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Introduction
I purchased two 1984 Sequential Drumtraks drum machines designed by Sequential Circuits. Both in need of repairs.
Drumpad & Front Panel Switch Cleaning
Before any rework these pads would stick, squeak, and produce glitchy sounds when hit. The instrument was miserable to play. I found this resource which helped me clean the contacts. I have repaired two Drumtraks and have had to clean the pads thoroughly first.
Switch Operation
After removing the cap gently with a flathead screwdriver, this is what you will see.
Contaminated Contact
This pad did not produce any sound. Others that were similar would produce inconsistent sounds when hit. I sprayed Deoxit D5 and scratched the contacts with a flathead screwdriver.
Schematics
Switch Matrix Schematic
U102 & U103 (CD4042B ) are quad-package clocked D-Latches. Latched bits turn on the n-channel bjts - turning on the corresponding LED of the seven segment display or indicator LED.
The CD4042B takes in 4 data lines and outputs 4 buffered outputs and their compliments.
U106 (MC14503B) is a non-inverting 3 state buffer (high output state, a low output state, and a high-impedance state).
U105 & U107 (TC4099BP) are 8-bit latches that drive the matrices.
CPU Schematic
U207, 208, 209 & 210 (HM6116 ) are Read-only Memory for the Drumtraks.
Misc./PSU Schematic
U275 is the mixing amplifier leading to the main audio port
Voices 1-3 Schematic
Bass - This is the channel I was having trouble with. Hitting the Bass pad would not generate any audio from both the main output and the CH1 isolated output.
Snare/Rim - Same EPROM different pads.
Voices 4-6 Schematic
Cymbal - This sound is saved across 4 EPROMs
Ride - Also saved across 4 EPROMs
Snare/Rim - Same EPROM different pads.
Hi-Hat - Open and closed sounds share a EPROM
Clap/Tamb & Cowbell/Conga - These are grouped to a ROM
Resources
https://www.polynominal.com/site/studio/gear/drum/sci_drumtraks/sequential-drumtraks-service-manual.pdf
http://www.electrongate.com/dmxfiles/drumtraks/index.html
Google Sites
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