
