[Elecraft] KPA500 #181

[Brendan Minish]

Hi Peter

Diagnose/fix the Isolation problem between U3 and the heat spreader
before proceeding, Isolation here is 'not optional' it's required.

Inspect U3 carefully for signs of damage. Check for 240 Ohm between U3
pin 1 and U3 pin 2  (this tests R4 a SMT resistor on the underside of
the PSU board )

U3 controls the power to the cooling fans, is fed from the HV and if
shorted will prevent these operating 

IF you are lucky your 0HV message will go away once you ensure that the
insulation between the heat spreader and U3 is ok.

If this does not cure the problem also check to see if the HV interlock
switch is being depressed correctly by the top cover  

Be sure to test to see if the fan speeds are all working correctly
before operating the amp (setup, fan and step thought the speeds ) 



On Wed, 2011-08-03 at 17:49 +1200, Peter Dent wrote:
> My KPA500 went together well EXCEPT I could not get isolation between U3 and
> the heat spreader but  I continued assembly any way.
> 
> Now when I switch on I get 0 HV message in the readout.
> 
> BTW the reason for the delay between assembly and this email is that the XYL
> and I have just spent a week in VK3 land (Melbourne) Australia..
> 
> Any thoughts or suugestions?
> 
> Peter  ZL1PWD
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-- 
73
Brendan EI6IZ