-- In
PolySix@yahoogroups.com, Paul T <sharpfish@...> wrote:
> I have a JX-3P (as well as a polysix) the 3P didn't share the same chips/problem as it's rackmount version (or Juno 106) as far as I recall.
Right you are - The JX-3P does not use the dreaded resin-coated chip used by its sister and close cousins - That's what I get for presenting facts from memory!
Here's a quote from (
http://www.joness.com/gr300/GR-700.htm) that actually credits Kerry with his YouTube video and fix:
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If you are familiar with the eighties Roland synthesizers, then you have likely heard about the dreaded 80017a VCF/VCA chip failure issue. Many synthesizers built by Roland in this period used the 80017a chip: the Juno 106, MKS-30, HS-60 and of course the GR-700. The 80017a is basically a voltage-controlled filter and a voltage-controller amplifier on a single, customized chip made for Roland. The actual components in the 80017a were found as individual elements in the earlier Juno 60 synthesizer: an IR3109 and two BA662 chips. The IR3109 was also used as the heart of the excellent -24 dB low-pass filter in the Roland GR-300.
Why exactly Roland chose to consolidate those three chips (and some surface mounted resistors and capacitors) onto a single ceramic chip dipped in plastic remains a mystery. Arp did something similar with its 4034 filter module, perhaps to (unsuccessfully) dodge a lawsuit from Moog. In any case, early in the process there were failures with the chips, and Roland issued a service bulletin and replaced lots of chips. Then, as the chips aged, problems started to show up with again. Third party suppliers started making clones of the original chips using modern equivalents. And I sold quite a few working chips on ebay after gutting GR-700s for parts. I extensively tested these chips, and no one had a subsequent failure from the chips I pulled. But this bothered me: would it be possible to modify a GR-700 in some way that would guarantee against a future 80017a chip failure?
As it turns out, the answer is to remove the problematic resin coating around the components. And this was not my idea, someone sent me a link to a YouTube clip showing how to get the job done. I happened to be working on a GR-700 that needed five (!) 80017a chips. I had five failed chips on hand, and used the Acetone procedure to remove the resin. Each chip was then individually tested in a special socket, running continuously for 12 hours with no failure. As each chip passed the test, I labeled it and replaced it in the GR-700.
The result is flawless operation. I do not know why the resin causes problems, but I am guessing that with aging the resin builds up electronic capacitance, causing the chip to fail once the temperature in the synthesizer warms up. This is the best possible solution to the 80017a problem. You keep the original chips that Roland designed, maintaining the sound of the instrument, and you protect against future failures as well.
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Once again Kerry - Thanks from all of us! One important consideration is that there are sensitive resistive components built into the ceramic substrate of the 80017a chip, so it is a wise precaution to coat the acetone-stripped chip with a conformant silicone or polyurethane material prior to reinstallation in order to ensure stable operation over the years.
Tony