[Elecraft] KPA500 270V Failure

[Dr. William J. Schmidt]

This happens a lot... search the forum for past msgs.  It's not the HV power
supply that is the problem.  That power supply powers the PIN diodes for TR
and RX... and it is more likely that the PIN diodes shot craps and shorted
the power supply.  There are two voltage Test Points "TP" on the board under
with the diodes and  you need to check the voltages on those test points.
That will tell you everything you need to know.  Will post the voltages when
I find them.


Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ 

Moderator – North American QRO Group at Groups.IO.

email:  bill at wjschmidt.com


-----Original Message-----
From: elecraft-bounces at mailman.qth.net <elecraft-bounces at mailman.qth.net> On
Behalf Of Bruce Forsberg
Sent: Sunday, July 25, 2021 4:31 AM
To: Elecraft at mailman.qth.net
Subject: [Elecraft] KPA500 270V Failure

Today when using my KPA500 I switched it into operate mode from standby and
received an error message of 270V ERR. This is the first time I have seen
this error. I partially disassembled the amplifier and measured the 270V
voltage and it is 70V, which is close to what the HV voltage measured on the
front panel says. After finding some old outdated schematics on the internet
it looks like there is a diode capacitor voltage multiplier circuit that
takes the HV voltage of approx 70V and brings it up to 270V. I am assuming I
have lost one of the diodes in the chain.
Unfortunately Elecraft has used tiny diode packs and even put 2 of the 3
packs between electrolytic capacitors on the board, which I will have to
remove. Has anyone else seen this problem with their KPA500? And how did you
go about fixing this?

Thanks,
Bruce, WB6IZG
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