[Samba] net domain join fails - classic DC

[Ken Bass]

I've got a rather old setup for several computers and VM's here at home. 
It is fairly static--the other day I was decided to remove and then 
re-add one of my Linux servers to the domain. My setups it the old 
smbldap and openldap setup. Centos 7 recently updated to 4.6.2.

When I tried to join a Linux machine named 'backup' I got an error:

Failed to join domain: Failed to set password for machine account 
(NT_STATUS_WRONG_PASSWORD)

Over on the PDC:

[2017/11/21 15:36:18.948960,  2] 
../source3/passdb/pdb_ldap.c:524(init_sam_from_ldap)
   init_sam_from_ldap: Entry found for user: backup$
[2017/11/21 15:36:18.949212,  3] 
../lib/util/charset/convert_string.c:435(convert_string_talloc_handle)
   convert_string_talloc: Conversion error: Illegal multibyte 
sequence(xxxxxxx)

[2017/11/21 15:36:18.949261,  0] 
../libcli/auth/smbencrypt.c:770(decode_pw_buffer)
   decode_pw_buffer: failed to convert incoming password

It has been so many years (and versions of samba) since I set this up, I 
don't remember many of the details. :(

On linux server 'backup', I can run 'net rpc info' and it accepts the 
root/domain admin password and shows the domain and domain sid. It is 
just the join step that is failing.

The PDC has 'server max protocol = NT1' set while the backup has server 
max protocol set to SMB2. I 'assume' when joining the domain if 
negotiates the protocol.

Any ideas / suggestions? Thanks.