You can enable test mode on the MZ-R2 in two ways: one requires you to solder a jumper, the other requires you to press some buttons... Either works just as well. I prefer pressing buttons:
Tada :-) The display will cycle by first showing the firmware version, then all the LCD segments, then by going blank, etc... Press PAUSE to freeze the display for a moment and press << and >> to move the laser and magnetic heads towards/away from the spindle motor.
When you enter test mode it generates a 1 KHz maximum amplitude (0 dB) signal from the headphone and line out jacks until you press VOL +/-, PLAY, STOP, PAUSE, or <>>! (Instant signal generator :-)
To disable test mode:
Navigating the menu structure within test mode becomes a bit challenging to explain without the service manual. There are 4 main menus:
VOL +/- changes the main menu number, while PLAY drops into several sub menus (010, 020, ... 110, 120, ...), like the ENTER key on PCs.
Whithin sub menus, VOL +/- changes the sub menu number, while PLAY drops into actual settings (011, 012, ... 121, 122, ...) STOP jumps back to the main menus, like the ESC key on PCs.
Whithin settings, VOL +/- changes the value (for most settings), while PLAY takes you to the next setting. PAUSE saves the value into the EEPROM while STOP jumps back to the sub menus. Careful now!
The only unusual equipment required for some tests includes an error counter, a laser power meter, and a calibration MD (for CD mode adjustments). Othewise, a voltmeter, an oscilloscope and a blank MD (for MO mode adjustments) will do.
Change the MO Bias Focus in the test mode. It is in the section "026" (MOFCBIAS). I changed the value from 7A to 90. Now, I finally converted my $400 paper weight into a recorder again!