> From: David Clarke
>
> Brett - the batteries are going to be used to power the RAM, but only
> when the unit is shut off.
>
> When main power is applied to the unit, the RAM will be
> powered by the
> on-board power supply.
>
> If the Polaris is fully functional when it is powered up (e.g., if
> you're able to save patches, recall patches, etc.) then you can be
> reasonably confident that the RAM itself is fine.
>
> When power goes away, (and when it comes up) there is a
> circuit on-board
> that switches the CMOS RAM power to/from the battery. This
> is shown in
> the "Battery Back Up Power Supply" circuit in the schematics:
>
> http://www.rhodeschroma.com/content/polarisservicemanual/polar
> isserviceschematics/computermemorydatapanelbuffersbattery.pdf
>
> If the problems only occur across a power-cycle, then the most likely
> implication is that there's something not quite right with
> regard to the
> operation of that circuit.
>
> > I have new D-cell batteries in and I check with a
> > voltmeter that indeed 3.1V is getting to the main board when
> > the power is off.
>
> It's not exactly clear from this note where the voltage was
> measured -
> but you'll want to measure it at the +5V Batt location on the
> CMOS RAM
> chips themselves (e.g., pin 26 or 28 of those devices) to
> confirm that
> it is making it to where it is needed.
>
> If it is there, you'll want to watch that voltage location with an
> 'scope to confirm that during the power on/power off the
> voltage doesn't
> glitch low.
>
> If it isn't there, then it's just a matter of tracing back to
> find where
> where the battery volage is 'lost' from the batteries (e.g., CR1 bad).
>
> Good luck, and let us know how you make out,
CR1 is the most likely culprit. If anything even momentarily shorts the
memory power line to ground, that will blow out. That could be diagnosed
easily enough with a meter. If it's bad, it should be replaced with either
an equivalent germanium diode, or perhaps a Schottky diode. A regular
silicon diode can be used in a pinch, but will not tolerate as low a battery
voltage before the RAMs lose their data.
--
Ciao, Paul D. DeRocco
Paul mailto:
pderocco@...