Rhodes Chroma Polaris

> From: Paul Kavicky
> 
> My Chroma Polaris II has an issue where the sweep red light 
> doesn't work. All other membrane panel switches and lights 
> function properly. It used to work and due to a long period 
> of touring away from the synth I cannot say when it stopped working. 
> 
> I have just completed the membrane panel update and that has 
> went well. It didn't cure the issue with the sweep light not 
> coming on. Perhaps someone could point me towards which 
> things in the polaris I should be looking at specifically or 
> is having a light go out a likely possibility? if there is 
> some particular connector I should be looking at, or wire, or 
> whatnot. I'd just like to be pointed in the right direction 
> so that I could possibly troubleshoot this some more while 
> the synth is still apart. 

Are you saying that the function works, but the LED stays off? It's most
likely just a bad LED, although you can check this with a multimeter by
measuring the voltage across it when it is supposed to be on. If the LED is
open, the voltage will be a typical TTL logic 1 output voltage of at least
3.5V. If the shift register is bad, it will be less than the on voltage of
the LED, which is about 1.5V. I believe the LEDs we used predated the
high-efficiency LEDs that are available now, so try to find a crappy old
low-efficiency one, or the replacement will look a lot brighter.

There was also an issue with the shift registers that drive the LEDs
sometimes being mis-clocked by ground noise, which was solved in many
production units by soldering a capacitor around 0.1uF between the digital
ground on Z6 pin 7 and the nearby LED ground bus. If that mod has already
been done, it will be clearly visible on the circuit side of the board way
over on the left end of the panel. If it has not been done, tacking a
capacitor in there may help.

If the function doesn't work either, recheck the alignment between the tails
on that side of the panel and the connector. But it's hard to imagine
misalignment only affecting one switch, instead of a whole matrix row or
column.

Any feedback on the membrane replacement process? Were the directions clear?
Anything I should change?

-- 

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...