[Elecraft] [K2] No TX Power Out

[Don Wilhelm]

David,

When making the Transmit Signal Tracing tests, stop at the *first* place 
where the RF voltage is substantially *lower* than the expected value.  
That stage has inadequate output.  In other words, if the transmit mixer 
has low output, one can expect low output at all points in the transmit 
chain beyond the mixer - even though those following stages may be 
working fine.

Since your first failure stage seemed to be the transmit mixer, check 
all components shown around U10 on the schematic.  Be certain you are 
getting enough RF voltage from the VCO to U10 pin 6 (0.5 volts 
minimum).  Additionally, you must have a good signal into U10 pin 1 - 
check the amount of RF voltage at TP2, then both sides of C167 and 
finally U10 pin 1.  There should be only a small dropoff of the BFO 
signal as you progress along that path.  Use the level at TP2 for the 
reference level.

73,
Don W3FPR

David Gilmartin wrote:
> Hi,
>
> This is my second K2 build
>
> Just got to Alignment and Test Part III and can't get RF out.
>
>
>
> Receiver tests OK
>
> Supply is 13.8V
>
> 8V regulator gives 7.59V
>
> 5V regulator gives 4.99V
>
> AGC threshold is 3.6V (highest voltage I can get) - same as first K2  
> built.
>
>
>
> No measurable power out - display says 0.1 W in Tune mode
>
> Indicated current:
>
> 220mA - RX
> 520mA - TX
>
> Indicated Voltage:
>
> 13.4V - RX
> 13.2V - TX
>
> 4.97V on VPWR at pin 2 of U8 with key down
>
> RF detector components and soldering checked OK
>
>
>
>
> Basic Voltage Checks:
>
> D6 anode goes to 240mV on TX
>
> D7 anode goes to  7.49V on TX
>
>
>
>
> I am having difficulty with the Mixer, Buffer, Band Pass Filter, T-R  
> Switch and subsequent tests.
>
> I have built the RF probe and it works OK. All of the measurements for  
> the tests above show a trace of voltage on switching to TX which then  
> disappears.
>
>
>
>
> Problem in the T-R Switch or am I missing something obvious?
>
> Any help appreciated.
>
> David
> EI9EUB
>   
>