Arp Pro-DGX Monophonic Analog Synthesizer came. Condition „not working". PSU was already re-caped. Synth turned on but no other signs of life.
For better trouble shooting I layed all the pcbs across my bench.
I then found out that the keyboard electronic wasn´t working. Nearly 50% Were faulty and had to be replaced. At that time the synth came back to life, but only for "auto trigger". So I had to replace two more logic ICs, and I also had to clean the keyboard contacts and I also had to adjust these.
I decided to replace the tantalum caps with electrolytic in some places. One transistor looked damage, but wasn´t. Cleaned and lubricated the sliders, pots and switches. Made sure the modulation strip was also working well.
I made some minor calibration/adjustments. Synth is fully working.
There are lethal voltage exposed in electronic devices. Unless you know what you are doing, don’t try this. If you following along, you doing so at your own risk.
I’m documenting repairs for my reference and yours.
I do synth restorations and repair with a specialty in vintage synthesizers, drum computer and other vintage gear, based in Düsseldorf, GER. Get in touch about your synth situation!