A WLM Welmu organ in for repairs, what a neat opportunity to check what’s inside one of the babies of “Hammond of Karkkila”! Let’s dive right in :)
Opening the top cover, I found the simplicity of the mechanical assembly instantly appealing. Minimal but still functional and very service friendly. Remove about ten screws and you’ll have the electronics exposed. The top cover comes off in one piece and there’s even a simple solution for putting the keyboard into service position. No need to start figuring out temporary service supports!
Gotta just love this small detail, it’s just _so_ handy for servicing. If only all keyboards/synths would have similar attention to detail :).. The active electronics mostly consist of standard 74-series logic chips. Not too difficult to predict that this organ will remain serviceable for a looong time!
The PCB on the right edge has some dried up spillage on it, otherwise nothing that compressed air couldn’t handle.
On to the actual repair stuff then.. In advance, the owner reported this Welmu having defunct keys so whilst waiting to get my hands on it, I was hoping all the time that it’d be somewhere else than on the oscillator circuit. In old organs, a fault like this usually translates to either the key contacts or the oscillator circuit. The former requiring less investigation to repair, of course. Which one is in question, can be easily diagnosed by playing through the keys; if you have the same defunct keys repeating over each octave it’s most likely the oscillator circuit (osc source or frequency divider sections). If it’s random keys, the contacts are the more likely culprit.
But not to fear; snapped contact rods under the keyboard, so it’s only mechanical repairs required. The common rail (with which individual rods make contact) looked awfully hand-bent at places. Guess someone has applied quick “repairs” before :).. Not that I had exact idea what to replace the snapped rods with. I just had to try making a rod from a piece of stripped and tinned cable despite I knew (even before soldering one in) that it’d fail horribly. Sure enough, a couple of presses on the key with a rod like this and it was already bent out of shape.
After spending a good while looking for anything-else-likely-suitable but still unable to come up with any “new” replacements, I decided to try a “half-way” solution with one of the snapped rods. Here, about half of the length of a rod was replaced with the stripped/tinned cable. The “original” half of the rod is used to make the contact, whereas the tinned half guides the rod somewhat to right direction. This solution proved functional, after a short break-in period the modded rods settled into their “final” shape (the tinned half slightly giving in). After spending a good while playing the modified/repaired keys, I was unable to detect any further changes in the overall shape so I decided to call it a repair :)
Before returning the Welmu, I spent a good few moments recording multisamples out of it. Even bothered miking up the keyboard to get the key clicks stored! Maybe they’ll even turn into usable sampler patches some day ;)..
If you know your finnish and feel like reading a bit of WLM history, check out this WLM page at Wikipedia.