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ollie · Jan 17, 2001, 05:34 PM

Hi,

how can i reset the power managment unit on an iMac DV SE 400?

Do i just zap the PRAM or is there anything further to do?

Ollie

giantmike · Jan 17, 2001, 05:59 PM

If I'm not mistaken, the only Macs with a PMU are powerbooks. The power management unit is used to better manage the power when a powerbook is running on battery power (I think I hit my daily allowance for the word power now).

If I'm wrong, someone please step in and correct me.

------------------
The Mac Information Depot. Why go anywhere else?

aircargo · Jan 24, 2001, 01:45 PM

There is a PMU reset switch on the bottom of the iMac chassis. I had to reset mine (400-DV). To gain access you must remove the bottom cover of the case, and remove the metal screen/shield (6 screws total). The switch is not labeled on the circut board (what is nowdays?). I suggest you go to the Apple support site, and do a search on PMU reset. I dont have the link handy but I found all my info there on doing mine and the instructions are clear, with a picture of where the reset switch is on the circut board. I printed the instructions and pic and it went smoothly. The hardest part was figuring out where they hid the screws to get the case apart :-)

Good Luck
Doug

ollie · Jan 24, 2001, 02:18 PM

Thanks a lot

Ollie

Damien · Jan 24, 2001, 02:31 PM

The "PMU" reset switch you describe on the bottom of the iMac isn't a PMU reset switch. It is the CUDA, which is on every desktop Macintosh produced for years.

The purpose of the CUDA is to reset the logic board, which also resets the PRAM and NVRAM. There is no power manager on the desktop Macs or iMacs.

You must be very careful when resetting the CUDA. If you press the CUDA too many times in rapid succession, you can crash the CUDA chip and have to replace your logic board. If you are going to do this, press the CUDA only once and only for 3-5 seconds with the computer unplugged (some people also like to pull the backup battery).

Again: you really shouldn't be doing this process unless you're very comfortable with your computer and understand the hardware. If you damage your LB by crashing the CUDA chip, you've violated your warranty and are SOL. Just be careful and conscientious.

Damien Barrett
Apple Solutions Expert

oscar · Jan 25, 2001, 04:04 AM

I have a program which claims to reset the PMu on any mac that has one, email me if you want it.

Damien · Jan 25, 2001, 08:21 PM

I'd be interested in seeing this program. What's its name?

Are you sure you aren't confusing PMU with PRAM? Two very different things; and there are a dozen or so PRAM resetters out there...

aircargo · Jan 25, 2001, 11:26 PM

Ok, I went to the Apple Tech Info Library and found the link. Read it and judge for yourselves whether it's a PMU reset or not.

iMac: Resetting the Power Management Unit (PMU) on the Logic Board http://til.info.apple.com/techinfo.nsf/artnum/n95002

Doug

aircargo · Feb 2, 2001, 01:36 AM

No comments from the experts? Must be a PMU reset. Apple seems to think it is.

regards,
Doug

oscar · Feb 3, 2001, 07:26 AM

No, claims to reset the power manager, no docs though, but seems to do what it claims

zac4mac · Feb 3, 2001, 03:37 PM

It appears the old CUDA is gone, as another TIL article discusses resetting the PMU in a Gigabit G4. Similar behavior, but more touchy. Thanks for the warning Damien, I laffed when you said you could do damage with repeat button pushing... then I read the TIL, Damn.

aircargo · Feb 3, 2001, 07:09 PM

I have to backtrack here, and agree with Damien, that caution is the key word here. I take it for granted that the person doing the procedure is the best judge of their ability to do something like this. Yet, I'm sure there are plenty of repair facilities that have made a nice profit on those that have misjudged their abilities :-) I had to snicker when I read Apple's warning about "pushing the reset many times in rapid succession" (or something to that effect) could damage the PMU. Not a procedure for a person with a nervous condition. I found the warnings and instructions / diagrams at the Apple tech site to be very thorough. The procedure took about 15 - 20 minutes, start to finish.
Off topic, I'm about ready to take my soldering iron to this 400 DV, if I can get that little headphone / audio circut board out. After reading Apple's procedure to get the board out though, that project is still in the debating stage (assessing abilities!). I have enough of an electronics background to be a nuisence. LOL. I cant believe how they seemed to design the entire computer around that little circut board. As a cautionary note to anyone with kids or teenagers that like to use headphones, the headphone jacks on the iMac are not anchored to anything other than the circut board itself. This means any undue stress on the headphone plug, via the cord or bumping something against the plug (keyboard, whatever) is transmitted directly to the solder connections between the jack/circut board. Maybe this lack of forethought on the designer's part has been changed in the newer models, not sure. Thought that piece of info might be useful to anyone seeing their teenager stretching the headphone cord to it's limits.

regards to all
Doug

Jsnuff1 · Feb 4, 2001, 12:49 AM

just to clear things up apple dosent have cuda chips in thier new systems, it was replaced by the PMU chip which controls power mangagment pram and the clock, i think its got its own cpu, its a prety interesting chip.