Crumar Musical Instruments User Group.

Greetings,

I have two Crumar Bit One keyboards that have bad voices.  One has
three working voices, and the other has a single working voice.  I do
have schematics and board layouts, but have not been able to get
anywhere with them.

The two Bits are different revisions, one with CEM3328 and the
other with SSM2044 filters.  The circuit boards within each are not
interchangeable.

I do have a meter and a scope, but haven't been able to determine
which (if any) signal paths may be defective.  My knowledge of
electronics is basic, so while I can replace parts and generally poke
around with a meter, I don't know how to diagnose with the scope
beyond looking at the waveform going in and out of chips.  I haven't
yet located the lack of signal that would indicate failures.

I do have a few spare filters of each type, but it appears that the
problems with these are not the filters, since no matter how I swap
and change them around, the bad voices are always in the same place,
such as 1,5,6

I also tried rearranging some of the other socketed ICs, and swapped
common ones from one board to the other, but the problem does not
change at all.  It seems that both boards may have the same problem
(missing, non-filter related voices) but I'm definitely lost.

Any suggestions or insights would be appreciated, in particular, what
sorts of parts are likely to fail on these instruments.  These were
unused for over a year, due to these problems, only more voices have
failed as time has gone on.  I would very much like to get at least
one of these working again.

Thanks very much for your consideration.

> I have two Crumar Bit One keyboards that have bad voices. One has
> three working voices, and the other has a single working voice. 

Which one (2044 or 3328) has the three working voices?  
Is it all the upper or lower voices that have failed, or a random 
selection? 

> I do have schematics and board layouts, but have not been able to 
> get anywhere with them.

Do you have schematics for both versions?

> I do have a few spare filters of each type, but it appears that the
> problems with these are not the filters, since no matter how I swap
> and change them around, the bad voices are always in the same place,
> such as 1,5,6

At least that means the expensive bits are OK...

> Any suggestions or insights would be appreciated, in particular, what
> sorts of parts are likely to fail on these instruments. These were
> unused for over a year, due to these problems, only more voices have
> failed as time has gone on. I would very much like to get at least
> one of these working again.

If you open the noise slider, do any of the dead voices pass/filter
the noise?  That might give you a clue if it's the DCOs or later in 
the signal path.


Steve

> Which one (2044 or 3328) has the three working voices?  
> Is it all the upper or lower voices that have failed, or a random 
> selection? 

Hmmm... Now I can't remember - I'll have to hook them up again to be
sure but I think the one with only one good voice was the one with
3328s.  The voices that have failed are very specific to the note
order.  If I press one key and keep it held down, then press another,
etc... I can determine how many voices of the six are working.  They
are always dead in the same order, such as: 

1-quiet, 2-working, 3-working, 4-working, 5-quiet, 6-quiet

or 

1-quiet, 2-quiet, 3-quiet, 4-quiet, 5-working, 6-quiet

> > I do have schematics and board layouts, but have not been able to 
> > get anywhere with them.
> 
> Do you have schematics for both versions?

Unfortunately, I only have schematics for one version - but since I
can't find anyone in the state that fixes vintage keyboards, I'm kind
of stuck.  My ability to read schematics is quite basic.  I can find a
component in the diagram, then find the actual part on the board, but
that is about it.  Knowing what part may be responsible for the
problem is beyond me.

I got a basic oscilloscope expecting to be able to read the output
from each signal pin of the ICs in each circuit path, assuming that
one of them would be suspiciously flat-lined - but I haven't found
anything like that in poking around so far.  Everything seems to have
power and is moving signals along.
 
> If you open the noise slider, do any of the dead voices pass/filter
> the noise?  That might give you a clue if it's the DCOs or later in 
> the signal path.

I'll have to give that a try, although from what I recall, the noise
was audible.  I'll write again as soon as I get them tested again.  

Thanks very much for your consideration!!

> Hmmm... Now I can't remember - I'll have to hook them up again to be
> sure but I think the one with only one good voice was the one with
> 3328s. The voices that have failed are very specific to the note
> order. If I press one key and keep it held down, then press another,
> etc... I can determine how many voices of the six are working. They
> are always dead in the same order, such as: 
> 
> 1-quiet, 2-working, 3-working, 4-working, 5-quiet, 6-quiet
> 
> or 
> 
> 1-quiet, 2-quiet, 3-quiet, 4-quiet, 5-working, 6-quiet

It would be interesting to see if the faulty voices are all
one or other side when you go split.

> I got a basic oscilloscope expecting to be able to read the output
> from each signal pin of the ICs in each circuit path, assuming that
> one of them would be suspiciously flat-lined - but I haven't found
> anything like that in poking around so far. Everything seems to have
> power and is moving signals along.

I'll see which version schematics I have and suggest a few useful test 
points to measure.

> I'll have to give that a try, although from what I recall, the noise
> was audible. I'll write again as soon as I get them tested again. 

OK.


Steve

--- In crumar@yahoogroups.com, Steve Ridley <spr@...> wrote:
> > Hmmm... Now I can't remember - I'll have to hook them up again to be
> > sure but I think the one with only one good voice was the one with
> > 3328s. The voices that have failed are very specific to the note
> > order. If I press one key and keep it held down, then press another,
> > etc... I can determine how many voices of the six are working. They
> > are always dead in the same order, such as: 
> > 
> > 1-quiet, 2-working, 3-working, 4-working, 5-quiet, 6-quiet
> > 1-quiet, 2-quiet, 3-quiet, 4-quiet, 5-working, 6-quiet

Well, in my chip swapping, I've managed to make things worse... 
Here's the current state:

SSM2044 1-bad, 2-working, 3-working, 4-bad, 5-bad, 6-bad
Working voices coming from Lower, No Noise generator audible

CEM3328 ?, Lower making warbly noises, No Noise generator audible

> It would be interesting to see if the faulty voices are all
> one or other side when you go split.

Does the above answer this?
 
> I'll see which version schematics I have and suggest a few useful test 
> points to measure.

I have the schematics for the later revision with CEM 3328 VCFs

> > I'll have to give that a try, although from what I recall, the noise
> > was audible. I'll write again as soon as I get them tested again. 

I'll have to see if I can reverse my chip swapping and get back to
where I started to see if the noise actually did work.  At this point,
the instruments are accepting data loads, but don't the patches are
not playing correctly at all so I definitely made a mistake.

TGIF!

Update

CEM3328 1-bad, 2-bad, 3-bad, 4-bad, 5-working, 6-bad

Lower making warbly noises coming from voice 1 circuit TL072ACP which
is incidentally about 500 degrees and burned the dickens out of my
finger.  When cooled with compressed air or freeze spray, it quiets
down, No Noise generator audible

Any idea why this component would be running so hot?

Hi,

I don\ufffdt have a Bit One, but check Pin 4 of the TL072 against ground and
even Pin7 against ground. Me thinks that the TL gets maybe ground onto
Pin4 or Pin7, or some voltages are missing (Pin 4 should have a negative
voltage, pin7 a positive, -maximum- at +/-18 Volts!) and that causes the
overheat. Check for some chips called 7805/78L05 /
7812/78L12/7815/78L15/7905/7912/7915 and measure their outputs. Those
componets have three pins and usually a heatsink installed. Left pin ist
the VCC input, middle is usually ground, right pin is the output. A 7805
should output a fixed voltage of 5 Volts, a 7905 a -negative- voltage of
5 volts, a 7812=12 Volts positive etc. Same goes to the other "78" and
"79"-Chips. Even check their middle pin against case ground, maybe they
get from somewhere voltage where they shouldn\ufffdt.

Greetings
Stef


neurokrash wrote:

>Update
>
>CEM3328 1-bad, 2-bad, 3-bad, 4-bad, 5-working, 6-bad
>
>Lower making warbly noises coming from voice 1 circuit TL072ACP which
>is incidentally about 500 degrees and burned the dickens out of my
>finger.  When cooled with compressed air or freeze spray, it quiets
>down, No Noise generator audible
>
>Any idea why this component would be running so hot?
>
>
>
>
>
>
>
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>
>  
>

>> It would be interesting to see if the faulty voices are all
>> one or other side when you go split.
> 
> Does the above answer this?

I think so.
 
>> I'll see which version schematics I have and suggest a few useful test 
>> points to measure.
> 
> I have the schematics for the later revision with CEM 3328 VCFs

Hurrah!  I have the early verson (SSM2044).  I've just posted them
in the files section.  If you put the 3328 version up, we'll both have
a full set.


Steve

> Lower making warbly noises coming from voice 1 circuit TL072ACP which
> is incidentally about 500 degrees and burned the dickens out of my
> finger. When cooled with compressed air or freeze spray, it quiets
> down, No Noise generator audible
> 
> Any idea why this component would be running so hot?

Because it's died.  Several of possible reasons.

1.  Check the supply.  For a TL072 you should have -12v on pin 4
    and +12v on pin 8 (NOT pin 7).  

2.  Has it been accidentally been put in wrong way around during
    chip swapping?  Easily done...

3.  Faulty components connected to an input or output. 

4.  Sometimes chips just die.

First check that the power supplies are right, measured against ground
(eg the sleeve of the output jack or a 0v test point).  

If the power is OK, try another TL072 and see if it's OK - they're so 
cheap it doesn't really matter if you kill another one.  If the new
TL072 doesn't get hot, measure the DC voltages on the output pins 
(1 and 7) and report back.



Steve

> Hurrah!  I have the early verson (SSM2044).  I've just posted them
> in the files section.  If you put the 3328 version up, we'll both have
> a full set.

Great news!  Well, I posted some of the pages, not including the board
layouts, since I didn't want to use up all of the remaining upload
space.  I couldn't compress the images much more without losing
detail.  Please be sure to download the files!

I can send the rest privately or post it elsewhere.

Thanks!

Hola,

neurokrash wrote:

>>I don\ufffdt have a Bit One, but check Pin 4 of the TL072 against ground and
>>even Pin7 against ground. Me thinks that the TL gets maybe ground onto
>>Pin4 or Pin7, or some voltages are missing (Pin 4 should have a negative
>>voltage, pin7 a positive, -maximum- at +/-18 Volts!) and that causes the
>>overheat. 
>>    
>>
>
>I'm not detecting any continuity between ground and pins 4 or 7 on any
>of the TL072s.  Is that the right thing to look for?
>  
>
The other poster was right, it is Pin4 and Pin8, i\ufffdm sorry.

>I cannot find 780x or 781x, but there is one 7912 on the PSU board,
>and it measures:
>Left 0
>Middle -17v
>Right -12v
>
>  
>

Middle -17? -Sure- the middle pin? Normally must the left pin provide 
the -17 volts, middle pin ground and right pin the -12 Volt. If the 7912 
gets overheat, it will raise the output voltage. But with overheat i 
mean "burning".....

Yup, better check the PSU first......

Greetings
Stef

> I don´t have a Bit One, but check Pin 4 of the TL072 against ground and
> even Pin7 against ground. Me thinks that the TL gets maybe ground onto
> Pin4 or Pin7, or some voltages are missing (Pin 4 should have a negative
> voltage, pin7 a positive, -maximum- at +/-18 Volts!) and that causes the
> overheat.

I'm not detecting any continuity between ground and pins 4 or 7 on any
of the TL072s.  I am also not detecting continuity between pins 4 and
7 on each IC.  Is that the right thing to look for?

Pin 4s: -11.5v
Pin 7s: -9.9v, 0, or +10.5 (only one 14 ICs)
Pin 8s: 11.14v

> Check for some chips called 7805/78L05 /
> 7812/78L12/7815/78L15/7905/7912/7915 and measure their outputs. Those
> componets have three pins and usually a heatsink installed. Left pin ist
> the VCC input, middle is usually ground, right pin is the output. A 7805
> should output a fixed voltage of 5 Volts, a 7905 a -negative- voltage of
> 5 volts, a 7812=12 Volts positive etc. Same goes to the other "78" and
> "79"-Chips. Even check their middle pin against case ground, maybe they
> get from somewhere voltage where they shouldn´t.

I cannot find 780x or 781x, but there is one 7912 on the PSU board,
and it measures:
Left 0
Middle -17v
Right -12v

All three pins have continuity with the case ground, but only when the
connecting cables for the other boards are connected to it.

Suggestions?

Thanks!

> > Any idea why this component would be running so hot?
>
> Because it's died. Several of possible reasons.

My basic thinking was that if this one got damaged, perhaps there was
another component nearby that was responsible.

> 1. Check the supply. For a TL072 you should have -12v on pin 4
> and +12v on pin 8 (NOT pin 7).

Depending on the TL072, I'm getting:

Pin 4s: -11.5v
Pin 7s: -9.9v, 0, or +10.5 (only one of the 14 ICs)
Pin 8s: 11.14v

> 2. Has it been accidentally been put in wrong way around during
> chip swapping? Easily done...

None of the TL072s are socketed, so that isn't the culprit at this
point. I was thinking of putting in sockets for all components that
are suspect so I'll be sure to be careful to that.

Backing up for a minute here, both of my Bit One keyboards had been
repaired and were functioning properly a few years ago. One of them
spontaneously developed a crackly noise problem, so it was taken out
of service. The other was stored functional for some time while I
moved, etc... Taking them out of storage, I expected to clean some
contacts and be ready to go, but instead a lot of things had
apparently failed while these instruments were in storage and unpowered.

> 3. Faulty components connected to an input or output.
>
> 4. Sometimes chips just die.
>
> First check that the power supplies are right, measured against ground
> (eg the sleeve of the output jack or a 0v test point).

I did find a 17v output on the PSU, but haven't determined if that is
incorrect and/or where that reading may be coming from. This is Pin5
of the connector going from the PSU to board P-1108.

> If the power is OK, try another TL072 and see if it's OK - they're so
> cheap it doesn't really matter if you kill another one. If the new
> TL072 doesn't get hot, measure the DC voltages on the output pins
> (1 and 7) and report back.

I need to go buy some parts, but will appreciate it if you can suggest
whether other related parts killed these TL072s.

Thanks!

> Middle -17? -Sure- the middle pin? Normally must the left pin provide 
> the -17 volts, middle pin ground and right pin the -12 Volt. If the
7912 
> gets overheat, it will raise the output voltage. But with overheat i 
> mean "burning".....
> 
> Yup, better check the PSU first......

Yeah, I triple checked.  I'm supposed to be using the case ground,
right?  -17v  Of course this changes if I unplug the cables that
attach the PSU to the rest of the keyboard.

Would you suggest that PSU is damaged, or is something attached to the
PSU causing this problem?

Strangely enough, the keyboard partially function, can load sounds
from tape, play sounds, etc...

Thanks!

Oops, one more correction:

I did find a 17v output on the PSU, but haven't determined if that is
incorrect and/or where that reading may be coming from. This is _Pin6_
of the connector going from the PSU to board P-1108. (not pin 5)

Am I correct that these groups have no edit message function? :p

> Yeah, I triple checked. I'm supposed to be using the case ground,
> right? -17v Of course this changes if I unplug the cables that
> attach the PSU to the rest of the keyboard.

I can't remember if the case is 0v or not - don't bet on it.  I would 
expect the outside of the output jack to be at 0v, but look for the
0v connections on the power supply connector to be sure (JA4-5, JB 2-4, 
J0 2-4).  BTW, the same PSU appears to be used in both versions.

> Would you suggest that PSU is damaged, or is something attached to the
> PSU causing this problem?

It could be either.  You could have a faulty 12v regulator (note, the
pinouts of the +12v and -12v regulators are not the same) then one of
the rails might go quite high (like 17v).  OTOH, if the 5v rail got
shorted to chassis, then the -12v might measure -17v to chassos and the
+12v would measure 7v.  

So, unplug the power connectors and measure the +12v and -12v on the 
PSU board, using the PSU 0v as ground. 

If the PSU measures OK, switch off and reconnect one connector at a
time, switch on and see which board is causing the problem.  

> Strangely enough, the keyboard partially function, can load sounds
> from tape, play sounds, etc...

Most of the control sysem of the synth runs on a +5v supply, which is 
clearly working fine.  

And PLEASE WATCH OUT FOR THE MAINS!


Steve

Is this the early or late Bit 1 we're looking at?

> I'm not detecting any continuity between ground and pins 4 or 7 on any
> of the TL072s. I am also not detecting continuity between pins 4 and
> 7 on each IC. Is that the right thing to look for?

Not really. 

> Pin 4s: -11.5v
> Pin 7s: -9.9v, 0, or +10.5 (only one 14 ICs)
> Pin 8s: 11.14v

Pins 4 and 8 look reasonably close to +12v and -12v.
Pins 1 and 7 are the two outputs (it's a dual opamp)
and -9.9v  and +10.5v are not usually god signs.

Which TL072 is it?  IC number?

>> Check for some chips called 7805/78L05 /
>> 7812/78L12/7815/78L15/7905/7912/7915 and measure their outputs. Those
>> componets have three pins and usually a heatsink installed. Left pin ist
>> the VCC input, middle is usually ground, right pin is the output. A 7805
>> should output a fixed voltage of 5 Volts, a 7905 a -negative- voltage of
>> 5 volts, a 7812=12 Volts positive etc. Same goes to the other "78" and
>> "79"-Chips. Even check their middle pin against case ground, maybe they
>> get from somewhere voltage where they shouldn´t.

Pinout of the 7912 is different from the other two.  0v is at one
end.
 
> I cannot find 780x or 781x, 

They're on the P-1108 board.  Might be near a heatsink at the 
back? (Sorry, it's 5 years since I looked inside my Bit 1).

> but there is one 7912 on the PSU board, and it measures:
> Left 0
> Middle -17v
> Right -12v

That looks good to me.

You could find and measure the 7812. Should give around +17v on 
one end, 0v in the middle and +12v at the other end.  But the
measurements on the TL072 suggest that power is getting there.
I'd remove the hot TL072, put in a socket and fit another TL072.
If it get's hot, you have a bigger problem, but they're cheap 
enough to risk it.  Buy two.  




Steve

Hi! the other i cleaned my DS-2, before cleaning it. one oscillator wouldn't 
work, then after spraying everything with a contact cleaner. when i plugged 
it in, the oscillator worked! but after a minute it didn't again. what you i 
think i should do next?

diego



http://www.monsterbot.org

http://www.monopond.150m.com





>From: Steve Ridley <spr@...>
>Reply-To: crumar@yahoogroups.com
>To: crumar@yahoogroups.com
>Subject: RE: [crumar] Re: Bit One Repair
>Date: Tue, 15 Aug 2006 14:36:17 +0200 (CEST)
>
>
> > Yeah, I triple checked. I'm supposed to be using the case ground,
> > right? -17v Of course this changes if I unplug the cables that
> > attach the PSU to the rest of the keyboard.
>
>I can't remember if the case is 0v or not - don't bet on it.  I would
>expect the outside of the output jack to be at 0v, but look for the
>0v connections on the power supply connector to be sure (JA4-5, JB 2-4,
>J0 2-4).  BTW, the same PSU appears to be used in both versions.
>
> > Would you suggest that PSU is damaged, or is something attached to the
> > PSU causing this problem?
>
>It could be either.  You could have a faulty 12v regulator (note, the
>pinouts of the +12v and -12v regulators are not the same) then one of
>the rails might go quite high (like 17v).  OTOH, if the 5v rail got
>shorted to chassis, then the -12v might measure -17v to chassos and the
>+12v would measure 7v.
>
>So, unplug the power connectors and measure the +12v and -12v on the
>PSU board, using the PSU 0v as ground.
>
>If the PSU measures OK, switch off and reconnect one connector at a
>time, switch on and see which board is causing the problem.
>
> > Strangely enough, the keyboard partially function, can load sounds
> > from tape, play sounds, etc...
>
>Most of the control sysem of the synth runs on a +5v supply, which is
>clearly working fine.
>
>And PLEASE WATCH OUT FOR THE MAINS!
>
>
>Steve
>
>
>
>
>
>Yahoo! Groups Links
>
>
>
>
>
>
>

_________________________________________________________________
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--- In crumar@yahoogroups.com, Steve Ridley <spr@...> wrote:
> You could find and measure the 7812. Should give around +17v on 
> one end, 0v in the middle and +12v at the other end.  But the
> measurements on the TL072 suggest that power is getting there.
> I'd remove the hot TL072, put in a socket and fit another TL072.
> If it get's hot, you have a bigger problem, but they're cheap 
> enough to risk it.  Buy two.  

So is there supposed to be 17v coming out of the 78xx parts which are
connected to the PSU and VCF board?  I want to make sure that one of
these hasn't failed in such a way that it is sending too much voltage
and subsequently cooking parts.

In any case, I did manage to find them.  I didn't see them on the
inverted little P-1108 board (whoops) but I plan to check them out
once I hear back and get some replacements.

In the meantime, I socketed the whole VCF board and put everything
back together.  After I had it powered up for a while, one of the
original TL072's literally went up in smoke.  I am pretty sure it was
the one that was running hot before, although it ended up in a
different socket.  I had marked the IC, but put it in one of the other
TL072 sockets - so I'm hoping that means the part was bad and not the
circuit.

I do have replacements for many of the ICs on the board (not including
most of the VCFs or any VCAs) but I want to get a little more sure of
things before I smoke a bunch of new parts.

I read a data sheets on the 7805 and 7812 from my P1108 board, and
didn't see any indication that these were intended to output anything
outside of 12v or 15v.  Can you verify that 17v is okay, or could
these parts be the problem?

Thanks very much!

neurokrash wrote:

>I read a data sheets on the 7805 and 7812 from my P1108 board, and
>didn't see any indication that these were intended to output anything
>outside of 12v or 15v.  Can you verify that 17v is okay, or could
>these parts be the problem?
>
>  
>

Yup, i also don\ufffdt knwo any 78xx part which outputs +17 Volts. The 
-incoming- Voltage (left pin) should be approx. 17 Volts on a 7815 for 
example, where its output voltage must be -flat- +15 Volts. A 7812 which 
gets a input voltage of +17 Volts is in my opinion too much; i even 
don\ufffdt know a constellation where 0V is connected on the left pin and VCC 
on the middle. Buit, if the schematics tell te same, -then-. it must be 
correct.

 I had a while ago also some trouble with a simple Microcontroller, 
where its VCC was connected to a 7805. I simply forgot to lower the 
input Voltage of the 7805 and it gots straight +12 Volts. The 7805 
didn\ufffdt liked that and produced a output voltage of over +7 Volts, 1.5 
Volts over the maximum current of the Microcontroller, which got death 
after approx. 20 seconds later caused by overheating. The 78XX series 
automatically turns off when overheating and switch back on after a 
cooling time, but often much too late.

Greetings
Stef

Woohoo!

Thanks to the help of each of you, I got the SSM2044 Bit repaired! It
turns out that the problem was a combination of bad TL072 op amps and
one bad filter. Since I socketed the whole VCF board, I was able
to switch out the TL072's until most of the voices were working, then
I was able to narrow the problem and replaced one of the filters.

Thanks to everyone!

The CEM3328 Bit; however, still needs some work.

So far, I have three voices "sort of" working.  At least two of the
filter ICs seem to be bad, such that when I press a key, a faint knock
sound is heard on that voice, and nothing else.  I'm sure that I will
need a few more filters and a handful of TL072s, since rearranging
these allowed me to get the first three voices working.  I'm not quite
sure how the lower 9 TL072s correspond to the 6 filter voices yet.

One other problem is that the voices are out of tune, like the detune
slider is moved, although it isn't having any effect at all.

I think that one of the 4051 ICs may be at fault here.

Comments?

>> I read a data sheets on the 7805 and 7812 from my P1108 board, and
>> didn't see any indication that these were intended to output anything
>> outside of 12v or 15v. Can you verify that 17v is okay, or could
>> these parts be the problem?

No, the 17v (approx.) is on the input pin to the regulator.  The 7812
should give +12v on it's output, the 7912 should take in -17v and give
-12v on the output.


Steve

While you are at it and are working at 2 kinds of Bits...

I'm a huge fan of the SSM filter sound, but have a CEM filter Bit01
(the rack). I was wondering: could I simply pull out the CEM filters
and replace them with SSMs?

And yes, I'm completely ignorant of electronics. just a musician...


--- In crumar@yahoogroups.com, Steve Ridley <spr@...> wrote:

>
> 
> 
> >> I read a data sheets on the 7805 and 7812 from my P1108 board, and
> >> didn't see any indication that these were intended to output anything
> >> outside of 12v or 15v. Can you verify that 17v is okay, or could
> >> these parts be the problem?
> 
> No, the 17v (approx.) is on the input pin to the regulator.  The 7812
> should give +12v on it's output, the 7912 should take in -17v and give
> -12v on the output.
> 
> 
> Steve
>

> I'm a huge fan of the SSM filter sound, but have a CEM filter Bit01
> (the rack). 

There are more than one SSM filter sounds.  The SSM244 will not sound
the same as same as the SSM2040 (early Prophet V) or SSM2045.  The 2044
in the early Bit 1 is a sort of folded up Moog ladder but with it's own
distinctive sound, the 2045 is more like a Curtis filter and the 2040 
isn't much like anything else.  Similarly, different CEM filters have
different sounds - CEM3020/3028 sound fifferent to a CEM3350 or CEM3089.

Look here for technical data on different filter chips:

http://www.synthtech.com/cem/cemsynth.html (scroll down)

and here for what filter chip is in what synth:

http://www.synthtech.com/cem/cemsynth.html
 
> I was wondering: could I simply pull out the CEM filters
> and replace them with SSMs?

Only if you like silence and smoke.  Different type of chip,
different connections on different pins.  It wouldn't work
and it would probably be an expensive experiment.

You need to buy an early Bit 1, or maybe a Siel Opera 6 / DK600
if you want the SSM2044 sound, or see the links above if you want
the SSM2040 sound.

> And yes, I'm completely ignorant of electronics. just a musician...

Nothing wrong with that.  It's people who _think_ they know about
electronics that worry me...

Does anyone know the serial number where the Bit 1 changes from SSM 
to CEM?  My Bit 1 is SSM and has a number in the 240s I think (must check). 

Does that help, or have I just muddied the water?

Steve

Many thanks! Not muddy at all.

--- In crumar@yahoogroups.com, Steve Ridley <spr@...> wrote:
>
> 
> > I'm a huge fan of the SSM filter sound, but have a CEM filter Bit01
> > (the rack). 
> 
> There are more than one SSM filter sounds.  The SSM244 will not sound
> the same as same as the SSM2040 (early Prophet V) or SSM2045.  The 2044
> in the early Bit 1 is a sort of folded up Moog ladder but with it's own
> distinctive sound, the 2045 is more like a Curtis filter and the 2040 
> isn't much like anything else.  Similarly, different CEM filters have
> different sounds - CEM3020/3028 sound fifferent to a CEM3350 or CEM3089.
> 
> Look here for technical data on different filter chips:
> 
> http://www.synthtech.com/cem/cemsynth.html (scroll down)
> 
> and here for what filter chip is in what synth:
> 
> http://www.synthtech.com/cem/cemsynth.html
>  
> > I was wondering: could I simply pull out the CEM filters
> > and replace them with SSMs?
> 
> Only if you like silence and smoke.  Different type of chip,
> different connections on different pins.  It wouldn't work
> and it would probably be an expensive experiment.
> 
> You need to buy an early Bit 1, or maybe a Siel Opera 6 / DK600
> if you want the SSM2044 sound, or see the links above if you want
> the SSM2040 sound.
> 
> > And yes, I'm completely ignorant of electronics. just a musician...
> 
> Nothing wrong with that.  It's people who _think_ they know about
> electronics that worry me...
> 
> Does anyone know the serial number where the Bit 1 changes from SSM 
> to CEM?  My Bit 1 is SSM and has a number in the 240s I think (must
check). 

> 
> Does that help, or have I just muddied the water?
> 
> Steve
>

Yeehaw!

The CEM3328 Bit is now fully repaired.

This one had some bad CEM3328 filters, bad TL082 op-amps, and then was
mostly functional aside from being out of tune and having one voice
still out.  I decided that the problem was probably not from the lower
filter board, since switching things around down there didn't change
the bad voice, so I looked at the upper board.  There I found another
row of TL082 op-amps, so I socketed these and began moving the chips
around.  The bad voice followed a chip, so I replaced it and presto!

It is worth mentioning that some of the TL082s were running pretty hot
- about 110-120 degrees f.  One of them was over 220 degrees!  I
swapped these out until I got a full set that were 100 degrees or
below.  It's 82 here, so that seemed acceptable ;)

I tuned the wacky voice by adjusting one of the potentiometers on the
left side of the upper board, with the detune slider in the middle. 
Seems okay now, but I'm not sure why it went so far out of tune(?)

Here are some of the things that I learned while repairing the Bits:

1) Your finger is not a good diagnostic instrument.  I found this out
by trying to check the temperature of an IC that was running at around
220 degrees.  Bad idea, get a temperature probe for your meter
instead.  I got a meter with the temperature probe for $30 on ebay.  I
would guess that you can get a probe that plugs into any meter for
less.  If you really have money, Fluke makes a nifty device that uses
a laser and infrared, so you point a laser pointer at the chip, and it
tells you how hot it is!  I didn't spring for this, but may in the
future.  In any case, finding chips that are running inexplicably hot
is very helpful.

2) Print out the datasheets for ICs that you plan to test.  It
definitely helps to know where to look for supply voltage, ground,
output voltage, etc... Everyone's help from here in the forum was
invaluable in getting me started.

3) Check the ribbon cables.  Some of the cables do not have connectors
on both ends, but instead are soldered to the board.  Many of these
failed while disassembling and assembling the keyboard.  They are more
than 20 years old, so I can't complain - but if you take the keyboard
apart, then put it back together and things get worse, be sure to
check these since the little exposed wire likes to break.

4) If you don't know what to test (like me) socket the board ;)  I
didn't know how to read the schematics well enough to clearly trace
the circuit path for each voice, so I desoldered all of the ICs on the
board, put in sockets, then started to switch the ICs around and/or
leave some out (with the power turned off!).  I could then test each
voice individually and figure out which chips controlled which voices.
 That made it possible to narrow down the problems, and to find the
bad parts.

Thanks to everyone for all the help!

And thank you for your great advice. I already had mine offered for sale with some defects. 
But I just couldn't leave the thing alone. I had a nasty hiss coming out of it and 
occasionally a voice 3 and 4 far too loud. I checked the datasheet of the 3328's and found 
some strange voltages on the 4th 3328 which I could trace down to a resistor near the 
LM13700N that needed resoldering. Voice 3 and 4 back were okay now. In a less 
professional way (touching everything possible point) I was able to find another point to 
be resoldered and now It's fully functional. INo more hisses and crackles. Not even one 
component replaced!

--- In crumar@yahoogroups.com, "neurokrash" <spamkiller@...> wrote:

>
> Yeehaw!
> 
> The CEM3328 Bit is now fully repaired.
> 
> This one had some bad CEM3328 filters, bad TL082 op-amps, and then was
> mostly functional aside from being out of tune and having one voice
> still out.  I decided that the problem was probably not from the lower
> filter board, since switching things around down there didn't change
> the bad voice, so I looked at the upper board.  There I found another
> row of TL082 op-amps, so I socketed these and began moving the chips
> around.  The bad voice followed a chip, so I replaced it and presto!
> 
> It is worth mentioning that some of the TL082s were running pretty hot
> - about 110-120 degrees f.  One of them was over 220 degrees!  I
> swapped these out until I got a full set that were 100 degrees or
> below.  It's 82 here, so that seemed acceptable ;)
> 
> I tuned the wacky voice by adjusting one of the potentiometers on the
> left side of the upper board, with the detune slider in the middle. 
> Seems okay now, but I'm not sure why it went so far out of tune(?)
> 
> Here are some of the things that I learned while repairing the Bits:
> 
> 1) Your finger is not a good diagnostic instrument.  I found this out
> by trying to check the temperature of an IC that was running at around
> 220 degrees.  Bad idea, get a temperature probe for your meter
> instead.  I got a meter with the temperature probe for $30 on ebay.  I
> would guess that you can get a probe that plugs into any meter for
> less.  If you really have money, Fluke makes a nifty device that uses
> a laser and infrared, so you point a laser pointer at the chip, and it
> tells you how hot it is!  I didn't spring for this, but may in the
> future.  In any case, finding chips that are running inexplicably hot
> is very helpful.
> 
> 2) Print out the datasheets for ICs that you plan to test.  It
> definitely helps to know where to look for supply voltage, ground,
> output voltage, etc... Everyone's help from here in the forum was
> invaluable in getting me started.
> 
> 3) Check the ribbon cables.  Some of the cables do not have connectors
> on both ends, but instead are soldered to the board.  Many of these
> failed while disassembling and assembling the keyboard.  They are more
> than 20 years old, so I can't complain - but if you take the keyboard
> apart, then put it back together and things get worse, be sure to
> check these since the little exposed wire likes to break.
> 
> 4) If you don't know what to test (like me) socket the board ;)  I
> didn't know how to read the schematics well enough to clearly trace
> the circuit path for each voice, so I desoldered all of the ICs on the
> board, put in sockets, then started to switch the ICs around and/or
> leave some out (with the power turned off!).  I could then test each
> voice individually and figure out which chips controlled which voices.
>  That made it possible to narrow down the problems, and to find the
> bad parts.
> 
> Thanks to everyone for all the help!
>

--- In crumar@yahoogroups.com, "monodist" <monodist@...> wrote:
>
> And thank you for your great advice. I already had mine offered for
sale with some defects. 
> But I just couldn't leave the thing alone. I had a nasty hiss coming
out of it and 
> occasionally a voice 3 and 4 far too loud. I checked the datasheet
of the 3328's and found 
> some strange voltages on the 4th 3328 which I could trace down to a
resistor near the 
> LM13700N that needed resoldering. Voice 3 and 4 back were okay now.
In a less 
> professional way (touching everything possible point) I was able to
find another point to 
> be resoldered and now It's fully functional. INo more hisses and
crackles. Not even one 
> component replaced!

Hmmm... Both of my Bits have a lot of hiss - Isn't this normal? 
Perhaps you were having extra offensive hiss?

> LM13700N that needed resoldering. Voice 3 and 4 back were okay now.
In a less 
> professional way (touching everything possible point) I was able to
find another point to 
> be resoldered and now It's fully functional. INo more hisses and
crackles. Not even one 
> component replaced!

Ah yes, that is the 100,000 mile service.  It is the 200,000 mile
service you have to look out for ;)

My Bits were worked on several years ago when resoldering of most of
the boards was necessary.  We went over almost everything since a lot
of the solder joints were bad, and put in sockets for the filters. 
After that, they worked fine for a while, but I think the time (about
24 years, right?) and perhaps a bad voltage regulator took their toll
on some of the parts.  Fortunely, most of the parts in there are
common and cheap, only .50 or $1.  I probably spent a total of about
$60 repairing both Bits, and I have enough spare parts for another 10
years.  Since I didn't know what was bad, I just bought replacements
for almost everything, socketed all of the ICs on the lower board(s)
then started switching them out.  The only expensive parts were the
filters - about $10 each, and fortunately I had a few leftover from
the 100,000 mile service.  I grabbed a few more from the Internet, and
hopefully now that the super high temperature op-amps are out, the
filters would be exposed to such extremes again.

Cheers!