Rhodes Chroma Polaris

Alas, that wasn’t it. Solid connections there, and when I measured the output of the ALT buffer I made sure to probe at the input pin of Z46 in the timer circuit, so I know the signal was making it that far.

Past that I’m not sure I understand the tuning routine enough to know what I’m looking for. Could it be something in that timing circuit?

e

> 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@... <mailto:pderocco@...>

> From: Eric Frampton
> 
> 	Alas, that wasn't it. Solid connections there, and when 
> I measured the output of the ALT buffer I made sure to probe 
> at the input pin of Z46 in the timer circuit, so I know the 
> signal was making it that far.
> 
> 	Past that I'm not sure I understand the tuning routine 
> enough to know what I'm looking for. Could it be something in 
> that timing circuit?

It could be. But I'd still like to know if the channels sound
normal-but-out-of-tune if you forcibly enable them.

-- 

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

> From: Eric Frampton
> 
> Yes, when forcibly enabled the channels sound completely 
> normal otherwise.

Other question: when you forcibly enable the channels, does the first
oscillator sound in tune? I'm wondering if it gets part way through the
process on each channel before failing, perhaps failing on the pulse width
or the filter. If oscillator 1 is sour, then I'd concentrate on the "Timer
Interface Serial I/O" section. If it is in tune, then the problem may be
elsewhere.

The auto-tune measures the period at four pitches for osc 1, then osc 2,
then the pulse duration at two widths for osc 1, then osc 2, then the
period of filter self-oscillation at two pitches. Sometimes you get a clue
by where it fails.

If you need help figuring out the Timer Interface Serial I/O section, let
me know. Or, if you have spare parts, you could try replacing the ICs in
that section, and hope that fixes it.

-- 

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

Hi Paul -

> Other question: when you forcibly enable the channels, does the first
> oscillator sound in tune?

Sadly, it does not. It tends to sound perhaps slightly more in-tune than the second oscillator on a given voice, but that ain’t saying much.

> I'm wondering if it gets part way through the
> process on each channel before failing, perhaps failing on the pulse width
> or the filter. If oscillator 1 is sour, then I'd concentrate on the "Timer
> Interface Serial I/O" section. If it is in tune, then the problem may be
> elsewhere.

If I auto-tune any one voice and probe at the tuning buffer, I can see 4 quick waveforms, and that’s it.

> The auto-tune measures the period at four pitches for osc 1, then osc 2,
> then the pulse duration at two widths for osc 1, then osc 2, then the
> period of filter self-oscillation at two pitches. Sometimes you get a clue
> by where it fails.

Based on this description, on a given note it seems to be failing after the first oscillator, then jumping out of the routine.

> If you need help figuring out the Timer Interface Serial I/O section, let
> me know. Or, if you have spare parts, you could try replacing the ICs in
> that section, and hope that fixes it.

Thank you for that offer! I think I’ve got some of those IC’s around, so I think I’m just going to try the shotgun approach on the timer circuit. I’ll get those dropped in then report back.

e

Hi Paul (and list) -

Following up from my last report, I did go on and change all the timing circuit logic, starting with Z37, and that was indeed the ticket. Specifically, Z37 (74HC393) failed, and somehow Z46 (1489A) hadn’t completely failed, but the tune routine seemed to occur faster and the tuning more consistent with it replaced.

Yay, another Polaris is back to life!

Thanks, all.
e

> On Jan 26, 2016, at 11:11 PM, 'Paul D. DeRocco' pderocco@... [chromapolaris] <chromapolaris@yahoogroups.com> wrote:
> 
> > From: Eric Frampton
> > 
> > Yes, when forcibly enabled the channels sound completely 
> > normal otherwise.
> 
> Other question: when you forcibly enable the channels, does the first
> oscillator sound in tune? I'm wondering if it gets part way through the
> process on each channel before failing, perhaps failing on the pulse width
> or the filter. If oscillator 1 is sour, then I'd concentrate on the "Timer
> Interface Serial I/O" section. If it is in tune, then the problem may be
> elsewhere.
> 
> The auto-tune measures the period at four pitches for osc 1, then osc 2,
> then the pulse duration at two widths for osc 1, then osc 2, then the
> period of filter self-oscillation at two pitches. Sometimes you get a clue
> by where it fails.
> 
> If you need help figuring out the Timer Interface Serial I/O section, let
> me know. Or, if you have spare parts, you could try replacing the ICs in
> that section, and hope that fixes it.
> 
> -- 
> 
> Ciao, Paul D. DeRocco
> Paul  mailto:pderocco@... <mailto:pderocco@ix.netcom.com>
>