Re: Z-RAM ultra 2... replacing the battery?

[mjmahon@aol.com (Michael J. Mahon)]

Wayne Stewart wrote:

>Gary wrote:
>
>> Yes, I had it running for several hours last night, and several hours
>> tonight. I guess I could leave it run overnight and see if that has an
>> effect, but I tend to get nervous about leaving elderly electronics running
>> without me there to keep an eye on them, at least when I've just taken them
>> out of storage... I'm sure I'm just being paranoid, though.
>> 
>> When I pull the card again, I'll test the battery leads with a voltmeter
>and
>> see if I get anything,
>
>I'd think that if it wouldn't work after a few hours, more time isn't
>likely to help. Having a rechargable battery, you'd think that the
>charging circuit would power the clock even with a dead battery. If
>you can, it'd be nice to check the voltage at the battery leads when
>the IIc is running in case it's the charging circuit that's not
>working

That's right.  The circuit operates from the battery _only_ when
the computer power is off.

That means that the software is choking because the clock
currently contains an invalid date/time.  Try running the clock
setting software and see if that fixes it for a warm boot (since
the battery is still not known to be working).

If that works, then try it after a power cycle--since the battery
may be working fine after being recharged a bit.

If that works, try lengthening the power-off interval to see
if the battery holds enough charge to be useful--eventually
it should keep running for a few months of no power if it's
working as it should.  (In this case, that means that it will
take a near-capacity charge and its self-discharge rate is
sufficiently low.)

If the clock won't work with power applied, then it won't work
with a new battery either.

So, if the clock works after setting, but the battery doesn't
hold a charge, the next step is to replace the NiCd battery
with an equivalent--3.6v about 100mAh.  The capacity rating
is non-critical, but the voltage should be adhered to, since
the clock chip is rated for a certain minimum "hold setting"
voltage, and three cells (3.6v) was the design voltage.

Occasionally, you may get lucky and find a clock chip that
continues to work correctly down to 1.8v, which would allow
the use of two _fully charged_ cells producing 2.4v (minus the
0.6v forward drop of the blocking diode in the circuit), but the
designers didn't want to count on it, and neither would I.

_Do not_ substitute a non-rechargeable battery or (especially)
a lithium cell for a NiCd, unless you also disable the recharging
circuit, since that is risking leakage or worse.

-michael

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