Ibook G4 grey screens after resolder

Here's one for the hardcore Mac re-builders. After a re-solder to fix a lockup issue, G4 gray screens when HD installed, but "HFS Volume Verified" by DU with HD installed in an external USB case.

History:
1) Got a Darwin kernel panic, tried to go around it by opening classic before panic. It worked, until computer locked up and I had to force shutdown.
2) Then would only boot to flashing question mark folder (fqmf).
3) Tried to resolve with Safe Mode, Single user, Open Firmware, Disk Utilities.
4) Replaced, partitioned and formatted HD, installed OS 10.3.9 booted normally, yeah!
5) Computer warms up, get spinning colored disk, reboot, then fqmf, get 2STF/8/3:ATA-100ata-6-Master error (HD 100 bus error).
6) Cool computer on a/c vent, boots normally until warm, locks up again, boots to fqmf, repeat. Thinking heat related short in HD connector.
7) Read a thread on cracked solder joints on logic board HD connector.
8) Sure enough, under 16x magnification find cracks around a half dozen pins on HD connector.
9) Re-solder connector pins, careful not to overheat anything, confident it will fix problem.
10) Enthusiastically reboot... GRAY SCREEN! From that point on will only chime to gray screen, never gets to apple and will no longer respond to attempts to enter Safe Mode, Single User, or Open firmware.

Facts:
With HD installed, boots to gray screen. With HD installed and install disk in, boots to gray screen then to install disk but Disk Utility looks for disks but never stops looking and HD makes vibrating noise. With no Hd installed, boots to fqmf. With HD in an external USB case, boots to fqmf then defers to installation disk, Disk Utility finds HD and verifies volume normally with no errors.

Mistakes: Unknowingly used wrong flux when soldering (zinc and Hydrocloric acid formula) obviously not intended for electronics. Wet flux may have still been under connector at startup. Neutralized acid with baking soda water (next day), let dry.

Questions: What is directly under the HD connector on the logic board that may have been affected by acidic/conductive flux? Is the PCB actually multilayered (more than just front and back)? If flux turns out not to be the problem than IYHO what caused the working system to gray screen after resolder? (rechecked all solder joints, all good)

External case with Firewire (to boot from) should be here tomorrow, may answer more questions. Thank you for your time and patience. Referals would be greatly appreciated. At this point it is a battle of wills. I could just replace the logic board, or buy a new computer for that matter, but am determined to see this fix through. I feel like I am only a few steps away from having it back again, I'm just running out of troubleshooting ideas.

Thanks again, Will Fixit.