[Elecraft] Re: K2 S/N 02676 Hi Current on tune

Sat Dec 14 20:52:01 2002

Hi Bob,

The Gate of Q2 should be zero when the transmitter is on.  If its got a
significant voltage on it, then
Q2 will conduct and turn on the receive path through D3 and D4 which
connects some of the
receiver circuits to the transmitter circuits. Probably not a good thing.

The voltage labeled "8R" is high only during receive. This is controlled by
Q2 on the Controller
Board. On the controller board, check the gate of Q4 to make sure it goes
low during Tune.
Controller Board Q2 (2N3904) should then turn off. The "8R" line is also
pulled to ground during XMIT
by Q23 on the RF card (when "8T" goes high, it turns on Q23.)  (sheet 1,
lower right corner).

The only defective component I found in my K2 was Q2 on the Controller
board. It was shorted, so the
receiver still worked fine. Fortunately I  happened to find it while doing
resistance checks before
turning on the xmitter.

While trying to track down the problem of 8R, you may be able to limit the
overheating by opening
the wire jumper W1 on the RF card (and remove the 160M board if you have it
installed). This will
keep the RF power out of the RX circuit.  Use an ohmmeter to check the
diodes and the transistors
by measuring with the probes in both directions.

73/ Bob - AG5Q

=====================================

----- Original Message -----
From: "Robert C. Abell" <[email protected]>
To: <[email protected]>; <[email protected]>; <[email protected]>
Sent: Saturday, December 14, 2002 4:48 PM
Subject: [Elecraft] Re: K2 S/N 02676 Hi Current on tune

> Don,
> Tnx very much for your input. I have spent the better part of this PM
> looking for shorts in the T.R Switch ccts.,  the Band-Pass,  Low-Pass
> Filter ccts. and RF Output Detector cct., no luck, no obvious shorts.
> I have also discovered that diode D4 also becomes hot, but not as hot as
> D3. 8 volts measured on G of Q2 but becomes unstable after Tune function
> is activated. Go figure??
> Any further suggestions would be REALY appreciated.
> Thanks, Bob VE3XM
>
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