Korg Polysix project gets a new life

When you are into vintage stuff you fantasize about being one of those lucky people you hear about who scores some great piece for a ridiculously low price. In my experience those sorts of deals mostly happen in the meat space, and you have to meet luck halfway at a minimum. This is why I go to garage sales, thrift stores and the like as often as I can, to give luck fertile ground to grow on.

On a visit to an occasionally fruitful thrift store (one never divulges ones sources) I made one of my best Bugatti-in-a-barn type synthesizer purchases: a Korg Polysix project for $35. Before you fall off your couch there are two points to consider: this was when a nice Polysix could be had for perhaps $800-1000 and when I say project, I mean project. Someone had removed ALL the socketed ICs.

As found with the exception that I bought that high C key separately – stuck it there so I wouldn’t lose it. You’d have bough this right? AS IS, as though anything is ever other than that. A lot of the circuit boards were loose in the case. First order of business when I brought it home was fishing all the loose screws out of it and using them to secure the boards as best I could to avoid damage when being moved around.
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Korg Maxi-Korg 800DV / Univox K3 part 7: Back together

The Maxi-Korg project languished for a while before a flurry of activity got it working back in March. Let’s review my to-do list from September of 2020 as a means to provide updates:

I still need to refinish the wood cheeks to use the originals until I can get new made

Still using the original wood. Once it was all back together I decided I needed some quality time making sounds with it before I took it back apart for any reason. This is not to say I won’t ever replace the wood, but probably not for a while. It can only be original once.

I need to clean up and remove some paint speckles around the bodywork from someone painting with a roller near this – hopefully it is latex paint

This was time consuming and as one can imagine with TINY paint spreckles it was tedious. After trying some mild cleaners and wood or plastic tools it was decided that my fingernail was the best implement for removing the paint from the textured metal bodywork. There are some areas where there is still a haze of discoloration from paint, but I can live with it.

Looks pretty good above. Superglued key is still holding together! I bought some new black oxide hardware for the panel – I’ll see if I can get my son to swap it sometime soon. Keeping company with some frequent collaborators. I spy a Source and a System 100.

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Korg Maxi-Korg 800DV / Univox K3 part 6: Controls clean up

With the keyboard all cleaned up, the circuit boards capacitors replaced and much general clean up attended to, I turned my attention to the controls – the sliders, pots and switches that you interface with to play the instrument. The Traveler sliders in the VCF section felt awful when I first checked out this synth. They were stiff and notchy when they would move. I figured worst case I would have to find suitable replacements for the 4 of them. I don’t remember if I even tried any of the other controls – once I got bad news I just moved on.

Starting at the end. The controls have all been cleaned and it’s nearly ready for final assembly at this point.
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Korg Maxi-Korg 800DV / Univox K3 part 5: The wood I

Wood. Seems incongruous on a piece of sophisticated electronics. I offer a few reasons why: It’s a Japanese thing – the harmony achieved balancing the electronics and metal with the wood; it’s a vestigial thing – from the days when a keyboard meant a piano forte; it’s a manufacturing thing – in 197* plastics were not so hot and a wood case was just easier to not mess up. Being practical I am going to say it’s a combination of the three.

So what about wood anyway? The smoke cleared enough that I was comfortable going outside to do some sort of work after nearly a week of awful smoke from all the fires here in California. I grabbed the wood chunks that go at either end of the keyboard (that I bet the last guy who owned this keyboard called cup holders), some sandpaper and some restore a finish and headed outside.

The cup rings are sad, but part of the patina that allowed me to buy this for not an unreasonable amount of money. I needed to sand these because the moisture had the finish lifting. Putting restor-a-finish on them would have made them look, but not feel better.
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Korg Maxi-Korg 800DV / Univox K3 part 4: Capacitor list

Okay, you read in the last post about how the easiest way to come up with a capacitor list is find someone who has done the job you are looking to do and get them to give you their list. And then I talked about how I made a list, but I didn’t post it. Well, by popular demand, here is my Korg 800DV capacitor list. I will give you the board by board list, the specification changes I made to try and buy in bulk and the final list I ordered from Mouser.

Another shot of my freshly recapped boards because yeah, it was a lot of work and I’m happy to have done it and happy it’s done.
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Korg Maxi-Korg 800DV / Univox K3 part 3: Capacitor replacement

Electrolytic capacitors go bad eventually, Maybe not tomorrow, maybe not next week, but eventually they go bad. If I was a tech fixing this Maxi-Korg on a budget for a kid who just dragged it home from a garage sale I would probably insist on recapping the power supply and replacing the tantalum capacitors, doing some testing and sending her on her way with a $60 repair bill and a few words of encouragement to take care of this neat thing she is now the keeper of.

That is not the situation. I am a guy who likes to do it once and do it right as much as possible. I am going to replace all the capacitors. Top to bottom, inside out – even the couple of tantalum caps tacked onto the back of some of the sliders. And why not there’s only like 60 or so.

I did mention it was all apart right? The 800DV is two 700-Ss under one roof with a nice complement of controls to blend the two. The two boards on the left are one 700-S, the two on the right are the other, and the board in the middle is the blender. Those big black squares are the potted “IC”s. A lot like the early Yamaha dudes found in a GX-1.
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Korg Maxi-Korg 800DV / Univox K3 part 2: Unpacking and Assessment

Covid-19 has slowed the delivery providers to somewhat of a crawl, but I think FedEx is handling it better than the others. The Maxi-Korg was delivered only a few days later than was initially estimated. I didn’t take any pictures unpacking it – looked just like the auction photos. Was poorly packed, but somehow made it with only one of the rubber feet poking its way out of the box. I can live with that.

When I spend more than a few hundred dollars on something I tend to dig right in to see what I am up against. The sliders and pots were really sticky and hard to move so I opted not to turn it on, but rather save that fingers-crossed moment for after replacing all the electrolytic and tantalum capacitors. No sense in risking too much electricity getting through a shorted open capacitor and taking out a transistor.

I think this picture conveys the state of this synth well. This was the first time I encountered dead fully grown roaches in a synth. Nothing a good vacuuming can’t handle. See those light blue/violet capacitors? They are way past their expiration date. If they work now, great, but they are sure to start failing with some power cycling.
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Korg Maxi-Korg 800DV / Univox K3 part 1: The Purchase

My birthday is next month and every year I buy myself a piece of vintage gear (not sure why, but I hate the word gear for music equipment) – usually it’s a project and the price reflects this, so I start my search well in advance of my birthday – hoping something will turn up. Last year it was an untested Roland Jupiter 6, the year before was a Moog Source. This year I was thinking either a Korg Maxi-Korg or a Roland SH-7 or RS-505.

The other night this Maxi-Korg was listed on eBay for more than I wanted to spend on one, and it was untested, but I figured I’d submit a offer I was comfortable with and see what happened because sometimes you have to throw caution aside and go for it. Especially when you are looking at something you’ve wanted for a long time. Early the next morning my phone chimed because my offer was accepted!

Doesn’t look too bad right? The middle E key is clearly broken – a fairly easy and inexpensive thing to replace or, if the broken parts are in the synth, you can glue it back together. We shall see.
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