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Now that hundreds of our new SP Basic kits are in the hands of owners, there's been a few consistent claims describing a situation where the Ail D/R switch only works when the USB connection is present.  Also reported is that certain features dependent on the MENU and/or EXIT buttons at startup only work if the USB connection is present (in ER9X, for example, one can auto-select a model by holding down various buttons but it always defaults to model 1 unless the USB is present).

A few of those people that reported this anomoly were given replacement units and in zero cases were the problems resolved.  This strongly indicates that this has to do with a variance in the 9X itself.  The reliance on USB power hints at the cause, and I believe I can fix it in future batches but that doesn't help you if you're reading this looking for answers!

The simplest resolution I've come up with is to power the SP Basic from the 9X battery, so that it remains powered when not in use.  Why?  It is the "floating state" of the unpowered SP Basic's pins that are causing problems with certain switches.  {In previous designs, I inadvertently avoided this problem by using logic chips that disconnected all the pins when not in use.  Someone pointed out to me that this was technically unnecessary because of certain resistors present on the 9X.  It seems those resistors aren't always doing the job they're supposed to}  Powering the board removes this problem.  The only downside of this fix, besides having to do the work, is that the board constantly draws power whenever the radio is turned on... however, the amount of power is pretty small and you shouldn't notice it.

Please note that after performing the fix described below, you should keep your 9X powered OFF when connecting it to the computer.  This is because your battery power and USB power are going to be shared after this point.  It shouldn't cause any harm to have both on, but there's no reason to and leaving it off will be safer.

The fix entails soldering a single wire between the SP board and the 9X.  The position of each are indicated below.

Location of solder point on SP Basic to fix power issue.

Location of solder point on 9X mainboard to fix power issue.