E-Piano was a bit more complicated repair compared to the Vermona string synth. PSU had dried up filter electrolytics and one of the earth wires fell off.
Following a pot cleanup all was working well except tremolo.
See the unusual but very reliable slider pot
I noticed some of the electrolytic caps were getting warm due to ESR. After the replacement piano was quieter with less strain on the PSU however the tremolo generator still wasn’t oscillating.
Both of the transistors were OK, all the surrounding resistors as well, electrolytes were replaced so the only culprit left were the foil capacitors and indeed once replaced by small electrolytic caps (the only 470nF I had in my spares drawer) tremolo sprung to life. I managed to later replace electrolytics with foil polypropylene condensers and tremolo was much nicer and more stable sounding afterwards.
This Synth came to me following a damage suffered during transport. Joystick was loose /broken and it wouldn’t turn on or even when it turned on it would just display nonsense and wouldn’t react to any of the presets.
The core of the issue was a semi shorted battery and the spring clip from the joystick wedged under one of the PCB’s causing short of some sort.
With battery and the offending spring clip removed all sprung to life and worked just fine when presets were loaded.
I managed to glue the joystick together, but I sourced replacement module in the meantime.
Vintage synth from Eastern Germany, you can smell the communist era inside of it. Very typical earthy smell of brown PCB boards. All it needed to bring back to life was thorough cleanup of all the keyboard contacts and slider pots. After an hour and a half with compressed air and IPA it’s back in business.
Slider pots are actually very good design, fully open accessible and designed to be cleaned, sadly I forgot to take picture.
The way this one sound is just pure filth, it’s harsh…….
Another day, another field repair, this time on multi-track cassette recorder. It took me a while to locate, PCB had a hairline crack all around the ground plain pad where the input power connector was located.
Half an hour job from start to finish.
Very quick in flight repair of non functional Vermona drummer in the mid of the recording session.
Fuse holder in the PSU section was so corroded it stopped working.
srubbed it clean temporarily to let the session continue and later on I’ll replace the PSU caps and solder new fuse holder in.
This was an interesting one, the main issue customer had was with added modification not working. This modification was done sometimes in the 70’s and it took me a while to figure out how the mod was done.
Basically the bottom octave of the pedal had a contacts duplicated to the lowest octave of the bottom manual and one of the BUS wires which used to be associated with one of the draw bars was instead taken externally via additional BASS coil and switch to the extra jack output.
When I managed to resolve this issue with non operational bass there was still fair amount of hum. This was partly because the modification created ground loop. I resolved this by earthing the additional output in the same place as the main out was. This removed some of the hum but there was still fair amount of it left. With ground loops eliminated this had to be caused by the aged electrolytic condensers in the PSU. Following a brief discussion and estimated Bill Of Materials and work involved decision was made to do full recap.
Modules had a mixture of original Mallory american condensers from 1950’s and old TESLA electrolytics from sometime in the 70s.
Since the dual/triple modular caps were not available during the communist era somebody who did the work in the 70’s installed replacement caps inside the chassis and sadly placed them right next to the power resistors. Such a high temperatures are a recipe for a quick death of electrolytic and that’s exactly what happened. One of them popped and leaked out and the other had also the safety valve popped.
I replaced all the electrolytics throughout and utilized modular caps made by JJ in Slovakia. These are great for typical PSUs of Valve amp designs.
Result is one happy customer and L100 sorted for another 40 years