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Re: Another QMX+

 

Thank you, Jerry,?

It appears that this issue is fixed.? I just made 40 restarts with IC401 replaced and suffered no very loud or very quiet starts.

Thanks to everyone who chimed in on the problem.? Learned to look for the ground connection, and that chip labels have a standard orientation with respect to ground, and that Hans draws the silk labels in standard orientation, except when he doesn't (eg IC407) where he puts an explicit pin 1 marker instead,

And thanks to Mehmet for the excellent photo which does help cement everything.

Now to figure out why the QMX+ thinks my antenna is better than NanoVNA does.

-- 73 -- rec -- ad5dz --

On Wed, Feb 19, 2025 at 5:06?PM Jerry Gaffke via <jgaffke=[email protected]> wrote:
Roger,
?
You have it figured out.
On my IC401, there's a shiny flat round dimple over pin 1.
?
When holding an SOIC package such as IC401 such that the print is right side up,
pin one should be in the lower left corner.? Counting from pin 1 counter-clockwise
around the chip to go from pin 1 to pin 8.? The schematic has pin 6 grounded, if
you look closely with a bit of magnification (or at least better eyes than mine)
you will see an obvious connection to the ground plane around it.
You can check this connection with an ohmmeter to one of the big round mounting holes,
which are also connected to ground.? Pin 7 has VCC,? there's a labled VCC pin at JP106
near the far end of the front panel that you can check connection to.
?
Try looking at the chip under whatever magnification you have with a very strong light.
Slowly turn the chip this way and that, at the proper angle the text on the chip (and the dimple)
should suddenly stand out.? The text is perhaps laser etched, not printed with ink which
could wear off.
?
Jerry, KE7Er
?
On Wed, Feb 19, 2025 at 03:00 PM, Roger E Critchlow Jr wrote:
Going to need some help here.? I'm replacing the IC401, the CS4334 DAC, because of intermittent bad audio output levels at startup.? But I need confirmation on the proper orientation of the chip.
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