Does a 12" PowerBook have a PRAM battery on the logic board?

I've already run Apple Hardware Test, both quick and extensive. No issues were found.

I should have added this in the other post. Looking at the logic board, near the connector where the trackpad ribbon cable plugs into the logic board there's something that resembles an "on board battery." I can't get a good look at it but it looks like it could be a battery of some sort or perhaps a capacitor. The way it's connected is very similar to the way PCs connect batteries to mother boards.

Resetting the PMU and PRAM isn't needed, as an FYI. This is what the owner told us. I suspect he stumbled across a sequence that appeared to him to work that involved resetting these and it *seemed* to work when in fact what he was really doing was powering it on and off between resets, and powering it on and off seems to be equally as effective.

Here's what I've found:

1. In it's dysfunctional state, when the power button is pressed you hear the optical media "engage", you can hear some slight noise from the unit, but that's as far as it gets. Pressing the "CAPS LOCK" button verifies that the unit is seeing power, it just seems to have suspended it's booting process even before it getss to POST.

2. The unit can be CONSISTENTLY started using the following procedure:

a. Turn the power on as in (1.) above and let the unit sit there in it's semi-on state for 2 minutes.

b. Power the unit off. I do this by pressing teh CAPS LOCK key to verify that the unit is receiving power and then holding the power button until the CAPS LOCK button goes out.

c. Press the power button. Voila....the unit will now start. However, the amount of RAM, time, and probably other settings as well will be lost


This whole thing seems like a charging/discharging problem. If you leave the unit powered off for between 4 and 5 minutes, powering it up always leads to the condition described in (1.) above. If you let it stay in the condition stated in (1.) above, where it's receiving power, just not running, the item will go ahead and start after about two minutes....but PRAM values seem lost.

Exactly how does the PRAM retain it's values?

From what I can tell, this device uses a "mega capacitor" to maintain the charge on the memory. It looks almost like a battery that I put into one of my old cameras. This capacitor sits between the trackpad and the optical drive. The owner of this system did a DVD upgrade himself and it appears in the process he actually knocked this capacitor off it's base on the mother board. It superficially APPEARS to be connected because there's a bar on the top end of the capacitor soldered to the motherboard that's holding it in place, but the bottom end broke off the motherboard.

The boss of our company theorizes as follows:

1. The PRAM and NVRAM has a high impedance, and when the mega capacitor is properly connected and without power, the discharge rate based on the RC time constant is very long (probably weeks...maybe months).

2. When power is turned off it's the duty of this effective RC network to maintain PRAM and NVRAM since the discharge rate is so slow.

3. With this capacitor busted off, the only capacitance that exists in the circuit is likely that of RF bypass capacitors and any other capacitors that may be used to filter out the supply. Since these are likely much, much lower in value the RC time constant becomes minutes instead of days/weeks/months.

I think this is a good theory for the following reasons:

1. If the unit sits, powered off, for any amount of time greater than 3-4 minutes and it's powered up, the unit comes on, but the CPU doesn't start processing. The optical media initializes, the caps lock key will light, and if you listen closely to the unit you can hear stuff running....but the CPU doesn't start. The conjecture is that the all PRAM/NVRAM parameters have been lost and when the CPU starts it sees nothing there and hence, does nothing. The unit is actually running, it just doesn't do anything.

2. If the unit sits, powered off, for any amount of time greater than 3-4 minutes, the following process will allow it to start up:

a. Turn the power on and leave it on for about 2-3 minutes. This is the dysfunctional state identified above, but what seems to be happening is that the effective RC network is being charged.

b. After several minutes, turn the unit off and then immediately turn it on.

c. The unit boots successfully.

d. We can turn the unit off, and turn it on again, and it will successfully boot as long as we do it relatively quickly (within a minute or two), but if it's left off more than that then the "game" identified in steps a-c must be repeated.

To me this implies the unit relies completely on the "mega-capacitor" to retain voltage on the PRAM/NVRAM. It sort of makes sense because the equivalent impedance of a battery is low compared to that of the RAM chips and it would have the effect of limiting the RC time constant needed for the unit to retain it's PRAM/NVRAM parameters for a very long period of time. That isn't to say the battery isn't supplying anything to the unit when power is off...it may very well be, but I suspect it simply isn't doing it to this circuit.

Does this theory make sense?