[Elecraft] KPA100 problem

[Don Wilhelm]

Jerry,

That means U4 is not the problem, the problem is somewhere in the 
rectifier stack and goes away when you lift the anode of D7.

Check both D7 and D8 for proper orientation (use the parts placement 
diagram since the board silkscreen is covered).  Check for a solder 
bridge across the leads of C38.  Be certain C35 is soldered properly.
If you lift the anode of D7 and place a 0.1 uF capacitor from the 
"flying lead" of D7 to ground, what is the voltage at the D7 anode?

I know that did not fully identify the failure point, but hopefully it 
gives you some clues.

73,
Don W3FPR

n0jrn wrote:
> Gang:             I need some advise please.
>
> I'm trying to finish my KPA100 but I can't seem to get beyond voltage tests 
> on page 46 of the manual.
>
> I should be getting 90 to 150 V's at the junction of C77 & R11 but only 
> getting 47 volts.
>
> I should be getting -5 to -25 V's at pin 8 of U4     BUT   I'm only 
> seeing -4.1.
>
> I did some research in the archives and came up with a few ideas.    Checked 
> D1 - D8 and T3 pads.  All diodes pass continuity test and T3 seems fine and 
> shows zero resistance between pads.
>
> Checking the schematics prompted me to lift the anode of D7 to remove U4. 
> In doing this,  the voltage at the junction of R11 came up into spec and 
> shows 150 V's.
>
> This means that U4 is drawing the circuit down.  SO,   I sent Elecraft an 
> e-mail and Gary sent me a new MAX1406.          Figured I would install it 
> and all would be good.        NOT !
>
> After installing the new U4,    I rechecked voltage at R11 and found it is 
> still just 47 V's.
>
> I've double checked orientation of U4,  and it's fine.  I was very careful 
> to observe anti static procedures when installing the new chip.   SO,   I'm 
> confused and not sure where to go from here.
>
> Any advise would be greatly appreciated.
>
> Thanks & 72:           Jerry           N0JRN 
>
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