Was the Apollo 13 CM guidance computer fully shut down?

Question

I was watching the movie Apollo 13, and one thing struck me as quite odd. According to Wikipedia,

[Movie director Ron] Howard went to great lengths to create a technically accurate movie, employing NASA's technical assistance in astronaut and flight controller training for his cast, and even obtaining permission to film scenes aboard a reduced gravity aircraft for realistic depiction of the "weightlessness" experienced by the astronauts in space.

However, around 63 minutes into the movie, during the command module shutdown scene, the movie shows the command module's guidance computer being shut down followed by mission control stating "computer off" and specifically confirming shutdown of the CM computer with indications on one of the big screens in the background that would appear to state that the telemetry values are out of range.

What I find weird is that even after the DSKY digital display is turned off and during the "Odyssey signing off" scene immediately following it, the CM computer DSKY shows the STBY light seemingly turned on. According to Wikipedia, standby mode was originally designed for use in mid-flight and to reduce the CM computer's power consumption from 70 W to 60-65 W, though "in practice ... this feature was never used".

Obviously some things were changed for dramatic effect in the movie (for example, the apparent proximity in time between the cryo tank fans being turned on and the explosion, which in the movie is depicted as being on the order of a few seconds whereas in reality it took considerably longer), but this seems like a really silly mistake to make if one sets out to make a technically accurate movie.

• Was the CM guidance computer completely shut down following the accident on Apollo 13, or was it simply set to standby mode?
• If it was set to standby mode and the computer was designed to allow standby mode for long stretches of mid-course flight, why was this seemingly so much of a problem if (presumably) when needed the computer could relatively easily be powered back up for only a marginal increase in power drain for the short period of time it would be needed?

Bonus question:

• Even considering NASA's desire to make it possible for the crew to operate the spacecraft (relatively) autonomously, was the Apollo CM even designed so that it was possible for the astronauts to fully power off such a critical system as the main guidance computer in the middle of the flight?

Answer 1

If I get you correctly, this should be the moment from the movie you're talking about:

   

And this is the corresponding part of the movie script:

JACK SWIGERT
- Now... Do we know for sure that we can power this thing
back up?... It's going to get awfully cold in here.

ANDY (CAPCOM - WHITE)
- Copy that, Jack. We'll just have to deal with that later.

INCO - WHITE
- Computer off.

TELMU - WHITE
- We're clear.

CONTROL - WHITE
- We're go on the LM.

ANDY (CAPCOM - WHITE)
- We confirm shutdown, Jack. Lunar Module now in control.

JACK SWIGERT
- Roger that, Houston. This is Odyssey. Signing off.

JIM LOVELL
- Freddo, we're gonna have to execute some sort of a burn
here, it's just a matter of when.

JIM LOVELL (to SWIGERT)
- Did they shut us all down in there?

JACK SWIGERT
- Yeah.

To not bore you with too many details, yes, the DSKY warning lights stayed on after the power down of most of the Command Module systems and before moving to the Lunar Module. Here's the part from the Apollo 13 Technical Air-to-Ground Voice Transcription that should clear all doubts:

Mission Time: 02d 17h 39m 52s

Joe Kerwin (CAPCOM): Okay, Jim, since we're in LOW BIT RATE now, we cannot monitor the DSKY for program alarms, et cetera, and we recommend that, in order for you to do so on board, you push in the following circuit breakers: On panel 11 and panel 16 the ANNUNCIATOR / DOCK / COMPONENT circuit breakers. That will allow you to monitor your DSKY warning lights. Over.

The same transcript is also available in a bit more convenient (searchable) format on spacelog.org. And this is how the real Apollo 13 DSKY looked like:

                      

                             ^{DSKY panel on the Main Display Console of Odyssey, the surviving Command Module of Apollo 13
                             (Source: Bruce Yarbro, Papertrainer.com)}

Now, if you checked the Apollo 13 mission transcript, you probably noticed that the movie script actually has little to do with the real mission's transcript, but I guess that's OK since the procedures involved with shutting down CM systems were really nothing like flicking a standby allowed switch and setting AGC in a power-saving mode, like the movie depicts. This was in no way a normal flight computer to a standby mode procedure. It was a shutdown, as much as possible and involved a lot of on site reprograming, turning off circuit breakers and following exact sequence order so the computer could be later turned back on and still consume as little of power as possible while the crew occupied the LM on their way back to the Earth. The mission transcript attests to this with dozens of pages of comms lasting several hours, something that happened in the movie in a maybe a few seconds. Probably for the better too, I doubt we'd be having a discussion on the accuracy of this movie, if it actually was more accurate. Rare few would ever go and see it.

This hopefully answers your first two questions, now for the last one, if the Apollo CM was even designed in such a way that it was possible for the astronauts to fully power off such a critical system as the main guidance computer in the middle of the flight? No, this was certainly not something that the Apollo missions were designed for but it obviously wasn't impossible either. A lot of ingenuity went into saving the crew of Apollo 13 and getting them safely back home. The ground team was working around the clock to think of ways to solve problems the crew was faced with, and powering down the CM merely being one of them. Apollo missions of course had all kinds of contingency plans (emergency power down being one of them), but with this one, everyone was thinking on their feet:

03 07 34 23 LMP Okay. Is it going to be better to write this
                on a blank page, Vance, or can we use some portion
                of the power down list there in the contingency
                book that already exists.
03 07 34 33 CC  Stand by 1.
03 07 36 03 CC  Aquarius, Houston. Over.
03 07 36 07 CDR Go ahead.
03 07 36 08 CC  Slight delay here, Jim. It will be a couple of
                minutes before we read that up to you, and we're
                looking at the contingency checklist power down
                and that's on page 5. You might be getting that
                out while we get all ready to give it to you.
03 07 37 03 LMP Could you give us that page number again. Page 5
                doesn't make sense.
03 07 37 14 CC  Okay. Make that power 5 in the contingency
                checklist, Fred. And it's the - -
03 07 37 24 LMP - - that's better.

TL;DR: Yes, this shot makes sense in the Apollo 13 movie, even if the script didn't follow the mission transcript exactly to the letter: