[Elecraft] K2 receive problem

[Brian Mury]

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