[Elecraft] KPA500 #181

[Ron D'Eau Claire]

Geoff is quite right. The test is to ensure there is not a short circuit
from the tab of U3 to the heat spreader, indicated by a reading such as you
see when the DMM leads are touched together. There are paths between the tab
of U3 and ground through the power supply circuit. These paths include
various transistor and diode junctions so the resistance one sees depends a
great deal upon the voltage applied by the DMM. That voltage varies widely
among the various models and makes of DMMs, so it's not possible to provide
an exact value or resistance. 

Ron AC7AC


-----Original Message-----
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: elecraft at mailman.qth.net
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
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