[Elecraft] K2 #6425 low/no sensitivity - suggestions?

[TF3KX]

PROBLEM SOLVED.

I found a "full size" MC1350 at a local electronics store (the last one they
had, back in old storage...).  Replaced it for the modified SMD-version
MC1350 I had received from Elecraft - and this fixed my sensitivity problem!

I still don't feel comfortable with the low 8V level, but will leave it as
is for now and probably get a replacement regulator when I'm done building
the K2.

Hope others will learn from this.  73 - Kristinn

TF3KX wrote:
> 
> Hi - I am in the process of constructing my K2 and have two problems that
> may or may not be related.
> 
> Problem 1:  Low, almost nonexistent RX sensitivity during Alignment II.  I
> can manage to copy a carrier from my MFJ antenna analyzer and I have used
> this to verify that IF and input circuits are peaked.  Injecting this
> signal into the antenna terminal I can also verify that PRE and ATT work
> as expected, as well as the crystal different filter bandwidths.  Using an
> IF carrier from the MFJ I have poked a low level signal into various parts
> of the IF chain.  An interesting thing is that I hear this signal much
> weaker in the K2 audio when I touch it to the INPUT of IF-amp U12 (MC1350)
> than to its OUTPUT.  In other words, that IF amp does not amplify, but
> rather attenuate the injected signal.  I have re-checked all connections
> around U12, re-flowed the solder, checked T7 and removed the overload
> diodes D40 and D41 - with no improvement.
> 
> Problem 2:  Low 8V regulator output, 7.56V.  As a result I could only
> adjust the U2 pin 5 voltage to 3.60V using R1, in Alignment I.  Probing
> the voltages derived from the 8V supply, they are of course 5-10% lower
> than expected.  All DC voltages on U12 are consequently a little low, but
> otherwise not abnormal.
> 
> I plan to get a local replacement for the 8V regulator, just in case.  But
> does anyone have comments on the low sensitivity?  Would the low 8V level
> be a possible cause for this?
> 
> 73 - Kristinn, TF3KX
> 

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