Re: QMX - smoke - another C107/Q108 failure
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I think that given all of the people experiencing blown components due to power supply issues (including myself), there is a case to be made for a redesign of the power supply. Something like an can replace 38 parts in the current design with 8, with significantly better performance in every way. The frequency of the part can be externally synchronized, but you can also simply configure it for 2.2 MHz, where every harmonic is a minimum of 400 kHz from any of the amateur bands covered by the QMX.
Yes but...?
1. What about the eye-watering price? There are two versions in stock at Digikey, LTM8078IY and LTM8078EY. The price at 520-quantity?(1 tray) is $11.52 and $10.47 resp. Plus taxes of course... for comparison, since I have the two SMPS boards on the QRP Labs shop at $10? I'm sure you can imagine that the parts costs are way way less than one of these LTM8078; consider that the $10 price also includes the 6-layer PCB, the two female header connectors, SMD assembly factory costs, shipping, taxes, other costs etc.?
2. One of the main reasons for using a discrete component buck converter when the QDX Rev 3 PCB was designed, having the discrete component buck converter for the PIN diode forward bias generation, was that the global semiconductor crisis was in full swing, and adding an unusual part to the BOM seemed distinctly unattractive compared to a handful of discrete parts which are much easier to find. The QMX design inherited the buck converter from QDX. Whilst the global semiconductor crisis has receded somewhat we are still nowhere near back to the old days where you never ever thought about availability because you never had to. Looking at the available stock in Digikey (1050 of the EY and 3410 of the IY) isn't terribly encouraging in that regard.?
3. Being a BGA package, replacement would truly be beyond the reach of most of us here...
4. We are getting through building a larger and larger number of QMX now that the whole team are building them here. Originally, while we still had a long list of QDX, QCX-mini and QCX+ on the waiting list, only one (the most experienced and accurate) team member was building them, in order to build up experience of potential hazards. Of all the QMX I have yet seen, other than the Q103/Q104 Drain short (manufacturing problem) I have yet to see a failure that is not attributable to shorts, damaged components or other construction errors.?
73 Hans G0UPL
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