Ok, after messing around with the radio on my own and then getting the "official" mod, here's a summary of the various diode mods for the Z1A:
Icom Z1A mods
[B]+[#]+[POWER] = Extended Receive.
VFO *DISPLAYS* 50-299.900 and 300-999.900.
AM Aircraft band enabled.
SET mode now has a new "PLACE" function for setting
the direct entry starting digit.
There is room for four diodes in the Z1A located on the CPU board to the left of the ribbon cable connector. On a US version, only the bottom two are installed. D15 is just below and to the right of the four diodes. These diodes are bigger than the rest of the surface mounted components and are easy to spot.
The official ICOM mod (which I unofficially saw...) is to remove D15 for extended TX and to use the above keyboard mod for extended receive. According to the sheet, the 800-900 band is NOT available in US versions.
| | | | <---- Installing diodes in either of these seems to do
+-+ +-+ nothing.
| | | | <---- IN: US Version 144-148 TX 440-450 TX
+-+ +-+ OUT: Extended 136-174 TX 380-470 TX (Lose auto-repeater
^ and tone encode)
+------------ IN: US 144-148 TX 440-450 TX
OUT: European 144-148 TX 430-440 TX
"D15"--> | | <---- IN: US Version Stock
+-+ OUT: Extended TX 136-174 380-470 (keeps auto-repeater
and tone encode)
A word of warning about messing with the four diode pads: If you detach either one of the installed diodes, the CPU will reset and you'll lose ALL of your memories. (found that out the hard way...) D15 doesn't seem to affect the memories at all.
Since the 800MHz band is not available in US versions, my guess is that there's a keyboard mod to unlock it instead of a diode. The diodes only seem to control the country versions.