Jupiter-4 restoration... thoughts?

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ApolloBoy
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Jupiter-4 restoration... thoughts?

Post by ApolloBoy » Thu Apr 19, 2012 10:05 pm

Ever since I recapped my Jupiter-4 a few weeks back, I've been thinking of doing more work on it in order to make it even more reliable than it already is. One thing that I'm thinking of doing is replacing all of the old CMOS logic chips and replacing them with socketed modern equivalents, as those tend to be very fragile. I'm getting a desoldering station soon so I shouldn't be encountering any of the difficulties that I had with the recapping.

So I was wondering if anyone had any thoughts about this and what other steps I should take to make my JP-4 rock solid. I've also been thinking of replacing the calibration pots but I'm not sure about that yet.
Had: DX7, AX-60, SR-16, Yamaha TQ5, 01/WFD, Juno-106, MG-1, JX-03
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Re: Jupiter-4 restoration... thoughts?

Post by schmidtc » Thu Apr 19, 2012 10:19 pm

Most B series CMOS are pretty reliable, but if the chips end in AE it might be worth it to you. I prefer the "if it ain't broke don't fix it" approach.

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Re: Jupiter-4 restoration... thoughts?

Post by adhmzaiusz » Fri Apr 20, 2012 2:47 am

Yea, I'd say with cmos it either works or it doesn't... performance wise you probably won't notice any differences in replacing anything. There is no in-between of performance in logic, since its either 'high' or 'low' or "01110111 01101111 01110010 01101011 01101001 01101110 01100111" *

•translated that means 'working'
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Re: Jupiter-4 restoration... thoughts?

Post by Don T » Sun Apr 22, 2012 4:38 am

Well, as far as replacing all the CMOS chips goes, I've learned the hard way that sometimes the modern ones don't work. For instance, when rebuilding an old Yamaha SK-15 that was having issues, there is a 4013 that controls the output relay, firing it not long after the machine starts up. Was getting no output past the relay, so I swapped it with 3 different much newer ones. Turns out the relay contacts themselves were bad. Not a single one of those new chips would fire that relay, only the original would. Luckily it was still good after all. In general, I'd leave working ones alone unless there was a good reason to switch because of current load on the power supply, like in a Polymoog.

As for replacing trimpots, if it has the really old completely open type, I'd go for it, especially given the very involved calibration procedure in the JP-4. I'd use sealed cermet ones myself. In some cases, I've gone as far as to replace a really touchy adjustment (i.e., the value changes widely even if you just barely touch the pot) with a multi-turn pot, especially if the original trimpot is used for V/Oct., scale/width, and bias adjustments.
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Re: Jupiter-4 restoration... thoughts?

Post by Steve Jones » Tue Apr 24, 2012 5:41 am

Quite a few Roland synths have circuits where the CMOS chip has to be a particular brand. The sub oscillator in the SH-101 comes to mind, the JP8 has some chips that need to be very specific also.

My best advice if you are going to do this is to service the synth first so that EVERYTHING is working. Then re-cap/re-chip one section of each board at a time. Plug it back in and test it. That way if you screw something up you will know where to look. It is suicide to just go ahead and re-chip an entire machine end to end. When you turn it on and a whole lot of stuff doesn't work you won't know where to start trying to fix it. Do it section by section and test each stage.
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Re: Jupiter-4 restoration... thoughts?

Post by ApolloBoy » Tue Apr 24, 2012 5:58 am

Well I've already recapped much of the synth (did the entire motherboard, all the voice cards and the PSU) so that's out of the way for the most part. The only sections I have left are the ensemble and key assign boards and those only have a handful of caps.

Anyway, I think I'm going to hold off on replacing the CMOS chips unless the synth starts acting funny, but I'm still considering replacing most of the calibration pots. I noticed that the fine tune and scaling pots for the voice cards seem to be multi-turn units so those will be the only ones I'll leave alone.

Also, does anyone know how the tuning knob on the front panel is wired up? I'm trying to put in a replacement and the service manual was no help. I don't want to potentially burn out a pot through trial and error so I'd really like to know.
Had: DX7, AX-60, SR-16, Yamaha TQ5, 01/WFD, Juno-106, MG-1, JX-03
Want: OB-6, Prophet 6, Jupiter-6

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Re: Jupiter-4 restoration... thoughts?

Post by Steve Jones » Tue Apr 24, 2012 6:27 am

Another very common problem with JP4's that causes all kinds of erratic behaviour is cracked PCB track on the earth trace on the top panel boards.
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Re: Jupiter-4 restoration... thoughts?

Post by ApolloBoy » Tue Apr 24, 2012 8:09 am

Steve Jones wrote:Another very common problem with JP4's that causes all kinds of erratic behaviour is cracked PCB track on the earth trace on the top panel boards.
The top panel PCBs are in good condition as far as I can tell, so I can rule those out. My Jupe's tuning was a bit unstable tonight but I think that was due to temperature changes and not anything else.
Had: DX7, AX-60, SR-16, Yamaha TQ5, 01/WFD, Juno-106, MG-1, JX-03
Want: OB-6, Prophet 6, Jupiter-6

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Re: Jupiter-4 restoration... thoughts?

Post by ApolloBoy » Mon May 07, 2012 1:49 am

Can anyone with a JP-4 open theirs up and take pics of how the tuning knob on the front is wired up? Just found a replacement pot and I have no clue how it's wired, even after looking through the service manual.
Had: DX7, AX-60, SR-16, Yamaha TQ5, 01/WFD, Juno-106, MG-1, JX-03
Want: OB-6, Prophet 6, Jupiter-6

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Re: Jupiter-4 restoration... thoughts?

Post by Don T » Mon May 07, 2012 2:41 am

ApolloBoy wrote:Can anyone with a JP-4 open theirs up and take pics of how the tuning knob on the front is wired up? Just found a replacement pot and I have no clue how it's wired, even after looking through the service manual.
The service manual isn't obvious, but here is the relevant section:

Image

The pot connects to J3 as shown. It is wired as follows: If you are looking at it from the "top", i.e., the knob end, the right terminal goes to pin 1 on J3 (+15V), the center terminal goes to pin 3 of J3, and the left terminal goes to pin 2 of J3 (-15V). In my copy of the service manual, it looks like both pin 1 and 2 on J3 are marked "-15V", so I just traced back along the schematic to be sure.

Even if this is unclear, just make sure the wiper of the pot is connected to pin 3 of J3. If you want to be double-sure, it's the pin with either zero or a couple volts on it when the synth is powered up. The other two will be either +15 or -15 Volts. Hook up the outer two terminals only (the one that go to + and -15V) then connect a DMM with the + probe to the wiper of the pot and the - probe to ground. The voltage should get more positive as the knob is turned to the right, and more negative when turned to the left.

Even then, as long as the wiper of the pot is wired correctly, the worst that can happen if you wire the outside terminals backwards is that the pitch will go the opposite direction of the markings on the control panel when the tuning knob is turned. If that happens, just go back in and switch them.

Hope this helps
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Re: Jupiter-4 restoration... thoughts?

Post by ApolloBoy » Mon May 07, 2012 6:28 am

Got it working! Turns out the voltage points for the pot were actually labeled on the bender board so I was able to get it wired up correctly on the first try. Thanks for the help though!
Had: DX7, AX-60, SR-16, Yamaha TQ5, 01/WFD, Juno-106, MG-1, JX-03
Want: OB-6, Prophet 6, Jupiter-6

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Re: Jupiter-4 restoration... thoughts?

Post by ApolloBoy » Wed Mar 02, 2016 4:27 am

So here I am almost four years later and I'm starting to think about continuing this project again. I still want to finish recapping the entire synth by doing the ensemble and key assign boards, and I also want to clean the keyboard as I have a D key that likes to retrigger every now and then. Anyone here have experience dealing with early Roland keyboards like the one used on the JP-4?
Had: DX7, AX-60, SR-16, Yamaha TQ5, 01/WFD, Juno-106, MG-1, JX-03
Want: OB-6, Prophet 6, Jupiter-6

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Re: Jupiter-4 restoration... thoughts?

Post by m_P » Fri Mar 04, 2016 4:59 pm

I had a beautiful JP-4 which had the Midi I/O mod fitted to it.
I thoroughly recommend getting that upgrade, as it replaces the original cpu and adds a ton of functions.
Don't wire up the portamento though.. It changes the sound of it.

I had a few issues with keys if I remember correctly. They can be a bit of a pig to clean the keybed, as the tracks are the old type that Roland used.. I need to rack my brain a bit more to remember..
I took it to a tech and he sorted it easily though.

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Re: Jupiter-4 restoration... thoughts?

Post by ApolloBoy » Sun Mar 06, 2016 7:10 pm

m_P wrote:I had a beautiful JP-4 which had the Midi I/O mod fitted to it.
I thoroughly recommend getting that upgrade, as it replaces the original cpu and adds a ton of functions.
I've definitely been looking into that, especially now that I have an SQ-1 and the Jupiter-4 doesn't have any kind of external control except for the arpeggiator clock.

One other thing I'd like to do is replace the hardwired power cable with an IEC socket, as I hate hardwired cords in general and I can easily swap out the power cord in case something goes wrong. I'd like to use a normal panel mount connector, but I'm not too big on cutting a big hole in my JP-4 so I'll most likely use a cable mount one instead.
Had: DX7, AX-60, SR-16, Yamaha TQ5, 01/WFD, Juno-106, MG-1, JX-03
Want: OB-6, Prophet 6, Jupiter-6

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Yamaha CS01
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Location: Campbell, CA

Re: Jupiter-4 restoration... thoughts?

Post by ApolloBoy » Sat Mar 19, 2016 8:26 am

I had time to clean the keyboard while I had my Jupiter-4 apart tonight, and it's actually ridiculously easy to clean. Once you have the keyboard out of the synth, flip it over and you have access to the busbar and metal prongs. In my case the keyboard had a ton of dust, so I just cleaned it out with some canned air and it was fairly nice looking afterwards. The issue I had with that one D key is totally gone too.
Had: DX7, AX-60, SR-16, Yamaha TQ5, 01/WFD, Juno-106, MG-1, JX-03
Want: OB-6, Prophet 6, Jupiter-6

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