Stan Dye via groups.io <standye@...> wrote:
?If your receive is working properly, it's probably not a component on
the main board - most of the receive section components are on Vcc.?
Does receive still work?
Hard to tell. There's normal noise, so it probably works at least
partially, but I don't want to stress the board more...
I would measure the main-board resistance between the 5V rail and gnd,
without the power supply in place.? This should have several Kohms of
resistance, if not, there is a failure somewhere on the main board.?
Hopefully it is OK and the only failure is in the 5V supply.
23 ohms, measured on the main board with power supply boards removed.
No wonder the inductor is getting bloody hot.
I isolated it by lifting the Vcc pins of the ICs one at a time until the
short disappeared.? But this IC being damaged also destroyed all signal
receive functionality.
I think this is what I'll do -- make a list of possible components and
just disconnect them one at a time, measuring the resistance.
An option to consider is to order a set of the little power supply
boards from qrp-labs (on their spare parts page) - they are very
inexpensive, and may save you some troubleshooting and repair.
When (if) I fix the issue with the short on the main board and verify that
everything works, I'll think about it -- right now I have a linear
regulator instead of a 3V3 buck one, which seems to work just fine.
Another option I considered is designing a custom board with just a power
switch and two linear regulators instead of these two boards. I don't like
the idea that the control loop goes via the CPU. Of all design decisions
in the QMX, and despite the trick with adjusting the switching frequency
so the harmonics don't interfere with reception, I'm not a big fan of this
solution.
Thanks!
