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
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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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? ? 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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? ? >
? ? >? ? 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
? ? >
? ? >
