Roland Jupiter 8 Repair

Hello,

I picked up a Roland Jupiter 8 at the end of last year and finally now have the time and equipment to get started with the repair. Anyone here have experience with this unit?

I saw some threads a few years back by a member Steve Jones that showed his knowledge of the synthesizer. Any help would be greatly appreciated!

As of were I stand now. I got the synth for next to nothing from a guy who was selling it for his friend. It was sitting in a case in a practice studio for a least 10 years non-functional.

When I opened it up the power supply section was gutted and there was a Dr. Sound modification installed for MIDI IN/OUT.

I tried a few power supplies I had around but surprisingly this unit draws a decent amount of power and they couldn't handle it. So since then I have acquired a Triple Output Power supply and Digital Scope and ready to debug.

I noticed so far that the unit does not always boot up right away but after a few on-off-on-off i can get it started and it looks like it boots. 8 Patch Number LEDS flash on from left to right and the Main Display shows ready. It is responsive to button touches and seems to be reactive.

BUT NO SOUND.

I have checked the VCO output test points and they are 0-10V and responsive to the MOD wheel modulation but they have no response at all to the keyboard? SO possible problem with keyboard scanning?

I have the service manual and ready to start digging,,,,but I first want to run the unit in test mode but not sure how to accomplish this? I put both switches on interface board to test and boot-up but the display just shows 32--.

Any ideas?

Hi,
how do you get the 10V on VCO testpoint ?

Also whats this MIDI-Interface ? Is it a third-party modification ?

cheers
Arne

AK79 said:

Hi,
how do you get the 10V on VCO testpoint ?

Also whats this MIDI-Interface ? Is it a third-party modification ?

Click to expand...

-I measured 0-10V Square Waveform on a oscilloscope

-Yes it is a third party modifcation

Lucky guy  [ to have one ]
not as lucky to have to fix it , but
hope you get it going

I would try to get rid of that Midi Interface for troubleshooting.

Normally these things are squeezed in between the Keyboard-Scanning and the rest on that type of synth. So if you got the impression that the sound-path basically works but does not respond to the keyboard that would be the place to start.

Did you try to drive the synth via MIDI ?

Yes. One of the first things I tried was driving it with MIDI and then trying External Control Voltages,,,,but no luck with either.

I was thinking the same thing about the MIDI modification PCB (total hack job by the way, sandwiched board/scotch tape/flabby piece of insulating plastic/jumper wires going all over)... and it is now removed and bypassed until I get some other functionality going.

external CV ? DCB ?

Jupiter 8 only has CV/Gate outputs....

or do you mean you injected CV directly into the circuit somewhere ?

BTW : Observe the CV / GATE outputs, if there is nothing on both then it is likely to be a power supply problem. If only CV is working then look at the Control Signal buffer, if only Gate is working then check Keyboard Read Buffer. Page 20 in the Service Manual

Opps sorry yes you are correct there are no CV Inputs. I did that test a few months back and forgot that. I only tried MIDI,,no injected CV.

I currently have the synth running off a triple output Lab power supply and current draw looks ok, so if there is any power issues..they must be either voltage regulators gone bad or power not getting to a particular IC.

Stop!  Before you mess with the guts anymore, the first thing you want to do is re-load the factory patches.  Those things had very unstable memory, so reloading the patches through the "cassette" input is necessary every once in a while.

You can find a WAV file of the factory patches here:

http://machines.hyperreal.org/manufacturers/Roland/Jupiter/

Well Im not so sure how re-loading the factory patches is going to help me here? But i can give it a shot.

But tonight I was able to produce a glorious Jupiter sound!! 

After tracing through the Module PCB I could see that the VCO was functioning, the VCF Filter Section also was responding correctly to my changing the frequency cutoff...however after the VCA there was nothing. So I thought there must be a triggering issue.

The keyboard output uses a 8 by 8 matrix encoding bus to represent the 61 keys,,HIGH if not pressed and LOW if pressed. I looked at one of these lines and went all up and down the keyboard but never saw it go LOW. Which is strange because the keyboard assembly is very simple just switches with diodes shorting this Line to Ground when pressed. How could this be broken? Bad cable?

Anyways I forced one of the lines manually to ground with a lead and out came my first sound!

Any ideas on what could be wrong with the keyboard circuit?

Ok so from the keyboard PCB to the interface PCB is 2 cable bundles. Somehow they were in the wrong position.....

SWAPED THEM AND IT WORKS!!!

So far looking good. Every note functioning and minus some buttons that are very hard to push and sliders not in best condition no other issues.

Ill play some with it some and see if all functionality is good.

Yeah !

Congratulations!

FYI come join us at roland-jupiter.org