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Dr. Böhm (Hohner) Digital Drum Machine restoration / repair. This one was is a beast. Great machine, but also a great damage that was done by the leaky battery. I recommand. If you have such Dr. Böhm Digital Drum Machine (or Hohner) please check and/or replace the (rechargable) battery NOW! Time is running...
On the 1st picture you may think, it looks ok.
But I can easily spot the green substance on the pcb around the battery. If you didn't spot it now I will give you another picture. You should see it in the 2nd picture.
If you still don´t see the substance take a look after I removed the battery.
The problem with this substance is, that it damages (eats away) your copper traces. As you can see here.
First you have to determine what substance that is. If its base or acid. And then you take the opposite to neutralize that substance. In this case I used citric acid with a q-tip (and) toothbrush and then ipa. If you do this carefully you have a good chance to nearly stop the process. I cleaned it as good as I could and rebuild the traces. Maybe next time I use a replica pcb, since desolering and rebuild a lot of traces was a lot of work.
I replaced all parts, incl. all ic sockets, resitors, capacitors etc... everything except cpu,ram and rom.
The next common failure point on these machines are the switches.
I tried to clean and glue them back together which, ... works (quite well)... but I was lucky and found some nos parts.
The Böhm is now rock solid. Dr. Jay got it resurrected.
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!
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