Reviving old records and doing a retro tours became huge trend lately. I was asked by local band Tatabojs to resurrect their dual manual organ Vermona for their upcoming retro tour Futuretro
Upon inspection I discovered several functions weren’t working. No Vibrato or Tremolo, no Reverb, whole percussive section was dead. bongos were rather crunchy, synth section (bass pedal) controls weren’t working and there were about 3 or 4 keys not playing the 16′ register. Not to mention all the switches and pots were properly noisy.
Actual oscillators themselves were in good shape and only troublesome devices were the electrolytic decoupling caps. Following the replacement with new ones signal was much stronger and according to the specs in the manual.
Design is rather simple, it consist of precision foil caps and adjustable coil master oscillator for each note followed by transistor dividers. These circuits are incredibly stable and don’t drift noticeably at all.
I started slowly one by one following the smaller daughter boards and tackle issues one by one.
Tremolo and Vibrato functions are based on low frequency oscillator and there were no oscillations at all. Problem was with 3 foil capacitors in the oscillator circuit. They deteriorated over time and following the replacement with modern WIMA foil caps both Tremolo and Vibrato function sprung to life.
The further I was troubleshooting individual functions it became apparent capacitors (predominantly the electrolytic ones) are the main cause of all the issues. I have therefore decided to do full recap of the instrument. Pretty much all of the old caps with few exceptions I removed measured really bad ESR or some were actually partly conductive as if they had a resistor in parallel.
Following the full recap most of the organ functionality was restored, WAH WAH, Vibrato, Tremolo, Bongos, Percussive section to some extend as well and overall signal to noise ratio changed dramatically. Especially top manual was giving really strong signal but the lower manual remained weak and the manual ratio pot had to be pushed all the way towards the lower manual to have any decent balance between the two. Issues with missing 16′ notes remained and percussive section while now working was rather short and the slider made no difference to its length.
One of the missing 16′ notes was due to bad germanium transistor in the divider circuit while the others were due to physical wires not being soldered on properly. There were cold solder joints on two and one wire fallen off completely.
Percussive section just needed trim pot cleanup and re-calibration and all was good.
Broken reverb was purely due to broken off wires from the spring reverb, all was good when i re-soldered them in place.
Now with entire organ working and all functions doing what they should I remained puzzled by the sheer volume difference between top and lower manual. It took me several hours of head scratching just to realize after all that somebody who repaired the instrument before me wasn’t thinking quite right.
Slider pots used by Vermona are of amazing construction. Virtually indestructible and easy to access to clean them. They were clearly designed to be maintained and the tracks themselves are made out of some sort of conductive plastic which doesn’t wear at all. After just a brief wipe with IPA and re-lubrication with fader lube, they are like new. The only weak spot is the track itself is secured to the rest of the mechanism by plastic lugs which ends are melted to secure it in place. These get fragile over time and break which results in the track coming loose. Somebody before me didn’t think quite right and replaced this plastic lug with screw and didn’t think about the need to insulate the nut and bolt. It cause this dual pot to be partly short connected between each other and therefore it was impossible to get the manual balance right. I have used some fiber washers and all was good since. Use of plastic M3 nuts and bolts would be even better, but I didn’t have any at hand.
Once this last issue was resolved only left to do was new hinges, locks and handles on the case and this monstrous organ was ready to go back to the customer.