Can I repair this Alesis Micron synthesizer? (Part 2)

Two weeks ago, I posted a video showing my thought process on finding the flaw in a used #AlesisMicron #synthesizer and an attempt at starting a #electronicsrepair. The synth had a weirdly distorted output and all the knobs, the mod sliders and the pitch wheel didn't work.
Here's a follow up and a conclusion to that story. No table of contents this time, you well need to watch the whole thing or not at all. ;-) There's a conclusion at 08:54, though, if you're in a hurry.
First part: • Can I repair this Ales...
Things I read while preparing this video:
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components101....
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Here's what I have in my setup at the moment. Want to have that, too? Please use the followings links and support me:
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Strymon Nightsky www.thomann.de...
Strymon Volante www.thomann.de...
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Zoom MS 70 CDR www.thomann.de...
Korg NanoKontrol 2: www.thomann.de...
Korg NanoKey: www.thomann.de...
Akai EWI USB www.thomann.de...
Zoom R24 www.thomann.de...
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Yamaha MT7 www.thomann.de...
Some bands / artists I've been following for a long time are (among others) Massive Attack, Pink Floyd, Pet Shop Boys, Archive, A-Ha, Yes, Porcupine Tree, John Mellencamp, Jean-Michel Jarre, Metallica, Peter Gabriel and Perturbator. So my music will kind of sound like those (without ever reaching the greatness of those artists, of course). :-)

[@AstonThaRat]

Great video. My Micron had a scratchy volume pot when I purchased it used. I found a website that sold replacement parts and ordered the entire pcb that houses the volume knob. Quick easy fix and also rather affordable. That was 17 years ago and it’s still working flawlessly.

[@mr_floydst]

Thanks for watching! That's great to hear.

[@darwiniandude]

Enjoyed both these videos, thanks. :) Picked up a Micron cheaply finally, used to sell them back in the day - FB marketplace had one locally with manuals PSU and a USB-midi interface for the equivalent of $130 USD. Others had already jumped on it but he sold it to me because I said I'd just take it, other people wanted to come to his house and test it etc. Anyway when first powered on there was a loud background static hum, RF noise, and very low signal output. Sounded like a ground loop type noise. Anyway it was just the volume pot - moving the volume through it's full range up and down constantly for a few minutes while playing made it better and better and now it works fine. Some of the preset sounds are a bit dated with their design and effects, sound very late 90's early 2000's VA, as you'd expect - but I made an INIT patch and slowly built up some basic sounds, a square/pulse with slow PWM movement, experimented with the various filters. The RP (arp) filter doesn't sound like the filter in my Behringer 2600 where you turn up the resonance and the bass disappears, but I later realised that it's emulating a later ARP filter, likely from the late 2600's or ARP odysey. When set to the MG filter (moog) it does respond very much like that on my 2600 clone, as early 2600s had a ladder filter design which was pretty much a copy of the moog filter. So I found that impressive, for a cheap little synth... lots of different filter types which do respond in typical ways to the originals. I quickly found I was getting drive/distortion even though it was off... there is a POST oscilator level control mixer for each osc, and maybe others, anyway turning these down and it sounds nice and clear. Time consuming to program but actually very capable. And 37 full size keys is great for the studio, a nice little controller keyboard. 25 is too few to be useful and 49 too large often. Anyway - enjoyed these repair videos. :)

[@mr_floydst]

Thank you! And congrats on that nice little synth. (I personally found no place for it in my setup, which I try to limit to 4 hardware synths max)

[@darwiniandude]

4 synths is some serious restraint, but very sensible. :) I guess it helps that one is an EX5 which covers so much sonic ground.@@mr_floydst

[@mrz80]

@@mr_floydst Thou 'rt a better man than I... I'm at 5 (QS8.1, Micron, Nanosynth (I really dig Alesis), JV-1010 and Blofeld), well, 7 if you count the two guitar synths (GR-50 and SY-1000), no 9 (I also have two SR-16 drum gizmos but one of them is still busted).

[@blackrazorus]

Great conclusion! Sounds fantastic now!

[@mr_floydst]

Thanks! I'm so happy one of my viewers helped me.

[@FredBloggs919]

Top tip when buying used/faulty electronics - Check with the seller as to whether any repairs has previously been attempted! If in doubt, check the case screws too for any signs of unusual wear. Got to say that that synth still sounds great! :)

[@mr_floydst]

Thanks for watching! Luckily, this ended well. I still need to post a video on this synth now that it works again - it has some really unique features and ideas.

[@jonclyne2918]

Good one Floyd. I am in the process of bringing a Micron back from some serious damage. I love seeing the problem solving process on equipment I am familiar with. Thanks for sharing.

[@mr_floydst]

Thanks for watching!

[@arcanics1971]

Got to admit, I loved the broken sound- though it would have limited use. This was a fascinating video and you should be commended for your explanation, because even *I* understood! And I am not exactly an electronics nerd. My GCSE physics teacher would tell you I am certainly not very good with this area. But I followed your helpful explanations. It was a brilliant watch, so thanks to you and your helper! Nice work, both of you!

[@mr_floydst]

Thanks, Scott! You witnessed the process. ;-) I'm still flabbergasted someone could be so helpful and choosing not to get a short spotlight for it. ;-)

[@arcanics1971]

@@mr_floydst Indeed. The person referred to should be given a medal!

[@Slider2732]

Great fix! I'd never have thought to check the pot wiring.

[@mr_floydst]

Thanks! Me neither - as I said in the end of the video, thinking about a thing "logically" only gets you so far. I'm super lucky my viewers (and one of my viewers in particular, who chose not to be mentioned) are so knowledgeable.

[@WoodyPianoShack]

great perserverence!

[@mr_floydst]

Thanks! I could sometimes hear "Siana Gears'" eyes roll from afar ;-), and I'm super thankful for all that patient and knowledgable support.

[@SianaGearz]

@@mr_floydst Me rolling my eyes? Absolutely not, you don't think all of us had similar struggles at some point potentially decades ago?

[@JulianToler]

Great detective work and successful cure. You have really earned a Sherlock Holmes hat!

[@mr_floydst]

Thanks 🙂

[@Jake-Balibari]

Congratulations! I keep the link as I just bought one Micron.

[@mr_floydst]

Thanks for watching! And congrats on the Micron. This is one great-sounding 2000s synth.

[@dustyaudio]

Ep 2! Excited to see what happened

[@mr_floydst]

My explanation is a bit lacking in parts (for example, I left out the assumption that the previous owner shorted the pitch wheel, frying the Q28 transistor). But I think I learned a thing or two while doing this.

[@johnsaunders6510]

Good stuff. Well done.

[@mr_floydst]

Thank you kindly!

[@jmcbeady8210]

Great job!

[@mr_floydst]

Thanks!

[@Frozirra]

I’ve gotten hardcore into synth kits and repair, tbh I wish I could understand how the components changed sounds but I’m cool with just following the lines and swapping parts that don’t do what the service manual says they should be doing

[@mr_floydst]

Thanks for watching! As I said in the video, I'd never have been able to solve this problem myself, without my awesome viewers. ;-)

[@Death_By_Media]

Wow , what an odd combination of issues . You got the rarest of them it seams .

[@SianaGearz]

Not really weird? Someone wore out the pitch wheel, which is not surprising, because it's made out of garbage, actual garbage. Tried to repair. Shorted out the reference voltage to ground while fiddling with it, basically shorted the first pin of the potentiometer to the last. The reference voltage emitter-follower transistor was thus forced to pass all the power supply current, ALL of it, and it understandably went for a smoke and never returned. Nothing particularly odd about it.

[@Death_By_Media]

@@SianaGearz Well in 20 plus years of broken synths I’ve never had those issues separate or compounded and likewise never read them in forums researching issues ... so rare to me . Which is where I get my perspective and opinion from My life experience . Is that ok ? Allowed with you all mighty regulator of what I find rare or obscure ?

[@mr_floydst]

@@Death_By_Media I should have mentioned this theory in my video because it's very likely how it happened. When I opened the synth, I was clearly visible someone had tried to "repair" the pitch wheel. Unfortunately, I didn't film that.

[@SianaGearz]

@@Death_By_Media Watch your language young man; i won't apologise for what i said. You however shall reconsider.

[@Death_By_Media]

@@SianaGearz 🤣 I appreciate the “ young man “ wish I still was ...that 20+years of tinkering with synths isn’t my whole age even by half . Either way I just think we could all due with less people feeling the only thing they have to offer in comments is to try and invalidate others opinions with their own subjective opinion. Neither of us are writing a paper on the subject nor are either collecting data on what is or isn’t most common in a statistical analysis. To my original point the microns have a few arguably very well know problems . The main Data encoder failing , the dac on the output board , and memory corruption scrambling the os . To me it was ironic that he didn’t have any of those issues as the amount of forum threads on them is rather long . Cheers .

[@patrickfitzgerald2861]

This was very interesting, but fingers crossed that my Akai Miniak keeps working perfectly. It would be a sad day for me, since I love the goofy little thing, and there's no way I could fix it myself. 🤞🤞🤞

[@mr_floydst]

Thanks for watching! the most common failure of old synths is leaking capacitors. Those are easy to spot and relatively easy to fix.

[@patrickfitzgerald2861]

@@mr_floydst I'd certainly give repair a try, but I'm hoping for zero fail, especially since I use it lightly, and always at home.

[@unclemick-synths]

Interesting video. I wonder how that sawtooth helps with the reading of the potentiometers? I must look for the schematic. Nice jam at the end.

[@SianaGearz]

The relevant schematic is at 1:00 in the vid. The sawtooth and comparator form an ADC. The FPGA serves the input, but it has no ADC; on the other hand, it can precisely time signals very easily. Transistors Q10 and Q16, above the comparator IC in the schematic, form a constant current source. It trickles current into a ceramic capacitor C6 (presumably C0G type), which then forms the rising sawtooth voltage. C6 gets shorted out regularly by Q1 to reset the sawtooth, about every 0.8ms. The sawtooth then gets supplied to all the V+ inputs of the comparator. The V- inputs are connected to 4 individual signals - pitch wheel, two mod sliders, and then a multiplexer that supplies a number of other readings, including a calibration reference reading. As the V+ input sweeps through the voltage levels, eventually it reaches the voltage of the input and the comparator output turns on, thus converting all the input voltages into timed pulses. Because the constant current source consumes some voltage and the sawtooth can never reach the supply voltage, they must generate a voltage that is lower than that to supply the potentiometers, that's the POT_REF. So they take something like 4/5th of the supply voltage, and run that through an emitter follower, which subtracts another junction.

[@unclemick-synths]

@@SianaGearz thanks for the clear explanation.

[@Synthetech]

usually when I see a "broken" Micron on eBay, it does not work because the seller is trying to use a DC adapter/supply instead of a 9v AC supply. A DC supply will turn it on and make the menu/buttons work, but no sound will work.

[@mr_floydst]

Thanks for sharing this info! This will be helpful.

[@SianaGearz]

Wait why? Uhhhh... OHHH THE INVERTER/CHARGE PUMP outputs, -9V and -18V. Yeah that's maybe a little unusual, honestly i'd just call it a design defect and just re-engineer the power section of the main board :D The -18V seems to not even go anywhere, looks like they mindlessly copy pasted this section from somewhere else. -9V will not receive any current on a DC adapter so the in/out opamps will be choked off. Normally this would call for a 7660 industry standard converter instead of requiring an AC low voltage supply, which is why you don't see so many synths with this behaviour, but yeah whatever.

[@mrz80]

@@SianaGearz Take a look at the main board schematic top right near the headphone out. The -18vdc feeds Q4, which is part of the output muting circuit which looks like it turns on and off a pair of JFETs that when turned on short the output stage op amps to ground, thus silencing the output. No -18v, no output. That's why using a DC power supply makes it look like the instrument's failed.

[@SianaGearz]

@@mrz80 Oh right very good. Thanks for finding the actual use for -18V. So the open drain or active-low FC_MUTE is supposed to activate the transistor Q4, creating a voltage gradient across R84 to bring the MUTE net above ground level, and -18V is the unmuted state? By biasing the JFET to -18V, the JFET DS current is choked and the opamp output is unmuted. Fundamentally muting with a -9V line would have been doable as well, but the JFET they had chosen needs below -12V to turn off reliably. Just making sure i understand what's going on there.

[@asgjdafghesyusgf]

Circuit benders are crying themselves to sleep after watching you fix this synth. 😂

[@mr_floydst]

I am fully aware of my incompetence, but hey, people enjoy horror movies. :-)

[@asgjdafghesyusgf]

@@mr_floydst Don't be so hard on yourself! I was actually thinking the loss of audio eccentricity would be the thing to upset them. I'm 100% sure a non-zero number of active circuit benders are far less technically competent than you've shown yourself to be.

[@mr_floydst]

@@asgjdafghesyusgf Ah! Ok, I didn't see it that way, haha. 🙂

[@herberdth]

Where did you find the service manual? I got one which never advances beyond first text on display. Believe a wrong power supply was connected once.

[@mr_floydst]

Thanks for watching! I used www.bing.com/search?q=alesis+micron+service+manual

[@herberdth]

there you go! Thanks! I am just used to these manuals being hidden. @@mr_floydst keep up the great material.

[@SianaGearz]

The symptom sounds like a broken firmware update. Firmware updates were released as SysEx files that an end user can apply themselves, you can guess what happens if that goes wrong, and of course that's not the whole firmware image, a partial one, so you can't reconstruct the firmware IC contents just from the update. Someone should dump the image of the known working firmware chip, so that other devices with this fault can be restored without replacing the whole mainboard. There is apparently just one, it's the Intel Flash with a version sticker on it. This is attached to the main processor, a Motorola ColdFire, which then loads the firmware into the FPGA on boot from there as well.

[@JonathanDotExe]

Wow it must be very satisfying to havw it finally working. Are you still planing to sell it after all this "story"?

[@mr_floydst]

That was _so_ satisfying. Yes, still planning to sell it. I will take a look at what makes this machine tick beforehand, of course, cause when @snupps_synth_channel says it's great you better listen ;-) But I made it a rule for myself not to have more than 4 synths at once, and I even with that rule in place, some machines tend to gather dust more than other ones.

[@the_musiccellar]

So the pitch wheel was one of the problems? Or the bad transistor? I have trouble with them going out of tune occasionally

[@mr_floydst]

Connecting the pitch wheel in the wrong polarity makes the transistor blow up, disabling all the other controllers. It also makes the micron calibrate the controls incorrectly, leading to that jittery sound. (That last sentence is only a theory, I don't want to proof-check it because I don't want to blow up the transistor again).

[@mrz80]

Found this to be very interesting, as I'm currently looking at a broken Micron on Reverb for a "can't walk away from that" low price. :D

[@mr_floydst]

Thanks! Glad it was useful.

[@mrz80]

@@mr_floydst I've got the thing partially pulled apart. I replace the busted main encoder, and now I'm chasing down failed solder joints, busted connectors, etc. It lights up and displays "Alesis Micron" and then freezes. No control inputs work, no music comes out, nothing.

[@mrz80]

I finally determined it was apparently the victim of a botched firmware upgrade. The main board is completely unresponsive. I was able to find a replacement main board, and now it works perfectly. Isn't it fun putting the thing back together? :) Just need to replace some missing knobs. Looking forward to delving into the remarkable depths of this gizmo!

[@SianaGearz]

@@mrz80 The whole firmware is on the Intel Flash chip, someone should dump a known working one so one needn't replace the mainboard.

[@mrz80]

@@SianaGearz So you're saying I might be able to resurrect the old mainboard? How, when it doesn't make it far enough into its boot sequence to accept a firmware update? Unsolder the flash chip and use some kind of flash card programmer?

[@user82938]

So if you had fixed the pitch wheel first, it would have sounded good, but the knobs would do nothing?

[@mr_floydst]

No, that would not have worked, because that transistor at Q28 was fried, leaving the synth without a reference voltage. It was only possible in the order I showed here.

[@-_-MARANTZ]

WOW. LiSTEN TO HER NOW-_-b/''

[@mr_floydst]

Thanks for watching! Indeed, indeed. ;-)

[@proctormacbelle4904]

great follow up video! very enjoyable. one small point you might have missed is that we typically say current flows (somewhat counterintuitively) from the collector to the emitter, not the other way around. i believe this comes from the crt days where the emitter was an emitter of electrons (and not of "conventional" current). see clip at kzbin.infoUgkxeVvIfpN54fl9U7ADOnh3gt662GIacqkG for where in the video i mean.

[@mr_floydst]

Thanks for pointing that out! There are some inaccuracies (and things I left out) in this video - I think it's clearly visible I'm in the process of learning new things and re-learning long forgotten things. ;-)