$domain = (Get-ComputerInfo).CsDomain

$srv = Resolve-DnsName -Type SRV "_ldap._tcp.dc._msdcs.$domain" |
       Sort-Object Priority, Weight |
       Select-Object -First 1

$dc = $srv.NameTarget.TrimEnd('.')
$tnc = Test-NetConnection -ComputerName $dc -Port 389

$dc
$tnc | Select-Object ComputerName, RemotePort, TcpTestSucceeded, PingSucceeded