Search found 496 matches

by adamstan
Fri Jul 11, 2008 7:21 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

can you post sound file?

I suppose, that changing rest of S/H caps in that voice should help.
by adamstan
Fri Jul 11, 2008 6:56 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

Hey, I just installed new Polyester caps for width and put back in the original Polypropylene for pitch (because my replacements havent arrived yet) It appears the detune problem is gone. Pitch tracking is still poor. So I think I'll need to replace C205 as well. What do you mean be poor pitch trac...
by adamstan
Fri Jul 11, 2008 6:02 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

As some reviewers at harmonycentral stated, in Polaris PWM affects sawtooth wave. It may happen - waveform selectors are really strange to me - it seems that you get pulse wave in one setting, and mix of sawtooth an pulse in the other, but you cannot mute pulse wave with waveform switch. So now I'm ...
by adamstan
Thu Jul 10, 2008 7:40 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

Yeah, that value seems correct, but if you have ordered new one, I would replace it anyway. I'm a little surprised that only PW cap was wrong, because it appears strange to me that "dirty" voltage on PWM input affects overall pitch (as PWM has nothing to do with sawtooth). However, it is possible, t...
by adamstan
Thu Jul 10, 2008 5:56 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

I've just found something interesting on rhodeschroma.com page
bad voice (detuned and poor pitch tracking). New S/H caps fixed voice problem
So I think we are on good way :-)
by adamstan
Thu Jul 10, 2008 5:43 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

If it's .33nF (and if it has 331 written on it, there is no other possibility ;-) ) then it is waaay to small. It certainly should be 6.8nF capacitor. When you're at it, check C205 and everything should become clear.
by adamstan
Thu Jul 10, 2008 5:16 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

Make sure it is C207, not C206, which should be .033 - sometimes designators are printed on board in strange way - check where does it connect. As .033 is much larger than 0.0068, that shouldn't be a source of your trouble - it would just cause pulsewidth to change somewhat slower. The most importan...
by adamstan
Tue Jul 08, 2008 9:21 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

justinvm wrote: Adamstan. The capacitors in the service manual have magnitude .0068 but no unit is specified. Do I assume this is uF or F ?
AFAIK American service manuals use uF by default, so this will be .0068uF - 6.8nF
by adamstan
Mon Jul 07, 2008 11:30 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

It might be difficult - that way you can only detect if they are short, but that's not enough. I would suggest replacing those 4 caps I've mentioned before (C104 to C107) - they are cheap - and check if that solves the problem. If not, the next thing to check is that 8x1Meg resistor ladder - just ch...
by adamstan
Mon Jul 07, 2008 11:15 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

So check the components responsible for CV for VCO B - C104, C105, C106, C107 capacitors and Z110 resistor ladder. If all ICs are OK, these are the only parts that may affect pitch in such weird way.

Oh, and also check all decoupling capacitors on chips power lines.
by adamstan
Mon Jul 07, 2008 11:01 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

So it looks like the capacitors fault - maybe it lost some of its capacitance or is shorted, so it doesn't hold CV, and you get pitch or PW modulation at the CV refresh rate. Is bad VCO sharp or flat?
by adamstan
Mon Jul 07, 2008 10:53 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

Does the bad VCO track the keyboard, pitch bend etc or does it just run at constant frequency?
by adamstan
Mon Jul 07, 2008 10:48 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

For me, the next suspects (after the capacitors) would be Z101 and Z102 4051 chips.
by adamstan
Mon Jul 07, 2008 10:29 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

Updated my previous post :-) The actual S/H circuits for pitch, PWm and filter cutoff are drawn on Page 5 - within the voicing circuit, as these have to be handled polyphonically.
by adamstan
Mon Jul 07, 2008 10:22 am
Forum: HELP!
Topic: CHROMA POLARIS TROUBLES, CEM 3374.
Replies: 43
Views: 2893

There's only one DAC and sample n hold circuit for all voices. But i'm obviously going to have to check it out. That's true for patch parameters I suppose. But for pitch voltage (controlled by keyboard) you need separate S/H per voice - and if a synth has autotune, then it has separate CV S/H cell ...