PICTORIAL / INSTALLING THE REPLACEMENT COMPONENT: Bowman guides the Pod within close proximity of the big dish antenna.

He slowly rotates the Pod so that the doors are facing the antenna and exits, carrying the replacement component.

He floats his way to the antenna and presses a key on the IBM forearm panel of his spacesuit.

The antenna stops rotating.

Pool watches him on the video screen of the command module.

At the big dish antenna, Bowman opens a panel to replace the component.

BACK INSIDE DISCOVERY.

INT POD BAY: Hal stands by.

The faulty A.O. unit lies on a testing bench connected to electronic gear. Bowman and Poole stand for some time checking their results. Various tests are applied - circuit continuity, pulse sequencer, environmental vibration, VK integrity.

BOWMAN: Well Hal, I'll be damned if I can find anything wrong with it.

HAL: Yes. . . . it's puzzling . . . . I don't think I have ever seen anything quite like this before . . . . I would recommend that we put the unit back in operation and let it fail. It should then be a simple matter to track down the cause. We can certainly afford to be out of communication for the short time it would take to replace it.

COMMUNICATIONS AREA.

MISSION CONTROL: X-Ray Delta One, this is Mission Control, roger, you're a one-niner-three-zero. We confer with your plan to replace number one unit to check fault prediction. We should advise you however, that our preliminary findings indicate that your onboard niner-triple-zero computer is in error of predicting the fault. I say again, in error of predicting the fault.

I know this sounds rather incredible, but this conclusion is based on results from our twin niner-triple-zero computer. We are skeptical ourselves and we are running cross-checking routines to determine reliability of this conclusion . Sorry about this little snag fellas, and we will get this info to you just as soon as we work it out. X-Ray Delta One, this is Mission Control two-zero-four-niner, transmission concluded.

HAL: I hope the two of you are not concerned about this.

BOWMAN: No, I'm not Hal.

HAL: Are you quite sure?

BOWMAN: Yea, I would like to ask you a question though.

HAL: Of course.

BOWMAN: How would account for this discrepancy between you and the twin 9000?

HAL: Well, I don't think there is any question about it. It can only be attributed to human error. This sort of thing has cropped up before and it has always been due to human error

POOLE: Listen Hal, there's never been any instance at all of a computer error occurring in the 9000 series has there?

HAL: None whatsoever, Frank. The 9000 series has a perfect operational record

POOLE: Well of course I know of all the wonderful achievements of the 9000 series, but are you certain there's never been any case of even the most insignificant computer error?

HAL: None whatsoever, Frank. Quite honestly I wouldn't worry myself about that.

BOWMAN: Well I'm sure you're right Hal, uh . . . fine, thanks very much. . . . Oh Frank, I having a bit of trouble with my transmitter in C Pod, I wonder if you would come down and take a look with me?

POOLE: Yea.

BOWMAN: See you later, Hal.

INT POD BAY.

BOWMAN: Rotate C Pod please, Hal.

POOLE: What sort of trouble you've been having, Dave?

BOWMAN: Well, I've been getting some interference on D channel.

POOLE: Hmm . . . we'll have a look at it.

BOWMAN: Open the door, Hal.