[Elecraft] K1 minor stumbling block...

Wed Jul 1 21:10:19 EDT 2009

Anthony,

There is nothing wrong with the resistance readings.  Yes, greater than 
means just that, and it can be much greater than.  Different DMMs will 
indicate different values for very high resistance, and the value marked 
in the manuals as 'greater then' is intended to address these differences.

OTOH, your voltage readings do indicate some problem.
P1 pin 15 is the 6B voltage rail and should have the same voltage as the 
output of U6 - check it there.  If the output of U6 is less than 6 
volts, check the input which should be 8 volts.
If the input to U6 is OK, then you either have a soldering problem, or 
there is a short somewhere on the 6B voltage rail - look for solder 
bridges all along the path - consult the schematic to see where all the 
points that connect to 6B are located - check them all.
BUT
Before checking the 6B voltage rail, resolve the problem with the 
voltage to U3 pin 6.  This is the voltage to the LM386 and until that is 
normal, none of the other voltages at U6 will be correct.  Again, this 
is a voltage rail, so either the driving device (U5) is not working 
correctly, or there is a short on the 8V voltage rail somewhere.  Check 
the voltages at the source - U5 output pin should be at 8 volts, and the 
input pin should have about 12 volts on it.  Is U5 getting hot - if so, 
suspect a short at its output (anywhere on the 8V voltage rail - use the 
schematic to see what all connects to it), but if it is not getting hot, 
look first for a solder connection problem.  Reheat the solder 
connections using a hot soldering iron (700 to 750 deg F).  Make certain 
the solder has flowed out onto the solder pads such that the edge of the 
solder is an almost invisible line.  If you can easily discern the edge 
of the solder, the soldering pad did not receive enough heat.

In my years of repair experience, soldering is the most common builder 
failure, followed closely by poorly tinned toroid leads.  It seems that 
many builders are afraid to apply adequate heat, specially to the solder 
pads and the soldering looks like a ball sitting on the pad.  Inadequate 
heat also leads to too much solder applied for some reason or another 
that I have not yet figured out.  Elecraft uses thru-plated holes, and 
750 degrees applied for up to 5 or 10 seconds will not lift a pad, and 
modern thru-hole components are designed to withstand soldering 
temperatures for up to 10 seconds as well.  It takes both heat and time 
to damage either the board or the components.  A normal solder 
connection will flow solder in the 2 to 3 second range.  If your solder 
flows in less than 2 seconds, the iron is too hot, but if it takes more 
than 3 seconds for the solder to flow, the iron is too cold.

73,
Don W3FPR

Anthony Hardwick wrote:
> Hello,
>
> I am building my K1, and have completed the first section of the  
> build, and am at the DC Voltage check  stage on page 30 of the  
> manual.  While the unit seems to have passed the actual "smoke test"  
> aspect of the initial application of 13.1V of DC power, I am getting  
> 0V DC readings at P1 pin 15, and also U3 pin 6.  Furthermore, U3 pin 5  
> only reads .015V DC, rather than 3.8 - 4.2
>
> In chart form as the manual lists:
>
> Test Point (+)	DC Voltage		My DC Voltage
> P1 pin 15		5.8 - 6.2			0
> P1 pin 16		(supply - 0.3V)	12.79 (correct)
> U3 pin 5			3.8 - 4.2			.015
> U3 pin 6			7.6 - 8.7			0
>
>
> Also, In the resistance checks on page 29, I am curious about a couple  
> of readings:
>
> P1 pin 8 should read >100k.  I am getting 1.77M, which certainly is  
> greater than 100k, but it seems excessively so.  Also P1 pin 16 should  
> read  >1k, but I get  5.18M, which again is >1k, but it seems  
> outrageously high, so I'm guessing it's tied in with my issue above.   
> Also, U3 pin 5 should read  >10k, but I get another quite high reading  
> of 5.15M.  Finally, on U4, I'm getting 5.13M on pin 6, and 5.6M on pin  
> 7.
>
> If anyone has some ideas for me to try to track down my problem I'd  
> appreciate it.  While I have tried to be very careful in treating  
> static sensitive components, I wonder if I may have accidentally  
> damaged one (or more).
>
> Thanks!
>
> Anthony, W6GC
>
>
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