Rhodes Chroma Polaris

> ... I can load patches and everything works but once the Polaris
> powers down, nothing is retained in memory - patches, tuning,
> settings all wiped.

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/polarisserviceschematics/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,

David Clarke