Vintage Synth Repair

Hi, new to the list. I have two questions pertaining to an ARP Axxe

1) It seems to me that the CV Memory needs alignment or repair. If a
note is depressed and released, the pitch slowly climbs. If the key is
depressed and held, the pitch remains constant.

2) When a key is released, occasionally the note will release and
sound again. I've yet to look at how the keyboard functions, the
schematics show a switch, but I am not sure how the switching was
implemented.


Any help and guidance would be fantastic!

Thanks,

Mike Hunter
http://www.ombient.com

--- In vintagesynthrepair@yahoogroups.com, "thainmlh" <mike.hunter@...> wrote:
>
> Hi, new to the list. I have two questions pertaining to an ARP Axxe
> 
> 1) It seems to me that the CV Memory needs alignment or repair. If a
> note is depressed and released, the pitch slowly climbs. If the key is
> depressed and held, the pitch remains constant.
> 
You can try cleaning the circuit board top and bottom around the CV memory circuit, from 
memory it is a very high impedence circuit with a single FET and a dual FET and discharge 
capacitor, so if ther is contamination on the board, particularly in humid weather, there could 
be leakage. As this is a sample and hold circuit it needs to be leak free. 

Otherwise you would be looking at  (depending on which version Axxe you have) C13, Q5 or 
Q6.

I have posted the service manual on my downloads page at
http://www.paintingwithsound.co.nz/downloads.htm. Look for the section
"Keyboard Control Voltage Memory". Because the note is climbing I
would look at Q6 first as it is probably leaking current into the
sampling cap c13. Regards



--- In vintagesynthrepair@yahoogroups.com, "thirteentech"
<thirteentech@...> wrote:
>
> --- In vintagesynthrepair@yahoogroups.com, "thainmlh" <mike.hunter@>
wrote:
> >
> > Hi, new to the list. I have two questions pertaining to an ARP Axxe
> > 
> > 1) It seems to me that the CV Memory needs alignment or repair. If a
> > note is depressed and released, the pitch slowly climbs. If the key is
> > depressed and held, the pitch remains constant.
> > 
> You can try cleaning the circuit board top and bottom around the CV
memory circuit, from 
> memory it is a very high impedence circuit with a single FET and a
dual FET and discharge 
> capacitor, so if ther is contamination on the board, particularly in
humid weather, there could 
> be leakage. As this is a sample and hold circuit it needs to be leak
free. 
> 
> Otherwise you would be looking at  (depending on which version Axxe
you have) C13, Q5 or 
> Q6.
>

Thank's to paintingwith sound and thirteentech! Sounds like excellent leads
to follow..will do!

 

Mike Hunter

mike.hunter@...

Web Sites:

http://www.brainstatik.com

http://www.ombient.com

http://www.mayakara.net

 

 

 

  _____  

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of paintingwithsound
Sent: Tuesday, July 15, 2008 6:59 PM
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re: Arp Axxe - CV Memory problem - De-Bounce
Keyboard?

 

I have posted the service manual on my downloads page at
http://www.painting <http://www.paintingwithsound.co.nz/downloads.htm.>
withsound.co.nz/downloads.htm. Look for the section
"Keyboard Control Voltage Memory". Because the note is climbing I
would look at Q6 first as it is probably leaking current into the
sampling cap c13. Regards

--- In vintagesynthrepair@ <mailto:vintagesynthrepair%40yahoogroups.com>
yahoogroups.com, "thirteentech"
<thirteentech@...> wrote:
>
> --- In vintagesynthrepair@ <mailto:vintagesynthrepair%40yahoogroups.com>
yahoogroups.com, "thainmlh" <mike.hunter@>
wrote:
> >
> > Hi, new to the list. I have two questions pertaining to an ARP Axxe
> > 
> > 1) It seems to me that the CV Memory needs alignment or repair. If a
> > note is depressed and released, the pitch slowly climbs. If the key is
> > depressed and held, the pitch remains constant.
> > 
> You can try cleaning the circuit board top and bottom around the CV
memory circuit, from 
> memory it is a very high impedence circuit with a single FET and a
dual FET and discharge 
> capacitor, so if ther is contamination on the board, particularly in
humid weather, there could 
> be leakage. As this is a sample and hold circuit it needs to be leak
free. 
> 
> Otherwise you would be looking at (depending on which version Axxe
you have) C13, Q5 or 
> Q6.
>

I had a similar issue w/ an Axxe. It turned out to be a broken around  
trace on the sampling cap mentioned below.

Quoting paintingwithsound <cfmh@...>:

> I have posted the service manual on my downloads page at
> http://www.paintingwithsound.co.nz/downloads.htm. Look for the section
> "Keyboard Control Voltage Memory". Because the note is climbing I
> would look at Q6 first as it is probably leaking current into the
> sampling cap c13. Regards
>

Well, cleaning the CV Memory section of the board seems to licked the
problem.high impedance indeed!

 

Cleaned the keyboard contacts (what a clever, yet archaic mechanism) and
licked that problem as well.

 

 

Thanks again for the suggestions! The Axxe works like a charm now!

 

Mike Hunter

mike.hunter@...

Web Sites:

http://www.brainstatik.com

http://www.ombient.com

http://www.mayakara.net

 

 

 

  _____  

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Mike Hunter
Sent: Tuesday, July 15, 2008 8:00 PM
To: vintagesynthrepair@yahoogroups.com
Subject: RE: [vintagesynthrepair] Re: Arp Axxe - CV Memory problem -
De-Bounce Keyboard?

 

Thank's to paintingwith sound and thirteentech! Sounds like excellent leads
to follow..will do!

 

Mike Hunter

mike.hunter@ <mailto:mike.hunter@...> verizon.net

Web Sites:

http://www.brainsta <http://www.brainstatik.com> tik.com

http://www.ombient. <http://www.ombient.com> com

http://www.mayakara <http://www.mayakara.net> .net

 

 

 

  _____  

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of paintingwithsound
Sent: Tuesday, July 15, 2008 6:59 PM
To: vintagesynthrepair@yahoogroups.com
Subject: [vintagesynthrepair] Re: Arp Axxe - CV Memory problem - De-Bounce
Keyboard?

 

I have posted the service manual on my downloads page at
http://www.painting <http://www.paintingwithsound.co.nz/downloads.htm.>
withsound.co.nz/downloads.htm. Look for the section
"Keyboard Control Voltage Memory". Because the note is climbing I
would look at Q6 first as it is probably leaking current into the
sampling cap c13. Regards

--- In vintagesynthrepair@ <mailto:vintagesynthrepair%40yahoogroups.com>
yahoogroups.com, "thirteentech"
<thirteentech@...> wrote:
>
> --- In vintagesynthrepair@ <mailto:vintagesynthrepair%40yahoogroups.com>
yahoogroups.com, "thainmlh" <mike.hunter@>
wrote:
> >
> > Hi, new to the list. I have two questions pertaining to an ARP Axxe
> > 
> > 1) It seems to me that the CV Memory needs alignment or repair. If a
> > note is depressed and released, the pitch slowly climbs. If the key is
> > depressed and held, the pitch remains constant.
> > 
> You can try cleaning the circuit board top and bottom around the CV
memory circuit, from 
> memory it is a very high impedence circuit with a single FET and a
dual FET and discharge 
> capacitor, so if ther is contamination on the board, particularly in
humid weather, there could 
> be leakage. As this is a sample and hold circuit it needs to be leak
free. 
> 
> Otherwise you would be looking at (depending on which version Axxe
you have) C13, Q5 or 
> Q6.
>

On Tuesday 15 July 2008 16:20, thainmlh wrote:
> Hi, new to the list. I have two questions pertaining to an ARP Axxe
>
> 1) It seems to me that the CV Memory needs alignment or repair. If a
> note is depressed and released, the pitch slowly climbs. If the key is
> depressed and held, the pitch remains constant.

I've hit that one before,  but can't recall just what it was.  Bad op amp 
someplace?  Trace your CV through the circuit,  back,  until you find 
something funny.

> 2) When a key is released, occasionally the note will release and
> sound again. I've yet to look at how the keyboard functions, the
> schematics show a switch, but I am not sure how the switching was
> implemented.

The ARP keyboards used two contacts (some of the early stuff used three),  one 
to determine the CV and the other to generate gate and trigger signals.  Look 
at the relative timing of these when you press a key -- which one makes 
contact first?  Scope your gate and trigger signals,  if you have a scope.

-- 
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

On Thursday 17 July 2008 11:22, Mike Hunter wrote:
> Well, cleaning the CV Memory section of the board seems to licked the
> problem.high impedance indeed!

Oh yeah!  They told me at the factory (when I was there in 1977 :-) that 
they'd originally tried to make those boards with a coating on them but that 
too much moisture and other contaminants were retained,  and it created all 
sorts of problems...

> Cleaned the keyboard contacts (what a clever, yet archaic mechanism) and
> licked that problem as well.

Cool.

-- 
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

--- In vintagesynthrepair@yahoogroups.com, "thainmlh" <mike.hunter@...> wrote:
>
> Hi, new to the list. I have two questions pertaining to an ARP Axxe
> 
> 1) It seems to me that the CV Memory needs alignment or repair. If a
> note is depressed and released, the pitch slowly climbs. If the key is
> depressed and held, the pitch remains constant.
> 
> Any help and guidance would be fantastic!
> 


Thoroughly  clean the PCB top and bottom around the FETs and CV memory capacitor in the 
control voltage memory circuit section. This is a high impedance circuit and any dust, 
c.smoke or other contaminants will cause CV leakage.