FAT Freebass / MAM MB33 Problems + Midi channel settings

[Circuitbenders]

hmmm, every freebass i've ever seen is labelled 12V AC, the dark face MB33 i had was labelled 12V AC but the silver face MB33 is labelled 15V DC. They are all the same machine although the early models has a single sided light brown board where as the later ones have a better quality double sided green board. The early ones seem to die more often than the later ones.

I don't think its the voltage regulators as i've tested them on a dead one against a working machine and they output the same. I'll check out the capacitor but i don't think thats going to be it.

On a working machine when you start it up you get that single low twanging tone and then you hear a kind of octave of notes sweep down as it performs what i assume is the autotune. On a dead machine you get the single low note but you never hear the notes sweep down, as if the startup crashes as it tried to do the autotune and can't go any further.  That sounds like a firmware problem to me but you think it might just not be able to get a stable enough tuning?

[catweazle]

I'm not shure it is a "can't not tune right" problem (only a idea). I had two MB33 (silver) ones none
had this problems. So pictures of the circuitboards could help to find out differences between
older revisions or freebass <-> MB33 differences.
It could really be a firmware error, then we can try to find out how the autotune thing work
and hack it that way it is always in tune (emulate a "in tune" state).
Maybe the microcontroller sweeps down the frequency of the oscilator (VCO)
and compare it wtih a internal generated tone (i don't know how it really works).
Analysing the signals on the microcontroller pins while in autotune mode could get some help
(comparing working and dead machines). If someone has a oscilloscope or logic-analyzer.
Maybe a pin changes its voltage level if the thing is tuned, so setting the pin to that level will do the job.

[catweazle]

here is a easy to build logic-analyzer for the PC parallel port:
http://www.xs4all.nl/~jwasys/old/diy2.html

[spk]

thank you guys for such an immediate response and in-depth discussion !
altought i am not so good in digital electronics.
just want to characterize my failure more detailed:
when i am powering the fb,   i can hear octave slide, filters etc are working, when moving pots.
but when it ends, midi LED is going off and no response either.
i had some thoughts that it is opto-isolator faulty (it would be not so hard replacing)
but if it's that philips chip, that seems it's dead end...:/

what do you think about replacing entire midi <-> cv decoder?
which is possible to order as a component
http://highlyliquid.com/kits/mpa/. there is only two parameteres controlled by midi anyway.
thanks

[catweazle]

Yes, midi to CV/GATE will work.
Gate signal
Pin 4 on the microcontroller, cut trace at pin 4 and
apply +5V for Note On and  0V(GND) for NoteOff

CV signal:
Have a look at the DAC (digital analog converter) 20pin IC,
http://www.national.com/mpf/DA/DAC0832.html
this DAC chip converts the digital signal from the microcontroller into a analog current
not voltage, this is a bit tricky. But I can measure a control voltage ~0..5V at pin 2 at the
14 pin TLC274 IC, cut trace at pin 11 on the DAC0832.

I only have MB33 (silver version), so I hope it's the same ICs inside FB etc.
good luck

[Circuitbenders]

The first Freebass i had that died like this, i just found the filter enevelope trigger point, added a 5v trigger input and made it into a rackmount filter unit with the filter FM mods.

I find it weird that i get so many emails from people with dead Freebass' and MB33's and yet this forum is the only place on the net that i've ever seen any discussion about the problem. You'd think that if its that common there would be loads of people discussing it and a solution would be found.

Or maybe its down to a single cheap component thats only just starting to go wrong in every machine..........

[catweazle]

... maybe MAM would make money repairing it ...
kind of a predetermined breaking point
but without a schematic it is a bit difficult to find the failure.

[Circuitbenders]

Replaced the CNY17 & the cap by the power input.

No difference.

[catweazle]

To see if the microcontroller is working you can do the following,
there is a 20pin IC 74HC373 (adress latch for eprom),
check if the DAC0832 does something,
measure pin2 at the TLC274 opamp.
look at the pins on these ICs  if they are toggling around
with a "soundcard oscilloscope" for example: http://www.zeitnitz.de/Christian/Scope/Scope_en.html
     
   testlead
        <=------
                  |       100nF
     1M pot |   |<----| |------=> to soundcard audio in
                  |
                _|_ gnd

But if the MIDI LED goes on, the microcontroller is probably working because the MIDI LED is controlled
by microcontroller pin14 via a transistor (siiting beside the LEDs).

damn, I don't have a dead one, somebody send me a dead one
low priced for a poor student for educational purpose only

[spk]

yes, it is strange indeed that its the only place about fb - mb problems..
maybe the faultiness is not so common, or the instrument itself not so popular..
anyway thanx for being one and only!

and one more question.
could you give me the insert point for CV and gate feed?
if i would like to use it with external MIDI/CV gadget ( often used to control 303/808/909)
as my midi led is not glowing when sending data i am pretty shure it is decoder's fault.

example of external midi/cv : http://cgi.ebay.nl/ws/eBayISAPI.dll?ViewItem&rd=1&item=130203115482&ssPageName=STRK:MEWA:IT&ih=003#ebayphotohosting

thnx
spk

[Circuitbenders]

example of external midi/cv : http://cgi.ebay.nl/ws/eBayISAPI.dll?ViewItem&rd=1&item=130203115482&ssPageName=STRK:MEWA:IT&ih=003#ebayphotohosting

Thats a MIDI to DIN sync converter, you're not going to get very far with that as its for syncing old kit that has an onboard sequencer.

damn, I don't have a dead one, somebody send me a dead one
low priced for a poor student for educational purpose only

I've got a dead silver face MB33 i can donate to the cause. Its got holes drilled in it as i had mods installed before it died and theres some bodging i've had to do to replace parts as the solder pads peel off the second you desolder anything on the early versions, but its no use to me at the moment as it is and if we can work out what the problem is a whole load of machines can be saved from the scrap heap. I hope so anyway as i've just got another early version  Freebass that i'm scared to actually work on as i can just tell its going to die 

You live in germany don't you catweazle? PM me and we can try and sort something out

[catweazle]

@spk:
see post #19, or anybody got more information for cv/gate insert points?

Yes, you'll need a CV/Gate converter. The highly liquid kit mpa would work.
CV should be 0..5Volt  and Gate 0/5V  (Roland compatible, Korg is inverted)

cool idea to build a sequencer into the "dead" mb33.

[squidfanny]

I'm just wondering if it is possible to add a couple of CV inputs on my freebass?

It would be quite useful to me if I couple automate the filter and the the envelope from my computer...

I know it's a long shot, but would it be possible to automate the filter from the MIDI input?

cheers.............:-)

[Gordonjcp]

If someone donates me a knackered Freebass then I'll try and work out what fails.  It can't be *that* difficult.  I'm happy to cover postage (to G61 postcode area), or collect within about 50 miles of Glasgow.

[Circuitbenders]

I'm just wondering if it is possible to add a couple of CV inputs on my freebass?

It would be quite useful to me if I couple automate the filter and the the envelope from my computer...

I know it's a long shot, but would it be possible to automate the filter from the MIDI input?

A filter CV input isn't that hard, the only problem is that the filter is closed at 3.3V so a 0-5V input doesn't really work straight out. You can get around that with a voltage divider and chosing the right place to inject the CV. Next time i have a Freebass open i'll post a photo.

You'd need an external midi-cv convertor with an aux output though as in order to automate the filter from the midii input you'd probably need to re-write the firmware.

If someone donates me a knackered Freebass then I'll try and work out what fails.  It can't be *that* difficult.  I'm happy to cover postage (to G61 postcode area), or collect within about 50 miles of Glasgow.

I've just sent my dead MB33 off to catweazle so with any luck we'll have a solution to this one soon.