A detailed guide of how I resolved a couple of issues with my Roland SH-101 synthesizer. Biggest problem was – no sound except for filter resonance. Some of the faults of my machine are described in other places on the web but a good bunch of them lacks resolution. So read on to find out what I did.

Opening up

If you have the modulation grip installed, you may want to remove it. Remove the wiring either way. If you don't own a grip you can defintely leave the four screws for Grip and strap holder in place (left and right side). Go on removing all screws from the bottom plate. Note, in the middle row of screws there are two with metric thread connecting to two brass spacers underneath. All other screws are of the same type, more or less.

Before I acquired my SH-101 it must have had a hard time since there was rust all over the place, signs of battery leakage in both the battery case and on the boards, a crack near the pitch bender, several fader caps loose and others bent to one side or the other.

So first of all there was some mechanical work to do:

• derusting housing and keyboard frame (metal brush, sand paper, zinc spray)
• thorough cleaning of all keys (household cleaner) and keyboard rubber contacts (benzine/isopropyl alcohol)
• straightening of bent sliders with two pliers, one holding the slider right above its housing to prevent damage to slider board and housing, the other doing the bending
• adding small portions of ABS plastic to the guide slots of worn out fader caps by dissolving remains of an old keyboard key or broken LEGO in Acetone and applying the solution with a tiny brush – note, a very thin layer inside the slot helps already a lot to tighten loose fader caps
• fixing the crack with Acetone (use sparingly and keep an eye on prints on the housing - they could get damaged, so do fixing from bottom side), reinforcement with ABS remains from bottom side, cutting small pieces of original grey ABS from inside and dissolving it to make up the crack on top, filing, polishing and finalising the structure of the make up after drying

SH-101 PSU check

First thing to check electrically is always voltages. Pick up Ground from the jumper closest to the edge of the board between IC2 and C11.

An SH-101 is powered by a 9 - 12V wall wart (DC, center negative). One interesting thing is, these 9 or 12V are used to drive some of the ICs directly, on the mainboard e.g. IC5 (9022 Op Amp) or the most precious IC14 (IR3109 Filter). This means on the other hand, don't exceed this voltage too much or damage may happen. I strongly recommend using a good (low noise!) regulated power adapter.

The other interesting thing is that the Roland engineers built an oscillator (TR1 SD571 and TR2 SC1815) to provide AC that is stepped up to above 20V with a tiny transformer and then rectified back to DC (D1/D2). Next is a regulation circuit to provide the other voltages needed in this 2½ octaves beast: ±5V (IC2 M5218), 14V (TR3 2SC1815), 15V (IC1 M5218). The PSU got rather complex to allow for running the instrument on batteries.

In this particular SH-101 all voltages were present, although I had slight irregularities. There is a tinkered image available on the internet showing multimeter voltage screenshots in different places of the 101 PSU. That image is not completely wrong but it shows measurements from places not well chosen. If you are not sure what the correct and working voltages should be please have a look at my commented schematic below. I also hope this helps to clarify the various voltage symbols in the schematics.

Please note, in place of C7 (1µ/50V) the original schematic says "C2 .01c". Maybe the available schematic is a bit outdated, there are a few other hints. But more likely this is simply a copy/paste mistake in the drawing. However, I know there are at least two revisions of the mainboard. Later boards contain coil L1 (4,7µH) in the PSU replacing a jumper, and resistors 199 and 210 (both 2,2kΩ) connecting GND and +5V, while a wire from their common connection goes to CPU pin 26. Pin 26 is cut from the +5V rail on the circuit board and thus the 10kΩ resistor between Pin 26 and Pin 20 becomes obsolete. There might be further improvements I did not notice at a glance. My 101 is an older model.

A strange thing is, IC1 (5218 Op-Amp) is driven by the 20V rail on pin 8 although this component is rated for 18V max. I doublechecked this with another One-oh-One (20.3V, thanks, Christian!) and this seems to be correct. Still, it is making one a little nervous.

No sound problem

Actually, this was resolved easily. IC13 is the VCO, the famous CEM3340 found also in devices like Prophets, Oberheims or Jupiters. On pin 16 check for 15V. Voltage was ok but output was completely missing on pins 4 and 8. Shorting the corresponding sliders didn't help. Since the keyboard was working (I could play with Freq set to 5 and Resonance and Keyboard sliders all up) and pin 15 received flipping voltages while playing I had to conclude, this Curtis 3340 was all dead. Luckily these ICs are available again through a variety of sources. I installed a socket and a new VCO – sound was back.

Funny thing was, the Pitch Bender and Tune knob worked in reverse – bending upwards or raising the pitch with the tuning knob resulted in a lower frequency and vice versa. I did not care for the moment.

Sad, by the way, that the third available 3340 waveform (triangle, pin 10) is not used at all by design.

Ok sound, but where is the noise?

Next on the list was the noise circuit. Noise is doing two things: one can add white noise to the sound and use noise as a modulation source. Both was not working so it wasn't likely that just the noise slider was faulty.

The noise circuit is fed by the 14V rail, voltage was ok at R83/R84 and IC12 pin 8. So I took the oscilloscope and probed IC12(a), realizing that noise was only present on the input side of the Op Amp (non inversed pin 3), an old 9022. To doublecheck I shorted the noise to the filter side of R109-R112 (not the ribbon side), and voilà, noise was there. I installed another socket and replaced the IC with a TL022, which is a modern days equivalent. Check.

Side effect: The pitch bend and tuning knob issue was gone and this makes sense, since both controllers are connected to the b-side of IC12. So if you have a pitch bender functioning the other way round, this could be the solution.

Note, TR23 (SC945) is a selected component and got a white dot for that reason. If you have to replace that install a 3 pin socket and check several transistors for the best noise result.

VCF Bender Modulation

While the pitch bender worked again I realized that filter modulation did not work. This time I really suspected the slider and shorted it to check and yes, that was it. And no, oh no. There is no source on the internet for 20mm 100K linear sliders. All those 30mm sliders would be available but not the short ones.*

So I desoldered the pot and opened its housing to do a cleaning first. Eventually, the problem turned out to be a broken path. Luckily, it was not the resistor path but the ground side. So I fixed this with some layers of liquid conducting silver painted on the tiny and clean slider board. I don't expect this to last forever but hopefully until I found a source for replacement sliders.

Btw, the crack near the bender was the result of a bad or unselected part, Roland is to blame. The bender frame is kinked on the edges and fixed with two screws. These kinks come a bit late, maybe by a quarter of a millimeter. So there has been some pressure on the housing right from the start. I solved this by attaching thick paper as a washer.

Bouncing notes keyboard

Now basically everything was working and I thought of calibrating the synthesizer. I hoped this would help resolve another funny issue. While playing the keys from low to high it felt like octaves were bouncing. Ok, not really octaves, the pitch would drop or raise extraordinarily every 8 notes. So I had a few strange intervals on the keyboard between keys next to each other. Another symptom was the impossibility to adjust the three D/A voltages according to the procedure described in the service manual (see SH-101 D/A Converter Adjustment in box on this page). Voltages were way off and could never reach the specified multimeter readings by trimming.

Since basic D/A circuit calibration did not help and since the keyboard symptom followed an 8-scheme I assumed a digital problem and one of IC7 (4050 hex inverting buffer) or IC10 (4052 de-/multiplexer) to be the culprit. I had both ICs in stock, installed sockets once more and gave that a try without further measurements. The outcome was, only IC7 was defective. So back to calibration.

Calibration: Problem with VCO pitch spread

Now I got the voltages right quite easy by adjusting VR1/VR2/VR3. But I could not get the VCO pitch spread right. Trouble was, one octave was always slightly more than an octave while VR6 was already turned fully counter clockwise which means 0 Ω. Keyboard and CV input led to the same result. First I thought some other VR might need some further adjustment but after some fiddling it was clear, there must be another fault, or the new CEM3340 Rev. G (IC13) had slightly different specs. Remember, Roland used selected ICs marked with a white dot, presumably due to better linearity (Aha!) and low frequency performance. See Roland Service Information 100248. This sheet also advises to lower R108 from 470Ω to 330Ω to increase the tuning range, which became standard from serial number 553.000 and up. However, tuning range was not my problem.

Sadly, I could not nail the reason for this deviation in intonation. So I looked at the schematic and decided to lower the resistance of R106 which is in line between VR6 and IC13. Since I had installed the board already in the synth I decided to put another resistor in parallel following Ohm's law. The schematic says 1.69K, my Multimeter said 1.67K and I thought let's bring it down to around 1.5K. To achieve this I piggibacked a 15K resistor on R106, see image above. This helped absolutely, the synth is now in tune and wonderfully playable. Well, in tune for most of it's range. There is still some deviation in the highest octave but since I use the synth for basslines mostly I can live with that.

UPDATE 8/2025: I have a solution for the deviation/tuning in the hi end. I made a custom circuit, see below.

Finally solved

A Roland SH-101 is such a great and flexible mono synth. And I love the ability to program sequences very quickly and to trigger them by e.g. a DR-55 DBS Out or a TR-707 Rim track. I enjoy it a lot, not only for bass or leads. Thanks to noise also as modulation source I found it possible to make entire drum sets.

Addition: Tubbutec SH-1oh1 (or µTune)

The original blog post is from spring '21. In late summer '22 I had another SH-101 here (and owner Yuval Miller) to have the Tubbutec SH-1oh1 Midi upgrade installed (not for him, for his synth only). The installation manual implies that it is simple to do that, provided you have some soldering experience and the right tools. If you don't want to do that yourself and you live in the Berlin area, drop me a note.

Some hints about the installation. Tubbutec recommends using a 14 mm drill for the MIDI sockets. If you stick to the 5 pin DIN sockets, use a 15 mm Forstner drill instead and drill with slow speed. Start in reverse drilling direction for some rotations, to mark the area before doing real harm to the housing. Depending on the spot where to install the sockets, protect the possibly installed circuit board with some layers of cloth. Hold the housing tight (get help from another person) and support the area where you are drilling with one of your own hands to prevent cracks in case you use to much pressure while drilling. For the socket screws, use a 2.8 - 3 mm drill. Tubbutec provides a stencil for all the holes, stick that with film tape to the desired spot on your housing. To prevent drill drift when starting to drill, use a sharp nail before and a little hammer and mark the spots with a tiny dent. When installing the screws for the sockets, protect the nuts from getting loose by adding thin lacquer to the screw thread.

The SH-1oh1 mod is much more than just Midi In and Out and I definitely recommend it, among other things you get another LFO and a lot more non volatile sequencer RAM. For any futher information visit the Tubbutec website. However, since my grey SH-101 has some deviation in the highest octave due to the oscillator chip replacement, the SH-1oh1 µTune edition could be the better choice in my case since then all micro tuning issues could be solved note by note. Actually, I have not tested that yet but it's on my list.

SH-101 tuning issues: update 2025

In the summer of 2025, I had another SH-101 sitting on my workbench with severe damage all over (including the CEM3340 being dead) and even damage to the housing. Someone had installed some modifications on a large custom board along with 5 pots, 2 switches and 3 jacks. The former owner said when the unit was functional, none of them ever worked or he never figured out what they were supposed to do other than drain the batteries quickly and let the unit get hot. At first glance, the circuit board did not resemble any of the known 101 mods.

After the most basic repairs and restoring the synth's playability, the custom board remained dead, so I decided to remove it along with all the loose wiring, plug the holes in the case with colour-coordinated ABS and restore the synth to its original state. As with the other 101s where the IC13 oscillator chip was replaced, it was difficult to get it tuned properly, even more difficult than last time. I had difficulties both in the low and the top end.

Eventually I took a thorough dive into schematics and CEM3340 analysis, among them the excellent writeup by Tom Wiltshire/Electric Druid. I was looking for some possibly degraded component in the 101 circuitry that influenced linearity. There are a couple integrator amp sub circuits, means op amp circuits with a cap in the feedback loop. These are prone to high impedance so to counter that a resistor is put in parallel to the cap. What if such a resistor got bad? IC9a and IC12b are directly involved in the CV path so I checked the involved components – but nothing, nada.

Then I got the impression that something being wrong on 3340 pin 13 (FM input) could result in Misophonia triggers. FM input is not used at all here, still there is a cap and 2 resistors to prevent floating. All in spec, I replaced them anyway. To no avail. Finally I desoldered the polystyrene cap C41 responsible for the oscillation, just to check, I did not think this could ever get bad. But hell yes, it was nearly 20% below spec. So I replaced that with a 1nF polypropylene cap from Wima and alas, the synthesizer's tuning was almost on spot directly.

But after the standard calibration procedure I still needed some extra voltage for the very hi end in the 7th octave (trust me, I was really glad I still hear that). So first I installed VR30 (20k) to replace the standard 10k resistor that Roland put here. Not enough. So after some deliberation, I made a small op amp circuit and voilà, now I have a trimmer to boost the treble even higher than necessary in case of doubt. The tiny board can simply be glued onto the original board next to the filter section. If you have the same problem - tuning problems in the treble range - and if you are interested in this mod, please drop me a note. I will collect feedback regarding demand to see if it's worth to have a low cost board made in a small series.

A last word about tuning in case you wondered. You may have spotted in the SH-101 schematic that you could add +15V to the CV circuitry via R102. You'd have to put a solder blob and short a certain point close to IC13. Basically, this shifts the whole tonal range some notes upwards. Useful if your tuning trimmer is out of range.

Conclusion

I hope this writeup could help you. If it did or if you have questions, I'd be glad if you leave a comment.