Roland SH-1000 unstable tune

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Mrhands
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Roland SH-1000 unstable tune

Post by Mrhands » Fri Aug 05, 2022 10:29 pm

Hi, I need help with the old guy Roland sh-1000.

The tune is the main issue...

I have to do the calibration, but before that I'm trying to get it stable.

I will try to explain the issue: For example, when I play and hold a F1, it looks stable. But if I play a note higher like a F3, and again a F1, now the F1 sounds something closer a G1 and it will falling slowly to F1, like a portamento very very slow. (Muchs slower that would be possible with the portamento fuction on)

The portamento works great when is on.

Another stranger thing is that the noise volume is changing a little how the "Random Note" fuction plays. It is not normal, right?

Any tips are welcome 🙏

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crochambeau
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Re: Roland SH-1000 unstable tune

Post by crochambeau » Sat Aug 06, 2022 1:51 pm

I'm just spit-balling. My SH-1000 is not yet in the condition to reveal anything on this, as it's dead to the world at the moment.

Sounds like the CV being fed into the VCO does not discharge completely when you transition from a high note to a lower note. Higher notes being a higher voltage, and it taking a moment for that voltage to drain off.

To stick with the water analogy (forgive me, I'm waking up over here and this is how my brain works), there is a restriction in the pipes, or a resistive ground path in a circuit node that manages DC to AC in the VCO.

I have not really digested the Roland SH-1000 schematic to identify likely problem areas, but my knee j**k reaction hinges on poor (resistive) grounding as an investigation starting point.

The noise fluctuation could be a similar issue, or it could be that the random note generator (which probably uses the noise as a signal source) is loading the noise section down at some point.

TL;DR, have you tried measuring grounds for each board and exercising the inter-board connectors?

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Re: Roland SH-1000 unstable tune

Post by Mrhands » Mon Aug 08, 2022 3:59 pm

I will check these points out! Thanks.

Another thing... Do you know what is that "pot" below the synth? Looks like a screw, but is a pot. I didn't find what its set.

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crochambeau
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Re: Roland SH-1000 unstable tune

Post by crochambeau » Mon Aug 08, 2022 5:37 pm

Mrhands wrote:
Mon Aug 08, 2022 3:59 pm
I will check these points out! Thanks.

Another thing... Do you know what is that "pot" below the synth? Looks like a screw, but is a pot. I didn't find what its set.
I'd expect it is a "master tune" adjustment, but mine is unmarked as well.

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Re: Roland SH-1000 unstable tune

Post by Mrhands » Wed Aug 10, 2022 1:13 am

The power on circuit looks right. It's difficult to solve this... :(

I recorded a video to show the issue better....


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Re: Roland SH-1000 unstable tune

Post by crochambeau » Wed Aug 10, 2022 4:39 am

Yeah, that ain't right.

What sort of equipment do you have for troubleshooting?

In looking over the schematic I see numerous drawings of what the signal should look like when probed with an oscilloscope. Access to that sort of tool may be helpful.

That said, if you're still holding off on the calibration process because it's out of whack, I'd suggest simply performing the calibration.

It is not outside the realm of possibility that your machine is simply out of calibration. When things go WAY OUT, it's not uncommon to have to perform the steps multiple times. Calibration should be harmless, and may familiarize yourself with the machines temperament.

Good luck!

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