Okay here is exactly what I did to fix the red tint issue on my PDP-LX5090. Please note that the service menu can be dangerous and you do this at your own risk.
Step 1 concerns connecting your TV to Hyperterminal. If you are already okay with issuing RS232 commands, proceed to step 2.
Step 1
You will need:
A computer with serial port (you can buy USB to serial adaptors if you don’t have one).
A serial cable (9 pin to 9 pin, female to female, straight not null modem).
Hyperterminal (included with XP).
1. Connect the computer to the TV with the serial cable.
2. Start Hyperterminal (Start > All Programs > Accessories > Communications >HyperTerminal).
3. It will ask you to create a new connection. Name it whatever you want (TV for example) and choose an icon (can be any) and click OK.
4. On the next screen (Connect To), ignore the phone number field and change the ‘Connect using’ drop down box to your serial port (usually COM1) and click OK.
5. Next you will see ‘COM1 Properties’. The default bits per second or Baud rate is 9600 for Pioneer displays.
6. Set BPS: 9600, Data Bits: 8, Parity: None, Stop Bits: 1, Flow Control: None and click OK.
7. Next go to File > Properties and open the Settings tab. Click on ‘ASCII Setup..’ button. Make sure ‘Send line ends with line feeds’ is NOT checked and make sure ‘Echo typed characters locally’ IS checked. Click OK and Click OK on the properties screen.
8. You should now be set to communicate with the TV. To test all is okay, put the TV in standby (red light on front).
9. Now type PON in the Hyperterminal and press Enter. The TV should turn on (blue light). Now type POF and press return and it should go back to stand by. Please note typing in Hyperterminal is odd and everything will appear on one line. This is normal. Don’t try to move the cursor with the mouse or anything like I did. Just type commands (even if they overwrite what you have just typed) and press Enter. That’s it.
10. Hopefully the TV responded to PON and POF. If so then you are ready to do the fix.
Step 2.
1. Make sure your TV is in stand by (red light on front).
2. Type PON and press Enter (TV should turn on).
3. Type FAY and press Enter (Enter Factory Mode).
4. Type CPM and press Enter (Clear pulse meter).
5. Type CHM and press Enter (Clear Hour meter).
6. Type POF and press Enter (turn TV off).
7. Unplug TV for 15 seconds or so.
Note changes are not visible until the TV has been turned off and on again.
That was all I did. The red tints have gone and black luminance is back to normal. If you see sparkles on the screen you may need to adjust VOL SUS and the VOL RST P as mentioned in this forum although mine did not need adjusting.
Good luck to anyone trying this technique and please be careful. Messing around in the service menu will probably invalidate your warranty and could break your TV.
Good luck