Roland Jupiter 8 VCO1 drift

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DesolationBlvd
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Re: Roland Jupiter 8 VCO1 drift

Post by DesolationBlvd » Thu Aug 27, 2020 7:38 pm

Don T wrote:
Wed Aug 26, 2020 3:45 am
DesolationBlvd wrote:
Tue Aug 25, 2020 11:58 am
Looked at the output of pin 6 on IC 3A, and switching between waveforms had no effect.
Ok, scope or DMM, Probe pins 8, 9, and 11 of the 3046, and repeat same test for each pin, looking for any changes from saw to square.

Also, not sure if you have seen this site, but it may be useful:

https://jup8restoration.wordpress.com/2 ... rd-repair/
So what should I be looking at on those pins - the DC voltage, or the waveform?

I'm having a feeling that it's not the 3046. The tuning is otherwise stable.

Don T
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Re: Roland Jupiter 8 VCO1 drift

Post by Don T » Fri Aug 28, 2020 11:18 am

DesolationBlvd wrote:
Thu Aug 27, 2020 7:38 pm
Don T wrote:
Wed Aug 26, 2020 3:45 am
DesolationBlvd wrote:
Tue Aug 25, 2020 11:58 am
Looked at the output of pin 6 on IC 3A, and switching between waveforms had no effect.
Ok, scope or DMM, Probe pins 8, 9, and 11 of the 3046, and repeat same test for each pin, looking for any changes from saw to square.

Also, not sure if you have seen this site, but it may be useful:

https://jup8restoration.wordpress.com/2 ... rd-repair/
So what should I be looking at on those pins - the DC voltage, or the waveform?

I'm having a feeling that it's not the 3046. The tuning is otherwise stable.
Any slight change of voltage when switching from Saw to Square. Remember, 12 cents is not a lot of difference in voltage, so you may have to use your scope (DC coupled), and set the sensitivity high. Also, while probing, I'd compare VCO 1 against a known good voice, looking for any differences.

DesolationBlvd
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Re: Roland Jupiter 8 VCO1 drift

Post by DesolationBlvd » Sat Aug 29, 2020 3:01 pm

Probed the pins on the 3046, switching between saw and pulse on VCO1. The voltage did not change.

I have attached a clip, each time rotating through the eight voices. First is VCO1 and pulse only. There seems to be a weird bleed on the odd numbered voices. There is no bleed if set to triangle, saw, or square. Second is a test of tuning with both VCOs on pulse, satisfyingly in tune, at least as much so as my OB-8. Third is when I flip VCO1 to saw and change nothing else. This is where the tuning gets thrown off.
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Don T
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Re: Roland Jupiter 8 VCO1 drift

Post by Don T » Sat Aug 29, 2020 4:53 pm

DesolationBlvd wrote:
Sat Aug 29, 2020 3:01 pm
Probed the pins on the 3046, switching between saw and pulse on VCO1. The voltage did not change.

I have attached a clip, each time rotating through the eight voices. First is VCO1 and pulse only. There seems to be a weird bleed on the odd numbered voices. There is no bleed if set to triangle, saw, or square. Second is a test of tuning with both VCOs on pulse, satisfyingly in tune, at least as much so as my OB-8. Third is when I flip VCO1 to saw and change nothing else. This is where the tuning gets thrown off.
Ok, that's just messed up! If the CV doesn't change, the pitch isn't supposed to change, unless...

Let me go look at that schematic again. Are both tempco resistors solidly against the 3046, and with thermal paste?

Perhaps the "bleed" is due to the odd-numbered voices allowing the highest overtones of a saw wave through? It sounds as if a high=pass filter is turned almost all the way up.

As tedious as this is, it may be time to probe voltages in VCO 1 and compare to any other good VCO while playing the same pitch.

Don T
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Re: Roland Jupiter 8 VCO1 drift

Post by Don T » Sat Aug 29, 2020 5:01 pm

Oh, you do have a copy of the service manual, yes?

DesolationBlvd
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Re: Roland Jupiter 8 VCO1 drift

Post by DesolationBlvd » Sat Aug 29, 2020 6:14 pm

Yep, just the second edition which is missing the first edition's Theory of Operation. I think that might be very helpful to me, seeing as I used the Theory of Operation from the DMX service manual to fix its hi-hat not properly closing.

Here's another clip. The bleeding responds to the pitch of VCO2. It does not respond to the waveform of VCO2.
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Don T
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Re: Roland Jupiter 8 VCO1 drift

Post by Don T » Sun Aug 30, 2020 10:23 am

Ok, after looking over the schematics again, I've got nothing. Sorry

DesolationBlvd
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Re: Roland Jupiter 8 VCO1 drift

Post by DesolationBlvd » Fri Sep 11, 2020 8:37 pm

Revisiting the JP-8, of note is that my +10V and -5V on the voice cards is closer to +12 and -6V respectively.

I tried to look for a rogue signal modulating the pulse width on VCO1 to create the bleed, but couldn't find it.

KSS
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Re: Roland Jupiter 8 VCO1 drift

Post by KSS » Sat Sep 12, 2020 5:31 am

Did you correct the voltages yet?
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DesolationBlvd
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Re: Roland Jupiter 8 VCO1 drift

Post by DesolationBlvd » Sat Sep 12, 2020 9:17 am

I'm actually stumped on the +10 / -5 adjustment. I followed the source to the mod-con, but there isn't a trimmer like for the 13.

Mine measures 11.35 at C61 and -6.1 at C62. (11.3, -6.13 on the lower board)
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KSS
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Re: Roland Jupiter 8 VCO1 drift

Post by KSS » Sat Sep 12, 2020 10:26 am

What type of resistors are R85,86,87,88? If they're carbon comp, replace them. R86, 88 set the 'constant' current for their zeners.
When you measured the too-high voltages, were the rails normally loaded?
Zeners will naturally vary, but they should be in the 5% range, and you're reporting more like 20%.
Treat utility modules as stars instead of backup singers.

Treat power supplies like Rockstars instead of roadies!

KSS
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Re: Roland Jupiter 8 VCO1 drift

Post by KSS » Sat Sep 12, 2020 10:30 am

Do you have a scope?
If so have a look at the rails. There might be something you'll see on scope that is misinterpreted in a meter-only reading.

Edit: and of course look at the main rails too. What do they measure?
Treat utility modules as stars instead of backup singers.

Treat power supplies like Rockstars instead of roadies!

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Re: Roland Jupiter 8 VCO1 drift

Post by KSS » Sat Sep 12, 2020 11:02 am

Just read the thread. Hadn't done that before.

Still feel like you should check the rails and zener regulated voltages -one should ALWAYS do that- but don't really think they're currently the direct source of the problem. They may still however have been the contributing factors to creating the problem in the first place. Which is why i wouldn't 'take them off the table' just yet.

Since the thread has actually two different reports, can you clarify which exactly is your current problem?
Does it go flatter after auto-tune on the single VCO of a board pair where the 2nd VCO tunes fine?
Are Saw and Pulse always different? Or only after auto-tune?

I'm presently believing something related to auto-tune, and find it potentially significant that the pitch difference between pre and post AT for the two WFs is exactly doubled in Hz. If indeed that describes your present situation.

Presently expecting this to be a cap or cracked R, or marginal trace problem.
Treat utility modules as stars instead of backup singers.

Treat power supplies like Rockstars instead of roadies!

KSS
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Re: Roland Jupiter 8 VCO1 drift

Post by KSS » Sat Sep 12, 2020 11:04 am

Speaking to the marginal trace problem -well, the R and C too- can you give us a photo of the VCO in question? PCB both sides. Both zoomed on the problem VCO and also wide enough to see both at once.
Treat utility modules as stars instead of backup singers.

Treat power supplies like Rockstars instead of roadies!

Don T
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Re: Roland Jupiter 8 VCO1 drift

Post by Don T » Sat Sep 12, 2020 6:11 pm

If I remember correctly, a lot of Roland power supplies do not have a negative rail adjustment. I assume because the value isn't as critical.

DesolationBlvd
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Re: Roland Jupiter 8 VCO1 drift

Post by DesolationBlvd » Sat Sep 12, 2020 6:14 pm

KSS wrote:
Sat Sep 12, 2020 11:02 am
Since the thread has actually two different reports, can you clarify which exactly is your current problem?
Does it go flatter after auto-tune on the single VCO of a board pair where the 2nd VCO tunes fine?
Are Saw and Pulse always different? Or only after auto-tune?
On my JP-8, the saws on the odd numbered voices are slightly flat compared to the pulses, and this is both before and after auto-tune. The auto-tune seems to work fine for the pulse.

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Re: Roland Jupiter 8 VCO1 drift

Post by Don T » Sat Sep 12, 2020 10:40 pm

DesolationBlvd wrote:
Sat Sep 12, 2020 6:14 pm

On my JP-8, the saws on the odd numbered voices are slightly flat compared to the pulses, and this is both before and after auto-tune. The auto-tune seems to work fine for the pulse.
Ah, this I did not know. I thought it was affecting only one voice, not all of them on a card. That means I had you looking in the wrong place for a voltage drop when switching from saw to square. Let me dig through the schematics again

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Re: Roland Jupiter 8 VCO1 drift

Post by KSS » Sun Sep 13, 2020 12:28 am

DesolationBlvd wrote:
Sat Sep 12, 2020 6:14 pm
On my JP-8, the saws on the odd numbered voices are slightly flat compared to the pulses, and this is both before and after auto-tune. The auto-tune seems to work fine for the pulse.
And the even numbered saws match their pulse outputs?
--------
Glad i asked. Like Don T, I thought we were talking about one vco being out. period. Details matter.
Treat utility modules as stars instead of backup singers.

Treat power supplies like Rockstars instead of roadies!

DesolationBlvd
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Re: Roland Jupiter 8 VCO1 drift

Post by DesolationBlvd » Wed Sep 30, 2020 3:15 pm

KSS wrote:
Sun Sep 13, 2020 12:28 am
DesolationBlvd wrote:
Sat Sep 12, 2020 6:14 pm
On my JP-8, the saws on the odd numbered voices are slightly flat compared to the pulses, and this is both before and after auto-tune. The auto-tune seems to work fine for the pulse.
And the even numbered saws match their pulse outputs?
--------
Glad i asked. Like Don T, I thought we were talking about one vco being out. period. Details matter.
Sorry I forgot to respond to this thread. Yes, the even saws match the pulses.

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