Ta-da!? Shorted cap 301.? Greg, thanks for you help and encouragement
taking me somewhere I was hesitant to go.? A friend brought an iron that
functioned as heated tweezers to our club Saturday coffee gathering, and
I was able to pull it off.? Not sure about putting one back; I may go
for a traditional thru hole piece instead of one designed for surface
mount.
This thing is SMALL. For a moment I couldn't find it, then noticed it
trapped between my finger and fingernail. Couldn't even feel it.
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On 3/23/2024 07:27, Greg McCain via groups.io wrote: Well,
I personally would carefully remove the cap and then check continuity
between pins 1 and 2 at the LCD display itself.
If it still shows a short, the problem is probably:,
-- a bridge between? pins 1 and 2 of the LCD solder connections
--? something in the LCD internals
-- or possibly something off in the PAD resistor PAD circuit on the
other end. There's a Vcc feed over there too.
And of course, check the cap itself for a short once it's out of the
circuit. If it is shorted, that's the culprit.
Good luck. Not sure if you are comfortable with working like that on
small SMDs.
Greg
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On Fri, Mar 22, 2024 at 11:41 PM, Al Simons
<al@...> wrote:
I pulled the trimmer this afternoon, and it shows ~22k as spec'd, and
the wiper goes smoothly over that range. I don't remember whether it
went all the way to zero at the ends or not, but I've put the wiper
mid-range in my testing and it doesn't change the apparent short
between
VCC and GND.
I have raised the black pin spacer blocks on JP303 and 304 to make
sure
there was nothing extraneous being hidden, but the board is clean.
I tried to pull the jumpers on display pins 1 and 2, to isolate the
problem to the display board or the carrier board that has the various
components on it, but I was unsuccessful on getting them unsoldered
enough to be able to pull the wires.
So of your list, I think we are down to a shorted C301, or a short on
the display board.? Any other ideas welcome!
Good night.
-Al
On 3/22/2024 18:59, Greg McCain via groups.io wrote:
> C301 sure looks like a bypass capacitor for the 5v feed into the LCD
> board. There to send little spikes and ripples on Vcc (the output of
> the 5V power supply) safely down the ground.
>
> One side of it should have continuity with pin 2 of JP303 (the four
> pin connector).
>
> The other side, I believe, should not show continuity with that
pin 2,
> when checked with an ohm meter.
> And of course, there should also not be continuity directly between
> the actual contact ends of the capacitor, unless perhaps . . .
>
> C301 is indeed shorted . . .
> OR There is a short between pins1 and 2 on the LCD component itself,
> OR there is a short through the trimmer resistor (R305)
> OR? if the trimmer resistor can actually be set to '0' ohms.
>
> Can you confirm that the trimmer resistor is? turned all the way
> counter-clockwise (when looking right down on the top of the
bugger)?
>
>
> Greg
>
> Greg McCain
> gamccain50@...
>
>
> On Friday, March 22, 2024 at 07:27:20 PM EDT, Al Simons
> <al@...> wrote:
>
>
> With the display board out of the radio, I measured 0 ohms
between pin 2
> of the 4 pin connector (GND), and the pad to the right side of C301,
> which is marked VCC on the trace diagram. Seems "odd." Possible
shorted
> C301? Unfortunately, I have no surface mount skills or equipment.
>
> What is a path forward?
>
> 73,
> -Al WA1TYB
>
> On 3/22/2024 15:44, Greg McCain via groups.io wrote:
> > Hopefully something simple and/or obvious.
> >
> > Don't forget to check the 2 header connectors on the main
board too.
> >
> > Good hunting. Let us know if you solve it.
> >
> > Greg KI4NVX
> >
> >
> >
> > Yahoo Mail: Search, Organize, Conquer
> >
>
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>
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> >
> >? ? On Fri, Mar 22, 2024 at 5:05 PM, Al Simons
> >? ? <al@...> wrote:
> >? ? Greg, THANK YOU.? Pulling the display board lets it come
up, drawing
> >? ? ~150mA at 6V. The terminal program is running, so it seems
that at
> >? ? least
> >? ? part of the CPU is OK.? Now to figure out what I did wrong
with the
> >? ? display board!
> >
> >? ? Again, thanks.
> >? ? -Al WA1TYB
> >
> >? ? On 3/22/2024 14:36, Greg McCain via groups.io wrote:
> >? ? > Just a quick thought.
> >? ? >
> >? ? > Without the control board will the unit even power up
since the
> >? ? rotary
> >? ? > push to power on won't be available?
> >? ? >
> >? ? > You might try just removing the display.
> >? ? > If the current stays up, then the fault might be in the
display
> >? ? board
> >? ? > or the 5v power board.
> >? ? >
> >? ? > I've seen other posts where faults/ bridges/shorts in the
power
> >? ? > boards' connector chains have caused odd problems. I took the
> advice
> >? ? > in the build instructions and clipped the one set of pins
back
> >? ? about a
> >? ? > millimeter or so because I could definitely see I that a few
> >? ? were too
> >? ? > long and extended past the solder pads and awful close to
other
> >? ? items.
> >? ? >
> >? ? >
> >? ? > Greg
> >? ? >
> >? ? >
> >? ? > Yahoo Mail: Search, Organize, Conquer
> >? ? >
> >
>
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>
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> >
>
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>
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> >? ? >
> >? ? >? ? On Fri, Mar 22, 2024 at 2:32 PM, Al Simons
> >? ? >? ? <al@...> wrote:
> >? ? >? ? Just completed my Rev 3 QMX assembly. It performs the
USB stick
> >? ? >? ? emulation ok, to place the FW file on board. I did
this both on
> >? ? >? ? initial power-up and by jumpering AUX2 to GND.
However, after FW
> >? ? >? ? load, when I press the left knob it draws power for an
> >? ? instant and
> >? ? >? ? then powers back down to 0.000A.? I'm using 7V, limited to
> 200mA.
> >? ? >? ? I have inspected all my joints w/ a magnifier, all
seem fine but
> >? ? >? ? I'm considering buying a USB microscope.
> >? ? >
> >? ? >? ? To start troubleshooting I want to check the power
boards.? For
> >? ? >? ? easier access, is it safe to power up the unit without the
> >? ? control
> >? ? >? ? board and display boards plugged in?
> >? ? >
> >? ? >? ? I've been monitoring this group since I placed my
order.? I
> think
> >? ? >? ? I remember a reference to a troubleshooting guide by
Hans, and
> >? ? >? ? another report of this failure mode, but I can't find
either.
> >? ? >? ? Pointers to either would be greatly appreciated. I'm aware
> of the
> >? ? >? ? troubleshooting log Hans has posted about units he's
fixed,
> >? ? but it
> >? ? >? ? doesn't mention this failure.
> >? ? >
> >? ? >? ? Thanks for any advice and pointers.
> >? ? >? ? 73,
> >? ? >? ? -Al WA1TYB
> >? ? >
> >? ? >
> >
> >
> >
> >
> >
> >
> >
>
>
>
>
>
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