Re: 27MHz instead of 7MHz at inputs to IC3 #problem

Shirley Dulcey KE1L

27 MHz suggests a different problem - a short on the board that is
causing the Si5351A reference oscillator signal to show up at IC3.

On Wed, May 1, 2019 at 6:09 PM James Daldry W4JED <@jimdaldry> wrote:

Hi, Bill

Before I did anything rash, I would do a full reset and then set it up for 7 mhz.



On 5/1/19 12:19 PM, Bill Creitz wrote:

40m QCX build completed in early April 2019.
Firmware: T1.00g

Initial symptom: no RF output.

Started troubleshooting at TRANSMIT signal path. Soon found...

On transmit, 27MHz squarewave appears at pins 4 and 10 of IC3. (Should be ~7MHz squarewave, as observed on another QCX built by a relative.) This suggests that IC1 isn't being programmed to output 7MHz signals.

What I've done so far:
-- Visually inspected IC1 pins for possible shorts (for the second time; also did that before the board was assembled). None found.
-- Visually insected IC2 (microprocessor) socket joints. All look good.
-- Removed and reseated IC2. Didn't fix the problem.
-- Visually inspected traces on board bottom from IC2 socket to IC1. No problems found.
-- Performed a system reset. Didn't fix the problem.
-- Verified continuity between IC2 pins 27 and 28 to IC1 pins 4 and 5.
-- Verified that R3 and R4 are 1K.
-- Verified that voltage at output of D1 is 3.3V.

I'm out of ideas. Any further suggestions would be greatly appreciated.

in Maryland

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