The only other idea I have is to remove, clean, and re-seat the display
cable. It has VDD pins next to gnd pins - maybe there is a short, or some
FOD.
On Mon, Oct 28, 2024, 3:23 PM Jim Ancona N1ADJ via groups.io <jim=
[email protected]> wrote:
On Sat, Oct 26, 2024 at 11:48 PM, Stan Dye wrote:
It could be U11, or it could be something dragging down the output of U11
(some other failing component presenting a too-high load).
It turns out that my board is version 4.2.1, the scrematic is
If you can manage it, I would unsolder and lift the output leg of U11
and see
if the output of the chip pops back up to 3.3V where it should be.
The regulator is LDO1. I managed to lift pin 5. With no load I measure 3.6
volts. If I put a 33 ohm resistor to ground, the voltage goes to 3.3. So it
looks like the regulator is okay. I measure about 3 ohms from VDD to
ground, which seems too low.
Another observation to make is to see if any of the chips is getting
warm to
the touch - if it is pulling down the 3.3V rail, it may be getting hot.
Not surprisingly, LDO1 gets hot if I leave the power switch on for more
than ten or twenty seconds. I can't feel anything else that's very hot
though. I tried lifting one pin of C47, but the measured resistance didn't
change.
And yes, a VDD of 1.7 is a problem. Maybe the initial 2V+ is enough to
turn
the processor on such that it can respond a bit, then as VDD goes down,
the
processor would likely fail.
I agree.
I'm running out of ideas. I doubt I could remove the smaller capacitors
without breaking them and if one of them was a near-short, I think it would
have burned up. I'm happy to hear suggestions of other things to try.
Thanks,
Jim
N1ADJ
