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Poly 800 Takes a while on start to get to tune, than tune is instabil

2015-02-27 by borislav.wurst@...

hi
My poly 800 Takes about 10 seconds until you Hear anything. Then the tune goes Up until it nearly stabilize But it still changes it tune...

I checked all the voltages and they Seem right.
Even exchanged the coil but still the same problem.

If i Touch a capacitor around the coil it changes tune down some halftones.
And it is not stable in tune. It goes Up very slowly when it reaches the normal tune.

And the Joystick doesnt Seem to work too. As when i try to pitch bend it very slowly changes the pitch and vcf and dco Modulation doesnt work at all.
I tried it With the Joystick not Connected But still the same Problem with the tune!
Batteries are Full and the powersupply works Fine.

Any suggestions?

I will try changing the capacitors

Thanks very much
Alex

Re: [korgpolyex] Poly 800 Takes a while on start to get to tune, than tune is instabil

2015-02-27 by gordon@...

On Fri, Feb 27, 2015 at 01:01:37AM -0800, borislav.wurst@... [korgpolyex] wrote:

> hi
> My poly 800 Takes about 10 seconds until you Hear anything. Then the tune goes Up until it nearly stabilize But it still changes it tune...
>
> I checked all the voltages and they Seem right.
> Even exchanged the coil but still the same problem.
>
> If i Touch a capacitor around the coil it changes tune down some halftones.
> And it is not stable in tune. It goes Up very slowly when it reaches the normal tune.

Which coil is this, the one in the power supply? Sounds like a lack of regulation somewhere...

> And the Joystick doesnt Seem to work too. As when i try to pitch bend it very slowly changes the pitch and vcf and dco Modulation doesnt work at all.
> I tried it With the Joystick not Connected But still the same Problem with the tune!
> Batteries are Full and the powersupply works Fine.

Make sure your power supply is rated for at least 1A. It's better to have far more current than you need at the right voltage, so it doesn't sag.

> Any suggestions?
>
> I will try changing the capacitors

Don't just start ripping capacitors out and replacing them, that can only make things worse. Work out if they're actually faulty first. I've changed a dozen or so faulty electrolytics in 25 years. They just don't fail that often, outside of cheap crappy switched-mode power supplies.

--
Gordonjcp MM0YEQ

Re: [korgpolyex] Poly 800 Takes a while on start to get to tune, than tune is instabil

2015-02-27 by borislav.wurst@...

it is the coil for tuning

the powersupply is fine! works perfectly on my ex800

the voltages are right, -5 and +5v coming directly after turning on.

what else wonders me is that it sounds like the filter frequencies is sweeping up with the tune...

after 30 seconds or so it nearly holds the tune, but still changes tune very slightly up

Re: [korgpolyex] Poly 800 Takes a while on start to get to tune, than tune is instabil

2015-02-27 by gordon@...

On Fri, Feb 27, 2015 at 01:59:20AM -0800, borislav.wurst@... [korgpolyex] wrote:

> hi
>
> it is the coil for tuning
>
>
> the powersupply is fine! works perfectly on my ex800
>
>
> the voltages are right, -5 and +5v coming directly after turning on.
>
>
> what else wonders me is that it sounds like the filter frequencies is sweeping up with the tune...
>

Can you measure the filter CV as you power it up? Could it be heat related?

It's time to get oldschool, the way we used to fix drifty problems in TVs and VCRs back when we fixed them instead of throwing them out. Get at it with a tin of freezer spray and a hair dryer. Gently heat and cool bits until you find one that seems excessively sensitive to heat.

I'd put a very small wager on you finding that it's either a regulator tranny or a disc ceramic capacitor somewhere in the PSU.

--
Gordonjcp MM0YEQ

Re: [korgpolyex] Poly 800 Takes a while on start to get to tune, than tune is instabil

2015-02-27 by Martin Ator

Check that you can hear the detune functions working 38 ,0-3 properly. No detune on 0 then some on 1 , more on 2 and most on 3.Check for battery acid damage on the circuit board, rusty IC pin in the middle of nice shiny ones etc.

On Friday, 27 February 2015, 10:19, "gordon@... [korgpolyex]" <korgpolyex@yahoogroups.com> wrote:

On Fri, Feb 27, 2015 at 01:59:20AM -0800, borislav.wurst@... [korgpolyex] wrote:
> hi
>
> it is the coil for tuning
>
>
> the powersupply is fine! works perfectly on my ex800
>
>
> the voltages are right, -5 and +5v coming directly after turning on.
>
>
> what else wonders me is that it sounds like the filter frequencies is sweeping up with the tune...
>

Can you measure the filter CV as you power it up? Could it be heat related?

It's time to get oldschool, the way we used to fix drifty problems in TVs and VCRs back when we fixed them instead of throwing them out. Get at it with a tin of freezer spray and a hair dryer. Gently heat and cool bits until you find one that seems excessively sensitive to heat.

I'd put a very small wager on you finding that it's either a regulator tranny or a disc ceramic capacitor somewhere in the PSU.

--
Gordonjcp MM0YEQ

Re: [korgpolyex] Poly 800 Takes a while on start to get to tune, than tune is instabil

2015-02-28 by borislav.wurst@...

detune works
Everything works But not The Modulation and pitchbend Joystick
But even without that the problem stays.
There is no damage On the board! And it is not the Transistors from the Power supply!

When you turn the poly of and directly On it is not completly down tuned But it Takes a while Till it reaches the Almost stable tune again...

Thanks very much

Alex