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OB-X problem
Old 30th June 2010
  #1
Here for the gear
 
🎧 10 years
OB-X problem

Ok, I cant be sure as this is the only OB-X i've ever owned...but I think it has a logic problem in the switch matrix...it could also be a problem with my logic heh

Stage 1: Turn both VCO's off using the OSC1 and OSC2 mixer buttons in the filter section. No Sound. All good so far.

Stage 2: Press the Sawtooth wave select buttons....and the VCO's still switch on, but the sawtooth LEDs stay dark. Pulse wave select buttons or OSC1/OSC2 mixer buttons switch them off again.... This seems wrong to me.

Alternative Stage 2(having done stage 1): Press Pulse wave select buttons, VCO's stay off, no LED..Seems correct and what I would expect.

So mixer section is stopping the Pulse waves from switching on but still letting you turn on the Sawtooth waves although with Sawtooth indicator LED's off? Does not compute.

Who's right, me or the machine!?
Old 30th June 2010
  #2
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dougt's Avatar
 
🎧 10 years
That's the normal operation. Both the X and Xa have this bug/feature. heh
Old 1st July 2010 | Show parent
  #3
Here for the gear
 
🎧 10 years
Quote:
Originally Posted by dougt ➑️
That's the normal operation. Both the X and Xa have this bug/feature. heh
Thanks Doug!! What a strange 'feature'..

Ok so I think I've fixed all the logic faults and I've repaired all the voice cards..all faults were dead 741's...

Now I've come to tune it up...VCO 2 is tuned an octave lower than VCO1 from factory with both frequency knobs fully CCW? Is that correct?

Also frequency knob on VCO1 just does octaves where as VCO2 has much more resolution? correct again?
Old 1st July 2010 | Show parent
  #4
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dougt's Avatar
 
🎧 10 years
Quote:
Originally Posted by The Doctor ➑️
Thanks Doug!! What a strange 'feature'..

Ok so I think I've fixed all the logic faults and I've repaired all the voice cards..all faults were dead 741's...

Now I've come to tune it up...VCO 2 is tuned an octave lower than VCO1 from factory with both frequency knobs fully CCW? Is that correct?

Also frequency knob on VCO1 just does octaves where as VCO2 has much more resolution? correct again?
Both VCOs should be the same pitch when their knobs are at 0. You might have a bad pot. Yes, VCO1 is only in octaves.
Old 1st July 2010 | Show parent
  #5
Here for the gear
 
🎧 10 years
Quote:
Originally Posted by dougt ➑️
Both VCOs should be the same pitch when their knobs are at 0. You might have a bad pot. Yes, VCO1 is only in octaves.
Thanks! I then noticed that the LFO was stuck on OSC2 FM all the time..traced it to bad 74C174 on the control board..swapped it out and it dropped the pitch of VCO1 down an octave to the same as VCO2 as well as fixing the LFO fault...heh

Seems like it's almost there...although the tuning calibration trims are horrible..I don't imagine it will stay in tune long with them in there..

Any recommendations to swap them out with?
Old 2nd July 2010 | Show parent
  #6
Here for the gear
 
🎧 10 years
Quote:
Originally Posted by The Doctor ➑️
Thanks! I then noticed that the LFO was stuck on OSC2 FM all the time..traced it to bad 74C174 on the control board..swapped it out and it dropped the pitch of VCO1 down an octave to the same as VCO2 as well as fixing the LFO fault...heh
This actually didn't fix the "VCO1 octave too high" problem...it couldn't possibly anyway...

When I went back to the synth it was an octave higher again...I couldn't work out why or if I had just imagined it was fixed earlier...I played around with all the controls and the bend circuits....then I hit Unison and it brought the VCO1 back to the correct octave!

I quickly saved the 'fixed' patch in memory then tried my old patches..the VCO went back to an octave higher with no way of turning it back..even Unison wouldn't do it this time...So hit my saved patch and it fixed the VCO back to normal...

So I erased all the patches I's saved in testing/calibrating with VCO1 an octave too high and saved all new patches with the VCO back to normal...seems OK now....but I still can't get my head round what is happening here!
Old 2nd July 2010 | Show parent
  #7
Here for the gear
 
🎧 10 years
Tuning the OB-X

Ok I did a tuning calibration of all the voices but I'm not sure if i'm doing it right...

Should I let it warm up for 10 minutes hit autotune so the voices are close then do the calibration? Or should I not hit autotune first so the voices are way out then.bring them in by hand and then hit autotune?

I did it the first way but Im finding after the unit has been on for an hour or so the some voices drift a bit and autotune doesnt seem to to tune them. Autotune only tunes them initially when they are way out.

EDIT: Seems to make no difference because you are supposed to hit test switch 1 beforehand which seems to do the same as auto-tuning.
Old 3rd July 2010 | Show parent
  #8
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Don Solaris's Avatar
 
4 Reviews written
🎧 10 years
Quote:
Originally Posted by The Doctor ➑️
Should I let it warm up for 10 minutes hit autotune so the voices are close then do the calibration? Or should I not hit autotune first so the voices are way out then.bring them in by hand and then hit autotune?
Don't auto-tune anything. Goal is to get those VCO to as close as possible. Later, when the machine is closed and you're playing it, it's easy to press the auto tune.

Just leave the machine 40 minutes on and tune VCOs to 440Hz. I must warn you this process is pain in the ass because as soon as you lower the lid, the temperature on the lower voice boards will change and VCOs will move. Same with the filters! This process can drive you nuts... so prepare.

Speaking of filters, set to self osc and use some spectral analysis software like Spectran, which will show you history of the previous filter, so that by hitting key 8 times, you have all 8 filters shown on the screen and see which one to tune.

BTW, and without ANY thinking, replace all the CMOS chips on the control board. Costs 40 bucks, takes 20 minutes. That's much less than tracing a problem with a scope!!! Do the same for the op amps. I will assume you replaced all electrolytes in the PSU and control board. It will solve many of the future problems... as these are reaching their life end stage.
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