Sequential Circuits Drumtraks

This was for producer Gino Wong of ReRed Recording, but I was excited to get it working for my own reasons, so that I could sample the drum sounds into my Electribe. Once I did get it working, I discovered that the SCI Drumtraks is super easy and fun to make beats on! I didn’t know this before, but the sounds on here are not synthesized, but rather are low-fi samples each on their own EPROM.

When the Drumtraks arrived, the display and the digital control side of things seemed to be working normally, but it made no sound. When I checked out the PSU, the +15V and -15V rails were showing 0V. Only the 5V rail was working, and that was enough to run the entire upper (digital) board. The power supply for this is surprisingly simple, even simplistic. So it was easy to identify that the tantalum capacitors between each voltage rail and ground were the culprit, shorting to ground. Once I replaced them (and the big electrolytics) everything sprang to life and I was jamming on those charming 80’s drum sounds. Just a little bit more mostly-preventative work was required.

a message from Dave Smith on the Drumtraks PCB

I found out that there are alternate sound chips you can buy (from Wine Country Sequential, for example) and that with an EPROM programmer, it’s possible to burn an EPROM with the appropriately-formatted sample of whatever sound you want.

Of course then I was thinking about how it would be funny to return a client’s Drumtraks with just one of the samples replaced by a fart sound or something. I would never do that though because it’s obnoxious and unprofessional. And I don’t have an EPROM programmer.

Service Tips:  the conformal coatings on the PCBs melt a lot as you desolder, leaving behind brown burnt-flux residue as usual, but also leaving behind a colorless residue that when it is on the solder pads is not visible but will give you a bad connection when you solder there again.  It’s important to clean the pads really thoroughly with isopropyl alcohol after desoldering, even if it doesn’t look like there’s anything on them.

Work done: recapped PSU to troubleshoot failure, then tested all functions, recapped other boards, replaced memory battery and deconstructed and cleaned tactile switches/buttons as needed.

7 thoughts on “Sequential Circuits Drumtraks”

  1. I’ve been lent a drum tracks by a friend who is offering it to me as is for 100 bucks.
    It seems to have a functional brain but may just need some buttons replaced.
    Run/Stop is dead, RIM, ACCENT, also.
    Bass, Ride, HI HAT OPEN and CLOSED and COWBELL are double triggering etc intermittently.
    The tempo ‘FASTER’ button seems dead. And the left arrow of the numeric keypad seems dead.

    My tech friend opened it up, desoldered a button to evaluate it’s mechanism. He decided he didn’t want to attempt to refurbish the buttons.
    Touching them they feel like simple spring loaded switches. I’m not a tach but I am guessing a simple contact of two wires.

    As a vintage drum machine reggae hipster, this machine was and still is used by Mad Professor the UK reggae dub producer. Since 1984 in fact.
    The sounds are similar or the same as the Oberheim DX which was the main tool for Steely and Clevie the production duo from Jamaica most known for introducing drum machine into reggae.

    Thus the value it has to me. I want to emulate these guys sounds.

    I notice you declared that you deconstructed and cleaned tactile switches as needed. Me being a non tech and my tech not wanting to attempt any repair. I thought I would ask for any advice, encouragement etc on how to possibly fix these buttons so I can have a working drumtraks.

    Maybe I could my tech to desolder all the buttons and mail them to you for servicing back to life if possible to bring them back to life. What about the numeric keypad? is that able to be cleaned. It’s only the left arrow not working for the keypad.

    Thanks for any hope.

    1. Hey, sorry for not replying to your comment sooner. It is possible to deconstruct the switches just by gripping the top plunger part (the part that pushes down) with your fingers and pulling it straight up. They don’t have to be removed from the board to do this. You can then just clean the metal switching parts with a Q-tip and rubbing alcohol, and if it’s really bad, let it sit with a little Deoxit D100 on it overnight and then clean it with alcohol again. The number buttons work the exact same way. We don’t derive much satisfaction or profit from doing this kind of tiny weird job for people so I am happy to encourage you to do it yourself! I have faith in you!

  2. Trying to repair one of these, did the recap of the Power supply, it reads fine now. But still no life. I only get a 0 on the display, and no sounds and no response from pushing anything. I have not recapped the mainboard – could that be the culprit?

    1. Sounds like your synth isn’t even booting at all. Using an oscilloscope, start off my making sure the CPU is receiving a clock and reset signal, then see if it is doing __anything__ by looking at its data lines! The Z80 CPUs in Sequential gear seem to fail frequently, it wouldn’t surprise me if that was the problem.

      1. Thanks for reply. I can see a clock signal on my osc. Have not checked rhe freq. but i think it is fine. The service manual mentions the reset signal being either high or low. Is low 1v and high approx 5v? I also measured the datalines. They were above 1v which the manual mentions as being a sign of failure on the datalines. Perhaps the demux cmos. How would a faulty dmux behave?

        1. It is receving reset signal. It is high. The frequency of the clock is fine measured it. I tried removing jumpers to upper board, still same voltage LVL on datalines 2.2 ish. If I remove Eprom and RAM i get 50 to 90mV on datalines except on D1 which is 3.53 V which goes to a 4053 dmux cmos Vss. Could scoping the datalines reveal anything? And what to look for?

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