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Powerbook 3400 won't keep PRAM settings

Message #1 - Posted 2005/06/18 - Ilkka Huikari

Hello all,

My Powerbook 3400c (200 MHz) will forget its time and date and all OpenFirmware settings, if the main battery and charger are both disconnected. After that it also won't power on unless the carger is connected even briefly.

At first I thought the pram battery is dead. I checked it, even peeled off some of the plastic to measure the voltages at the battery contacts, and it seems fine. When the charger is plugged in, I get 10-14 volts, and unplugged it has about 8 volts. Seems okay for a 7.2V battery, right?

So what's wrong? I have tried zapping the pram, I've held the reset button down for a minute, and the pram battery has been disconnected. So far nothing has helped.

BR, Ilkka

Message #2 - Posted 2005/06/18 - Grandpa Koca

Ilkka Huikari wrote:

Hello all,

My Powerbook 3400c (200 MHz) will forget its time and date and all OpenFirmware settings, if the main battery and charger are both disconnected. After that it also won't power on unless the carger is connected even briefly.

At first I thought the pram battery is dead. I checked it, even peeled off some of the plastic to measure the voltages at the battery contacts, and it seems fine. When the charger is plugged in, I get 10-14 volts, and unplugged it has about 8 volts. Seems okay for a 7.2V battery, right?

So what's wrong? I have tried zapping the pram, I've held the reset button down for a minute, and the pram battery has been disconnected. So far nothing has helped.

BR, Ilkka

Replace the pram battery. Voltage is one thing, it can't supply the current needed to keep the pram operational.

Grandpa Koca - SAHD for 6 - Keeper of the Perpetual Kindergarten

What is that dripping from my fingers?
Why it looks like time.

Message #3 - Posted 2005/06/18 - pailface88

I ssupect your PRAM battery becuase you should never be able to measure 10-14 volts on it with it charging. That suggests that the PRAM battery has failed in the 'open' mode (high internal resitstance). The battery should hold the voltage down, not let it rise to whatever high voltage might be used to charge it. In othere words, a rechargable battery behaves like a voltage regulator.

That you can measure 8 volts on the battery is confusing though unless you are measuring it with it disconnected, and of course with a high impedance meter such as almost any digital volt meter.

One thing that is common with the 3400's PRAM battery is that when they get old they leak, and that green corrosive stuff can migrate all the way thru the wires to the other end of the wires where they connect to the power board.

Message #4 - Posted 2005/06/19 - Ilkka Huikari

pailface88@yahoo.com wrote in message news:<1119115156.435833.76730@g14g2000cwa.googlegroups.com>...

That you can measure 8 volts on the battery is confusing though unless you are measuring it with it disconnected, and of course with a high impedance meter such as almost any digital volt meter.

I thought so too. And the battery was connected to the 'book. If the battery was dead, shouldn't the voltage drop close to zero as soon as external power is removed?

One thing that is common with the 3400's PRAM battery is that when they get old they leak, and that green corrosive stuff can migrate all the way thru the wires to the other end of the wires where they connect to the power board.

I wondered where that bluish goo came from. And yes, the battery looked like it had leaked under the plastic covering, but since it seemed to have voltage in it I thought the clock should still work. I guess I'll replace it anyway.

Suppose the wiring's gone bad all the way to the power board. How do I get to it?

br, Ilkka

Message #5 - Posted 2005/06/20 - Ilkka Huikari

Update.

I tore the powerbook apart today and studied it more carefully. Getting to the power board was easy enough once I figured out how to remove the trackpad panel.

You were right, the battery does indeed need replacement. Even though it read plenty of volts on its own, it only had just enough power to make a standard led glow (without a series resistor, mind you). That ain't a lot of current.

However, I still needed a reason to buy the (possibly expensive in Finland) battery. The wires were ok (though corroded all the way) so the voltage was reaching the power board. And memory chips and a clock don't need much current. But what I hadn't notice before was that when the charger was plugged in and the 'book turned itself on, there was a brief current draw from the pram battery. This brought the dead battery to its knees and obviously reset the clock and other settings. Substituting it with a lab PSU, the laptop worked correctly. And this confirms to me that a new battery will fix it.

Digging in there, I noticed a tiny fan. It didn't look like it was doing much of anything, at least cooling-wise. When is it supposed to run? At least the hard drive gets very hot, sometimes it becomes impossible to rest your hand on the left side of the trackpad panel.

br, Ilkka

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