[Elecraft] XV-144 Receiver RF Amp Bias Adjustments

[Don Wilhelm]

Colin,

The XV blinking all the powerbar lights is quite a different problem 
which really has a simple solution (in all cases I have seen it).  In 
some setups, it seems that noise is coupling onto the signal line to the 
firmware IC which triggers that situation (pin 26).  A .001 to .01 uF 
capacitor between the collector and emitter of Front Panel Q2 has cured 
it in all cases I have seen.  You might try adding that capacitor.

Capacitors across a relay coil can also "swallow" the back EMF kick when 
the relay opens.  Note that capacitors C85 and C61 are electrically 
across the coils of both relays (and K1 too).

73,
Don W3FPR

On 8/4/2011 8:36 AM, Colin VE3MSC wrote:
> Ok, I understand what you mean.  I'll open up the XV and compare to
> the schematic, as it shows the D15 across the coil, cathode not to
> D14. But nothing across K7, K6 coils on schematic.
> I've had a problem with output spikes on switching sometimes - power
> meter will show 1 bar for a fraction of a second. Sometimes the XV
> will blink all the powerbar lights and need a reset. Been trying to
> track this down. I slowed my rig QSK to 20ms from 15ms, and that
> helped a lot. Still seeing something not right.
>
> At 08:09 AM 2011-08-04, Don Wilhelm wrote:
>> Colin,
>>
>> No, I mean that D15 would be better connected directly to the coil of K5.
>> Right now, the cathode of D15 is connected to the cathode of D14.
>> You can cut that short trace between the diode cathodes and solder a
>> short jumper from the cathode of  D15 to the K5 coil + side - it
>> will be connected to the right place if you wire to the relay pin
>> (K5 common) just to the right (looking at the bottom side) of the
>> cathode end of D15.
>>
>> In actual practice, it it not critical that the change be made.
>>
>> 73,
>> Don W3FPR
>>
>> On 8/4/2011 7:01 AM, Colin VE3MSC wrote:
>>> Don - do you mean diode across the K6 and K7 relay coil or do you
>>> mean connect at the NO contact of K5 ?  From schematic in Rev E Owner
>>> Manual, it looks like K5 normally open contact provides 12T that
>>> connects to both K6 and K7 coils. The PN2222 preamp + MAR3 are
>>> powered by same 12T, and I expect a negative spike would be bad there.
>>>
>
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