Keyboard maintenance

My synthesizer needs a new main board!

The heart and soul of a synthesizer is its main board, the place where the nitty-gritty happens, where the most basic and the most important functions take place. If your synth turns on but the display shows weirdness, or if it boots up but gets stuck on one screen, or freezes up in the middle of your song, these are the sorts of things that can indicate that the main board – sometimes called the mother board – is faulty.

Repairing a non-working main board is not for the faint of heart. It requires an experienced tech with diagnostic tools to determine that this one chip amongst hundreds has failed, or that the ROM has been scrambled, or that pin 27 of the CPU chip isn’t receiving the correct reset voltage. It’s a process that takes many hours of bench time at expensive hourly rates.

If your main board has gone off to PCB heaven (PCB stands for printed circuit board), it is often quicker and cheaper to simply replace it. That process usually involves simply removing the old board (often as simple as unplugging wiring harnesses and unscrewing the board) and dropping in a new one. The hardest part of the equation is often finding a replacement circuit board. What do you do when your beloved SonoSlapper 6000 needs a new main board, and a Google search turns up no results?

At Syntaur, we’ve been having good luck finding main boards for lots of fairly recent instruments – meaning those of this millennium – simply by developing good relationships with the manufacturers. If there is a brand new main board out there, we can usually find it. Ok, we might not be able to find that mother board for the SonoSlapper 6000, but if you have a Korg Krome, or a Nord Stage, or especially a Yamaha synth or digital piano that needs a heart transplant, we can probably help.

Yamaha, in particular, makes so many different keyboard models that we’re always racing to keep up. At the time of this writing, we list parts for 630 different Yamaha models, and there are at least that many that we haven’t gotten to yet! So if you need a board for a Yamaha CLP or CVP Clavinova digital piano, or a Yamaha PSR portable keyboard, or a Yamaha stage piano or synthesizer, it may indeed be available even though the internet seemingly offers no hope. Yamaha is a huge company, and is probably the best for maintaining a parts inventory for their keyboards. And if they have a replacement main board tucked away somewhere, we can get it for you.

The trick is to not get dismayed by the fact that we may list a hundred parts for your synth on, but no main board. In that instance, let us know you need this board, and we’ll go on the hunt. At the bottom right of nearly every page on the site, you’ll see this link: ‘Can’t find the part you’re looking for? Make a request for it here.‘ Once we see your request, we can find out if the board is still available, and if it is, we’ll let you know how to special order it.

Even if the circuit board is out of production and not available from the manufacturer, all is not lost. We have an absurd number – hundreds and hundreds – of synthesizers in line to be either refurbished or scavenged for working parts, so we can also check our database to see if perhaps the synth model you need to repair is lurking in our warehouse. If so, we can test it to see if the main board is good.

Long story short: We’re happy to do a bit of research to see if we can find a main board for you. After all, we live to bring old synthesizers back to life! But I ask just one favor: Please don’t call to ask us this – use the website form mentioned above. That gives us a record of who is looking for what, and it makes it easy for us to do methodical checking. Otherwise, your request will get scribbled on a slip of paper, which then gets moved to someone’s desk, and then faces an uncertain future. My desk, for example, is arranged in archeological layers. Trust me – you don’t want your main board request to land there.

We often think these days that if Google can’t find something, it’s not to be found. But we’ve still got some tricks up our sleeves.

Keyboard maintenance

How to tell if your Juno-106 needs voice chips

It’s no secret that the Roland Juno-106 is a great analog synth – and that the proprietary voice chips are it’s Achilles heel.  These chips – one for each of the Juno’s six voices – were dipped in an epoxy coating when they were made back in the early 1980’s.  And decades later, it turns out that that epoxy starts becoming conductive as it ages.  A conductive coating on an electrical circuit = Not Good.

The fix is pretty straightforward, though you’ll want an experienced tech to handle the repair.  Because the problem is so common, Analogue Renaissance has remanufactured the voice chips with bullet-proof modern components, and their voice chips sound exactly like the originals.  You can purchase these from Syntaur here.  But installing them requires fluency with soldering – and especially with de-soldering.  It’s easy to get the circuit board too hot, and lift the delicate traces, causing even more trouble with your Juno.

But the first step is determining whether or not you need to replace voice chips – after all, each voice chip will cost about $60, plus the cost of installation.  (If you buy a complete set of six chips, you’ll get a discounted price.)  So it’s not cheap –  but it will certainly up the value of this classic synthesizer.

To determine whether your Juno-106 needs one or more voice chips, you will:

Boot up in test mode

Play notes, and see in the display which voice is sounding

Take note of any voices which sound irregular

Set the filter to self-oscillate, and check the individual voices again

Take note of any voices which sound irregular

Here are the details for doing each of these steps:

Boot Up in Test Mode

Power on the Juno-106 while holding down the KEY TRANSPOSE button; this will put the synthesizer in Test Mode. The display will read ‘-_’. Press the POLY 1 and POLY 2 buttons together, and now for each note played, the display will show which voice is sounding (‘-1’ through ‘-6’).

You may want to give the Juno five or ten minutes to warm up before you start getting serious about listening to voices.  It’s an analog synth, and it needs electrons flowing through those circuits for a while before it settles down and gets stable.  It’s no problem to play it during this warm-up period, it just may sound a bit goofy.

Play notes, and see in the display which voice is sounding

Play one note at a time, and the display will indicate which voice is sounding; the Juno will cycle through the voices consecutively.  So pressing a key repeatedly, for instance, will show -2, -3, -4, -5, -6, -1, -2, etc. in the display.  

Take note of any voices which sound irregular

If a voice sounds goofy while you are doing this, make a note of which voice it is.  If you hear a crackling sound every time voice 4 plays, you know that voice 4 likely needs a new voice chip.  Other tell-tale signs of a failed chip are voices that sound very thin, or distorted, that hang on after the key is released, or that don’t sound at all.

If a voice sounds just slightly askew, it may just need a calibration.  If the voice sounds out of tune, or a bit dark, for instance, that can be corrected by calibrating the Juno (the subject of an upcoming post).  Crackly, distorted, or hanging notes, on the other hand, are the indicators of a bad voice chip.

Set the filter to self-oscillate, and check the individual voices again

This is my favorite trick for finding bad voice chips – it works to ferret out a bad chip that sounds normal under most circumstances.  The idea is to turn off the oscillators completely (including the sub-oscillator), then make the filter self-oscillate – which means it will ‘play’ a sine wave.  Often, a faulty voice chip will lose this ability to self-oscillate.

To set this up, turn the pulse and sawtooth off, and set the SUB and NOISE sliders all the way down. Now, make the filter self-oscillate by setting the RES slider fully on – you should now hear a sine wave sound, and the FREQ slider will control its pitch. Set the VFC ENV and LFO sliders all the way down, and with the VCF KYBD slider fully upward (this opens the filter to match the keyboard tracking), the filter should play chromatically as you play the keys.

Take note of any voices which sound irregular

As you play notes with the filter self-oscillating, if a note doesn’t sound at all, that almost certainly indicates a failed voice chip.  So take note of the display when a voice doesn’t play, and like before, it will tell you the voice number which is bad.  If a note plays, but it noticeably out of tune, that’s another indicator that your Juno just needs a good calibration.

Now, you should be fully informed of exactly how many voice chips you need, and exactly which voices need them – in other words, which specific chips on the PCB need replacing.  

If you find that you need multiple voice chips, you might consider replacing all of them – if several have gone bad, then the others might not be far behind.  And your Juno-106 is a good investment – replacing all of the voice chips will ‘future-proof’ it, which will make it an even more valuable instrument!