SRV*C:\dev\symbols*http://msdl.microsoft.com/download/symbols;\\foo\build1234
Should work fine, if \\foo\build1234 is just flat PDB’s. Cache isn’t needed here; you just need to add the directory to your symbol path.
The cache keyword specifies where you want to cache your symbol files, and is useful for caching symbols locally from non-indexed shares (like \\foo\build1234)
cache*C:\dev\symbols;SRV*C:\dev\symbols*http://msdl.microsoft.com/download/symbols;\\foo\build1234
The above path would store symbols from MS’s symbol server and your symbol share to your local machine in C:\dev\symbols.
To debug symbol issues using windbg, do
!sym noisy
.reload <some exe or DLL in your session>
And then do some action that would force the PDB to be loaded. You’ll see where windbg is looking for files, and if it rejects a PDB why it did so.
!sym quiet
Will then suppress symbol prompts.