I can register the other 2 rca telefield 6.0 handsets

Page 26 says you can register 6 handsets. It sounds like there are handsets already registered. De-registering is on the same page.

https://panasonic.ca/viewing/ALL/KX-TG6431/OI/TG6431_PNQX1624YA/TG6431_PNQX1624YA.pdf

..

Please be bit specific about the problem

This sounds like a registration problem, the handset(s)
and the base have lost identification with each other.

I. To address this, first de-register the handset(s) ---
do this procedure for each handset:

0. Start by taking off the battery compartment cover....

1. press [menu]
2. scroll up/down to "Settings"
3. enter * 7 8 9 0 #
4. scroll down to "next page", press [select]
5. scroll down to "Register Clear?", press [select]
6. display asks "Confirm?" or "Register Clear??", press [select]
7. display reads "Ok" and chirps, press [ off ]

8. UNPLUG THE HANDSET BATTERY (why the cover was off)

9. Wait ~30 seconds, re-connect the battery & replace the cover

10. display reads "Not Registered" ===============================

II. To register the handset to the base:

1. press [Find Handset] on the base and hold for
~4 sec until the "In Use" lamp lights.
2. press # on the handset and set the handset into
the handset cradle on the base
3. within 30 seconds or so, the handset will either
chirp and display "Handset Registered", then
"Handset #1" or it will say "Registration Failed".

NOTE: the battery must be well charged prior to the
registration process, a weak battery may cause a
"Registration Failed". Charge the battery for a few
hours and try the registration ( II ) again.

NOTE: the base can only handle 5 handsets and will
increment the number of each handset registered
until "Handset #5" has appeared, even if some of
the handsets are lost/not in use. Trying to register
more than 5 handsets will result in "Registration Failed."
===============================

III. To clear the base of all handset registrations and
be able to start registering again at Handset #1:

1. press [Find Handset] on the base and hold past ~4 sec when the "In Use" lamp lights, at
about 10 secs the "In Use" lamp will begin to
blink.
2. release the [Find Handset] button momentarily,
then briefly press it again. After a moment,
all handsets that were registered to the base
(if any) will display "Not Registered" and be
ready for fresh registration
3. for multiple handsets, return to II. above and
register each handset in turn.
===============================
Good luck !!

Follow the instructions on page 38 of the manual.

Registering a unit Operating additional
handsets
Additional handsets
Up to 6 handsets can be registered to
the base unit.
Important:
L See page 6 for information on the
available model.
Registering a handset to a
base unit
The supplied handset and base unit are
pre-registered. If for some reason the
handset is not registered to the base
unit, register the handset.
1
Handset:
{MENU} i {#}{1}{3}{0}
2
Base unit:
Press and hold {LOCATOR} for 4
seconds until the registration tone
sounds.
L If all registered handsets start
ringing, press the same button to
stop. Then repeat this step.
L The next step should be
completed within 90 seconds.
3
Handset:
Press {OK}, then wait until a long
beep sounds.
4
{OFF}
Note:
L While registering, "Base
registering" is displayed on all
registered handsets.
L When you purchase an additional
handset, refer to the additional
handset's installation manual for
registration.

To de-register HANDSET #1:

1) Grab any working handset which is registered to your base (so HANDSET #2 or #3 in your case)

2) Press and hold the "END" + "#" key for 5+ seconds (wait for it to beep)

3) Choose the "Deregister HS" menu option

4) Pick HANDSET #1 as the handset ot de-register (since that's the "phantom" registered handset)

5) Once de-registered, you can de-register handsets #2 and #3 directly from each handset's "normal" menu interface (i.e. press "Menu", choose "Deregistration")

6) Thereafter, if you re-register your handset, they should start at HANDSET #1, then #2, and so on.

I had the same problem but I fixed it by:

1. Disconnect the battery on the handset.
2. Wait 1 minute and reconnect.
3. Register handset.

1. Delete or listen to all voice mail messages, if necessary, to clear the IN USE/Voice Mail light indicator.
Note: Skip this step if it does not apply to your MD Series cordless telephone model.
2. Press OFF on the base station and each handset.
3. Press and hold down PAGE on the base station until the IN USE light flashes slowly, then release.
4. Press and hold down PAGE again until the IN USE light begins to flash quickly, then release PAGE.
5. Quickly and fully press and release PAGE again.
6. Please register handset displays. Press OK to begin the registration process, or press EXIT.

I found a solution that fixed this problem (at least for me). On the vtech site they said to unplug the base unit for at least 5 minutes. Previously, I had only unplugged the base unit for a few seconds. This time, I left it unplugged for about 10 minutes or so and when I plugged it back in, everything was working fine. Apparently there is some sort of capacitor that must discharge long enough to completely remove power from the circuitry.

Good luck and I hope this works for you!

I would assume this could have been a product that was returned to the company that you purchased it from. Follow these instructions. 1. 1. Disconnect power from the base by pulling the plug out of the back of the unit. 2. Press and hold the Page button and while holding the Page button reconnect the power. 3. Continue to hold the Page button until the charge/in use light flashes rapidly. 4. Release the Page button. 5. Press and release the page button on the base once. All handsets are de-registered and HANDSET NEEDS REGISTRATION shows in the display. Then From the Handset Setup Menu: 1. Press the caller ID-volume ( 6 or 5) button to scroll to the REGISTRATION sub-menu. 2. Press the mute/program button to enter the menu. REGISTRATION 1YES 42NO - - -shows in the display. The default setting is 2NO. 3. Use the touch-tone pad to select 1 for YES or 2 for NO. Or use the caller ID-volume ( 6 or 5) button to scroll to 1YES or 2NO. 4. If you select YES, press the mute/program button. HOLD BASE PAGE FOR 5 SECONDS, THEN PRESS HANDSET PROGRAM shows in the display. (Your handset should be held near the base during registration process.) 5. Press and hold the page button on the base unit until the charge/in use indicator flashes. Press the handset mute/program button. REGISTERING shows in the display. HANDSET X REGISTERED shows in the handset display, where X is the handset number. You may now rename your handset. (Refer to Step 3 & 4 of Handset Name Section) NOTE: IF you are re-registering the handset through the handset menu; to rename your handset you must go to the Handset Name Section and start from the beginning step. I understand that you have tried the registation process. Sometimes with electronics, you have to start from ground 0, before it will work correct again. If there are further questions or comments, please post here. Please rate this solutn through fix-it. Thank you