Reflowing components on the board is usually a last-ditch effort and there are other things you could try before resorting to this.
- Remove installed RAM
- Check for any leaking caps
- Check PRAM battery
- Disassemble machine down to basics, eg. just LCD and logic board
- Clean all contacts, connectors with contact cleaner and freeze spray board before firing up
... I had a 3400/240c with similar issues, it was related to a faulty sound controller board/chip/PMU issue. It wouldn't start up properly, and when it would it would let out a screech from the speakers. Once the OS loaded, restarting with a PRAM reset made it work fine.
- Remove installed RAM
- Check for any leaking caps
- Check PRAM battery
- Disassemble machine down to basics, eg. just LCD and logic board
- Clean all contacts, connectors with contact cleaner and freeze spray board before firing up
... I had a 3400/240c with similar issues, it was related to a faulty sound controller board/chip/PMU issue. It wouldn't start up properly, and when it would it would let out a screech from the speakers. Once the OS loaded, restarting with a PRAM reset made it work fine.