from cold and dark, I do the following, battery switch to onstandby switch to on move IRS from off to nav I get ON DC indicated above the IRS selectors, It goes out on the left selector but stays illuminated on the right selector. After a short period I then get an alarm tone, I did not get this prior to HF4. Any ideas? Matt

You need to get either the APU or Ground Power ON.I can't explain more detailed, because i still don't have that knowledge. But you need more electrical power than just the battery.

Yes, you sure need more power. Either start the APU or get some ground power. Peter Wolf

That alarm is telling you that you're discharging your battery. Also, after you have the APU or GPU providing electrical power, make sure you put the IRS position in on the CDU

That alarm is telling you that you're discharging your battery.

Not at all. It simply means IRS R is running on battery. If you don't do anything it'll shut down after five minutes of battery operation. That's all it means. Excessive bat discharge is indicated by the BAT DISCHARGE light on the AC/DC metering panel.

I could've sworn I heard it once even though I wasn't aligning. Oh well, we all make mistakes.

I don't know either. On general principle (and to avoid the annoying horn...), just make sure to ensure your AC power supplies as one of your first items, at least before IRS alignment.

Yeah, even if its not the intended purpose of that alarm, I always used it to remind myself that I forgot to have APU/GPU providing power.