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Replacement Coils! - JX-10 MKS-70 & JX8P
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m4thlab
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26th January 2014
Old 26th January 2014
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Replacement Coils! - JX-10 MKS-70 & JX8P

I thought this warranted a dedicated thread, for those who might have missed it, buried in Fred's MKS-70 thread, plus I didn't want to hijack that space from him, which is dedicated to providing updates on his JX-10 & MKS-70 OS rewrite, which is an amazing project in it's own right!

I've been in contact with Mark from Billy Bob's Garage, synth repair and restoration in California, who have taken the initiative to manufacture what everyone presumed impossible, or too massive an undertaking... the T1 display converter coil!

His team was completing an MKS-70 restoration project when they realized they could no longer source the coil... not deterred, they decided to make it themselves!

I've followed the infamous coil issue closely for a few years now, well enough to understand that it would likely never be resolved and that the faulty and unrepairable/replaceable coil in the JX-10, MKS-70 and JX-8P was a "time bomb" and once it goes, man... it's gone and that's that. Many attempts had been made to engage with Roland for another run, and their third party supplier Sumida, manufacturer the parts, but the volume required for them to undertake the production run was in the thousands... and we all know how keen Roland are when it comes to revisiting their old machines.

Mark has not only been able to reproduce the parts, he has also identified and rectified a design fault in them that led to their eventual failure, and corrected it! These are USA made, in California, handwound, hand-soldered. They tracked down the necessary original ferrite cores and rings and re-engineered the coils. They have created a workable, affordable solution where none existed and would probably never exist. Something out of nothing. I'm actually astounded and very grateful.

What this means for owners of these synths is immense. I know every time I looked at those glowing green segments in my JX's display, sometimes there, sometimes not, that it was only a matter of time. You couple this with the work Fred is doing to bring snappier envelopes, PWM and even an arp to the JX-10 and MKS-70 and this is a true phoenix from the flames story. These synths are about to have the renaissance they deserve.

Mark told me that this particular venture has given him the idea to follow-up with other small, no-longer-in-production items and is turning his attention to recreating the original voice chips for the Juno 106. Some are already doing this, but he wants to replicate the original chips and use 1% or tighter tolerance components.

Anyway, I'm excited about this and wanted to share. I've ordered mine, when I get it I'll take some gut shots of the installation. Just search eBay and you'll find them.
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26th January 2014
Old 26th January 2014
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well i don't have this issue but it sounds like it's good to know about! thanks for sharing, will remember this
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26th January 2014
Old 26th January 2014
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Hi there.

Thanks for the info and it's nice to hear the coils may be available. However, I've searched Ebay and haven't find anything related to the coils for either the JX8P or JX10. Is there a website or a direct link? Thanks!

Update: I just noticed I had to search for "Billy Bob's Garage" on Ebay. Found it. Thanks!
m4thlab
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26th January 2014
Old 26th January 2014
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No worries guys :-)
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26th January 2014
Old 26th January 2014
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Does this apply to all Roland machines with vacuum fluorescent displays, including rack gear, etc?
m4thlab
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26th January 2014
Old 26th January 2014
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I'm not qualified to answer, but you can probably contact Mark via his eBay store to find out. I will say that the coils for the MKS-70 and JX-10 & JX-8P had different voltage ratings, so I'd say it's unlikely that these parts would be interchangeable between different Roland models. He may be able to tackle a specific issue for you however, so maybe reach out to him.
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27th January 2014
Old 27th January 2014
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First, let me say "thank you" to m4thlab for starting this thread. And also, "wow" the response to these coils has been more than I suspected.

There are some slight differences in the power requirements between the MKS70 and he JX10/8P. Because of that the winding ratios are slightly different. I took the coil I developed for the MKS and placed it in my test JX8P and it worked, but output voltage on several of the pins were different than the control unit. In one case, one of the pins registered an output over 50% higher than the original. Because of that, I created a separate coil for the JX10/8P. The MKS70 vision may have worked just fine, but I didn't want to take the chance.

I'm more of a hobby forensic electronics restoration guy, not a fundamental design person, so I'm a little befuddled by the differences in the flyback circuit roland used on the various machines. I didn't want to chance that some design engineer in the 80's realized a problem using identical part numbers but chose not to share that with the rest of us mortals:-)

My focus has been on restoration of synths in the past ten years. I live twenty five miles from Los Angeles so the availability of old cool gear is nice, but a lot of it takes some work to bring back up to par. However, in the past six months I have found myself looking more toward creating items long lost to the synth community. The interaction with all of you over the last couple of weeks has been wonderful. I don't have an answer yet as to how many different coils Roland used in their various units, but I'm going to spend some time looking over the service manuals and BOM (bill of materials) to see what I can find.

Just a quick note on what I found with the MKS/JX coils. I'm sure there were many reasons they fail, but the two that I found while working on this project was corrosion and sealant. Corrosion: I found small pockets of green corrosion (exposed copper) on several pins. This is likely caused by high temp manufacturing techniques used. The copper windings have a thin enamel coating that serves as an insulator. When hit with a soldering iron it vaporizes and turns into flux and the solder attaches to the now exposed copper. At least that is what is supposed to happen. I have a feeling that the solder did not wick all the way up the copper thereby leaving it exposed. Over time weather, heat, humidity, etc., cause the copper to corrode and break. The original wires are .0050 and .0070 inches thick. Very thin. The second issue I noticed was the sealant used to bond the ring to the core. This did not seem to be consistent. Some internal areas were thick, some thin, some non-existent. And an expanding/contracting energized field can have a field day with this. Fast forward twenty years and we find ourselves in trouble.

I counteracted some of these issues by using slightly thicker wire. This slightly lowered the operating temp and caused the resistance reading to drop slightly which in turn dictated slightly different winding ratios. I also used a better bonding agent than they used in a high speed production. Each coil is hand wound on a small custom designed winding fixture, hand soldered, and then tested before it is bonded and sealed.

Hope this helps.

Mark (tmcases) billybobs_garage
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