Dan,
When you have IC403 removed, check the voltage at the junction of R401
and R402, in both receive and transmit. It should be 2.5V in both
cases. If you have a short at one of the bandswitch capacitors, it
could go substantially higher in Receive and then trigger a latchup
melt-down of the chip.
The energy to produce this failure may have come from the 5 Volt
supply. You seem to doubt that, and that is legit.
It also might have come in from the clock generator, but that seems to
be working, as you can transmit power.
The remaining possibility is that the transmitter itself has fried
that chip, and probably the mux chip ahead of it , too, or that a
latch up as described above has happened.
These scenarios seem unlikely but cannot be discarded.
JZ KJ4A
On Fri, Aug 18, 2023 at 5:01?AM Daniel Walter via groups.io
<nm3a@...> wrote:
Kees,
Yes, I am sure there is no short between Q103/Q104. Tested 5 V line prior to installing the p/s and after and checked on self test via USB. 5 V line never any higher than 5 V.
--
73, Dan NM3A
