During some tests on the new Z80-MBC2 I realized that the circuitry of the USER led and key (that is the same used in the Z80-MBC) could cause in some cases an erratic behavior of the USER key (USER key not recognized when pressed).

The solution is easy, and the fix requires only to change the values of R14 and R15 (see the A041116 schematic) to 390 Ohm (both) as shown:

Remember that the USER led (D5) must have a forward voltage drop (Vf) of at least 2.7V (e.g. a blue led).

Please note that this fix is suggested only if you are building a new board or if you are experiencing difficulties with the USER key.

If you already have a perfect working board there is absolutely no need to apply this fix.