I have no idea what procedures QRP Labs has before shipping a QMX+,? so take this with as much skepticism as you can muster:
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My assumption is that they plug in a USB cable to program the STM32F and power the board up, not much more.
That USB cable is just a connection to ground and a couple pins on the STM32F, nothing anywhere near the PCM1804 gets touched.
A fake received signal would have to be driven into pins 7 and 9 of IC403, but that is well isolated from the PCM1804.
The power supplies on the QMX+ are complete, exactly as they will be when shipped to the customer.
I can't imagine any reason for the procedure to physically disturb the PCM1804 in a way that would not happen after a bad chip is replaced.
Any handling at QRP Labs would likely be considerably more benign than that of the typical kit builder who is adding dozens of parts.
My understanding is that the PCM1804 seldom (never?) fails once the PCM1804 has been found to work, either during initial testing at QRP Labs
for recent versions of the QDX and QMX+,? or after Jeff has replaced a PCM1804 (which I'd guess is now mostly on the QMX, since
the QDX and QMX+ have already been tested).? Older kits that did not have firmware loaded at QRP Labs don't have the PCM1804 tested.
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If the above is correct, it sounds to me llke the assembly house is stuffing bad parts.
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I could easily imagine that shorting the VCC rail (perhaps due to clearance issues around the front panel) would cause a spike in VCC when the short is removed, blowing the PCM1804.? However, if such failures seldom (never?) occur after the receiver has been found to be working correctly,?
that is probably not an issue.
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A complete bed of nails would not be required to test the PCM1804 on the currently untested QMX.? I would think it would just require applying VCC and VDD, a USB cable to a host computer that has appropriate test software, and appropriate signals at IC403 pins 7 and 9 that are 180 degrees out of phase.??
Getting this working properly could take several days that Hans does not have, but should not take weeks and a major hardware effort.
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Jerry, KE7ER
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On Fri, Jan 3, 2025 at 05:42 AM, Bruce Akhurst wrote:
I suspect ESD or power supply damage to an incomplete board would not be repeated once fully built.? ESD damage, to ICs in particular, is often evident only after a few weeks or months...
