RMI 368x part 1: voltage conversion and clean up

Years ago I bought a pair of RMI 368-X Electra-piano electric pianos for cheap. Like sub $100 for the pair cheap. Caveat – they were both 220V versions. Other caveat – neither was in good condition. Upside? The old guy I got them from said he bought one of them in the late 70’s from a touring British prog rock band. “The one with the wood.” he said. He couldn’t remember the bands name and these were popular enough with rock bands in the 70’s that it would be hard to deduce who it might have been.

In 2020 I bought a big house on 9 acres and after getting my life set up I resolved to get all my music equipment in one place and working. Low on the list was the pair of RMI 368-Xs hiding behind the camping gear in my mothers garage. Low until I decided I wanted a fully polyphonic basic piano to use. CS-60 wasn’t cutting it for simple composition and the Hammond was buried in the barn. The glowing Soundonsound review of the RMI added to my enthusiasm.

The worse off of the two is pictured above.

The 368-X is the same as the earlier 368 model, but has a plastic clam shell type enclosure where the earlier models had wood. Keys are basic Pratt-Reed and this example needs more than a few if I am going to replace the ones with cigarette burns. Someday I suppose I’ll fix this one up – especially if the asking price of $1000+ I see on Reverb is ever realized by anyone. One sits completed on eBay as I type here – sold for $875 with the foot controller and local pick up in Prescott Arizona. Maybe I’ll fix this up now so I can afford the Rhodes a friend is selling.

Lets move on to the wood one and fixing it up.

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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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Hammond S6 Chord Organ Part 5: Stuck in the (chord) Matrix

Well, I’m near the end of this saga. I washed the plastic chord button assembly and put a little silicone lube in each of the 96 holes. Can you imagine washing the knobs on a receiver with 96 knobs? Typing that reminded me I cleaned the knobs and slider caps on an old Soundcraft mixer that had maybe to 200… Maybe that’s why they called it the 200!

I also took A LOT of it apart last night and a little oil here and there has everything returning as it should. I spent so much time on this I didn’t get to the coupling caps or fuse adding. Will try and do that today.

I needed to get this assembly out to see what the mechanisms looked like so I would know how to proceed with lubrication or adjustment. The terminal strip on the far right is broken between lower 3rd and 4th connections – I think the power supply gave it a hard yank when it got free. Didn’t interrupt anything so I am going to ignore it.
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Hammond S6 Chord Organ Part 4: Fine Tuning

When I played the Hammond this morning it was back to happy – doing everything it was supposed to and in tune. I think I’ll just add a fuse and replace the amplifiers coupling caps this afternoon and try and see if I can get the PR-40 into a position where I can connect the two.

Okay so I played it again this afternoon and decided whatever triggers the pedal from the chord matrix was not working correctly. Cleaning the pedal contacts didn’t do anything so I decided to get into the mechanism of the chord matrix. On the Crasno site there is a picture of removing the chord button controls. I took their advice and taped the buttons to the panel so they wouldn’t all go through and end up everywhere. The matrix itself is an impressive mechanism. Whatever the note bars pivot on was hanging up and returning very slowly.

All I did tonight was get it apart then feed the chickens. I’ll do some internet searches and see if I can figure it out before I go much farther.

The bar you rest your wrist on just has this contact being made in it. When the contact is made, the chord sounds fuller.
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Hammond S6 Chord Organ Part 3: A good days work

There was an estate sale in my neighborhood I spent an hour at (no musical instruments other than an overpriced piano or Hi-Fi audio), a trip to be made to the hardware store for some building materials and trip to the store for dinner makings, so progress was a challenge. In the last set of pictures you can see the shadows are getting long. I started feeling some time pressure to get to it if I was going to have it together before I went to bed, I started rationalizing about at what point I could say I was successful. I still needed to test a bunch of tubes, find a 5U4 and make a power cord. I had to take a break and cook some steaks, but I ran back and forth between BBQ and the project. My dad joked he would hold the flash light. My back was getting tired, so I didn’t relish the thought of not being done by dark. I ate fast, but it was still delicious. Must finish. I decided if it was assembled, and the tubes tested before I went to bed I could take my time bringing it up on a variac and testing stuff the next morning.

Looks pretty good. That bar hanging down in front of the speakers is a volume swell control. I discovered it was also the power switch when I was testing things.
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