Hello all, I am going to be recaping my minimoog model D that has a new oscillator board. Just wanted to know if there were any other critical components that need replacement. I will be doing all electrolytic caps, power supply diode (installing diodes with higher current rating), and possibly replacing the trimmers on the oscillator board, they are the plastic type, and seem pretty worn. Would like to get everything in order so hopefully it wont need any service for a while, so didn’t know if anyone had any other suggestions on anything that needs replacement. Of course I would like to put one of those opto-key buss bar replacements in, but gotta save up some money first. But cant complain to much since this mini works great after solving its tuning problems and it was a yardsale find for unbelievably cheap.
I understand about replacing worn/scratchy trim pots (I suggest multi-turns style for greater precision, just make sure to align them so they’re accessible through the holes in the back cover). But why would you want to replace diodes in the power supply with more powerful ones ? The Mini isn’t a power hungry beast ? And why go to the trouble of replacing all the electrolytics caps if they’re still working perfectly fine (and still indicate the correct values on a capacimeter, like the ones in my 36 years old Mini which is probably older than yours)? Sure they can dry up with time, but then their value would change dramatically and cause audible problems, like hum, and change glide time (shorter) and enveloppes times (shorter too), and other quirks like that.
If your Mini doesn’t exhibit any of those symptoms, and all the electrolytics caps show the right value when measured, I wouldn’t worry about recapping. Unless you have time to spare…?
Yes, indeed. I wasn’t questionning the fact that they could be replaced as a preventive measure. It’s just that I didn’t see any point in doing so with more powerful ones, although it couldn’t hurt. And then, you’d be assured of a lifetime of worry free operation, at least from those components anyway.
Sorry for the late reply to this topic been out of town for a month. The reasoning behind replacing the diodes was my mini has the newer style oscillator board which I was told draws more current then the first one, and can stress the power supply, so replacing the power supply diodes may be a good idea. I think I may hold off on the electrolytic caps for now. The keyboard still has one key that jumps between notes, so need to clean the buss bar. Had all the keys working great, but one just started acting up again, and need to level the keys. The joy of owning vintage gear, always something to fix. Thanks for the reply’s.
Maybe you could replace the buss bar and contact springs with Kevin Lightner’s OptoKey board ? Then you wouldn’t have to fix the keyboard ever again ! http://www.synthfool.com/optokeycontacts.jpg
I have to agree with MC and NateH.
If you have the later VCO board (and it sounds like you do), it has quite an inrush current.
Three heaters in those uA726s and several opamps are the reason why.
But one nice thing is that the mounting holes on that board can accept a variety of different trimmer pin-bases.
Please note that if you replace those rectifiers with higher current types (say 1N5400 series), you may have to enlarge the PCB holes to fit their larger diameter leads.
Generally I think simply replacing them with new originals will be fine, but others probably won’t hurt.
Also, it’s not a bad idea to replace them if you plan on adding external accessories through the top power receptacles or one of my OptoKey systems. (thanks for the mention.)
The Optokey draws roughly 65-80ma, tho it also relieves a bit of the current normally necessary for the original keyboard.
The accessory ports are rated at 50ma ea, but I have no idea quite how much reserve current a Mini supply provides and of course, even while you might have stabilized VCOs, increased internal heat can cause VCA offsets and filter drift.
Btw, I’m not closed to the idea of selling an OptoKey as a kit at a substantially lower price, but one would have to be an experienced tech or engineer.
I haven’t offered them as kits yet because technical writing is not my forte and I fear having to spend hours providing support or repairing them.
And even if I did offer them, I’m really wary about asking others to assemble the small surface mount board with the DAC and other tiny components.
That tiny board has the most pricey parts of all on it.
Thanks for the reply kevin. I would love to try out the optokey as a kit. I have experience with surface mount from assembling FPGA boards at school. From the pictures it looks like the D/A are the only surface mount components. PM sent. Btw, What were the Regulated DC outputs used for originally?
