Hi William,
"
surmise it was heating
"
Consider as the surface mount current sensing resistor (assuming it is
surface mount)
is made to withstand solder reflow it seems unlikely to be heat. I've
had many surface
mount resistors develop hair line cracks due to vibration and board
flexing (in breadboards I built).
In failures I've seen due to heat, the resistor visibly changes color
especially in markings, white to
brown.
As long as you have the unit opened up, perhaps you should take a lupe
or magnifying glass, bright
flashlight and just look around for other cracks in components or solder
joints.
I hope I can work you on 40M FT8, I need VP2E.
Good luck
Chuck K0MV
On 3/3/22 08:40, Dr. William J. Schmidt wrote:
Sorry guys, this is not a trivial line voltage problem.
The 60V line to the PA does not sag that much (starts at 72V goes to 60V
under FULL LOAD as measured at the PA)... it's in the voltage divider for
the 60V/32 line or the connectors that carry it to the front panel processor
for digitizing. Changes with heat load. This amp is in the Caribbean and
there is plenty of excess heat and corrosion. (nb. I just replaced the
current sensing resistor in my K3S for the 100W module due to a hair-line
crack... surmise it was heating).
Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
VP2EHZ
email: [email protected]
-----Original Message-----
From: [email protected] <[email protected]> On
Behalf Of Naumann, Robert, W5OV
Sent: Thursday, March 3, 2022 9:11 AM
To: [email protected]
Subject: [Elecraft] FW: KPA500 faults
What line voltage are you running it on? If you're not on 240v, switching
to 240v would be the easiest and most effective improvement.
Doing so yields a 4:1 improvement in line voltage regulation / reduction in
voltage drop. Double the voltage, at half the current draw.
73,
Bob W5OV
-----Original Message-----
From: [email protected] <[email protected]> On
Behalf Of Dr. William J. Schmidt
Sent: Thursday, March 3, 2022 00:39
To: [email protected]
Subject: [Elecraft] KPA500 faults
I have a KPA500 that faults on low (60 VDC) voltage. After measuring the
power supply voltage at the PA module is perfectly fine. The voltage read
by the processor on the front panel via pin 10 of P1 is lower than it should
be and hence the fault condition. I suspect there is a voltage divider on
the LPF board that drops the 60 VDC to something that the processor can read
and digitize (in the 0 to 3-5 volt range). The set of schematics I have do
not show the voltage divider anywhere. does anyone have this part of the
schematics for the KPA500 so that I can adequately troubleshoot this amp and
get it on the air for the contest this weekend? Multiple notes to Elecraft
have gone unanswered.
Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
VP2EHZ
email: <mailto:[email protected]> [email protected]
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--
Charles K0MV
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