How to reset PRAM (or NVRAM) in 10.68 if "Command-option-P-R" on startup won't work?

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Level 2

244 points

How to reset PRAM (or NVRAM) in 10.68 if "Command-option-P-R" on startup won't work?

Using a 2007 white plastic iMac with 20" screen and 2 GHz Intel Core Duo, running OSX 10.6.8.

I need to try resetting PRAM/NVRAM to possibly solve a problem (about screen dimness, discussed here: iMac 20" 2007 display dims itself for no reason; "calibration" does not help).

HOWEVER, when I try the standard technique for resetting the PRAM -- Turn off, wait ten seconds, turn on and IMMEDIATELY hold down "Command-option-P-R" before the grey screen appears, then keep holding that key combination until the chime sounds a second (or maybe even third) time sounds -- NOTHING HAPPENS. The computer just restarts as normal. Only one chime, and then the startup proceeds uninterrupted, despite the fact that I continue to hold the keys down. I can't get it to recognize that I'm holding down the keys. I've tried it now ten times, different ways, different timing, and it just won't work no matter how I do it.

I've been using Macs since 1984 and so I know how to reset the PRAM, and have done it many many times with many computers over the years. So I know what I'm doing. Except this time, for no known reason, it won't work.

The keyboard is a standard Apple USB keyboard that came with the computer. The keyboard is functioning perfectly -- works fine when the computer is in use. So that's not the problem.

Questions:

Is there some way to reset the PRAM on this machine with this OS via some other technique -- Terminal command, system software, third-party software, whatever?

Also: Does this computer have PRAM, or NVRAM? Does it make a difference? If so, is there a way to reset the NVRAM?

If the answer is "No" to all the questions above, is there some way to "fix" the problem of not being able to reset the PRAM using keyboard commands upon startup?

Any help or recommendations would be appreciated.

Posted on Aug 28, 2014 4:23 PM

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Answer 1

Kappy

Level 10

361,731 points

Aug 28, 2014 4:25 PM in response to Tuffy Nicolas

See Resetting your Mac's PRAM and NVRAM.

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Answer 2

Tuffy Nicolas Author

Level 2

244 points

Aug 28, 2014 4:31 PM in response to Kappy

Kappy, I've read that page many times already today, and it does NOT contain the solution to my question.

First, it just gives the standard technique for resetting the PRAM, which as mentioned does not work for me.

And then it says that if that technique doesn't work, then try this other technique, linking to this page (PowerPC: "To continue booting, type 'mac-boot' and press return" Message), but on that linked page, it says, specifically, "Note: this article applies only to PowerPC-based Mac computers."

So, hmmmmm, now what?

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Answer 3

Kappy

Level 10

361,731 points

Aug 28, 2014 4:38 PM in response to Tuffy Nicolas

See Terminal command to reset PRAM? | Apple Support Communities.

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Answer 4

Tuffy Nicolas Author

Level 2

244 points

Aug 28, 2014 11:46 PM in response to Kappy

OK, I tried the instructions in that link about how to reset PRAM/NVRAM using Terminal.

Did it work? Well, I'm not entirely sure -- entering the commands did not by itself restart the computer, so I entered them, then had to manually quit Terminal and everything and restart it myself. And when it restarted, there was no double-chime or anything out of the ordinary -- couldn't really tell if the NVRAM or PRAM was reset at all.

But whatever happened or didn't happen -- it worked! Because after doing the Terminal command and then restarting, the computer seems to be back to normal brightness! (Can't tell for absolute sure, because I forgot how bright it was to begin with, but it's definitely brighter than it was before.)

The one thing I'm concerned about is that this Terminal command is somehow now "permanent" and will zap the NVRAM every time I restart the machine -- but a comment on the linked page says "Note that resetting the PRAM will wipe out the contents of the boot-args environment variable, which means the command would need to be reissued each startup," which seems to indicate that it isn't permanent. I hope.

Anyway, for the record, the screen dimness was at least partially and maybe totally rectified by doing the Terminal command to zap the NVRAM (at least I assume that's what happened), so as a result I'll give Kappy a "helped" star and note this thread as "answered."

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