Panasonic TV's after 1996 can be set to "Serviceman Mode" with the following remote control sequence:
Then, select the TIMER icon and set the SLEEP timer for 30 second.
Next, press the ACTION button twice to get out of the menus.
Now, change to channel 124.
Then, adjust the volume to minimum (0).
You're almost there - Hit the VOL down button on the TV itself (not on
the remote) and a red "CHK" should appear in the upper corner.
Now, if you press the ACTION and volume down buttons (again, on the TV, not the remote) you will toggle between AGING and factory setting modes.
Select factory setting modes (Serviceman mode). The POWER button on the remote control will select one of the five Serviceman Adjustment modes.
The modes are B - Serviceman VCJ SUB Adjustments. These include sub-tint, sub-color, sub-brightness, sub-contrast, colorkiller/ABL/gamma, audio and video adjustment, and vertical size.
C - Serviceman VCJ Cut-off adjustments. These include Red, Green
and Blue cut-off, red and blue drive, automatic fine tuning
(AFT), RF AGC (RF gain control), horizontal center, beam limit,
etc.
S - Serviceman Options Adjustments. These involce the PIP and
clock.
M - Serviceman MTS (Stereo/SAP) adjustments.
CHK - the mode you first entered. Normal picture and sound, lets
you check things over and still have a hotkey into the
service menu.
There is one more adjustment that isn't in the five modes, it's
global. When in either the yellow or red CHK mode, you can press
RECALL on the remote control to enter the purity firld check mode.
This lets you select a pure white, red, green, or blue screen. A
good thing to walk away from if you just want to temporarily freak
out the floor manager, but it will be fixed as soon as the TV is
turned off. To get out of Serviceman mode, press ACTION and POWER on the remote control cimultaneously for at least 2 seconds. The TV will momentarily shut off and then comes back on.
