To repair a Simmons SDS 7 Vintage Analog & Digital Drum Synthesizer can be time consuming. I was lucky to have some spare parts from a second unit. Since this unit came in as “non working” condition I decided to open it up and have a look. Everything looked ok so far. I started rebuilding the power supply. There were some signs of heat at the diodes, so I used an externel case mounted bridge rectifier for the psu.
I put new heat sink compound to the regulators. I don’t want to have a unit twice on my bench so I changed the electrolytic capacitors. They are old, heatstressed and not really expensive to replace (the Simmons here is already disassembled). Now I got all the correct voltages but one control voltage (necassery for the boot procedure) was missing, but easy to figure out and fix.
Now it was time to fix the cpu and ram card. Poking and checking around I found a faulty IC.
Next to clean up all buttons, “rotary”, connections (bus bar also) and change the battery. Be aware not to lose the spring inside the buttons.
For the “rest” I did the same as always. Cleaning, straighten things up, changing some more electrolytics on the voicecards, read out the eprom bins for back up. Btw, the one lose cable is not “just lose”. It acts as an antenna to receive and withe a circuit try to reduce digital noise. Here are the pics I took during restoration process.