Korg Minipops 3 Drum Machine (Univox) Schematic or advice?
Mark Black
Ok, it's a long-shot. Does anyone have a schematic (or better yet - a
service manual) for the Korg Minipops 3 Drum Machine? It was also
sold under the Univox name.
Failing getting a schematic is there anyone who can/will share
knowledge of the electronics in this old all-discrete-component
critter?
One of the sounds (cymbal, I think)is nothing but a "click" audibly
and appears on the scope as a single impulse, leading me to suspect a
problem with the oscillator for that particular sound. Trouble is -
this thing is loaded with germanium transistors & diodes along with
yards of wire and laid out in a non-service-friendly manner so
anything pointing to a particular PCB or component set would be most
helpful.
Thanks -
feklar
be that the ROM or the RAM has become corrupted. I suspect it might be this
if that is the only sound that is bad. Assuming it is a MIDI device, can
you control that patch with another controller and see if it still does
that? Patch the MIDI out into a computer and see if it works OK with a
patch to the general MIDI set on the sound card. If it still does that, the
onboard ROM or RAM is probably corrupted.
You could also check it by hooking it up to a computer and doing a total
memory dump and then save the dump to a file.. I think most decent MIDI
programs like cakewalk will do this, even the demo versions. Then the hard
part would be to find someone else who has the same machine (forums on MIDI
web sites and MIDI USENET groups) and have them do a memory dump, save the
file, and send it to you for comparison. But if the ROM is bad, you may
have to do this anyway to get a good copy.
It could be that doing a reverse complete memory program (dump) back into
the ste using the good file may fix it, but until the EPROM or RAM on the
device get replaced it may not last long. Of course it could have been a
freak power surge that caused the corruption, and the fix would last 20
years too...
If you are unfamiliar with MIDI and MIDI software, you may need the help of
the device's owner to conduct this testing.
Mark Black <mark...@hotmail.com> wrote in message
news:442bbec0.03041...@posting.google.com...
Mark A. Black
Actually this little guy is so old it pre-dates MIDI and has no integrated
circuits at all - not even an op-amp or voltage regulator. Not only that
but all of the diodes and transistors are germanium rather than silicon. As
you might imagine without integrated circuits there are a lot of transistors
& diodes to accomplish the very rudimentary sounds this machine is capable
of and there is absolutely no programmability other than accessing one of
the preset sound sets by pushing that switch.
The lack of any recognizable IC is one of my biggest problems in diagnosing
the machine - I just don't know where to start. Additionally the physical
construction includes a maze of bundled wiring and a set of PC boards with
something like 50 germanium diodes close-soldered between them making it
very difficult to even get a test probe on opposing ends.
I like your suggestions on troubleshooting procedure for more current stuff
though and will save for future reference.
Thanks again -
Mark
> in article fI3pa.1255$Bk5.9...@newssvr28.news.prodigy.com, feklar at
> fek...@rock.com wrote on 4/21/03 9:39 PM:
--
Mark Black
ma...@loud.net
feklar
groups of wires at random to try to trace the path of the pulse it pukes up
when the trigger control is activated, then narrowing it down and recording
the wire colors and paths, at least you could probably find where the signal
was flowing that way. You will get a lot of false signals from the amp and
preamp sections but if you are dogged it will probbaly finally lead to the
right section. Of all the pulses the ammeter detects when checking
different circuits, the weakest signal of all of them is the one you are
looking for. Need a pretty sensitive ammeter...
Mark A. Black <ma...@loud.net> wrote in message
news:BACC62A0.3B166%ma...@loud.net...
Asimov
--- on the topic of "Re: Korg Minipops 3 Drum Machine (Univox) Schematic or
advice?"
Try looking for a transistor package using only 2 pins being used
instead of the usual 3. I'm hoping this will be the noise source.
Perhaps this transistor died or one of the diode gates which channel the
cymbal pulse to it to generate the sizzle sound. Often the pulse went
through the noise generator to the mix bus, so if it's getting through
it may mean no noise is present. Try tracing the pulse along the mix bus
to a likely looking sub-circuit.
Those old drum machines were all invariably alike except in the details.
They consisted of a ring counter and a switch or diode matrix to decode
the drum beat instrument sequences (chacha samba rock etc). Manual
programming, if available, was done with flip-flops as memory storage.
The instruments tended to be generated using tuned damped oscillators
(bass, tom, etc). Snare would have noise added to that for the sizzle.
Cymbals would be simply pulses with noise. Very simple operation but
indeed complex wiring due to being built before the age of integrated
ics's. The same thing applies to electronic organs of the time. They
were basically simple circuits but with much wiring. By comparison today
ic's can communicate to one another with only one wire and a common.
MAB> Subject: Re: Korg Minipops 3 Drum Machine (Univox) Schematic or
MAB> advice? From: "Mark A. Black" <ma...@loud.net>
MAB> Thanks for the reply!
MAB> Actually this little guy is so old it pre-dates MIDI and has no
MAB> integrated circuits at all - not even an op-amp or voltage regulator.
MAB> Not only that but all of the diodes and transistors are germanium
MAB> rather than silicon. As you might imagine without integrated circuits
MAB> there are a lot of transistors & diodes to accomplish the very
MAB> rudimentary sounds this machine is capable of and there is absolutely
MAB> no programmability other than accessing one of the preset sound sets by
MAB> pushing that switch.
MAB> The lack of any recognizable IC is one of my biggest problems in
MAB> diagnosing the machine - I just don't know where to start.
MAB> Additionally the physical construction includes a maze of bundled
MAB> wiring and a set of PC boards with something like 50 germanium diodes
MAB> close-soldered between them making it very difficult to even get a test
MAB> probe on opposing ends.
MAB> I like your suggestions on troubleshooting procedure for more current
MAB> stuff though and will save for future reference.
MAB> Thanks again -
MAB> Mark
[snip]
Mark A. Black
Thanks to Asimov for the hints about the basic topology of old-school noise
sources. I tried to find such information on the web but was unable to
narrow the search enough, I guess. Or maybe no one talks of such things
anymore...
First time I took electronics in college we spent the first semester on
vacuum tube technology. Second time I took a course they barely mentioned
transistors and we were off into digital. Somewhere in-between was probably
the knowledge which would help me on this project.
--
Mark Black
ma...@loud.net
> in article MSGID_1=3a167=2f133.0_...@fidonet.org, Asimov at
> warpcastgate@-removethis-bbs.juxtaposition.dynip.com wrote on 4/23/03 8:33 PM:
Loren Coe
> hmmm. maybe use a small clamp-on AC or DC ammeter, clamping it on different
> groups of wires at random to try to trace the path of the pulse it pukes up
> when the trigger control is activated, then narrowing it down and recording
> the wire colors and paths, at least you could probably find where the signal
> was flowing that way. You will get a lot of false signals from the amp and
even more helpful would be finding someone who can really dig into the discrete
components. they are still living, maybe radio hobbyists but some surely are
lurking in Usenet. when i was the ace mainframe "fixer" of the day, guys
at the customer's site often amazed me when i got into discrete stuff, often
not wanting to know anything but the most general details of the purpose of
the circuit.
i got bailed out a few times by these folks and never have stopped admiring
the abilities that i never aquired. sure, i could have slugged my way thru,
in days, not hours, while the customer was climbing walls waiting..., but
learned (thank god) a "better method". good luck, --Loren