Rhodes Chroma Polaris

Hi all -

I’ve got a Polaris on the bench with some issues. It came in with a dying membrane, so the first order of business was to replace that. Done and working.

Once I was able to control the machine again, I discovered that all 6 voices fail autotune.

I hit Tune All and the computer disables all 6. LED doesn’t even blink - just lights once and goes out.
When I manually re-enable the voices, both oscillators on all 6 voices work and track the keyboard. They’re just out of tune and out of scale.
Checked the calibrations on the PSU, DAC, ADC according to the service manual, all are perfect to 4 decimal places.
Checked the DAC by sweeping filter and detune, and all bits seem to be working (no glitches).
Watching the Tune buffer on the output board on my scope, when I hit Tune all I see 6 waveforms flash by, then nothing.
The output of Z62, the 4051 mux'ing the tuning standard voltages to the DAC, looks right (at least, I can make out different voltages in the pulse train, and they’re all around 2.5-3V)
The output of Z31, Channel Control for the Aux switches, looks right (IOW, as I hit Tune All and probe each output, I can see each one go high for a moment)

Thinking that perhaps the v.7 EPROMS in there had begun failing, I burned fresh v.11 ones and installed them. No change.
Everything in the machine seems to be behaving fine (as best I can tell at this point) except auto-tune.

Dunno if this is relevant, but the headphone output seems a bit noisy - it’s a high-piched digital-sounding sort of thing. It’s low enough that it would probably disappear in a mix, but it’s pretty obvious straight out of the back of the unit.

Thoughts?

Thanks,
Eric

> From: Eric
>
> I've got a Polaris on the bench with some issues. It came in
> with a dying membrane, so the first order of business was to
> replace that. Done and working.
>
> Once I was able to control the machine again, I discovered
> that all 6 voices fail autotune.
>
> I hit Tune All and the computer disables all 6. LED doesn't
> even blink - just lights once and goes out.
> When I manually re-enable the voices, both oscillators on all
> 6 voices work and track the keyboard. They're just out of
> tune and out of scale.
> Checked the calibrations on the PSU, DAC, ADC according to
> the service manual, all are perfect to 4 decimal places.
> Checked the DAC by sweeping filter and detune, and all bits
> seem to be working (no glitches).
> Watching the Tune buffer on the output board on my scope,
> when I hit Tune all I see 6 waveforms flash by, then nothing.
> The output of Z62, the 4051 mux'ing the tuning standard
> voltages to the DAC, looks right (at least, I can make out
> different voltages in the pulse train, and they're all around 2.5-3V)
> The output of Z31, Channel Control for the Aux switches,
> looks right (IOW, as I hit Tune All and probe each output, I
> can see each one go high for a moment)
>
> Thinking that perhaps the v.7 EPROMS in there had begun
> failing, I burned fresh v.11 ones and installed them. No change.
> Everything in the machine seems to be behaving fine (as best
> I can tell at this point) except auto-tune.
>
> Dunno if this is relevant, but the headphone output seems a
> bit noisy - it's a high-piched digital-sounding sort of
> thing. It's low enough that it would probably disappear in a
> mix, but it's pretty obvious straight out of the back of the unit.

The most likely culprit is a bad connection to the output board. When
tuning, the signal from each channel is routed to a different line (ALT
OUT) to the output board, where it is squared up and fed back to the main
board on the SYNTH ZCD line. It could even be a bad ground to the output
board, which could account for the audio noise, too.

--

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

Do the voices glide instead of change pitch sharply? Maybe the fast/slow for the S/Hs...
I still suspect a low bit bad on the DAC. The oscillators would fail, but the filters would change almost OK. They have had a bad failure rate in the Polaris and the OB8.

Sent from my iPad

Hi JL -

> On Jan 27, 2016, at 8:55 AM, John Leimseider john.leimseider@... [chromapolaris] <chromapolaris@yahoogroups.com> wrote:
>
> Do the voices glide instead of change pitch sharply? Maybe the fast/slow for the S/Hs…

They change pitch as fast as they’re supposed to.

> I still suspect a low bit bad on the DAC. The oscillators would fail, but the filters would change almost OK. They have had a bad failure rate in the Polaris and the OB8.

I had a spare DAC in my parts box that I bought for another project that is tested and known working. I dropped it in there, and nothing changed.

I’m thinking I’ll try the shotgun approach on the logic IC’s in the timer circuit next.

e