Author Archives: analogrelics

A Voice from the Wilderness

Just a quick word on this blog, as I personally hate it when sites I like become inactive.

As may be obvious, this has not been updated in quite a while and I do not see that I will have time to do any sort of posting in the foreseeable future.  The interest is there, just not the time – I’m currently running a (non-music-related) small business and have a full-time day job.

I’ll keep the site active, as I still get occasional feedback that people have found it useful. I will also still respond to comments & questions.

Thanks!

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!

Breakfast Time

Another guitar-less noodling. I was going to say it’s much more current, but I just realized it came out in 1995. Yeah. Well, time flies when you’re having fun.

For some reason a lot of people seem to pick on this song, but I’ve always liked it. It’s not deep, isn’t complicated, and doesn’t make any grand statements. It’s just kinda fun. And actually, I cheated a little. There is actually some acoustic guitar in here,  pretty well buried in the mix.

Just Like Davy – Breakfast at Tiffany’s

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!

Kid’s Stuff

Being able to do character voices is one of those completely useless skills that’s still sort of neat. Posted without comment, other than to say these were incredibly fun to do.

The Rainbow Connection

From the first Muppet Movie, originally performed by Kermit the Frog (Jim Henson)

Can You Picture That?

Also from the  Muppet Movie,  originally performed by Dr. Teeth and the Electric Mayhem (Jim Henson, Jerry Nelson, Richard Hunt, Frank Oz)

Under the Sea

From The Little Mermaid, originally performed by Sebastian the crab (Samuel E. Wright)

Synth Price List – June 2012

No major structural changes. More models and a few new vendors added.

As always, the “Range” column represents the year-to-date average taking into account the availability of that particular hardware along with the difference between the high and low prices. A wide range indicates either low sales volume or large gap between the high and low (or both).

Synth Prices – June 2012

Who Needs Guitars Anyway?

With apologies to Alice DeeJay.

Since you actually have to PLAY guitar, I don’t tend to do a lot of guitar-based music. There’s a lot of classic rock I like, though, that’s guitar-based. What to do, what to do…

What I do is mangle the hell out the songs, by sequencing them and playing back using all synthesizers. The cool thing about using MIDI is that even if you’re a four-thumbed noodler (and I am), you can record as quickly or slowly as you like, and then tweak them. It just takes me a long time. A really long time.

Been messing around with this for ages – like, years (really). Finally decided to do something with it. Still not 100% happy, but since I have some other songs I want to give the same treatment I figured I’d better just mix it down & move on,  because at some point the quest for perfection sucks all the fun out of it. And after all, it’s just a hobby, so it’s supposed to be fun.

Just Like Davy – White Room