Vintage Synth Repair

hey guys, 

i've fixed both the modulation inputs for the filter and my noise
generator on my arp odyssey mk1 by replacing op amps. it's sample and
hold mixer doesn't modulate anything and i'm wondering if anyone has
an experience with this part of the synth. i've replaced op amp A2 and
the transistor Q3. One thing I haven't replaced is A3 which is a
unique part that i couldn't find for under $15! I noticed there was
mentioned of "Z3" working with a charge in C7, but i cannot find Z3
anywhere. 

do you think there are more op amps that i need to replace that are
feeding the signals INTO the S+H mixer or do you think there are op
amps that are suppose to be amplifying the output of the S+H... or
something else entirely?

thanks guys!
-johnny

Follow the S&H signal. Even though it usually are opamps and 
transistors that fails, it couls also be the simplest things. I once 
tracked the problem of an ARP to a broken standard small cap (not en 
electrolytic cap). It could also be a pull-dow resistor that have 
gotten out of range.


På 3. mai. 2008 kl. 01.46 skrev cockandswan:

> hey guys,
>
>  i've fixed both the modulation inputs for the filter and my noise
>  generator on my arp odyssey mk1 by replacing op amps. it's sample and
>  hold mixer doesn't modulate anything and i'm wondering if anyone has
>  an experience with this part of the synth. i've replaced op amp A2 and
>  the transistor Q3. One thing I haven't replaced is A3 which is a
>  unique part that i couldn't find for under $15! I noticed there was
>  mentioned of "Z3" working with a charge in C7, but i cannot find Z3
>  anywhere.
>
>  do you think there are more op amps that i need to replace that are
>  feeding the signals INTO the S+H mixer or do you think there are op
>  amps that are suppose to be amplifying the output of the S+H... or
>  something else entirely?
>
>  thanks guys!
>  -johnny
>
> 
tw.  :)

"Those great moments come when musicians are playing together..."
(Bob Moog)

There are various things to check.

First of all, does any signal get to the S/H circuit at all - and does it
get through.

Check pin 3 of A2 (that's the input) and then pin 1 of A2 (that's the
output of the S/H mixer); of course make sure that the fader for at least
one of the S/H sources is up.

Alternatively you could also just check the "S/H Mixer" modulation routings
from the front panel.


This part verfiees that A2 actually works.

Next, check if signal enters A3 (pin 3) and if the trigger signal is there
(pin 5). I'm assuming the LFO works, right? Set the LFO to trigger the S/H
and check if there is the LFO signal at pin 5 of A3.


-- 
Malte Rogacki gacki@...
----------------------------------------------------------------------------
"Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason why you
 get no sound out of it." (ARP 2600 Owner's Manual)
----------------------------------------------------------------------------

Ive seen exactly the opposite in vintage synthesizers.
Op-amp failures are common in my world. :)


--- scott frye <painintheamp@...> wrote:


---------------------------------
                
In my 25+ years on working in engineering and test
I've seen VERY VERY few op amps ever go bad.
Caps crap out far more and power resistors and 3
terminal regulators

Scott  Frye
AudioFixation
Consumer / Pro Audio Repair
Southern VT 

  



      
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I agree, with vintage synths dead op-amps are common, and so are dead OTA's and 
transistor arrays.  1458's, 4558's, 741's, CA3080's, CA3280's and LM 3046's come to 
mind.

--- In vintagesynthrepair@yahoogroups.com, Philip <eggwheatis@...> wrote:

>
> Ive seen exactly the opposite in vintage synthesizers.
> Op-amp failures are common in my world. :)
> 
> 
> --- scott frye <painintheamp@...> wrote:
> 
> 
> ---------------------------------
>                 
> In my 25+ years on working in engineering and test
> I've seen VERY VERY few op amps ever go bad.
> Caps crap out far more and power resistors and 3
> terminal regulators
> 
> Scott  Frye
> AudioFixation
> Consumer / Pro Audio Repair
> Southern VT 
> 
>   
> 
> 
> 
>       
> ---------------------------------
> Be a better friend, newshound, and know-it-all with
> Yahoo! Mobile.  Try it now.
>     
>           												
> 
> 
> 
>       __________________________________________________________
> Sent from Yahoo! Mail.
> A Smarter Email http://uk.docs.yahoo.com/nowyoucan.html
>

On Saturday 03 May 2008 13:54, scott frye wrote:
> In my 25+ years on working in engineering and test I've seen VERY VERY few
> op amps ever go bad. Caps crap out far more and power resistors and 3
> terminal regulators

Well,  I've been a tech for around 40 years,  and I have.  Lots of 1458 and 
4558 op amps go bad,  typically with the output sitting at the negative 
supply rail.

Caps,  yeah,  sometimes,  but I think that the whole recapping things is 
getting way out of hand.

Power resistors?  Sometimes,  but not that often.

3-terminal regulators?  Only if you abuse them,  or in poor designs.  Last 
time I managed to kill a couple of 7805s was way back in 1975 or so,  when I 
didn't really understand the requirements and didn't have enough heatsinking 
on them,  and continuous thermal cycling (taking it into shutdown and keeping 
on going there) will kill 'em sooner or later,  but since then _very_ few of 
them.

Easy test for op-amp fuinctinality:  Short the inputs.  Usually there's enough 
resistance in line with either or both of them that they won't see a problem 
in the driving circuitry,  and the pins are usually also right next to each 
other so the smallest handy screwdriver is workable if you have good lighting 
and a steady hand.  The output should go to halfway between the rails.  If it 
sits on one rail or the other it's bad.

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

I agree with Roy. In my 40 years of working on music organs, synths, amps,
etc. I find it very common for op amps to fail. I do always check the
coupling caps with an ESR checker and check the voltage regulators and zener
diodes, and I find very few resistor failures, but op amps are common. 

 

Keith A Niver

Certified MITA Technician

Niver's Inc

801 Columbia St

Hudson, NY   12534

518-828-0616, work

518-755-6960, cell

kaniver@...

-----Original Message-----
From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of scott frye
Sent: Saturday, May 03, 2008 1:55 PM
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re:arp odyssey mk1 sample and hold problem

 


In my 25+ years on working in engineering and test I've seen VERY VERY few
op amps ever go bad.
Caps crap out far more and power resistors and 3 terminal regulators

Scott  Frye
AudioFixation
Consumer / Pro Audio Repair
Southern VT 

 

 

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<http://us.rd.yahoo.com/evt=51733/*http:/mobile.yahoo.com/;_ylt=Ahu06i62sR8H
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On Sunday 04 May 2008 00:37, timothy kosiorek wrote:
> I agree with the Techs,I've seen many opamps go bad over the years,but I
> remember changing Opamps back when these vintage synths were still
> relatively new.I think everybody missed a key word in the original
> comment,this was from an engineer,engineers don't get into the real world
> of repairing the things they design,

I didn't miss that....

> I don't know any Techs that haven't at one time wished that the engineer
> that designed something would be sentenced to work on the something for
> eternity.

Damn straight!  :-)

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

The number of dead op amps I've seen in ARP synths is pretty high.
Especially that LM301 (or the variant ARP used) seems to fail regularly.
Coincidentally I currently have a MarkIII Odyssey sitting on my bench; and
coincidentally the op amp in the S/H circuit was dead there, too.

As far as the failure or non-failure of voltage regulators goes: I've had
about three or four devices during the last few weeks that had blown
regulators.

And of course tantalum caps...

-- 
Malte Rogacki gacki@...
----------------------------------------------------------------------------
"Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason why you
 get no sound out of it." (ARP 2600 Owner's Manual)
----------------------------------------------------------------------------

ah yes tantlum caps...I repair a lot of archaic 70's
arcade machines like space invaders etc...they have a
very high failure rate in my experience..

I agree about the re-capping epidemic...the amount of
time you hear 'you just need to re-cap it' these days
:o)

--- Malte Rogacki <gacki@...> wrote:

> The number of dead op amps I've seen in ARP synths
> is pretty high.
> Especially that LM301 (or the variant ARP used)
> seems to fail regularly.
> Coincidentally I currently have a MarkIII Odyssey
> sitting on my bench; and
> coincidentally the op amp in the S/H circuit was
> dead there, too.
> 
> As far as the failure or non-failure of voltage
> regulators goes: I've had
> about three or four devices during the last few
> weeks that had blown
> regulators.
> 
> And of course tantalum caps...
> 
> -- 
> Malte Rogacki gacki@...
>
----------------------------------------------------------------------------
> "Don't forget to TURN ON THE SYNTHESIZER. Often this
> is the reason why you
>  get no sound out of it." (ARP 2600 Owner's Manual)
>
----------------------------------------------------------------------------
> 



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On Sunday 04 May 2008 13:04, Philip wrote:
> ah yes tantlum caps...I repair a lot of archaic 70's
> arcade machines like space invaders etc...they have a
> very high failure rate in my experience..
>
> I agree about the re-capping epidemic...the amount of
> time you hear 'you just need to re-cap it' these days
>
> :o)

I'm amazed that there weren't more failures in the Omni,  what with them using 
a 25V cap in a circuit that could potentially see 30V across it.  :-)

> --- Malte Rogacki <gacki@...> wrote:
> > The number of dead op amps I've seen in ARP synths
> > is pretty high.
> > Especially that LM301 (or the variant ARP used)
> > seems to fail regularly.
> > Coincidentally I currently have a MarkIII Odyssey
> > sitting on my bench; and
> > coincidentally the op amp in the S/H circuit was
> > dead there, too.
> >
> > As far as the failure or non-failure of voltage
> > regulators goes: I've had
> > about three or four devices during the last few
> > weeks that had blown
> > regulators.
> >
> > And of course tantalum caps...
> >
> > --
> > Malte Rogacki gacki@...
>
> ---------------------------------------------------------------------------
>-
>
> > "Don't forget to TURN ON THE SYNTHESIZER. Often this
> > is the reason why you
> >  get no sound out of it." (ARP 2600 Owner's Manual)
>
> ---------------------------------------------------------------------------
>-
>
>
>
>
>       __________________________________________________________
> Sent from Yahoo! Mail.
> A Smarter Email http://uk.docs.yahoo.com/nowyoucan.html
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

At 15:21 Uhr -0400 04.05.2008, Roy J. Tellason wrote:

> I'm amazed that there weren't more failures in the Omni, what with them using
> a 25V cap in a circuit that could potentially see 30V across it.


There certainly are enough failures, especially given the number of
tantalum caps in the Omni (all in all there must be around 80 or more caps;
I didn't count them all). Failure of caps in the gating circuit usually
results in stuck notes.

I'm currently trying to fix an Omni, btw. Progress so far has been good but
there are still some problems.

I've heard about the problem with the "potentially 30V" issue but cannot
really see how this would happen - at least not for the main gating circuit
and the power supply decoupling. But then I'm not really fluent in those
things; so I would be glad if someone could give me an explanation (I'm
always eager to learn about this stuff).

-- 
Malte Rogacki gacki@...
----------------------------------------------------------------------------
"Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason why you
 get no sound out of it." (ARP 2600 Owner's Manual)
----------------------------------------------------------------------------

On Sunday 04 May 2008 17:14, Malte Rogacki wrote:
> I've heard about the problem with the "potentially 30V" issue but cannot
> really see how this would happen - at least not for the main gating circuit
> and the power supply decoupling. But then I'm not really fluent in those
> things; so I would be glad if someone could give me an explanation (I'm
> always eager to learn about this stuff).

It took a little digging since I don't seem to have my ARP stuff handy here,  
but I found my electronic copies of the schematic (which are nowhere near as 
handy for flipping back and forth quick between multiple diagrams...)

If you look at say the Upper Voicing Board where those 22uF caps are used, 
you'll see a point that's marked 0V for short release,  and -15V for long 
release.  This is incorrect!  That same error comes up in two different 
places,  I forget where the other one is.

Following that from the source,  which is the upper right corner of the Lower 
Voicing Board schematic,  you can see that point near the sustain footswitch 
jack and some transistors and whatnot quite plainly marked "+15V".  Since the 
negative end of all those tantalum caps is tied to -15V,  then what appears 
at the top end of them is going to depend on where you have the release 
slider set -- have it set for the longest release time and you'll have 30V 
across all those 25V tantalum caps.

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

At 19:32 Uhr -0400 04.05.2008, Roy J. Tellason wrote:

> It took a little digging since I don't seem to have my ARP stuff handy here,
> but I found my electronic copies of the schematic (which are nowhere near as
> handy for flipping back and forth quick between multiple diagrams...)
>
> If you look at say the Upper Voicing Board where those 22uF caps are used,
> you'll see a point that's marked 0V for short release, and -15V for long
> release. This is incorrect! That same error comes up in two different
> places, I forget where the other one is.
>
> Following that from the source, which is the upper right corner of the Lower
> Voicing Board schematic, you can see that point near the sustain footswitch
> jack and some transistors and whatnot quite plainly marked "+15V". Since the
> negative end of all those tantalum caps is tied to -15V, then what appears
> at the top end of them is going to depend on where you have the release
> slider set -- have it set for the longest release time and you'll have 30V
> across all those 25V tantalum caps.


Hmmmm.

I'm not quite sure that this is 100% how it works.

The +15V are the "Sustain Reference"; this is not what is going directly to
the sustain buss. This is (as far as I can see) the voltage passed to the
string control board; and the release slider then sends only part of it
back.

Indeed the 0V for short release is an error that is also to be found on the
lower voicing board. However the schematic for the string control board
gives those figures: long release -15V, short release +8V.
This is also the way it is printed on the schematic for the voice boards of
the Omni-2.

So the voltage difference would be 23V max which is pretty close to the 25V
rating of the caps but nominally still within tolerance

If I'm making any mistakes here please point them out; as I said I'm still
learning this stuff.

-- 
Malte Rogacki gacki@...
----------------------------------------------------------------------------
"Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason why you
 get no sound out of it." (ARP 2600 Owner's Manual)
----------------------------------------------------------------------------

On Monday 05 May 2008 07:30, Malte Rogacki wrote:
> At 19:32 Uhr -0400 04.05.2008, Roy J. Tellason wrote:
> > It took a little digging since I don't seem to have my ARP stuff handy
> > here, but I found my electronic copies of the schematic (which are
> > nowhere near as handy for flipping back and forth quick between multiple
> > diagrams...)
> >
> > If you look at say the Upper Voicing Board where those 22uF caps are
> > used, you'll see a point that's marked 0V for short release, and -15V for
> > long release. This is incorrect! That same error comes up in two
> > different places, I forget where the other one is.
> >
> > Following that from the source, which is the upper right corner of the
> > Lower Voicing Board schematic, you can see that point near the sustain
> > footswitch jack and some transistors and whatnot quite plainly marked
> > "+15V". Since the negative end of all those tantalum caps is tied to
> > -15V, then what appears at the top end of them is going to depend on
> > where you have the release slider set -- have it set for the longest
> > release time and you'll have 30V across all those 25V tantalum caps.
>
> Hmmmm.
>
> I'm not quite sure that this is 100% how it works.
>
> The +15V are the "Sustain Reference"; this is not what is going directly to
> the sustain buss. This is (as far as I can see) the voltage passed to the
> string control board; and the release slider then sends only part of it
> back.
>
> Indeed the 0V for short release is an error that is also to be found on the
> lower voicing board. However the schematic for the string control board
> gives those figures: long release -15V, short release +8V.
> This is also the way it is printed on the schematic for the voice boards of
> the Omni-2.
>
> So the voltage difference would be 23V max which is pretty close to the 25V
> rating of the caps but nominally still within tolerance
>
> If I'm making any mistakes here please point them out; as I said I'm still
> learning this stuff.

I could be mistaken about that -- my recollection is a bit fuzzy,  and I don't 
have my printed schematics at hand,  the electronic versions I was looking at 
onscreen being a less-than-optimum substitute (as in better than not having 
them).

I heard about this from a gentleman at the ARP factory whose name I 
unfortunately can't remember,  when I was there last -- in 1977!  :-)

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

great! i did print this out and put this with my oscilloscope probe, i
just haven't been into the lab at my school yet! i'll report back here
as soon as i know! thanks again!

-johnny

--- In vintagesynthrepair@...m, Malte Rogacki <gacki@...>
wrote:
>
> There are various things to check.
> 
> First of all, does any signal get to the S/H circuit at all - and
does it
> get through.
> 
> Check pin 3 of A2 (that's the input) and then pin 1 of A2 (that's the
> output of the S/H mixer); of course make sure that the fader for at
least
> one of the S/H sources is up.
> 
> Alternatively you could also just check the "S/H Mixer" modulation
routings
> from the front panel.
> 
> 
> This part verfiees that A2 actually works.
> 
> Next, check if signal enters A3 (pin 3) and if the trigger signal is
there
> (pin 5). I'm assuming the LFO works, right? Set the LFO to trigger
the S/H
> and check if there is the LFO signal at pin 5 of A3.
> 
> 
> -- 
> Malte Rogacki gacki@...
>
----------------------------------------------------------------------------
> "Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason
why you
>  get no sound out of it." (ARP 2600 Owner's Manual)
>
----------------------------------------------------------------------------
>