New computer installed!

Ok so results, let’s do image quality first. Like said, I wanted to give ATI one last chance even despite throughout the process, I found myself wondering “why do I even bother?”.

To boot with, the new motherboard proved immediately a whole lot better: SATA bus interference in the display image gone for good! Yay \o/. With the graphics cards, the surprising end result was that ATI ruled Nvidia in S-Video output quality, but Nvidia composite out was way better than S-Video on ATI.. wtf?! :)

Bye bye SATA interference :)

Factual performance upgrades are quite hard to evaluate.  The new system is slower to boot, but this is because of some hardware features that can’t be disabled (causing wait periods in the boot sequence). Overall, the emulation is definitely faster on some of the more CPU-intensive games, but they do not run smooth enough to be playable anyway.

Audio emulation did definitely benefit from the multithreading (far less skipping), at least after I understood to add the “-mt” switch on the MAME command line ;). The integrated soundchip on the new motherboard even has a better equalizer in its Windows driver, allowing me to better tweak around the short-comings of the Labtec speaker set.. Though even after these the sound I’m getting still makes me want to upgrade the speakers ;)

Speaking about upgrades, next up though I’ll probably be looking into doing something about the spinner. The current one just has too many issues, so I’m probably faster off getting something less DIY. Since I do have a Opti-PAC board getting a real arcade spinner is very much a viable option. Trackball might be nice to squeeze in too.. But not much space on the controller console though, so let’s see what I’ll end up with.

One additional / possible upgrade I’m trying to wrap my head around at the moment is how to incorporate a steering wheel to the cabinet. I got this lovingly retro Thrustmaster T1 wheel/pedal set for free, so of course I can’t just pass by the opportunity. The set is slightly repaired by someone, possibly also modded to be more robust than what the set is in its original configuration. Regardless of this, I got the set working fine with Model 2 emulator at least (Sega Rally, yay!), though it took a good while to do all the config stuff.

Slightly modded by someone but working fine nonetheless.

..if nothing else, I guess I’ll have to start working on a new “racing” cabinet ;)

When I got it, the DG-20 had serious problems deciding whether a note was held on the fretboard or not. In closer inspection it turned out that a previous owner had attempted some kind of repairs on the fretboard. Like said, it’s too bad that this person had decided to remove the rubber mat by pulling it off from the fretboard instead of doing it properly, in turn tearing the mat into three slices. To illustrate the structure just for you (<3), I made the this fancy mspaint diagram:

Slice diagram of neck / fretboard

So in its original configuration, the rubber mat attaches to the fretboard with the bits wrapping around the PCB edges. Once this combination is installed to the neck (double-sided tape and two screws used on the PCB), the mat will stay nicely put although it’s not actually fastened with anything else than surface contact.

Fretboard repairs

The owners method of choice for “repairing” the mat after the unsuccessful removal was to glue the top slice of the mat over the fretboard. Problem here, the glue used was this plasticky-blob-once-dry type of stuff and once it settled the blobs ended up pushing the mat away from the PCB contact surfaces.. D’Oh! And to make it even more of a issue the glue had been applied along the width and length of the fretboard, zig-zagging from one edge to another. Ok-ish for attaching the mat but totally silly in terms of switch contact! :)

Fancy gluework son, did you do it all by yourself?

So yeah first up: glue removal. Here, the rubber mat was no problem. It’s hard to get nearly anything to grip properly with rubber and lucky for me, the plastic glue used was no exception. It simply flaked off when gently scraped with a fingernail.

The fretboard PCB on the other hand, a slightly bigger problem. As mechanical removal methods are called for, it’s really easy to end up damaging the conductive top layer bits of the fretboard. My method here was to scrape off the glue with a flat screwdriver that had a slightly smoothed / rounded tip. The idea was to at least try avoiding heavier scratches and cuts. Scraping was done very gently of course, with light/small movements and almost no pressure on the screwdriver. Once I had the parts cleaned, I spent a few days doing a few switch contact improvement tests for the rubber mat (easy test subject). More on those in a bit.

A strip of masking tape to protect the contact surface..

For piecing together the mat, my initial plan was to use some vulcanizing glue (à la bicycle tire repair kit). But, not having any at hand, I ended up using black acrylate sealant. This can withstand about 10% stretch once dried up (and is also weather/water-resistant) so I’m guessing it should work  just as fine (in the long run) as the vulcanizing glue, even despite the seams are more fragile. Silicone sealant would probably work equally well too.

I used strips of painter’s tape over the fretboard PCB (to protect the contact surfaces) and applied small amounts of sealant along the side pieces using a toothpick. After this I inserted the top piece, aligned the frets to match up with the sides and secured the whole thing in place with tape for the drying up period.

..and glue + "contact" piece insert and aligned from one edge. Painter's tape for drying support.

Once dried up, the fretboard had to be dismantled for tape removal. The seams did probably move more than the “10%” during the process, but the pieces held together. Switch contacts work fine too, so it’s a confirmed fix!

Conductivity

Besides the repairing the mat, I also wanted to test a few things to try improving conductivity. Due to the structure of the mat (six long conductive stripes), it is a pretty easy “practice piece” for paint masks and such. Whatever ideas or work methods I can pick up in the process should be applicable towards repairing anything that uses a similar technique (conductive rubber mat over PCB), eg. old game controllers.

First up, graphite spray. The stuff I’m using is ‘Graphit 33‘ by Kontakt-Chemie. No idea what it actually consists off (graphite, obviously), but it’s great for making this and that conductive. For the paint mask I first tested a few types of painter’s tape, but these didn’t stick at all. Builders tape gripped slightly better, actually staying attached without any pressure applied on top.

Builder's tape attached to mat..

..and sliced, ready to receive paint.

Once installed, the mat gave excellent contact BUT very shortly after, also started making unwanted random contacts. Quick check on the contact surface and indeed, the paint was already flaking off here and there:

Graphite spray flaking off.

After a thorough cleanup I went for aluminium tape. This was applied in a similar fashion as the (orange) builders tape: One wide piece over the length of the mat and cut to strips using the mat as a guide. Whatever unevenness remained on the surface after this got smoothed flat with a fingernail. Excellent contact once again, but as the aluminium is more thicker than the spray there were some permanent contacts right off the bat. The gap between the PCB and the mat is just too narrow for this stuff.

Shiny and conductive, but far from usable.

The conductive strips measure about 13 to 17kΩ end-to-end on my DG-20; with the graphite spray this went down to 200Ω whereas the aluminium tape gave pretty much a clean zero. So to say, certainly usable methods if the adherence could be improved. Not that this really matters, since the contact issues turned out to be caused by the plasticky glue blobs on the fretboard.

Next up, I should probably try learning how to play this thing! Gotta admit that picking a trancey super saw with this thing is far more “super rock star” than any of the internal sounds,  despite my attempts at playing made me feel more or less like having wooden sticks instead of fingers :D. On anything more “serious”, it’s easy to imagine that the DG-20 should be very neat for controlling something more subdued and in a easy tempo, like long ambient-ish pads and drones.

Oh and the definite lesson with the repairs on this instrument: don’t try fixing stuff if you have no idea what you’re doing ;)

Definitely way more than "my DIY".

Ongoing for 8 days to date, I reckon she’ll prove the longest-winding project I’ll ever take on.. Promise I’ll save you from further work stage posts here! ;)

These here are what this post is about, the DG-20 headpiece string tuning mech. A complete original part above and the damaged below it.

Figured I’m probably faster off describing this mech stuff with images and thus took detailed workstep photos. Too bad that I forgot to disable ‘save as grayscale’ setting when editing/saving the following photos and noticed this only after upload/editing everything ready for this post! No way I can’t be arsed to edit/upload everything again, so you get to suffer “artsy grayscale”  this time around ;). If you have a DG-20 in need of similar repairs and wish to take the DIY route, you will need the following tools and parts:

• A vertical (press) drill
• A 3mm threading tool
• 2.6 mm metal drill  bit
• A lathe (!)
• A metal saw and a file OR a miniature power tool equipped with a (circular) metal cutting blade.
• Matching amount of M3*35 screws and M3*28 standoffs.

Great thing (at least for me) is, the mech designer(s) responsible for DG-20 have opted to use metric items on the headpiece mech. 3mm diameter/threading is used in the stock part, thus finding replacements is easy.

Step 1. Drill a hole to headpiece mech using a 2.6mm bit.

On the picture above, I’m using a thick piece of aluminium under the part. Since it’s a bit too small to clamp down properly just by itself, the extra piece provides drilling support.

Step 2. Thread the resulting hole for a 3mm screw.

Step 3. Insert the 3mm screw. Inserting a nut is recommended if using a hand saw.

When inserting the screw, test if you are able to remove it by fingers alone. If so,  remove it and add thread locking fluid in-between, and leave the joint to dry for a while.  The nut provides cutting support for the hand saw and is also good for verifying that the threading at the tip of the screw is ok, once cut and filed clean. Probably not needed at all if using a miniature power tool.

Step 4. Cut the screw according to nut. The nut will likely spin, so use your other hand to keep it in place.

Step 5. File the cut clean and remove nut. Half-way there! :)

Step 6. If standoff isn't through-hole by default, make it so. 2.6mm bit once again..

Step 7. ..and add 3mm threading throughout.

Step 8. Lathe the standoff to proper size, making it round in the process. The original hex standoff is slightly under 6mm in diameter (lucky guess: 5.7mm).

Step 9. Cut crossed slots on the other end. This will be used for adjusting the string tension with a Philips screwdriver. Use a miniature power tool (for more precise cuts) if you have one.

Step 10. Test for fit and file the standoff down to around 27mm. All done!

The 28mm hex standoffs I’m using here are just very slightly too long, causing excess turning friction/tightness once installed inside the headpiece. Trimming them down to something between 27.5 – 27.0 mm fixes this. One odd thing is that my caliper says the original standoff is about the same length (28mm), but when installed there still is the difference. Weird, but whatever.

Shortly after fixing this one headpiece mech, I eventually ended up replacing all the Allen / hex screws and standoffs with my DIY Philips type.  The screws are 3mm  (talking about the ones used to clamp the nylon string) so replacing them is equally easy, especially if you have a selection to choose from. I didn’t, so the only black screws I had needed a bit of extra work. Since the screw tips were slightly concave (with sharp edges), each one had to be filed flat to avoid damaging the nylon strings. Despite the edges didn’t look too sharp they did bite well enough into the nylon string once tightened, in turn taking it way too close to the point of snapping up.

Anyway, the replacement was well worth it as it makes more sense to have everything adjustable with a single tool. Even having the two different-sized Allen keys, as in the stock configuration, is pretty stupid.

With the recent sponsorship in mind, oh how I wish a certain well-known hobbyist miniature power tool brand would sponsor me and I could then stop having have to type (the lengthy) “miniature power tool” all the time ;)

*NUDGE* *NUDGE* *WINK* *WINK*

V2.0, now with fantastic freehand style! ZOMG!

Somewhat faithful to the previous one too ;)

The instrument Darth Vader would use if he was into playing..

Yes, it’s the silly looking (and ridiculously overweight) guitar synth straight from the 80s, made famous by Flight of the Conchords.. the Casio DG-20! You probably now know what to expect to be reading in this blog over the coming weeks.. ;)

I got my DG-20 from Wolf Rami of Nightsatan. Apparently he had bought a few of these and used them to piece together a single working one for his own use.  So I knew exactly what I was getting into and actually bought the unit, if no good for anything else, just for the enclosure and string mech alone. Cheap “raw materials” and all that.. Should the synth indeed turn out unrepairable, alternative uses shouldn’t prove to difficult to come up with. Anyway, Wolf warned beforehand that the electronics have presumably seen a bit of overvoltage and that the battery compartment cover and one headpiece screw are missing.

Arrival check and indeed, the synth doesn’t power up. Lucky me, Dan Newcome has been kind enough to upload the service manual online. This helps a lot with analysing the fault, as there’s no need go about it the hard way and spend (a lot of) time reverse-engineering the power circuit. With the help of the manual, I was actually able to analyze possible problem areas before I even got my hands on the synth!

Schematic for the power supply circuit of DG-20

If you look at the picture above, there are two main subsections in the power supply circuit. When divided vertically in half, there’s the “switch on” section formed by transistors T1-T3 on the left, and the “output” section formed by transistors T4-T6 on the right. Quoting the service manual, the “power on” sequence goes like this:

1. When the power switch is turned on, battery voltage is provided to the base of transistor T3 causing the transistor to turn on. Current from T3 emitter charges the 10µF capacitor.
2. The electric charge from the capacitor turns T2 on compulsorily.
3. Transistor T1 turns on providing the battery voltage to voltage regulating transistors T4, T5 and T6.
4. After being charged, the capacitor does not provide voltage to T2 base however, receiving VDD (+5V), the CPU provides +5V to T2 base by signal APO.
5. If the guitar is not played for six minutes, CPU lowers signal APO causing the transistor T1, T2, T4, T5, and T6 off.

..so in other words, the circuit also has a simple “battery saving function”, controlled by the signal ‘APO’ . In case you’re wondering “APO wtf?!”, this is probably derived from something like ‘Auto Power Off’ and not eg. Asian Productivity Organization..

..

Briefly checking for internal operating voltage, the +5V bus measured clean zero. Luckily no short-circuit to GND and no input voltage on the “output” section either, so the fault was now pretty much narrowed down to “switch on”. Checking for the functionality of this subsection step by step, it immediately turned out that T3 isn’t doing much. Here, the voltage “visible” to the base of T2 measured about 0.2V. Just to verify that there isn’t a connection issue between transistors T2 and T3 (they’re on separate boards), I tried to bend T3 back slightly to get a better contact for the multimeter lead. When doing this, a piece from the T3 shell fell off! Take a wild guess which is more likely cause of problem, a damaged T3 or a connection issue between the two transistors ;)

Pretty obvious damage on transistor T3..

The service manual lists T3 part type as 2sc1310F-T or 2SC1740LNSR NPN. Both seemed a bit obscure to be sourced from anywhere (read, very little plausible search results) so I didn’t bother looking deeper into compatible replacements. 2N3904 I have a plenty of, so I figured I’ll just give that a spin. It’s not like the part is doing more than off/on switching, so anything remotely similar should work just fine. Come to think of it, you could also bypass the whole “switch on” subsection, if the APO function is not needed.. Comparing spec-wise, the 2N3904 isn’t exactly a value-for-value match with the 2Sc1730. However it does have higher maximum values on all common ratings (Vceo, Vcbo etc.).

Other than this, 2N3904 isn’t pin compatible either. The base is in the middle pin, whereas on the 2SC1730 this is on the right pin.. A bit of plier work needed, so to say :)

2N3904 viewed from both sides, the bent base terminal is more visible on the flipside.

And that’s about it, synth powers up once again \o/. Gotta admit, the internal sounds are pretty (horrible) bog-standard “Casio 80s keyboard style”, but definitely have to test running them through guitar pedals and such later on ;)

To keep this post short, I’ll save the mech stuff for later. Dan has a bit of DG-20 disassembly pics in his blog post here, in case you want to check out a bit of the mech stuff beforehand. To boot with the situation is this for the headpiece screw:

Side-by-side, a complete and a damaged headpiece screw

I’m thinking a screw and a lathed board riser should work here just fine, but let’s see what I come up with.. Luckily these parts are all metric, so I can get away with M3 hardware I have plenty of. No need for silly imperial body part dimensions ;)

The boring shit

Anyone who’s into DIY electronics (or repairs) probably knows that selecting and sourcing all the bits & bobs needed can (more than often) prove bit of a headache.  Building up knowledge of reliable/usable parts sources takes time and any short-comings here can easily bring a project to a halt. Not that every shop stocks every single part you might need either.. Add things like specific part properties or plain ‘meh, done that already‘ to the mix, and you’re instantly in need of a wider shop selection.

I’m not sure if it’s just the fact that I live in Finland, but stepping outside the boundaries of bog-standard boring shit (like pictured above) usually equals placing orders abroad. This of course adds up to the project price tag in the form of shipping costs.  Placing orders “part or two per shop” hardly ever makes sense, nor would I constantly want to side-order parts  unrelated to the project just to even out shipping costs. Sure, the side-orders “maybe of some use later” but I shouldn’t feel like living in a part stock either :)

My geographical issues put to side, these things are but a few of the reasons eg. why I often add part codes and whatnot to my posts. Findings get shared with the hopes that maybe some of my notes would help a fellow DIYists locate what they might have not yet come across. Even something simple like a specific part type or who makes it can help a lot, when put into some usable context.. And got to admit, these notes have also saved my ass a plenty of times. Forgetting some detail is just that easy!

Ok enough with all the yadda yadda, returning to Klee.. I don’t see much point going through standard parts like capacitors and logic chips. Every proper parts shop stocks these, so the focus is going to be entirely on “the other stuff” a.k.a. parts that make up the user interface. What I have below should also works as a Klee hardware shopping list (of sorts), but if you’re planning on building one you should definitely read through all the documents. Spending a good amount of time considering what you want your Klee to be is not time wasted either. Like it is summed up in the build manual on page 4..:

The operating console of any piece of gear is probably the most important part of the design, and, with the electro-music Klee Sequencer, that is left totally in your capable hands. The front panel of the Klee Sequencer is its operating console, and you will find that is where a good 90% of your build time is spent. After that, that’s where 100% of your operating time will be spent, so think long and hard about how you want it to be arranged.

If my take on the design starts looking like something you’d want to build, go right ahead. Depending on how this project turns out, I might be even able to offer a set of enclosure parts for sale later on! Briefly listing through the Klee ‘UI’ parts, they consist of the following:

• 21 +1 potentiometers
• 24 +2 SPST switches (ON-ON)
• 16 DPST switches (ON-OFF-ON)
• 2 momentary push-buttons
• 1 SP8T rotary switch
• 22 LEDs
• 17 +4 Jack connectors

Here, the ‘+number’ marks the amount of additional parts needed for the Klee options which you can choose to install or leave out. The potentiometer types can of course be slide or rotary, or like in my case, a mix of both. Going for rotary type alone will make the layout more compact, but slides offer a better visual confirmation of each setting. Slides also allow adjusting multiple values with one hand. As for the switches, the Klee build manual lists 23 of the SPST switches as ON-OFF type, but ON-ON works just as fine. Just solder the wires like you would with ON-OFF type.

Problematic size?

The SP8T and potentiometers I have are all Alpha (Taiwan): RV-series for the rotaries, RA-series for the sliders and SR-series for sliders. Whereas Mouser stocks the rotary switch, all the rest are sourced from Futurlec.

Generally, I’ve been happy with Alpha potentiometers, but can see a potential issue with the sliders and namely in the form of sourcing spares. Checking for availability/compatibility is one important thing in the design process, despite there’s no way to entirely account for future market changes and such. Anyway, with this in mind, the 75mm travel length type (the current panel design is for) could prove difficult to source as 60mm seems more of a “standard” nowadays. Thus, I’m still wondering whether I should switch to the latter instead.. Other option would be to side-order a full replacement set for later use.

Neutrik NMJ4HC

Considering the Farnell deal, it was kind of a “late arrival” for this project as I had most of the hardware selected already. What little was missing were the connectors and LEDs, and so, I ended up with a set of chrome nose Neutrik jacks and Multicomp blu-green LEDs. Knowing that the connectors will see a lot of use in this project (as output signals get patched), the Neutrik jacks should prove very durable since the brand is generally considered pro-audio. Time and actual use will tell, of course..

The Multicomp LEDs instead turned out a disappointment. I was hoping that the ‘blu-green’ would translate to something cyan-ish (or at least blue), but their color turned out to be very close to green.. Something I’d really want to avoid for this project. I have an order out for some purple LEDs, hopefully these will turn out better.

Speaking of colors, this brings us to one of my favourite DIY-parts; potentiometer knobs! If there’s anything that defines the look of a project, knobs are certainly among the top contenders. If you’ve checked the previous posts for this project, you’ll probably recall that the slider knobs I have are yellow. For this project, I’m thinking of something bright and colorful in a “Waldorf Micro Q” kind of way ;)

The minicurls

Browsing around for rotary knobs I eventually stumbled across Musikding. Checking their selection made me feel pretty much like a kid in a candy store! After a decent amounts of  ”pick’n mix” I settled with yellow and purple 13mm minicurls and some 19mm pointers for the SP8T. Since my front panel design is pretty crammed, the smaller the knob diameter the more it will help with clearances. I also ended up side-ordering a bit of this and that for future reference, because I liked the Musikding selection so much.. Let’s see what of these I actually end up using.

The switches and push-buttons are some fairly generic no-brand type that I’ve had in my own stock for ages. Can’t recall where I sourced them (random side-order,  most likely), but should they turn out crap in use getting quality spares isn’t a problem. We’re talking standard miniature toggle switches after all, so Apem, C&K, NKK.. you name it.

That’s about it for now. Dying to get on with the build, so let’s see what the next Klee post brings :)

The Matrix-12 is a 61-note synth with three big LCDs, six value knobs and about 60 switches on the front panel. Internally, it is 12-voice polyphonic and 12-part multitimbral, each part responding to its own MIDI channel. Each voice provides two big fat VCOs (offering triangle, saw, pulse, and noise waveforms), one 15-mode VCF (offering various low pass, high pass, band pass, notch and phaser types, all complete with resonant squelch), five LFOs, five envelope generators, 15(!) VCAs, and one FM modulation generator for oscillator sync and cross-mod madness.

There’s also a lag generator (a sort of portamento that can be applied to anything, not just pitch), three keyboard-tracking generators, four ramp generators (a very simple two-level envelope) and, finally, one noise generator. And that’s just one voice. There are 12 inside here! All this sound-creating muscle is useless without an equally powerful control system, and to this end Oberheim came up with the ‘Modulation Matrix’ from which the machine takes its name. This system enables 20 connections per voice between virtually any parameters. For example, to increase the speed of an LFO with time, select LFO speed as the destination and a slow attacking envelope as the modulator.

The Matrix-12 that landed on my desk was in need of lever potentiometer and rotary encoder replacements. As is, the lever potentiometers had problems tracking smoothly (eg. resulting in pitch “warble”) whereas the encoders did a lot of skipping back and forth.. Working but unusable, so to say.

One of the the original Matrix-12 encoders removed from the circuit.

I chose to start repairs from the encoders, since spares were supplied with the synth (how considerate!). These were of Alps type EC11B15202AA, having 30 detents and sending 15 pulses per revolution (DPR & PPR respectively).  I didn’t bother measuring the original encoders more than checking what’s their DPR (=30). For some reason, the middle pin proved impossible to desolder clean off the PCB, so I ended up cutting the that as short as possible and soldering the cable on top. Not exactly ‘proper’ but better this than increasing desoldering temperature and risk damaging the board. As the spares were way smaller, adding a short extension cable was also necessary.

Comparing the ‘new vs. old’ feel, the detent “click” is way more softer on the new ones. Most of the times, they also require two clicks to increment/decrement the value being adjusted. Thus, you do end up doing quite a lot of dialing when adjusting for more than a few digits/steps. If there was support in the firmware for a encoder with a push switch, adding a decade incrementing/decrementing feature to that would be a welcome improvement.

New set of encoders installed. A bit of wire needed between the part and board because of a way smaller part.

Furthermore, I’m thinking a non-detented rotary (with a higher PPR value too) might actually prove better in use than a detented one. But no such spares “in stock”, so I chose not to bother myself with ordering this and that just for the sake of experimenting. If you’ve done a similar repair but with a different encoder, I’d be interested to hear how did that work out. Do leave a comment here with part specs (PPR etc.), if so.

If you have no clue what a Allen set screw looks like..

Ok encoders sorted out, on to the levers!  I somehow wish I would’ve taken detailed step photos during this part of the repair, since explaining the following mech stuff in any KISS way is difficult. And to add to this ‘incomprehension factor’, the repair itself got (sort of) ugly right off the bat.  So try to bear with me and maybe try IDing stuff from the pictures below..

The Matrix-12 has two lever units, both consisting out of similar parts: There’s the lever itself, a 10k potentiometer, a L-shaped bracket (with side flaps), a spring mechanism and a (brass)  calibration locking disc. The flaps on the bracket restrict the lever movement (and thus, potentiometer resistance) range whereas the spring mechanism centers the lever. The resistance range that is actually used measured about 2k with the center (rest) position set to 5k.  4k to 6k, in other words.

The lever assembly without the lever

The “ugly” bit was caused by the weirdo-sized Allen set screws (four per lever assy) for which I was totally unable to find a proper wrench for. These screws are used to fasten the locking disc and the lever to the pot shaft. I’m guessing they must’ve been of some imperial size, since a 2mm tool tip was too big, a 1.5mm was too small AND having a ‘full set’ of .1mm size steps in anything else than drill bits sounds ridiculously pointless.

I then switched to a torx screwdriver set. Here, a T6 tip proved too small and T7 too big, but the overall fit was slightly better. In comparison to the 1,5mm Allen, the T6 actually gripped a little bit when the tool was slightly tilted. This approach turned out a working solution (can you guess already?).. for all but ONE SCREW!

I gave this remaining screw a go with the T7, helping insertion by hammering it in.. Now it was a snug fit for sure, but the screw just stubbornly refused to move. Couple of more attempts and, just for the fun of taking this simple disassembly task to a whole new level, the screwdriver tip announced “fuck off, not putting up with this shit anymore” by SNAPPING in half! I know that eg. if kept in contact (esp. fastened overtight) with other metals over longer periods of time, brass threadings have the tendency to get stuck. But this amount of tightness felt maybe juuust a little bit ridiculous. Anyway, with the tool tip stuck inside the screw, well, not much choices..

..though I gotta admit, fair amounts of drilling was involved prior to “oh hammer, please don’t hurt ‘em”. Simply too much mech bits in the way to properly clamp the locking disc to a vice to do any hammering (nor drilling), so the potentiometer shaft + locking disc combo had to come off. First, drilled away the shaft locking clip to detach the combo, then drilled away both the screwdriver bit AND the Allen screw. Believe me, drilling away an entire screw isn’t anywhere near as easy as doing a hole on ‘soft stuff’, like a sheet of aluminium ;)

Lever mech and potentiometer disassembled, locking disc can haz new set screws.

Finally, maybe something like +40 minutes into drilling/milling/hammering, I had all the parts separate. Since the screw had to be drilled away, the resulting hole had to be threaded for a slightly bigger set screw. The ones I ended up using were M4 * 6 with a 2mm Allen insert. Matrix goes metric, yay \o/

Doing this replacement lead me to think that maybe, having a single set screw use a different wrench than all the others would be just downright silly..  Yeah ok fuck it, let’s enlarge and re-thread all the set screw holes to maintain consistency. You might be inclined to think that this bit of extra work is pointless but, in my opinion, this is how you do mech stuff properly.

The locking disc with M4*6 Allen set screws

Gotta admit that this locking disc is actually a quite neat solution to handle the potentiometer calibration. Once you have all the other mech assembled, centering the potentiometer becomes very easy. Just clip multimeter leads to the terminal where wires are soldered, set the potentiometer to read 5k, move the disc to its place and lock it down. Dead-center in no time..  And yes, the pots measured the same despite in-circuit. I do occasionally check for these kind of things, you know ;)

Log taper potentiometer installed for testing. The shaft still needs a bit of trimming (and the white cable some resoldering ;)..

As for the spares: I actually ended up replacing the original potentiometers with ones having a logarithmic taper. Once again, “what is ‘in stock’ and what isn’t” ..   The part type is Radiohm CIP20C. I didn’t bother measuring the taper curve from the original parts, but I guess it’s safe to assume that they were linear type. It just makes more sense considering the use.

Not that I just blindly installed the presumably-wrong-taper-spare either; of course this got compared! Despite the taper curve, to me the resulting pitch bend sounded pretty much the same with both. And verifying things resistance-wise, if calibrated to read 5k in the center position the overall range measured similar +/- 1k regardless of taper curve. Maybe this is because of the limited range used, maybe the log potentiometers I have were of the “cheap” type  (check taper diagram here, if you like).. Who knows.. Not that it matters really; adjustment issues gone, synth in a working condition and shortly after, I was deep into “synth lead solo land” ;)

Phew, this post got a bit longer than intended.. But I like repair stories and think they’re good for learning a variety of things. My contribution to that here should (at least) give you some idea of how even a simple repair could end up taking a way-longer-than-expected detour. Say, if you do electronics repairs, it might be a recommendable habit to say “ok give me time to check things through” instead of promising “come pick this up tomorrow”. You never know when a case like this might land on your desk ;)

2nd version

Next up on the “design menu” would be completing the sub-panel design. This will most likely require some minor adjustments to the layout too, as I’m yet to completely factor in all parts according to their third dimension too. Let’s see how tricky this gets.. Draftsight is 2D, so all the “3D” has to be done with physical items, pen and paper.

Parts-wise I’m still stuck looking for that (damn) SP8T switch, so the current layout is dimensioned according to a SP12T Lorlin rotary. In the picture above, this is the biggest circle immediately to the right of slide potentiometers. Hopefully these rotary switches come in enough a standard size, that leaving a clearance of few millimeters around the part will make most variants fit!

It's a start..

Other layer colors here are violet for PCBs, green for sub panel and yellow for front panel. The PCBs are supposed to stack up with the panel eventually, but positioning these three together will be about the last bit. Less clutter this way.

After getting started with sketching the layout, I shortly after decided to venture away from Steve’s design I mentioned previously. Thing here is, the option of both desktop and rack installation got too tempting to pass by altogether. Had I strictly followed the initial plan, it would’ve called for a way taller panel than I’d like (read: desktop version using more space). So, I started testing what rack unit compatible height would be optimal in regard to panel size. 4U was the answer; this roughly corresponds to 17.8cm. Still pretty ok for desktop too.. In the picture above, you can actually see the rack ears (minus mounting holes) as separate rectangles on both edges of the panel.

Briefly describing the “blocks” on the panel, there’s the step section (sliders, switches and LEDs) in the middle. Underneath this are the Master and Bus 1/2/3 Gate + Trigger outs with their indicator LEDs and merge switches. Step & Load buttons and input jacks are on the left. To the right of step section, there are A / B / A+B outputs (with and without Glide adjustment) and Range controls. My overall plan with the layout is to have all jacks next to the edges and not “among” the controls (eg. middle of the panel). This should help avoid blocking out controls when inserting cables.

I’m still uncertain about what parts to use in a few spots (eg. Step / Load buttons), so the layout is definitely not final. Also, some jacks could also be rotated, panel needs to be checked for labeling clearances and whatnot.. What part is already proving a bitch to source, is the SP8T rotary switch. I’m able to find plenty of SP6T and SP12T ones, but not a single (in-stock) SP8T. With this part missing, completing the panel design could easily grind to a halt.. So, if you know a good European source online, tips are highly appreciated. Just leave a comment :)