Bill,
In the KPA100, the normal Vss is about -25 volts, so suspect that
something may be loading that negative supply.
Pull U4 out and measure that voltage again. If it is still not negative
enough, you may have a problem in the T/R switch. Check for 90 to 150
volts on the highest voltage end of R11.
If that voltage is OK, look carefully at C34, C35, D7 and D8.
Put MCU 2.04P back in - it won't help with this problem, but there are
other things it will help with.
73,
Don W3FPR
On 11/19/2021 12:01 PM, Bill Coleman wrote:
Don,
Managed to do a little diagnosis.
I pulled the MAX1406 chip KPA100 U4.
I see proper continuity between pin 12 of U4 and pin 25 of the MCU, and pin 11
of U4 and pin 26 of the MCU.
Going back, I checked out the Vdd, Vss an Vcc voltages on U4.
Vdd is 14 volts
Vcc is 5 volts
Vss is -5 volts
It looks like, from the specification of the MAX1406 chip, it needs more like
-10 volts to work correctly.
I measured these on the scope before, so I only got vague responses.
I guess I’ll be investigating the Vss supply.
On Nov 19, 2021, at 11:25 AM, Bill Coleman <aa...@arrl.net> wrote:
Serial Number 2548.
The current MCU I have is version 2.04P. (latest)
The unit I swapped in earlier was, I think 2.03. I don’t have it with me, and
I’m not sure.
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
