Help with diagnosis of Crumar Bit One

neurocrash · Post by **neurocrash** » Thu May 21, 2009 2:49 am

Greetings,

One of my Crumar Bit One synthesizers has failed. This is the model with CEM 3328 filters

I had re-built it last year, to the best of my ability anyway, due to the lack of service available in my area. At that time, it was working perfectly. I have not used it for several months, and now it is not working.

It actually makes a few high pitched or sweep noises, which seem to be VCF oscillations, as the become more pronounced if I turn up the resonance. I don't think I'm hearing the DCO's at all.

I am wondering if this sounds like something that anyone can help me to diagnose.

The reason is that there does not seem to be anyone within several thousand miles of my location that will repair vintage synthesizers, so it would cost $200-300 just to ship it to and from any shop willing to look a it. I'm guessing that when the repair costs are added in, the total could easily reach $1000 which is more than this is worth - but I hate to junk such an instrument.

Previously, the problems with this instrument were generally voltage regulators, filters, and amplifier chips that were running extremely hot and/or had failed. As a result, I removed most of the failure prone chips and socketed the boards for easy replacement/diagnosis. When there was only one or two voices out, or distorted, I was able to make an attempt to trouble shoot - but with the current problem, I have no idea where to start.

I do have schematics, documentation, sound dumps, many spare chips for the ones that I had to replace, and access to additional parts. I do have a basic oscilloscope, multi-meter, soldering irons, supplies, etc... and have done a lot of basic electronics work in situations where I know what to do, so I can pull and replace chips and components.

The one thing I do not have is enough knowledge to know where to put the scope or meter to find where the failure is occurring.

I would even be willing to pay someone if they are able to read schematics and help me to diagnose the problem with this keyboard.

Thanks for your consideration

Post by **madtheory** » Thu May 21, 2009 12:51 pm

I feel your pain! I have one of these, great sound, but totally unreliable. Where are you?

There's a company in New York that understand these synths, I got the schematic off them. There's a few in the UK also, and they all seem to hate working on these things because they're so unreliable.

There is no service manual, so the schematic gives you test points but no values! So even if you handed it over to a tech, it's a very difficult job. You have to check the data sheets for all the chips, then try to reverse engineer what Crumar did with them, in order to figure out what the right measurements are at the test points.

But you know that already. It's not lack of knowledge is holding you back, it's Crumar's failure to provide the data.

Currently, one of the oscillators on mine is dead, and the other is totally out of tune. I'm hoping I just need to replace the four 65pf caps next to the osc/ clock chip, and attempt the incredibly annoying tuning procedure ( I have that written out if you need it). The memories also don't hold in mine, and the backup battery gets severely drained if you put one in. Oh, and two of the CEMs are dead too (and I've lost the 8 replacements I had

)

Kudos for keeping the thing alive. When you get it working again, sample it

neurocrash · Post by **neurocrash** » Thu May 21, 2009 3:34 pm

I just realized that my other Bit is out of tune, and the tuning knob isn't functioning. For that matter the detune slider and noise slider are dead too. All the voices and filters work, but out of tune with every other instrument. What a tragedy - I have two of these things and neither are usable. I am just hoping someone can tell me which chips or parts to replace, but it sounds like that may be a tough one.

Thanks!

neurocrash · Post by **neurocrash** » Thu May 21, 2009 10:37 pm

I realize this is going to sound insane, but I wonder if the best thing to do would be to buy another Bit. My original thinking when buying a second one was that I could use it to compare and troubleshoot the other one. Of course I got a surprise when I learned they were completely different boards inside, as I bought a different revision. What I really need are two identical Bits, so at least I would be able to compare scope and meter readings between a working vs. malfunctioning board. For now I'll keep hoping to find an experienced synth technician willing to do paid distance consultations.

Cheers

Post by **madtheory** » Thu May 21, 2009 10:51 pm

Well, if you like them that much... but I think the Bit One is a poor mistress, she will always let you down no matter how hard you try...

neurocrash · Post by **neurocrash** » Thu May 21, 2009 11:03 pm

Agreed! I just feel bad about junking an instrument that will never be made again, and my songs will have an empty spot where the Bit used to be. I keep trying to substitute other sounds, and keep getting disappointed.

http://www.youtube.com/user/JMPSynth · Post by **JMP** » Fri May 22, 2009 11:42 pm

neurocrash wrote:It actually makes a few high pitched or sweep noises, which seem to be VCF oscillations, as the become more pronounced if I turn up the resonance. I don't think I'm hearing the DCO's at all.

Mine made exactly this sound when the battery was dead. Got new battery off Ebay for about £1.50, slotted it in (no soldering required) re-load of the factory sounds via PC/WAV and all OK again. I trust you've already replaced this.....?

neurocrash · Post by **neurocrash** » Fri May 22, 2009 11:52 pm

Come to think of it, I do seem to recall the Bit making random high pitched noises when the memory is blank due to a bad battery, but I think that is different from what I'm experiencing as resonance can be heard as normal with the patches with filter sweeps or LFO>filters, only without the oscillators. Maybe I should record a sample.

I do have extra batteries on hand so there isn't any harm in replacing and re-loading a few more times.

Thanks!

neurocrash · Post by **neurocrash** » Sat May 23, 2009 12:19 am

madtheory wrote:Kudos for keeping the thing alive. When you get it working again, sample it

The specific character of this instrument that is lacking in many of my digital synths or sample players is the variation in tone that occurs at different velocities. As such, even a sample of every key would not be useful, with a program like AutoSampler, many samples per note at different velocities would probably sound good.

I've had this instrument since about 1988, and it has had major repairs at least four times, the last two by me. My problem now is that I don't know what to repair. I need to take the whole thing apart and inspect it for broken wires and bad solder. Aside from that, all I can think to do is socket more and more of the board(s) and try replacement chips and/or replacing every capacitor. I simply don't know how to trace the signal output path on the circuit boards with a scope or probe.

The other (SSM) Bit is at least partially functional, with the problem where the board behaves as if the mod wheel is on all the time. Until I figure out how to disable the mod wheel or otherwise correct this LFO problem, my only solution is to shut off LFO1 in parameter 1. For some sounds this is fine, as I'm not a mod wheel/vibrato guy, but I'm sure that some patches use the LFO for other things.

Thanks

neurocrash · Post by **neurocrash** » Wed May 27, 2009 5:40 pm

The semi-functional Bit is prominently featured in my entry for the Depeche Mode "Peace" remix contest.

http://www.beatportal.com/remix/detail/ ... wback-mix/

I hope to re-record it someday if I ever get the Curtis model fixed.

Cheers

Post by **madtheory** » Wed May 27, 2009 7:39 pm

A Bit 01 (the rack) just sold on ebay. These seem to be rare, but also more reliable. I wonder if the Bit 99 is reliable too?

neurocrash · Post by **neurocrash** » Wed May 27, 2009 7:50 pm

That's weird. I've been searching for Bit's regularly and haven't seen one. I would gladly buy an 01 if it is indeed more reliable than the keyboard versions.

Thanks!

Post by **madtheory** » Thu May 28, 2009 9:20 am

I have an autosearch setup. This one was BIN in a few hours. I was away for a brilliant weekend, so I missed it. For me the rack would be ideal, and that model has sysex also. Editing a storing on the computer would be a vast improvement on using WAVs into the tape port!

neurocrash · Post by **neurocrash** » Thu May 28, 2009 9:36 am

Still very strange - I searched completed listings on ebay for several countries including Ireland and can't find it. Do you happen to have the item number? I have found some ebay items not visible in my country can be found by specifically searching others. I'm guessing most of the Crumar Bits are not in the US.

Thanks!

Post by **madtheory** » Thu May 28, 2009 10:57 am

neurocrash wrote:Still very strange

Not really, a completed listing would not show up for you AFAIK. Here it is:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... SS:US:1123

Help with diagnosis of Crumar Bit One

Help with diagnosis of Crumar Bit One

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Re: Help with diagnosis of Crumar Bit One

Re: Help with diagnosis of Crumar Bit One

Re: Help with diagnosis of Crumar Bit One

Re: Help with diagnosis of Crumar Bit One

Re: Help with diagnosis of Crumar Bit One

Re: Help with diagnosis of Crumar Bit One

Re: Help with diagnosis of Crumar Bit One

Re: Help with diagnosis of Crumar Bit One

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