[sdiy] [seq] 615 Multi-Trak Memory Battery Probs.

[WeAreAs1 at aol.com]

Hello Dave,

A new battery drains in six weeks?  Sheesh.  There's probably not much in 
that unit that is connected to the battery, so it shouldn't be too hard to 
troubleshoot.  I don't have those schematics, but most likely, there's just the CMOS 
static RAM chip (or chips?), and probably a single CMOS gate IC (a 4001 or 
4011 or something like that) that handles the power-off logic to put the chip in 
low-power mode when you turn the power off.  In some rare cases, you'll find 
more than one gate IC that runs from battery power, but that is unlikely.

If you don't have schematics, you can figure out which IC's run off the 
battery just by Ohming them out with your meter at their power input pins (pin 24 
on the RAM, pin 14 on most CMOS gates).  If this doesn't make sense to you, 
ask, and I'll explain in more detail.  If you don't yet have an volt/Ohm meter, 
then go out and get one.  You'll use it, and use it often, until it (or you) 
dies.

If it was me, I would simply replace both the RAM IC (or IC's, as the case 
may be) and the little gate IC, and be done with it.  I wouldn't even bother 
trying to find out which chip is drawing excess current (hint:  it's probably one 
of the RAMs...).  But I'm lazy like that, and I have parts.  

One more thing -- there's also a little diode that's part of the backup 
circuit.  It'll be a 1N914 or 1N4148.  It blocks the main 5volt supply from getting 
back to the positive side of the battery.  You'll probably find it somewhere 
near the battery.  Replace that diode, too (make sure you orient it the same 
way as the old diode).  The diode could be shorted or leaking, and that would 
definitely mess up the battery while main power was on.

Good luck!

Michael Bacich