FAT Freebass / MAM MB33 Problems + Midi channel settings

[Gordonjcp]

If you can't get it working at all *and it is complete* then I'm quite keen to buy it as a project, replacing the seemingly-fragile CPU with something more modern.

[01012k7]

If you can't get it working at all *and it is complete* then I'm quite keen to buy it as a project, replacing the seemingly-fragile CPU with something more modern.

I decided to build a x0xb0x  now  i have a lot of parts for x0xb0x also have 2SC2291 2SC1583 out of the freebass and i guess the knobs i can sell too people who are bending the freebass.
also  the case will be for another project

i have just got main board and the socket board with usb solder on and also main cpu with os
i do have all the  carbon resistors and some of the other resistors and 2SA733P and 2SC536F i also have some IC also hardware and some caps ..think its the way to go for me now i have also order another 2SC1583...

[Circuitbenders]

Why not just buy some new parts for an x0xb0x and get the freebass working in some manner, or sell it to gordon? 

It seems a shame to pointlessly demolish a Freebass when it'd only cost a few £'s to just buy the parts you need for the x0xb0x new, rather than harvesting them from the freebass. You can get rack cases from loads of places.

[01012k7]

Why not just buy some new parts for an x0xb0x and get the freebass working in some manner, or sell it to gordon? 

It seems a shame to pointlessly demolish a Freebass when it'd only cost a few £'s to just buy the parts you need for the x0xb0x new, rather than harvesting them from the freebass. You can get rack cases from loads of places.

ok i understand what you are saying i would want £30 + post as parts that i could use would be  like £25 pounds to replace also this one is the one with the bad circuilt boards you look at it and the tracks fall off some damage around midi port when i got the unit the midi socket was like inside the unit had come off it work for about 5 hours then gave up after putting it on also have a 500ma ac/ac power adaptor with it .. ...

[Gordonjcp]

Work out the postage, and mail me off-forum.  30 quid sounds about right.

[darkest_star]

A reprogramming of the EPROM had no positive effect for my MB33. 
Now I have ordered a CPU and the both multiplexers 4051,4053 for a about 3 Euros in sum. I would starting to replace the multiplexers and finally the CPU. Of course I will solder socket. :-)

[darkest_star]

Like crustypaul I had also the suspicion that the CPU is the cause for my mb33-problem. So, I have started to replace the CPU first. It took only 10 minutes work (cut out the old CPU, remove the old pins, solder in a 40pin socket). But the behaviour is still the same. The CPU was not the problem. Therefore now I will replace the multiplexers 4051 and 4053.

But one question to all:
What happens, if you press the Autotune button while switching on the device (MB33 MK1)? On my system I hear no demo song; I hear nothing. But the midi-LED stays ON forever. If I switch on my MB33 without pressing the Autotune button the midi-LED goes OFF after about 5-10 seconds.
Thanks very much!

[darkest_star]

After replacing the two multiplexers 4051 4053 the MB33 behaves as before.  If I remove them from their sockets the midi-LED stays on. So, the Autotune procedure during power on seems to work.
I have resoldered every point in the digital part, without effect.
What I have found out accidentally is, that if I plug the 6,3mm cable into LineOut only half (not pushing up against) I can hear the Autotune process (without any manipulations inside the MB33). I'm not sure how a Autotune must sound. On my device I hear two parts: First I hear a constant sound (which can be manipulated e.g. with the waveform potentiometer) for few seconds. Then I hear a falling tone pitch sound. After this the midi-LED goes off. Seems to be ok, isn't it?

[Circuitbenders]

I explained what happens when you press the autotune a couple of pages back.

When you press the autotune button you won't actually hear it doing the tuning like you do on startup as it doesn't trigger the envelope. It takes about 40 seconds or so from when you press the button until the midi LED goes out again. While its doing the tuning the unit won't respond to midi.

Are you actually getting the CV and gate signals on the pins i mentioned in a previous post?

What you've described is the correct startup procedure. Why would you press the autotune as it starts up?

[darkest_star]

Are you actually getting the CV and gate signals on the pins i mentioned in a previous post?

I will check this again.

Why would you press the autotune as it starts up?

In the German manual (my native language) I can find a statement, that a demo song will be played if one presses the Auto-tune button while powering on the device. But on my MB33 I can hear nothing. 

If I have time again, I will measure the CV/gate signals you proposed and resolder all points on the board.

Btw, do you know about the three unused jumpers (one beside the Autotune jumper, and two in the analogue part) on the board?

[darkest_star]

So, now my MB33 is working again as it should.
First of all, I'm very sorry! The last few days I have done two big mistakes:
1. Since my MB33 was completely open I was shure that the audio out is the one direct beside the midi-in. My audio cable was plugged in VCF-in. 
2. I had reprogrammed the EPROM, but it was faulty. Now I have burned another EPROM (a different IC) and my MB33 blinks when receiving midi-in.

So, the real cause seems to be the original EPROM-IC. Because the old one is still not generating sounds... Even, if erased and reprogrrammed whith crustypaul's image.

And with the new EPROM-IC (burned with crustypaul's EPROM-image) I can hear the demo song (or better demo sequence) after the Autotune operation. 

Strange, but true. 

Now I want to thank you very much for help and support!!!!!

[Circuitbenders]

I've never noticed it does that demo sequence before. How odd, there doesn't seem much point to it.
If you start the thing up with the jumpers shorted near where the autotune button connects, it seems to go into a kind of test mode where it just plays a note endlessly. The jumpers to the rear on the right seem to give every note an accent when you remove the jumper block. I'm not sure what the jumpers in the filter section do.

What do you have to do to a synth to corrupt the EPROM? I would have thought that was pretty much impossible, especially with the rest of the synth surviving intact, and yet it does seem to happen on these things more often than you'd imagine.

It could be that you had a combination of problems on this synth. Maybe changing the CPU and the EPROM fixed it, but either on its own wouldn't have done.

[darkest_star]

I've never noticed it does that demo sequence before. How odd, there doesn't seem much point to it.

I think, it's good for testing the sound equipment (mixer, amps) or isolate failure causes because you don't need a midi device to send notes to the synth to get a sound output.

What do you have to do to a synth to corrupt the EPROM?

I've bought it at ebay as defective. So, I don't know about the history of the MB33. I find it interesting that the verify operation after erasing and reburning the old EPROM hasn't found any problem. It could also be a contact problem of the EPROM socket. To use another EPROM chip was completely accidentally, because I have found a similar EPROM (a 27256 instead of 27C256) in my box of spare parts and I've thought: The proof of the pudding is in the eating. 

It could be that you had a combination of problems on this synth. Maybe changing the CPU and the EPROM fixed it, but either on its own wouldn't have done.

Maybe. Now I have a working synth, where I could try out some circuit bendings. If I destroy something in the digital part I can replace the ICs very quickly. 
I'm very happy to found a forum of synth hobbyists and thank you very much for your support. Also thanks for the hints regarding the jumpers. I will try this out in the next few days. PErhaps I could find out the reason of the jumper in the filter section?

[chebru]

Hi,

I just received a Freebass FB383 yesterday. I was gearing myself up for some serious troubleshooting as the seller said that it was broken and didn't respond to midi messages. When it arrived I was pleasantly surprised to find out that the unit worked perfectly, as long as the midi channel was set up correctly - I'm guessing the seller didn't have access to the midi channel set up key posted on the first page of this thread. Thanks a million for posting it!

So, now I have a fully functioning Freebass, which is awesome, but I'm not so sure about those ugly black and orange plastic knobs, especially when I see the beautiful retro style knobs on the units on this site.

Where would I get hold of knobs like that, and what size would fit this synth?

Thanks in advance, and thanks once again for all the great info in this thread!

[bujbot]

I repair a lot of stuff and often don't share what I did, thinking it's too obscure a problem so no one cares ... so I'm trying to fix that going forward in case there's someone out there stuck and googling like crazy.

I fixed my MAM MB33 MkII that was showing the classic power on issue (Light never turns off).  Here's what I did to fix it up (in 2 parts).

1) There was no clock signal going to U86, this is because of U91:B, so I tuned TP18 until the U91 could operate as usual and send that pulse.

2) make sure to get the proper power supply if you are missing it.  Doesn't need to be that one that came with the unit, just the correct voltage with enough current overhead.  It will work with one slightly off, but it sounds a bit buggy.

Happy bending

*the MB33 mkii schematic is in this thread somewhere I believe.  U91 is LM393 and TP18 is the furthest trimpot on the bottom left when viewing the PCB from the top (across from the wave shape selector switch).