Hi all, I was wondering if anyone had any ideas on this problem w my mini-d , it used to work now it doesnt, specifically the input.
I put a mic on it and the level indicater flashes but there is no sound getting out.
In the service manual it just says to replace the filter board.
I dont wi$h to do that.
Any ideas on where I should begin to trouble shoot it? Trouble shooting is tough
Has anyone have this happen?
If so what was the outcome?
I appreciate any advice as Im a novice electronics person to these with out much coin for a qualified tech, ( I spent it all on the board:-),but Im trying to learn.
TIA
wilby
Microphones usually require a preamp going into the synth. Otherwise the signal is too weak going into the filter. Are you using a preamp, or just a microphone? If it worked before, check the filter settings. If the filter is indeed shot, you may need a new filter. That will be expensive.
thanks V, Ill try a preamp…weird I didnt realize that, before was a long while ago I may have used a guitar pedal or something.
thaks Ill try it…everything else seems to work fine as far as filter and that.
After scouting around the forum, I think the buffer board has been removed.
I wondered why I could never get the octave range calibrated.
Ill check that Pa idea out-thanks again.
You’re welcome. Maybe Kevin Lightner could hook you up with a new buffer board?
You don’t need a preamp for the external input on a Minimoog D. There is already a preamp on the filter circuit board (ext in amp and overload lamp driver).
Of course I’m sure that you flipped the toggle switch to the “on” position, right ? And the filter cutoff is opened all the way, right ? And the loudness contour sustain level is at maximum, and you ARE pressing a key on the keyboard, right ?(I know all these things seem obvious, but just wanted to make sure… 
)
If everything is set right, and there’s still no sound from the external input passing thru the filter, then it could be capacitor C20 on the filter board (doubtful). Or possibly a bad contact in the toggle switch in the mixer section, or something else…
I’m surprised that the buffer pcb has been removed ! Are you sure it was ever there ? What serial number is your Mini ?
I looked in the manual and it says any thing should work as it has a preamp already. example..guitar microphone, vocal microphone or what ever just plug it in and go. I assume this means any high impedance source, also the machine will not output to overdrive the input on itself by jacking out and in.
I think it must be something on the filter board like a cap or transistor or something. I guess Ill try and trace the audio signal and see where it stops. I just thought this condition may arose frequently and may have been more common than other things. I dont like to trouble shoot as I fear I may damage it further.
While Im in there Im going to check for the buffer board.
Since the overload lamp is showing a signal (when overloaded), there’s only 3 possible things here: 1- C20 is bad or has a cracked solder joint, 2- the toggle switch for the ext input isn’t making proper contact (dirty), 3- the connector for the filter board has a bad or intermittent contact on pin 17.
there’s only 3 possible things here: 1- C20 is bad or has a cracked solder joint, 2- the toggle switch for the ext input isn’t making proper contact (dirty), 3- the connector for the filter board has a bad or intermittent contact on pin 17.[/quote]
Ill try it in the morning this will be most helpful thank you!
Ill try it in the morning this will be most helpful thank you![/quote]
The preamp is obviously working, so the output signal path on the filter printed circuit board is as follows: one trace goes to the overload indicator lamp circuit (obviously working too), and another goes to one side of C20 (polyester capacitor with a value of 1 mfd and 63 volts maximum rating). Then the other side of that capacitor is going to pin 17 on the edge of the filter pcb. From that same pin17 on the female receptacle for board #4 (filter) on the bottom inside of the back panel of the Mini, there’s an orange wire going to the toggle switch for the external input where, when switched “on”, it is then mixed via a resistor (R46 (33K ohms) soldered on the switch contacts itself) with the sound coming from all the other sources (OSC 1-3 and w/p noise).
My bet is a dirty toggle (rocker) switch…
Hope this helps. Keep us posted…
Your input is appreciated, After looking over the manual some more, I think once this is fixed Im going to get rid of this crazy thing,
I traced the signal wire to the 1M pot, checks okay , from the pot to the board at pin 11, where it meets R78, 1M 1/2w, it appears to be open, so Ill test that first. I hope thats all it is.
The overload lamp is driven by the preamp circuit of the external input. The pot and everything else you’re talking about are before that circuit. And since the lamp is working when a signal is applied, R78 1K ohms (not 1M ohms) cannot possibly be open…
thanks, Im a lousey tech…darned meter, anyways I understand that now so I see if theres signal output at pin 17…and there is…!
so Ill checked this out next
"there’s an orange wire going to the toggle switch for the external input where, when switched “on”, it is then mixed via a resistor (R46 (33K ohms) soldered on the switch contacts itself) with the sound coming from all the other sources (OSC 1-3 and w/p noise).
I touched the orange wire near the switch and it broke off…so Ill reattach it and hopefully thats the ticket.
At this point, there’s not much else that can go wrong. Either that broken orange wire is the culprit, or that 33K resistor across the switch logs is (open or bad solder joint), or the switch itself is defective or dirty.
Once you get it working again, the trick of taking the output and sending it back to the external input is a great way to get a free saturated/distorted sound and many new timbres out of your Mini, without the need for an external overdrive effect pedal.
P.S. Don’t worry about you tech abilities, we’ve all misread a MM at one point or another…
added: yes it was, using the out to in patch to over drive it a little makes it sound even more enthralling, Imakes me want to keep it for a little while longer…
okay what the next problem you amy or may not ask/
, the 3rd occillator will not tune low enough to keep the pot in centre, I can only get it down to A# so what ive been doing is tuning to that and then turning the pot down a semi tone, this wont hurt the machine I dont think, I guess Ill try and tackle that if it gets worse.
Oh and yes there is a buffer board
I sure appreciate the help…I seldom used the input but thought Id give it a try to see what it does.
thanks much alien666…what it does is great!
You’re welcome Wilby! We can help each other out between fellow Canadians, eh ?
As for the OSC 3 tuning, how many tuning holes are there in the back of your Mini ? In other words, what version of the OSC board do you have installed in there ?
its the one with two pots per oci and 1 octave range switch. Ive got it tuned up pretty good now except for the 3rd being 1 semitone too high
First, I would check for proper power supply voltages at the OSC board.
+10 volts DC on positive side of C12 on OSC board, and -10 volts DC on the negative side of C11 on that same board. (they’re located at the bottom of the board, near the end of the right side of the left edge connector. They’re identified as 5r6uF (5,6 mfd).
You need a rather precise voltmeter in order to measure accuracy to at least 3 digits.
If the PSU voltages are not within specs, it can create the inability to tune some, or all, oscillators precisely. And a recalibration of the PSU is needed.
Also, make sure there is no CV offset, like pitch bend or other sources. Often, the Cinch Jones connector for the Mod Wheel assembly will make poor contact and induce a pitch bend offset, even though the pitch bend wheel is in its center notch !
**added:**The Mod Wheel assembly is easily taken out by removing the two top front screws. You can then access that connector and clean its contacts.
thanks for the real good advice
Ill look into it more when I get a better meter, Ive only got 2 decimal places and the + says 10.00 spot on the - .999 but then gos to 10.00 after a short moment, I checked the wheels and they seem okay I think theres probably some more iffy solder connections in there somewhere, but for now its a go…
w
Those voltages look okay.
It could be a slowly failing IC for OSC 3 (either 741 op amp or CA3046) on the OSC board, too…
But if moving the knob down a bit corrects the problem and the synth is still playable, I guess it’s tolerable.
Now, go play with it ! 
Oh I am and will…thanks once again for the:
“It could be a slowly failing IC for OSC 3 (either 741 op amp or CA3046) on the OSC board, too…”
Ive order a few 741’s just to have on hand, so when they get here Ill pop one in for #3 and hear what happens..
Cheers!