Forgot to Zap PRAM after new Pram battery and now no screen

Question

Forgot to Zap PRAM after new Pram battery and now no screen

Hi,

I installed a new pram battery into my old G4 800MHz workhorse. It started up great, telling me that my date and time settings were probably wrong. I figured this was due to the battery change. I clicked OK and then walked away for a moment to deal with crabby relatives. Walked back and saw my normal screen had changed to a black screen. I restarted. Same thing. I pulled out the new battery and put it back in, and then remembered that I had not reset the PRAM, so I held down the apple + option + P + R and used my foot to restart the computer. Same old black screen.

I tried hooking up the firewire to another of my Macs to troubleshoot with disk doctor but could not get the firewire icon to appear on the G4 *holding down the T key when restarting after hooking up the cable to my other mac).

Does anyone have any other ideas about what I should do?

Powerbook G4 800MHz fw, Mac OS X (10.3.9)

Posted on Nov 27, 2006 9:04 AM

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Answer 1

Nov 29, 2006 5:07 PM in response to Sheila Anderson1

Sheila,

You needed to reset the PMU (Power Management Unit) after the battery replacement by pressing the PMU reset switch on the motherboard instead of rebooting while pressing the Apple + Option + P + R keyboard combination. Pressing the PMU reset switch effectively resets the PRAM as you had mentioned.

The following are Apple's instructions for replacing the battery:

1. Disconnect the power cord and check the battery in the battery holder (BT1). The battery should read 3.3 V to 3.7 V. If the battery is bad, replace the battery, wait ten seconds, and then reset the PMU (refer to the next step). If the battery is good, go to the next step.

2. Press the PMU reset switch (S1) once on the logic board. Do not press the PMU reset switch a second time because it could stop the PMU chip from responding.

3. Wait ten seconds before connecting the power cord and turning the computer on.

The location of the PMU switch can be found here.

Apple also gives the following warning:

Important: Be very careful when handling the main logic board. Remove the battery when handling the logic board so the PMU is not affected. The PMU is very sensitive and touching the circuitry on the logic board can cause the PMU to stop responding. If the PMU stops responding, the battery life goes from about five years to about two days if the PMU is not reset.

Good luck.
Keith

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Answer 2

Nov 30, 2006 9:00 AM in response to Keith Parobek

Hi Keith,

Thanks for the detailed instrux. I will check it out and will let you know how things go.

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Answer 3

Dec 8, 2006 7:55 AM in response to Sheila Anderson1

Keith,

I checked out the diagram that shows me the PMU switch and I think I touched it but it seemed to be more of an internal screw that holds the external case to the internal body. I restarted it and got a blank screen.

I had our tech support people at work take a look at it when it was giving me a blank screen upon start-up and they said it was a matter of replacing the pram battery.

Before I made this post I had replaced the battery and started up without zapping and without touching the PMU switch. I got the start up song and the screen to light up that first time, but after I walked away from the screen it turned black and has stayed this way since then.

Is there anything else I can do other than take it back in, you think?

Thanks,
Sheila

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Answer 4

Dec 10, 2006 7:35 PM in response to Sheila Anderson1

Try things in Texas Mac Mans battery tutorial.

There is also Apple doc.#106464 in case you need it.

Cheers!
DALE

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