KPA500 #181

[Peter Dent]

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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[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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

--
73
Brendan EI6IZ

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[Geoffrey Downs-3]

The assembly manual says the resistance between the tab of U3 and the
mounting screw or heat spreader is "typically greater than 5000 ohms", so
it's not total isolation you're looking for, unlike the four rectifiers on
the rectifier board. In my case the DMM read 10,000 ohms between the tab of
U3 and the mounting screw and heat spreader, which I took to be ok. However,
I've not finished assembling the KPA500 yet, so there could still be smoke
when I finally switch on!

73 to all

Geoff
G3UCK

-----Original Message-----
From: Peter Dent
Sent: Wednesday, August 03, 2011 6:49 AM
To: [hidden email]
Subject: [Elecraft] KPA500 #181

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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html 

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[Richard Griest]

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[AC7AC]

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