OK, so I've done some more testing now and I don't think it's the joystick or tune board.
If I play a single note , say a C it shows 523.13 hz ( I haven't tuned it perfectly using the tune slider but in this case it doesn't have to be perfect as I will explain)
If I play a few notes it's fine but while playing chords it will go out of tune after a few presses. It seems to add some kind of offset to some of the notes not all of them and it seems to shift around the notes, some being in tune and then the next time they are pressed they are not.
The 523.13hz C note from earlier is now 519.22hz if I only press that key.
I can make the problem go away by playing a few more chords, and then C becomes 523.13hz again. If I keep playing chords the problem comes back and the whole cycle repeats.
I played an octave of keys one key at a time after power-up and the frequency intervals where close to what they should be.
I then played and octave of keys one key at a time after playing chords to make the fault appear.
I will have to see if the clock sources are stable.
I haven't as yet worked out if a certain combination of key presses are doing this but it will only go out of tune If I'm pressing chords. It won't do it I I only press a single note at a time.
On Thursday, 30 October 2014, 14:42, "Martin Ator cyllall@... [korgpolyex]" <korgpolyex@yahoogroups.com> wrote:
Thanks Mike.
It makes sense to check the joystick as they're vulnerable to damage being so exposed, there could be a damaged pcb track or something. I'll also try a heavier power supply and see if there's a change.
Ta.
On Thursday, 30 October 2014, 13:15, "Michael Hawkins korgpolyex800@... [korgpolyex]" <korgpolyex@yahoogroups.com> wrote:
I would start and go in this order:
POTs integrity in the joystick and tuning boards.
Wiring integrity in the joystick and tuning boards.
Check your PSU is 500mA or more. I know that Poly is supposed to run on 300mA 9V DC PSU's but I've found that to be right at the edge of being enough. Don't worry about blowing up your Poly, Poly will only use the current that she needs. However, voltage MUST be correct - 9 volts DC.
/Mike
On Wednesday, October 29, 2014 7:54 PM, "cyllall@... [korgpolyex]" <korgpolyex@yahoogroups.com> wrote:
Hello,
I've got a poly-800 here that sounds like it's having trouble staying in tune.
The more notes I play together the more it seems to go out of tune, like a detuning effect but not pleasant sounding.
I set the internal master oscillator as close as I could get it. I can play the C notes and they are all close to the correct frequency. If I change patches, play a little (it sounds out of tune now) and then go back to the patch I used for tuning (the one in the service manual) and press the C notes individually so I can check their frequency they are off a little from what they should be.
If I then press the 'Hold' button and then press a C note I can hear the note slewing back up to the correct frequency (that which I set before) and it will stay in tune for a few presses and then drift off again.
I have checked the power supplies and they are fine although I haven't measured it while I'm making the system work harder (playing notes).
I'm thinking lazy op-amp somewhere.
Anyone got a better idea?
Cheers
Martin