Repair Roland SRE-555 Chorus Echo Reverb Reparatur9. September 2019
Repair Arp Odyssey Vintage Analog Synthesizer Reparatur28. September 2019
This LinnDrum came in for repair not booting. Instead it showed the suspect "00" in the 7-segment displays, all other led lit up but no sound. Checking the inside I found the psu was repaired at sometime due some battery leakage. Voltages were a bit on the high side. I checked psu and fixed that. One component had wrong value. Then I checked the power safe circuit (reset), which had an issue. The voltage comperator ic was bad. I also noticed that power wasn't stable due to some weak solder joints around the molex connectors. So I re-flowed all suspect solder joints.
But this did NOT fix the (not) booting problem. So I took out the cpu board and powered it safely with my bench power. Still no luck. That was expected. Time to check some of the logic. Well, long story short. I found a faulty CPU, some bad ram and a handfull of bad logic ic including the 74c02 and two 74c32 which are crucial for reset and ram to work properly. After replacing all these components the LinnDrum came back to life. All isntruments were playing. I could "record" some pattern and play it back. And they were still present after switching off the LinnDrum for a while. That's a good sign.
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!