Category Archives: Synthesizers

Korg Polysix Battery Repair

Oh, the Korg Polysix.   A wonderful piece of vintage awesomeness, except for the unfortunate tendency for the on-board battery to self-destruct, taking the programmer board with it. I’ve done several of these in the past; this was by far the most challenging to work on.

This unit was not unusual in that the battery had indeed leaked, and I could immediately see several components were damaged. It was unusual in that not only did it have MIDI, it had an original Korg MIDI retrofit installed from the factory. I honestly didn’t know that Korg even made an interface for this. I also had no idea how difficult it was going to make the repair.

The first hint came in trying to access the KLM-367 programmer. The retrofit sits on top. Two of the larger CMOS chips that are normally on the programmer are instead installed on the retrofit, with ribbon cables leading back the the original sockets. There are also hard-wired (soldered) connections to the front panel controls, the key assigner, and the voice board. I pulled the ribbon cables, but had to leave everything else connected.

P6Guts

Factory installed by terrifying space monkeys.

When I first looked at it while the customer was present, the damage didn’t look too bad. With the board out of the unit, though, it was as bad any I’ve seen previously. One of the quad logic chips and one electrolytic capacitor were completely shot.  The cap would be removed for the battery modification, but the chip had to be replaced. In addition, many of the traces were bad.

These repairs are not normally difficult, just time-consuming. I removed the old battery and the damaged components, then cleaned the board. Using the component diagram from the service manual, I marked the traces that would need to be repaired. For the new battery, in addition to removing the capacitor there’s a resistor that has to be replaced with a diode. I also installed a socket for the new logic chip. Once all that was in place, it was time to start adding the wires to bypass all the bad traces.

P6TraceRepair

And this is why I’ve started wearing my glasses more often.
“Oh you need little teeny eyes for reading little teeny print…”

Double-checked everything, installed the new components, put everything back together, hit the power, and…success! Sort of.

The programmer seemed to be working. Kind of. The synth section, though, was not. There were several dead keys. Some of the controls worked and some didn’t. I could create a patch and it would store, but they all sounded horrible. Powered it off, pulled the board, and went over it again. I found one wire that wasn’t soldered correctly, and also noticed that the metal mount for the retrofit was shorting a couple of resistors. A quick dab of solder, a minor change of position, and after I pulled the keyboard and took care of the bad keys it  seemed to be working – almost.

This time, the synth section was perfect  and it sounded fantastic. The arpeggiator didn’t work, though, and while I could still store patches the behavior of the programming section seemed odd.  Realizing that the retrofit might be causing an issue, I tried to locate documentation. A web search turned up a user’s manual, but no schematics.  At least I was able to disable the external sync for the arpeggiator, so now the whole synth side worked as it should.

Ignoring the odd behavior, I tried reloading the factory patches from known-good WAV files. No dice. They’d partially load, but then I’d get an error. I ended up entering the missing patches manually. I also verified that not only does the MIDI interface work, but the additional patch storage locations are accessible.

In the end, the customer picked up the unit and was extremely happy, even with the quirky issue saving patches. It doesn’t affect playability at all, or patch selection. I told him that if I can locate the service information for the retrofit, he can bring it back.

And of course the other positive note is that after this one I’ll never be afraid of doing a Polysix battery repair again.

Prophet & Loss

Just had an interesting repair.

Customer had a Prophet 600. The unit powered up correctly, ran through the tuning cycle, and appeared to be perfectly fine – for about three minutes. Then the control panel would lock up and pressing buttons had no effect. If you turned it off and back on, the same thing happened. Obviously, unless you’re in a band playing REALLY short songs, this rendered it pretty much unusable.

The symptoms would generally lead me to think it was either a power or thermal issue. I dug up the schematics and checked all the voltages; they were all fine. The main chips – including the processor – are all socketed, so I popped them all out, checked for bent or mis-aligned pins, and reinstalled everything. No difference. It didn’t appear to be thermal – I got the same few minutes of normal operation whether it had been on for a minute or an hour.

In my day job I work with computers so at this point I’m thinking it’s a bad chip. The consistency of the failure, though, is unusual. In talking to a friend about it at some point in the conversation I was explaining that this unit is microprocessor based…which got me thinking (not as dangerous as it sounds). Once the unit finishes tuning, it has to monitor the status of all the front panel controls, not just the switches but also the rotary pots. Suppose one was dirty? It was conceivable that the CPU could read that as constantly changing, and hang up attempting to deal with it.

I removed all the knobs, removed the two control panel PCBs from the case, and cleaned & lubed all of the pots & switches. Plugged it back in, waited three minutes and then…it kept working. The first time I let it on for a couple of hours, randomly changing patches or moving controls every time I walked by. The second time, it was on for five hours – still no lockups. Re-loaded the factory patches, made sure the oscillators were properly scaled, and it was back to operating like it just rolled off the line.

First time I’ve run into this, but it’s conceivable that any programmable knobs-and-switches synth could develop this issue.

A New Direction

Wow…it’s been a busy few months.

I haven’t been able to do much posting (obviously). I’ve kept up the Synthesizer Price List, but haven’t posted any of the monthly summaries – that, I may do at some point in the future. What I *have* been doing is a fair amount of service work. I have one customer in particular who regularly brings me me interesting vintage toys to work with, and there have been numerous other random replacements, upgrades, and repair work for several other people along the way.

To that end, and because of the feedback from my satisfied customers, I’ve decided to actively start promoting the services I provide.

Up until now it’s primarily been a labor of love for me. I’ve spent close to twenty-five years buying, selling, repairing, modifying, and restoring all sorts of musical equipment, and nothing gives me more joy than finding some beat-up old synth, getting it functioning, and uniting it with someone who really wants it.

The way I see it,  my main goal – particularly with vintage equipment – is to keep this stuff running and making music for as long as possible. My intent is to focus on preserving and protecting the gear,  while still covering my expenses and my time.

It’s been a blast so far, and hopefully will continue to be.

 

Siel DK-600

A very interesting synth. It’s one of the first (or last) “original” analog synths with both MIDI and complete knobs-and-switches controls.

As received:

No backup battery installed
Missing most screws
One broken key & one key missing
Missing left end panel
Several broken plastic pieces
Adhesive goo all over panel
Bottom case full of mouse poo

It did power up, though, and made sounds when poked at.

Despite the odd end panels, it’s one of the easiest synths to work on I’ve run across. There are acres of open space, all the cables are nicely run, and everything is labeled. The one downside is the odd shape, which made fabricating replacement end panels a bit of a challenge.

When I removed the main board, under the keybed assembly, I got completely squicked out when I realized the case was full of mouse droppings. Although that was fairly gross, the other thing I found were bits and pieces of the foil wrapper from a chocolate coin. Which may have been rodent food, but since foil is (obviously) conductive it was also a disaster waiting to happen. I’ve gotten some pretty filthy hardware in the past, but this is the first one I’ve ever had to hit with Lysol.

At this point, locating replacement keys isn’t much of a problem. I have several sources, and apart from the fact that one is a slightly different color and is missing a bit of the front apron, they went in without a problem. The velocity-sensitive key triggering mechanism is unusual. In most of the other synths I’ve seen, each key has two contacts, one set slightly in front of the other. When a key is struck, the time difference between the two contacts is converted into velocity information. Here, instead of individual contacts a pair of buss bars is used, and the interval measured is the time between breaking contact with one and connecting to the other.

The missing backup battery was easy to identify – there was a screened sqare labeled “backup battery” on the main bord, with the terminals clearly indicated. After removing the old solder and broken terminals, I tried to find the most sutiable replacement. My first choice is always a standard CR2032 socket. The pin spacing was correct, but there were a couple of resistors and a disk capacitor in the way. Thought of just mounting it on the bottom of the board, but the plastic bottom case has a reinforcing rib running exactly where it would have ended up. With a little creative lead-bending, I was able to mount a 1/3 AA socket on the top.

Downloading the factory patches was a challenge. I was able to locate a WAV file, but spent more than an hour trying to match volume levels to get a clean restore, with no success. Finally, after much web searching, I found a SysEx dump that I was able to reload using MIDI-OX. Somewhere I also dug up the original patch list. The synth came with the patch list on a label stuck to the front panel – hence the paint chips – and I laid out the new list to match the original as closely as I could.

The patches loaded correctly, and everything sounded okay. The odd numbers on the keypad, however didn’t work. I was able to determine that one of the pins on the DIP-style connector on the ribbon cable was missing. These are readily available, but rather than wait until the next time I order from Mouser I rigged a small piece of metal in the socket so that it would contact the little stump of the missing pin. It works fine.

I’d iniitally intended to make very nice end panels, but because of the odd shape decided that a basic set would do, particullary if I was reselling the unit.So instead of oak, I used clear pine, and instead of mounting them on the outside of the case and filling in with more wood, I mounted them on the lip next to the edge instead. After filling in the original screw holes and painting the lip black, it looks fine.

One of the nifty things I didn’t realize until I’d actually finished working on it is that it has a set of fold-down legs to angle the unit upwards, making the control panel easier to access when standing. Kind of neat.

Determinng the value of something like this is always tricky. I’ve seen them sell for close to $800 on Ebay. However, I’d rather trim my nails in a Cuisinart than go through the hassle of trying to sell something this large and this vintage-y that way. I’ve done my time. Instead, I posted it on craigslist with a low yet still fair price. It sold within  a couple of days; the buyer was very happy, I got some hassle-free cash, and it went to a good home. Everybody wins!

Sequential Circuits Prophet 600

This was a recent repair job. When it was dropped off, the owner said it had a bunch of non-responsive keys and he wanted to see about getting the battery replaced. Testing it, however, showed an additional problem. The patches were all really, really wrong, and it would hang up randomly. I let the customer know; he just said “fix it’.

One of the things I absolutely love about older equipment is how easy a lot of it is to work on. Four screws, fold the control panel up, everything is there in front of you.  The date of manufacture – 10/19/83 – is clearly visible here. I was in high school when this rolled off the line.

I’ve got keyboard rebuilding down to a (tedious) science. As expected, it took about an hour. Also as expected, all keys worked.  I checked the battery; despite it being the original I was still getting the correct voltage. Since there’s no way to know how long that would continue, however, I went ahead and replaced it. Although it’s mounted from the top, I had a holder that was perfect for it.

Replacing the battery, of course, completely wiped out the memory. I was unable to get the factory preset WAV file to load, so I used MIDI-OX to push the SysEx files over. One bad thing about this unit is that there’s no indication that it’s receiving, so had to unplug it, schlepp it downstairs, and hook it back up to the amp to see if it worked. And it did! The memory must have been hosed from the start, because all the patches sounded fine and the locking up problem went away. But…

Two of the voices were really, really off; the oscillators were nowhere near each other in pitch. Since the unit tunes itself, that meant that the main voice board needed to be rescaled. Fortunately, SCI built in a relatively painless procedure for doing this. It took about twenty minutes, but after that it was all working perfectly.  I replaced a few missing screws, touched up the stain on the end panels, vacuumed the inside, cleaned the outside, and let the customer know it was done.

He got back a fully-functioning synth, and I got to mess around with a classic piece of vintage gear. And got paid for it,  too…everybody wins!

Roland SC-55 Sound Canvas – Part 1

Given that there are plenty of resources available for most of the sound-generating gadgets discussed on this blog, one may wonder why I even bother. Well, there are a few reasons. I tend to run across various oddball models and think it’s worth getting the pictures and demos out there as a resource. Since you can pick many of these up for a few dollars,  a quick overview and assessment by someone who’s actually got one sitting in their lap might be of use. Finally,  since I’m a hardware geek I like to relate my own experiences and perspective with some of this gear.

This particular piece is one of my all-time favorites.

I mentioned my experience with the IBM PC Music Feature in the K1000 post. Basically, it was a Yamaha FB-01 on a chip. Early soundcards were primarily focused on gamers, and the IBM card was one of the few that you could actually make real music on.

In 1987 the actual FB-01 module, along with the Roland MT-32, were among the first dedicated stand-alone MIDI modules. With limited editing capability, they provided the user with a large assortment of good-quality sounds. But…

Although the concept was the same, these boxes were not interchangeable. Sounds were arranged differently, banks were numbered in different orders, and voice allocation was handled as each manufacturer decided. The initial MIDI standard described how data would be transmitted and received between devices. There were, however, no standards that described what should be done with that data. In 1991, the General MIDI standard changed that.

The MIDI Manufacturer’s association and the Japan MIDI Standards committee decided upon a specific set of voices that would be mapped to specific program locations on any keyboard or module that met the GM standard. There were also specifications for number of voices, polyphony, and many other items. The Roland SC-55 Sound Canvas was the first GM compatible device, released within hours of the official adoption of the GM standard. Not surprisingly, as Roland was one of the more vocal proponents of GM.

The SC-55 module generates sound using both PCM and a variation of Roland’s own LA (linear/additive) synthesis. For compatibility with existing games and other applications, there are also a bank of MT-32 voices. There are 317 instrument patches and 9 drum kits. It is 16-part multitimbral with 24-voice polyphony, and built-in reverb and chorus, individually selectable for each MIDI channel.

Along with the SC-55, Roland released the SB-55 Sound Brush, a basic MIDI sequencer/playback unit the same size and style as Sound Canvas. The two units could be  rack mounted together as a complete composition and playback unit.

In addition to the various part controls, the front panel includes a headphone jack with volume control and a very handy front-panel MIDI-In jack. Rear interface consists of RCA L/R audio in & out, MIDI in, out, and thru, and the power jack.

Also included was a credit-card size remote control. It duplicated the major front panel controls of the SC-55 and could also control the transport functions of the SB-55.

I have yet to run across anyone who actual used it. Regardless of the intended function, the primary purpose of the remote seems to have been to get lost. I do still have mine, not through any particular care on my part but because I duct-taped it to the bottom of the unit.

There are limitations. Since this is in fact the first GM device, the specifications are spot-on. Many of the voices use more than one partial, cutting the 24-note polyphony down.

A common complaint is that the sounds seem “dull”. There is definitely a certain lack of high-end sparkle to many of  the voices, but (as always) in a performance situation this is not that noticeable. Listening critically to each voice in isolation, there are other noticeable flaws. The decay times may seem unnatural, and there is some noise associated with several patches.

It should be kept in mind, however, that the unit was design to operate multitimbrally, and this is where it really shines. All of the voices blend together extremely well. The Yamaha TG-100, a relative GM contemporary of the Sound Canvas, has better drums, but files played back don’t seem as polished; some instruments seem out of place in the final mix.

I’ve found that when working with MIDI files in Sonar, I frequently have to reset the Sound Canvas, particularly when using any of the alternate sound banks (power on the unit while pressing Instrument Up and Down, and then Yes to initialize). If I switch songs, it doesn’t always respond properly to program change and the voices won’t change. It’s not a big deal.

There’s a little trick I’ve found with the guitar voices, admittedly some of the weaker ones present. The Steel Guitar has a nice attack and tone, but no bottom end. The Jazz Guitar is fuller, but the attack is mushy. Layering the two, with the Steel at about one-third higher volume, gives a very credible acoustic guitar tone. Of course, in doing so you lose a voice and a MIDI channel.

The 24-note polyphony has been cited as a limitation, but in 20+ years of using it I can recall exactly one time when I had to deal with audible drop-outs due to exceeding this limit. Nowadays, since you would most likely be using a DAW to record the parts it wouldn’t be a problem.

Even with all the higher-end virtual instruments and a plethora of physical hardware to choose from, this is still my go-to device for arranging new material and orchestrating existing pieces. The sounds all feel like home to me.

In part 2, we’ll take a look at some of the other versions of this well-loved box, and hear some demo songs.

Synth Price List – May 2012

Format is the same, for a change. Added a couple of new manufacturers and a bunch of new models. I have several manufacturers with just one or two models; I may add them primarily to use as filler to make the pages come out even.

As explained in a previous post, the Range column represents a range of prices based on the high and low to date, but also takes into account the volume of sales. If the range is really narrow, either the item is very popular or the prices are always pretty close. Wide ranges indicate either a big disparity between high and low or a small volume.

In either case, it’s reasonable to assume that if you want to purchase something, seeing a price somewhere close to that range is a good thing.

Synth Prices – May 2012

Weekend Sale Finds – 6/3/2012

Didn’t actually do any yard sales or thrift stores this weekend. I did, however, stop at the Columbus Flea Market on the way to take a friend back home. Since I have several projects going right now, I really wasn’t looking to buy anything. But of course, any lost and lonely keyboards still tug at my heart – and my wallet.

Found two this time. A Casio CZ-230s synthesizer with stand, and a Casio MT-520. Both are a little beat up, but as usual the prices were way too good to pass up.

The CZ-230s is a bit of a rarity, and I’ll do a full-scale review later. It’s essentially a preset CZ-101 synthesizer, with built-in rhythms and limited editing capability. It’s also got strap pegs, so if I ever feel like completely nerding out I can dig out my cape,  put on a little Yes,  and keytar my way around the living room. Okay, that won’t be happening – but I could!

It’s missing one slider cap and one button, but is otherwise all there. The stand is actually quite cool, too. I haven’t run across one yet that can be adjusted to fit a mini keyboard.

 

The MT-520 is more common (in fact, I just realized I may have one already). This was a straight pity rescue. End of the day, tired seller, dusty little keyboard sitting in a pile of toys. I’ll clean it up, test it, and add it to the sale list.

Both of these were initially spotted by my eagle-eyed friend. Now, I’ve certainly had my share of unexpected finds, but lately the only credit I can take is for knowing what’s worth buying.  It’s good to know that when I go out with someone else there’s very little chance of anything sneaking by.

At current prices, both together would sell for around $140, with another $15 for the stand. Since I paid a very small fraction of that, I’m certainly not going to complain about having to clean ’em up a little.

A Tale of Two Polys

About a year ago I got a reasonably good deal on a Poly 61 and a Siel DK-600. Both were described as “working, but need TLC”. That turned out to be, at least in the case of the Korg, a bit on the charitable side. (The Siel is a future project.) Note that the picture above is not the unit in question – I really need to make more of an effort to take “before” pictures. Trust me, though, it was a mess.

Problems were, in no particular order:

  1. Half the keys were completely non-responsive.
  2. Most of the keys that did work only did so intermittently.
  3. Pressing down on the center of the keyboard caused the whole thing to go nuts – LEDs went random, the sound jumped all over the place. There was obviously a short somewhere.
  4. Most of the screws were missing.
  5. The battery was dead.
  6. A good bit of the plastic laminate on the case was gone, and the case itself looked as if it had been attacked by angry beavers.
  7. The joystick didn’t work.
  8. Although this wasn’t immediately apparent, the mylar ribbon cable that connects the two main boards was only being held in place by gravity and good wishes – it was cracked in several places.
  9. It was filthy.

It did, however, power on.  All the major parts were present; all the panel buttons and LEDs worked. It did make noise as long as you played very gently and managed to hit any of the few keys that functioned.   I added it to my “to be fixed one of these days” list & stuck it in the closet.

A couple of months later, I found another one on Ebay that had no bids on it. The case looked to be in good shape, but the seller said the keyboard didn’t seem to work and all the patches sounded the same (dead battery).  It was yet another as-is sale, as  they had no idea if anything else was wrong. So, I picked that one up too.

With two semi-functioning units my initial goal was to combine parts to come up with one working synth, but the more I thought about it the more it seemed like a really bad idea to trash a piece of vintage gear. So, I went with plan “B”.

Since I no longer have a wood shop, or even just the tools, making a new case wasn’t on the table. However, veneering the old one seemed just as good a choice.

Again in no particular order, here’s what I did

  1. Rebuilt the keyboard – I’ve done enough crappy Roland keyboards to have this down to a (tedious) science.
  2. Replaced the battery.
  3. Cleaned & re-aligned the joystick.
  4. Removed the ribbon cable and connectors, and replaced with regular wire. This was Not Fun – I had to solder both ends of something like forty wires to the headers on the logic boards.
  5. Replaced missing screws and standoffs.
  6. Removed the rest of the plastic veneer, repaired the damage to the case, and veneered with red oak.
  7. Cleaned all switches and pots.
  8. Reloaded the factory patches – which also verified the memory and tape interface work.

A couple of the presets seemed to be incorrect, but I chalked that up to the dodgy WAV file I had to use to restore the factory settings. Entering those patches manually took care of it.  The bottom line is that now I have one functional synth in a pretty sweet custom case.

  

And the other one? The electronics weren’t as bad. I replaced the battery and rebuilt the keyboard on that as well. The only thing not working is the arpeggiator.  Normally, I would be hesitant to dive into that level of repair, but based on the way it’s acting I know what the problem has to be – I just need to see if I can use the crappy schematics to find the chip that needs to be replaced.

Even if I sell it as-is, though,  I’m sure I can get at least $100 for it, which means I got the other one for a song. A squelchy, buzzy, pitch-bent, impersonal and oh-so-cool song.

Synth Price List – March 2012

Commentary to come later, but for the moment here’s the list. As usual, it’s grown a little.

Synth Prices – March 2012