Need help troubleshooting JP-8 bender issue

[sempervirent]

I posted this over on roland-jupiter.org but haven't heard from anyone. Reposting here and hoping that somebody knowledgeable can assist...

When I engage the ON switch for the VCF bender, it doesn't respond to bender changes, even with the slider set to the max.

Both VCOs respond (independently, as designed) to the bender when their switches are in the ON position. However, raising the VCO bender sliders changes the pitch of the current note even before the bender is engaged. This is unwanted because the pitch is not scaled to to the keyboard as you'd expect. I don't know if this is normal operation.

If the VCO behavior is normal operation, that's OK. But in that case it seems like either the VCF switch or slider is dead.

Everything else on the front panel and performance section (lower left) seems to work fine. I'd appreciate some advice from someone who can help me get this working again. It's 99% functional and I want to get everything working.

[Xero]

Originally Posted by sempervirent

I posted this over on roland-jupiter.org but haven't heard from anyone. Reposting here and hoping that somebody knowledgeable can assist...

that definitely doesn't sound normal, it shouldn't effect the pitch if the bender isn't moved, regardless of whether the switch is on/off. I bet your bender is not centered correctly or something. seems like it's off. My SH-101 actually has that same issue, but I haven't bothered trying to correct it yet as it's quite minor.

as for the vcf, well yeah, that sounds just flat out broke, hard to say if its just the slider or what, but i'm sure it's fixable...it could very well be that there's some failing components on that mod circuit board causing both issues...i'd check for all the obvious things first though like broken solder joints (especially around the sliders and stuff) and reseating any connectors going to that board...

[sempervirent]

Originally Posted by Xero

that definitely doesn't sound normal, it shouldn't effect the pitch if the bender isn't moved, regardless of whether the switch is on/off. I bet your bender is not centered correctly or something. seems like it's off. My SH-101 actually has that same issue, but I haven't bothered trying to correct it yet as it's quite minor.

as for the vcf, well yeah, that sounds just flat out broke, hard to say if its just the slider or what, but i'm sure it's fixable...it could very well be that there's some failing components on that mod circuit board causing both issues...i'd check for all the obvious things first though like broken solder joints (especially around the sliders and stuff) and reseating any connectors going to that board...

Thanks for the response. Yes, it is minor and I don't seem to use the pitch bend that much on my other synths anyway. I think the bender is centered though, because it does seem to rest perfectly in the center and when I use it for changing the VCOs the pitch interval sounds the same whether I'm changing the pitch up or down.

Looks like it's time to open it up and check for obvious things.

[sempervirent]

There actually is a broken solder joint. And it looks like somebody has had this problem before... Here's a photo of the bottom of the lower left panel:



Someone wrote "Black" and sure enough the black wire is disconnected. It seems like the wire would connect to the trace marked "4" (right above the brass screw at the bottom center) but I can't be sure. Going through the schematics now:
http://manuals.fdiskc.com/flat/Rolan...e%20Maunal.pdf

The three solder joints that connect the red, blue, and yellow wires definitely don't look original either. Maybe the whole thing was broken and badly repaired at some point in the past.

[amino]

Black should most likely be connected there. That trace is ground and black is usually ground.

My guess is that the pitch bend stick has been broken off and replaced. It happens to a lot of old Roland synths. If so you might have to "center" the pitch bender like Xero says.

[Xero]

i'd see if you can re-attach the wire. that does look like it should be the ground, since that trace is like shared by a ton of other things too. although it's odd that it'd be partially working without that connected, although maybe it is only used for the VCF? definitely seems like someone might have replaced the thing at some point, i'm just curious if the part they used is even correct, or maybe the VCF never actually was fully fixed in their repair job if they used a wrong/mismatched pot? hard to say for sure, but it should be easy enough to test.

[sempervirent]

Thanks guys. This machine was partially disassembled for cleaning and checkup before it was sold, so the seller is checking with the shop to see if they have anything to say. I couldn't make sense of the schematics but if the shop doesn't have any specific advice I'll just resolder the black wire and try it out.

Xero, I agree, it's a bit weird that anything in that area works at all. But portamento, the trigger switch, etc all seem to work normally. I'm wondering if the other wires are in the correct places – if something is crossed, that could explain the VCO issue too. The bender does work for the VCOs, it's just that the VCO sliders change the sound as if the bender was already in operation, and then the bender changes things on top of that.

[Jetty]

Originally Posted by sempervirent

Thanks guys. This machine was partially disassembled for cleaning and checkup before it was sold, so the seller is checking with the shop to see if they have anything to say. I couldn't make sense of the schematics but if the shop doesn't have any specific advice I'll just resolder the black wire and try it out.

Xero, I agree, it's a bit weird that anything in that area works at all. But portamento, the trigger switch, etc all seem to work normally. I'm wondering if the other wires are in the correct places – if something is crossed, that could explain the VCO issue too. The bender does work for the VCOs, it's just that the VCO sliders change the sound as if the bender was already in operation, and then the bender changes things on top of that.

I have a problem in that area too and have heard of at least one other case. There's something digital down there that needs to be checked and connected properly.

[backindauk]

Originally Posted by Jetty

I have a problem in that area too and have heard of at least one other case. There's something digital down there that needs to be checked and connected properly.

There is a 4051 multiplexer that can cause problems with pitch bender and the buttons if one of the circuits is not working. I'll check which one when i am not falling asleep on the keyboard

As with any similar patch-storing instrument of that era, the CMOS is starting to fail and that means what once was a very reliable synth (Roland are the king of reliability as far as vintage synths are concerned) is now a bit dicey. Also, some problems may only present when the keyboard has been running for a moderate to long period of time (hours) and can take a bit of work to get 100% sorted.

[sempervirent]

Quick update... After soldering it back to the right place (point #4 as marked in the photo), the pitch bender works as expected on both VCOs – awesome. The black wire was ground, according to the schematics.

The bad news is that the VCF still does not respond to the bender, even with the switch engaged and the slider set to any value. Could be a bad part there. I do hear a slight modulation when the bender is in motion, but it's more of a faint hum than a change to the VCF.

Tomorrow I'm talking to the tech who worked on this one before I bought it, we'll see what he has to say about the VCF issue.

[soundsubs]

my sh-101 has similar issues with the bender. basically the vco doesnt bend, but the vcf does open/close. i've looked at it closely and couldnt see anything out of order. but i'll look again for broken traces, etc.

[sempervirent]

Yeah, check it out. The bender wiring on this JP-8 looks a bit fragile (perhaps due to later service, not the factory), maybe your SH-101 is similar.

By the way, where are all the electronic music people in Colorado hiding out? Haven't really met anyone here with an interest in synthesizers... Although I did randomly talk to a guy at an electronics shop today who said that if I brought my JP-8 in for service I probably wouldn't get it back, because it would be right at home next to his Arp 2600!