ModularSynthesis - Custom Work

Custom Electronics and Repair

I spent 34 years at Tektronix working in all parts of the company - computer graphics, video and networking, and test and measurement (my professional information is on my LinkedIn page). I've since retired to enjoy my hobbies and I now have the time to devote to my music projects. I have the time and interest to be able to help and assist fellow Synth-DIY'ers with their projects. Contact me if I can consult or be of help or assistance with your project, repair, design, or restoration.

The number one problem I find in making fellow Synth-DIY'ers projects operational is soldering issues: unsoldered pins, incomplete soldering, or solder bridges. You have to wash and carefully inspect every pad with magnification to find these. I have added tips and information on my Modular Synth Tips page for soldering, cleaning, and inspecting PCBs as well as proper packing for module shipment. Hopefully these tips may save you some time and grief. Unfortunately I also encounter design errors and insufficient margin as well. These do take more time to find and correct.

Here are some sample projects that I have helped with.

Synth-DIY Repairs
Project:	Dana requested some help with a Polymoog® Resonator Dotcom-format module. I made necessary repairs, wired the front panel controls, and verified functionality. Dana's website is www.danacountryman.com
Quote:	"I'm playing with it now! Pretty cool! I don't know where I'd have turned without your taking my case on!"
		Jürgen Haible Polymoog® Resonator in a 2MU Dotcom-format module.
Project:	Steve requested help with an Elby ADSR Frac-format module. I made the necessary repairs and calibrated the module. The output could not be set below 7.5 volts so I adjusted it for 10V and added jumper pins select 10 volts or attenuate to 5 volts. Steve's website is smcmusic.net
Quote:	"The ADSR came today. I just tried it out and it works great. Man, that little mod you did with the resistor and whatever that thing is that enables you to engage the resistor or bypass it is INGENIUS. How the heck do you come up with this stuff? Thanks a million." (Steve is referring to the jumper pins for +5V or +10V output)
		Elby ADSR with the Gate, ADSR output, and flip-flop waveforms.
Project:	Todd requested help with a René Schmitz Korg MS20 filter Dotcom-format module. The frequency range and resonance were not operating correctly. The resonance problem was due to noise on the power pins. There are no decoupling capacitors on the PCB so I added them at each IC along with some bulk capacitance on the supply rails. The frequency range limitation was due to overdriving the OTA inputs which would clamp the output to the supply rail. I changed the OTA input voltage divider resistors to decrease the signal levels and it now works well and self-oscillates from 66 Hz to over 8 KHz.
		René Schmitz Korg MS20 VCF in a Dotcom- format panel.
I also have experience repairing these DIY modules:
	Bridechamber Ian Fritz 5Pulser Waveshaper Buchla 258-style VCO as described on the Muffwiggler forum CGS-26 Analog Logic CGS-48 VCO Jürgen Haible Frequency Shifter Jürgen Haible Tau Phaser Papareil Synth Labs Quantix-8 CV quantizer / wavetable oscillator YUSynth Noise / Sample & Hold ... and of course any of the modules that I have built

Troubleshooting and Repair by Email
Project:	Ken requested help with his EFM (Electronics For Music) Bassace MIDI synthesizer. We repaired his monosynth via email. I asked Ken to make certain voltage measurements around the VCO. Based on these measurements I isolated the VCO problem to the exponential converter circuit. I suggested various ways of testing and isolating the faulty component which turned out to be a bad CA3046 transistor array. Once we got the VCO working it was time to test the VCF, VCA, EG and finally the Slide circuit. I suggested setups and voltage measurements to take and we worked our way through each circuit correcting faults as we went. This repair took a lot of emails back and forth to work our way through the entire circuit.
Quote:	"Dave! It's oscillating! You were right a bad transistor array!" "It's tracking properly now. I'll let you know once I have everything buttoned up but it looks like everything is working!!!!!! "I wanted to thank you for all your help with all this. Looking back, there are over 80 emails between you and I. No one has ever taken this sort of time with me to troubleshoot a project like this and honestly I'm still quite surprised you stayed with me through all this. It's really, really cool of you. Without your help I wouldn't have been able to do any of it. I've learned quite a lot in the time we corresponded ... you're quite a teacher."
		EFM Bassace monosynth PCB.
Project:	Scott requested help with his Thomas Henry X-4046 VCO using the Fonik PCB. We repaired this VCO via email. I analyzed the circuit and asked Scott to make specific voltage and audio measurements. Based on his findings I isolated the fault to a specific sub-circuit and sent Scott another email of components to check. Scott found the problem and repaired his VCO. Success by email!
Quote:	"It seems R14 was indeed the culprit! I can't thank you enough, I was really at wit's end. Thanks Dave!"
		Problem R14 component on the Thomas Henry X-4046 VCO.

Vintage Synthesizer Repair and Restoration
Project:	I helped Anthony get his TimeMachine working via email and he requested help with four Aries modules: AR-312 EG, AR-317 VCO, AR-318 S&H, AR-324 Dual LFO. These were originally built as kits so some had original build errors as well as defective components. I could not obtain any PCB layout information and some of the parts are in seemingly random locations so tracing the circuit took time. Luckily the PCB is accessible from both sides. I created pages for each module with documentation, modifications, and photos.
Quote:	Wow, Dave, wow wow wow. You are amazing. The level of detail is phenomenal. You could have just said "yeah I had to change a couple parts and now it works" and I would have said "GREAT!" Thanks again, really, so much, for the work you did. Amazing! I have already recommended you to a friend. (Anthony is referring to the detailed descriptions of what I corrected on each module).
		Four nice vintage and complete Aries modules.
	The AR-312 Envelope Generator was straightforward to repair. I modified the Gate and Trigger inputs so the module will operate with 5V Trigger and Gate inputs.
		AR-312 Attack, Decay, and Release.
	The AR-317 VCO module realized my worst fear - a defective dual exponential converter U8. Aries potted the components in place on the PCB so there is no way to remove U8. Luckily it was only the NPN transistor that was bad so I epoxied a new one to the side of U8 for thermal conductivity. This module had a number of bad parts and several lifted pads with broken traces that were difficult to find.
		AR-317 VCO waveforms with a sawtooth core and triangle core from which the pulse and sine waveforms are derived.
	The AR-318 S&H / Clock / Noise Generator module was a challenge to repair. There were wrong transistors and transistors installed backwards so I had to check everything. There were a total of 14 faults in this module including previous repairs done incorrectly.
		AR-318 Sample & Hold running on internal clock.
	The AR-324 Dual LFO / Lag / Inverter module was the biggest challenge to repair. There were replacement transistors installed wrong and original transistors installed backwards so I had to check everything. There were a total of 20 faults in this module and only the simple inverter circuit functioned without repair.
		AR-324 three LFO waveforms and variable gain inverter.

Synth and Electronics Repair and Restoration
Project:	Josh requested help with his Fostex 3180 spring reverb. This is an interesting two channel reverb with BBDs prior to the spring reverb. It exhibited intermittent noise similar to that of a crackly record. There was corrosion in the tin connectors and unsealed trimmers so I cleaned all the front panel controls, trimmers, and connectors. I replaced the power supply electrolytic capacitors, rerouted the main AC wiring away from the spring pickups, and replaced all the gooey foam in the reverb springs.
Quote:	"Dave Brown provided excellent service. The Fostex Spring Reverb sounds 100% better now that it has been cleaned and its power supply re-capped."
		Fostex 3180 spring reverb.
Project:	This broken Casio CZ-3000 needed electronic and mechanical repairs including several inoperative keys and two broken keys. I repaired the keys by making a cardboard mold for the missing end tang, filling it with epoxy, and machining it to the proper shape. I replaced the missing key stops by making an aluminum clip which wrapped under the key as seen here. The repaired keys fit and play perfectly. This is an interesting keyboard using phase distortion synthesis. There is a good write-up of the CZ series at Mad Theory and the Electric Druid site has a nice explanation of phase distortion synthesis.
		Casio CZ-3000 inner electronics.
Project:	I met Byron at the PDX Synth-DIY meet and he requested help with a dead Peavey DPM4 synthesizer. I knew it had a battery on the PCB so thought there would be corrosion damage (see my DPM-C8 repair). We worked on this together and replaced the battery, cleaned up minor surface corrosion, checked continuity on corroded traces, reseated connectors and ICs, and got signs of life with "SYSTEM ERROR:00000000 1111ERR" on the display. Occasionally we could get past this error message and Bryon determined that reseating the low profile keyboard cable connectors was the final fix.
Quote:	"No more error on startup; no more sustained tones. I'm able to program it and save patches, so it is completely back to life now!"
		Peavey DPM4 PCB with a leaking dead battery

Custom Design
Project:	Bill requested a special version of my DJB-A440 Reference Oscillator that was selectable to operate at either 440.0 Hz or 440.5 Hz. I modified the software and sent him some programmed parts. Bill's website is www.dragonflyalley.com
		Modified DJB-440 with 440.5 Hz output option.
Project:	Alan requested help for a portion of his synthesizer project. I adapted the software for my MIDI processor to provide a custom split mode function. Three switches define the split key, one switch enables the split mode, and four switches set the MIDI channel for keys below the split note. I sent Alan programmed AVR processors and he built the hardware and performed a system verification of the functionality.
Quote:	"It worked first time and I am very pleased with the result. It does everything we discussed and interfaces perfectly with the M-audio and the Tyros3."
		Alan's DIY MIDI Split processor.

Audio Restoration and Conversion
Project:	This reel-reel tape of a 1970 Christmas broadcast produced by the radio class of Mount Hood Community College in cooperation with KRDR (now KRYN 1230 AM) in Gresham, OR. I digitized the broadcast and sent the tape and a CD to Mount Hood Community College for their archives.
Contents:	30 minutes Hosted by Larry Grant Greeting from Robert R. Carl, College Development Officer Music from the College Choir directed by Harold Malcolm Special announcement from Rob Carnaham, Student Body President
	Click to listen to the broadcast
Project:	Jason requested help with a transcription disc recording of his grandfather who was interviewed in the Marines on Iwo Jima in 1945. I took a straight tubular tone arm and made an extended tone arm using 5/16" aluminum tubing. I had to heat the aluminum tubing so I could bend the 22.5º angle at the cartridge. I mounted the new arm extended off a turntable so it could play the 16" transcription disc. I digitized the recording and made audio and data CDs.
		Rare 16" transcription disc of an interview of Marines on Iwo Jima.
	Click to listen to the interview
Project:	Bob had a 7" recording of his parent's wedding from 1960 and wanted it transferred to CDs and mp3 files. It was a 3.75 ips 2 track mono recording so I was able to play on my Otari MX-5050-QXH four track. I digitized, normalized, and equalized the recording and made audio and data CDs.
Quote:	"It's better than I could have imagined. Thank you so much for doing this. There won't be a dry eye in the place when they hear this."
		2 track mono tape transfer and restoration project.

Professional Engineering Consultation
Project:	I was responsible for Tektronix Regulatory on a global basis and am familiar with RoHS and REACH directives. Some of my experience dealt with vendors removing lead and leaving pure tin plating over the base metal leading to tin whisker growth. I also am familiar with zinc whiskers on my Hammond organ tonewheel generator (close-up photos of zinc whiskers can be seen on my zinc whisker photo page and at the bottom of my tonewheel generator photo page). I helped diagnose and confirm root cause issues for an electro-mechanical component a company was having issues with. As I began to understand the symptoms I suspected tin whiskers might be a possibility. I got some part samples and arranged for Scanning Electron Microscope (SEM) analysis on a Helios Dual Beam FIB (Focused Ion Beam) at the University of Oregon. An Energy-Dispersive X-raySpectroscopy (EDS) analysis confirmed the whisker was pure tin. Failure mechanism solved.
		Scanning electron microscope image of a 4.1 µm diameter tin whisker

home