Rhodes Chroma Polaris

> From: rob.ocelot@...
> 
> I finally had a chance to look at this and some of the 
> conductive trace on the membrane tail had flaked off.  Very 
> easy to do if you are repeatedly plugging and unplugging the 
> tail from the connector -- but fairly easy to fix with some 
> conductive ink (I used a copper based ink from a car defogger 
> repair kit).  Thanks, Paul. 
> 
> Both membranes are working fine but a few left panel board 
> problems have cropped up:
> 
> Osc 1 PW, Osc 2 PW and PWM, Sweep Rate, Sweep Depth, and 
> Keyboard tracking silders don't work.
> Master volume slider at lowest point still has volume
> filter cutoff slider curiously affects both cutoff and sweep rate!
> 
> My first thought is that the 4051 multiplexers are damaged 
> but I swapped them from another left panel board and the same 
> problem remains.  My second thought is it's actually a right 
> panel board issue but other than the single 4051 on the right 
> board I'm not sure where else to look.
> 
> Every slider was desoldered and tested working or revived.  
> Right panel sliders all appear to be functioning normally.  I 
> double checked the panel board interconnect and that is fine. 
>  I have a second complete top panel that works as expected so 
> I'm pretty sure the problem is confied to the panel boards.

If you have a scope, make sure you see good clean 0 to 5V signals on the
control inputs to the 4051 switches.

I still suspect bad sliders. When one slider affects an adjacent one, it
usually means that the adjacent one has a wiper that isn't contacting the
resistive element. If you have a scope, and you look at the ADC line going
back to the main board, you'll see all the voltages from the various
sliders (and other analog inputs), and moving each one should affect the
voltage only in its own time slot. A slider with an open circuit wiper
will have little or no effect in its own time slot, but you'll see the
voltage hanging over from the preceding time slot, with an exponential
decay on it, since the voltage only persists into that time slot as a
charge on stray capacitance.

Sliders very often go intermittent, so that the wiper makes contact some
of the time. The culprit is bent wiper contacts, or very dirty conductive
and resistive elements. It is often possible to repair these sliders by
carefully opening them up, cleaning the conductive and resistive elements,
straightening out the bent wiper contacts (and cleaning them), and putting
them back together. It's a delicate operation, requiring a good magnifier
and perhaps some pointed tweezers, but I've managed to fix quite a few.

-- 

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