[Elecraft] ALC THR level KPA500

[Jack Brindle]

First thing - upgrade the firmware to version 1.54, then try testing again. We will help you with the ALC if the problem still exists.
There were some changes in the area of ALC control between the version you have now and V1.54.

But, the question will be what transceiver are you using the KPA500 with, and why do you want ALC? We usually recommend not
using ALC, but in some cases it may be useful. The KPA500’s ALC circuitry is on the Front Panel board, and you are right, U8 (LM6482)
and D37 (BAT54 diode) are involved.

After you have upgraded the KPA500 to the latest firmware (V1.54), let us know how it is going.

73,
Jack, W6FB


> On Feb 1, 2025, at 8:18 PM, Herbert Botero <antecol2 at gmail.com> wrote:
> 
> Hello
> 
> 
> 
> My callsign is HK4T and I bought, second hand, an Elecraft KPA500 amplifier
> from the series 239 that works with firmare 1.38.
> 
> The amplifier works correctly in all its functions except for the ALC THR
> level control.
> 
> On the display the ALC THR value varies between 0 and 210, however the ALC
> output voltage remains constant at -7 V DC
> 
> What tests should we carry on to detect and repair the equipment?
> 
> I believe the problem is on the LMC6482 components or the zener D37
> (diagram No. 2). Does anyone know where those are located?
> 
> I am an electronic engineer and I have the equipment and knowledge
> necessary to carry out the repair with your collaboration.
> 
> 
> Best regards,
> 
> 
> 
> 
> 
> HERBERT BOTERO B.
> 
> ANTECOL  antecol2 at gmail.com
> 
> Tel.(+57) 4411 3952 y  Cel. +57 310 442 2012
> 
> Medellín - Colombia
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