OBERHEIM SYNTH

Having an odd issue with my OBX-a's pitch bend. When wide pitch selected, the voices seem to get wobbly and some voices fail, a tap on the paddle induces pitch instability. It's also not returning to pitch and is about a 1/2 step off. The center position on the wide setting seems to be very sensitive even after cleaning the pot. Narrow is perfect, no issues and no hint of instability.

Didn't dig in too deep. Just cracked open the J type 10K pot and cleaned it up (DeOxit) and re-soldered all connections on the pitch bend pot. No improvement on the wide setting. I have a NOS J type pot on order as a start.

Is there anything else in the pitch bend circuit that I should look at in addition to replacing the pot. I'll be getting into this over the weekend but I figured somebody might have seen this in the past.

James

at the other end of that wire harness there's probably a confused or dac or cv input point to the cpu.

not familiar enough to say for sure.  definitely reseat the connectors and clean them too at the main board end.

my ob8 has all kinds of funky quirks that are due to the board connectors inside being old.


z
 
NEW ALLIANCE EAST!!!!

--------------------------------------


New Alliance East - Mastering

New Alliance East - Facebook

X :::: B :::: S





On Friday, November 8, 2013 8:08 AM, FL_799 <fl_799@...> wrote:
 
  
Having an odd issue with my OBX-a's pitch bend. When wide pitch selected, the voices seem to get wobbly and some voices fail, a tap on the paddle induces pitch instability. It's also not returning to pitch and is about a 1/2 step off. The center position on the wide setting seems to be very sensitive even after cleaning the pot. Narrow is perfect, no issues and no hint of instability.

Didn't dig in too deep. Just cracked open the J type 10K pot and cleaned it up (DeOxit) and re-soldered all connections on the pitch bend pot. No improvement on the wide setting. I have a NOS J type pot on order as a start.

Is there anything else in the pitch bend circuit that I should look at in addition to replacing the pot. I'll be getting into this over the weekend but I figured somebody might have seen this in the past.

James

Thanks Nick, 

It's looking like it might a combination of a few small things. The pot is certainly suspect especially the resistance near center. 

Cleaned all of the connections this morning, cleaned the pitch pot (again), cleaned the feet of IC8, replaced that last three original elna caps in the synth on the mod/pitch board and 'exercised'/cleaned the pitch trim pots. It is almost 'right'. Might replace the trim pots anyway. Everything calibrated fine but unless I let the paddle pull itself back to zero, it still returns several cents sharp or flat when set for wide bend.  More stable then before and usable just as it sits. Needs a bit more center 'dead band' since the center is still very sensitive. I don't remember if this is normal or if I never noticed this in years past but I recall seeing a dead band resistor mod for this issue on another board when using a modern Honeywell/clarostat replacement pot.

The NOS AB 10K J type pot should be in next week, it should improve things a bit more. Hope this helps out somebody since a problem in this section can throw off an otherwise working Oberheim. 

James






On Friday, November 8, 2013 11:49 AM, Nick Zampiello <newallianceeast@...> wrote:
 
  
at the other end of that wire harness there's probably a confused or dac or cv input point to the cpu.

not familiar enough to say for sure.  definitely reseat the connectors and clean them too at the main board end.

my ob8 has all kinds of funky quirks that are due to the board connectors inside being old.


z
 
NEW ALLIANCE EAST!!!!

--------------------------------------


New Alliance East - Mastering

New Alliance East - Facebook

X :::: B :::: S





On Friday, November 8, 2013 8:08 AM, FL_799 <fl_799@...> wrote:
 
  
Having an odd issue with my OBX-a's pitch bend. When wide pitch selected, the voices seem to get wobbly and some voices fail, a tap on the paddle induces pitch instability. It's also not returning to pitch and is about a 1/2 step off. The center position on the wide setting seems to be very sensitive even after cleaning the pot. Narrow is perfect, no issues and no hint of instability.

Didn't dig in too deep. Just cracked open the J type 10K pot and cleaned it up (DeOxit) and re-soldered all connections on the pitch bend pot. No improvement on the wide setting. I have a NOS J type pot on order as a start.

Is there anything else in the pitch bend circuit that I should look at in addition to replacing the pot. I'll be getting into this over the weekend but I figured somebody might have seen this in the past.

James

>>  I recall seeing a dead band resistor mod for this issue on another board when using a modern Honeywell/clarostat replacement pot.

That was me. I'll see if I can find my notes over the next day or so.

Hi All,

I have an OBXa in for repair that has that mod. It is two diodes (1N914 or similar) in parallel (opposing polarities) connected to the pot wiper. The wire that was connected to the pot wiper is then connected to other end of the diodes and this junction also has a 100k resistor to GND.

regards,
rob.

On 12 Nov 2013, at 12:27, 65 Lotus <Lotus@...> wrote:

> 
> 
> >>  I recall seeing a dead band resistor mod for this issue on another board when using a modern Honeywell/clarostat replacement pot.
>  
> That was me. I'll see if I can find my notes over the next day or so.
> 
>

I have fixed this issue on multiple Oberheims. The deadband mod is not a good solution. The real problem is mechanical and oftentimes is two fold. The first issue is that the sealed pot used has got carbon powder built up inside on both sides of the wiper. The pot needs to be opened and cleaned or simply replaced. This will clean up most of the slop, however, the spring loaded pitch bender mechanism has two metal arms inside that are attached to a spring. These arms are supposed to hold the lever perfectly snug in the center position, but many times, one arm is slightly bigger than the other and needs to be filed down slightly where the arm hits the detent. You need to shave the arm very slightly so the detent can't wiggle between the two spring loaded arms. When you get it right, there will be no slop and no need for the deadband circuit (which doesn't actually work properly anyway). This has solved the problem in 100% of the oberheims I have fixed that suffered from the pitch bender not returning to exact center. This takes me about 3 or 4 hours to do, and I have done it many times. I would expect a first timer to take a couple of hpurs more. Definitely not a quick and easy fix, but worth it when done right.

-Rob Currier

www.NewEnglandAnalog.com

207-703-2350

Hi Rob and All,

Indeed, I did end up removing the (extra) deadband mod. The existing deadband circuit works fine as long as U8 is trimmed for 0V. The problem is that any offset at the NARROW switch (U14) - noticeable by a slight change in pitch when it is engaged - is trimmed by the CENTRE LEVER trimmer, which inevitably moves the bender out of the deadband range. I didn’t find a way out of this problem, but it seemed I was the only one concerned (not the client). I had stripped, cleaned and relubed the pitch bend pot but I shall also pay attention the the spring mechanism next time - although there was no noticeable slop…

rob.

On 19 Nov 2013, at 17:16, robiecurrier@... wrote:

> 
> I have fixed this issue on multiple Oberheims.  The deadband mod is not a good solution.  The real problem is mechanical and oftentimes is two fold.  The first issue is that the sealed pot used has got carbon powder built up inside on both sides of the wiper.  The pot needs to be opened and cleaned or simply replaced.  This will clean up most of the slop, however, the spring loaded pitch bender mechanism has two metal arms inside that are attached to a spring.   These arms are supposed to hold the lever perfectly snug in the center position, but many times, one arm is slightly bigger than the other and needs to be filed down slightly where the arm hits the detent.  You need to shave the arm very slightly so the detent can't wiggle between the two spring loaded arms.  When you get it right, there will be no slop and no need for the deadband circuit (which doesn't actually work properly anyway).  This has solved the problem in 100% of the oberheims I have fixed that suffered from the pitch bender not returning to exact center.  This takes me about 3 or 4 hours to do, and I have done it many times.  I would expect a first timer to take a couple of hpurs more.  Definitely not a quick and easy fix, but worth it when done right.  
> 
> -Rob Currier
> 
> 
> 
> www.NewEnglandAnalog.com
> 
> 207-703-2350
> 
> 
> 
> 
> 
> ---In oberheim@yahoogroups.com, <robhukin@...> wrote:
> 
> Hi All,
> 
> I have an OBXa in for repair that has that mod. It is two diodes (1N914 or similar) in parallel (opposing polarities) connected to the pot wiper. The wire that was connected to the pot wiper is then connected to other end of the diodes and this junction also has a 100k resistor to GND.
> 
> regards,
> rob.
> 
> On 12 Nov 2013, at 12:27, 65 Lotus <Lotus@...> wrote:
> 
>> 
>> 
>> >>  I recall seeing a dead band resistor mod for this issue on another board when using a modern Honeywell/clarostat replacement pot.
>>  
>> That was me. I'll see if I can find my notes over the next day or so.
>> 
> 
> 
>

The slop is really slight and it usually takes me a few tries to get it perfect. Did you replace the pot or clean it? If it isn't a new one, there can be a spot where the carbon is worn away, which would point toward just replacing the pot. If the pot is a replacement, the mechanism that attaches to the pot shaft has to be tightened at the exact right spot, at least that's how it is on the OBX. On the OB8, I'd need to look at the schematic again to know for sure. It sounds like the issue you are experiencing will take some experimentation to get right. Before you get into that, it would be prudent to replace U2 (1458), D1, and D4 just to rule them out as causes. If these don't fix it, then it's probably wise to check out the mechanicals.

-Rob

And, it helps to tug on the pot shaft slightly when tightening in order to preload the wiper against the carbon trace. This got rid of the last little bit of "return to zero" slop in the new-manufacture replacement pot on my OB-Xa.

  ----- Original Message ----- 
  From: robiecurrier@... 
  To: oberheim@yahoogroups.com 
  Sent: Thursday, November 21, 2013 5:01 PM
  Subject: RE: Re: [oberheim] Oberheim OBX-a pitch bend issue





  The slop is really slight and it usually takes me a few tries to get it perfect. Did you replace the pot or clean it?  If it isn't a new one, there can be a spot where the carbon is worn away, which would point toward just replacing the pot.  If the pot is a replacement, the mechanism that attaches to the pot shaft has to be tightened at the exact right spot, at least that's how it is on the OBX.  On the OB8, I'd need to look at the schematic again to know for sure.  It sounds like the issue you are experiencing will take some experimentation to get right.  Before you get into that, it would be prudent to replace U2 (1458), D1, and D4 just to rule them out as causes.  If these don't fix it, then it's probably wise to check out the mechanicals.  

  -Rob



  ---In oberheim@yahoogroups.com, <robhukin@...> wrote:


  Hi Rob and All,


  Indeed, I did end up removing the (extra) deadband mod. The existing deadband circuit works fine as long as U8 is trimmed for 0V. The problem is that any offset at the NARROW switch (U14) - noticeable by a slight change in pitch when it is engaged - is trimmed by the CENTRE LEVER trimmer, which inevitably moves the bender out of the deadband range. I didn’t find a way out of this problem, but it seemed I was the only one concerned (not the client). I had stripped, cleaned and relubed the pitch bend pot but I shall also pay attention the the spring mechanism next time - although there was no noticeable slop…


  rob.


  On 19 Nov 2013, at 17:16, robiecurrier@... wrote:




      I have fixed this issue on multiple Oberheims.  The deadband mod is not a good solution.  The real problem is mechanical and oftentimes is two fold.  The first issue is that the sealed pot used has got carbon powder built up inside on both sides of the wiper.  The pot needs to be opened and cleaned or simply replaced.  This will clean up most of the slop, however, the spring loaded pitch bender mechanism has two metal arms inside that are attached to a spring.   These arms are supposed to hold the lever perfectly snug in the center position, but many times, one arm is slightly bigger than the other and needs to be filed down slightly where the arm hits the detent.  You need to shave the arm very slightly so the detent can't wiggle between the two spring loaded arms.  When you get it right, there will be no slop and no need for the deadband circuit (which doesn't actually work properly anyway).  This has solved the problem in 100% of the oberheims I have fixed that suffered from the pitch bender not returning to exact center.  This takes me about 3 or 4 hours to do, and I have done it many times.  I would expect a first timer to take a couple of hpurs more.  Definitely not a quick and easy fix, but worth it when done right.  

      -Rob Currier




      www.NewEnglandAnalog.com

      207-703-2350






      ---In oberheim@yahoogroups.com, <robhukin@...> wrote:


      Hi All,


      I have an OBXa in for repair that has that mod. It is two diodes (1N914 or similar) in parallel (opposing polarities) connected to the pot wiper. The wire that was connected to the pot wiper is then connected to other end of the diodes and this junction also has a 100k resistor to GND.


      regards,
      rob.


      On 12 Nov 2013, at 12:27, 65 Lotus <Lotus@...> wrote:


          

          >>  I recall seeing a dead band resistor mod for this issue on another board when using a modern Honeywell/clarostat replacement pot.

          That was me. I'll see if I can find my notes over the next day or so.

I resolved my pitch bend issue. It was just a glitchy pitch bend pot and cleaning the pot would not clear the dead-band sensitivity.  Sourced a NOS AB J type 10K and everything is perfect as taper can be slightly different on the modern replacements. I agree that the pot shaft collar and return spring mechanism needs to be setup tight but enough clearance to run as friction free as possible.  Dead band and tuning on both narrow and wide is spot on.

James





On Friday, November 22, 2013 7:09 AM, 65 Lotus <Lotus@...> wrote:
 
  
 
And, it helps to tug on the pot shaft slightly when 
tightening in order to preload the wiper against the carbon trace. This got rid 
of the last little bit of "return to zero" slop in the new-manufacture 
replacement pot on my OB-Xa.
----- Original Message ----- 
>From: robiecurrier@... 
>To: oberheim@yahoogroups.com 
>Sent: Thursday, November 21, 2013 5:01  PM
>Subject: RE: Re: [oberheim] Oberheim  OBX-a pitch bend issue
>
>
>The slop is really slight and it usually takes me a few tries to get it  perfect. Did you replace the pot or clean it?  If it isn't a new one,  there can be a spot where the carbon is worn away, which would point toward  just replacing the pot.  If the pot is a replacement, the mechanism that  attaches to the pot shaft has to be tightened at the exact right spot, at  least that's how it is on the OBX.  On the OB8, I'd need to look at the  schematic again to know for sure.  It sounds like the issue you are  experiencing will take some experimentation to get right.  Before you get  into that, it would be prudent to replace U2 (1458), D1, and D4 just to rule  them out as causes.  If these don't fix it, then it's probably wise to  check out the mechanicals.  
>-Rob
>
>
>---In oberheim@yahoogroups.com, 
  <robhukin@...> wrote:
>
>
>Hi Rob and All, 
>
>
>Indeed, I did end up removing the (extra) deadband mod. The existing  deadband circuit works fine as long as U8 is trimmed for 0V. The problem is  that any offset at the NARROW switch (U14) - noticeable by a slight change in  pitch when it is engaged - is trimmed by the CENTRE LEVER trimmer, which  inevitably moves the bender out of the deadband range. I didn’t find a way out  of this problem, but it seemed I was the only one concerned (not the client).  I had stripped, cleaned and relubed the pitch bend pot but I shall also pay  attention the the spring mechanism next time - although there was no  noticeable slop…
>
>
>rob.
>
>
>On 19 Nov 2013, at 17:16, robiecurrier@... wrote:
>
>
>>>
>>>I have fixed this  issue on multiple Oberheims.  The deadband mod is not a good  solution.  The real problem is mechanical and oftentimes is two fold.   The first issue is that the sealed pot used has got carbon powder  built up inside on both sides of the wiper.  The pot needs to be  opened and cleaned or simply replaced.  This will clean up most of  the slop, however, the spring loaded pitch bender mechanism has two metal  arms inside that are attached to a spring.   These arms are supposed  to hold the lever perfectly snug in the center position, but many times,  one arm is slightly bigger than the other and needs to be filed down  slightly where the arm hits the detent.  You need to shave the arm  very slightly so the detent can't wiggle between the two spring loaded  arms.  When you get it right, there will be no slop and no need for  the deadband circuit (which doesn't actually work properly anyway).   This has solved the problem in
 100% of the oberheims I have fixed  that suffered from the pitch bender not returning to exact center.   This takes me about 3 or 4 hours to do, and I have done it many  times.  I would expect a first timer to take a couple of hpurs more.   Definitely not a quick and easy fix, but worth it when done right.   

>>>-Rob Currier
>>>
>>>
>>>www.NewEnglandAnalog.com
>>>207-703-2350
>>>
>>>
>>>
>>>
>>>---In oberheim@yahoogroups.com,  <robhukin@...> wrote:
>>>
>>>
>>>Hi All, 
>>>
>>>
>>>I have an OBXa in for repair that has  that mod. It is two diodes (1N914 or similar) in parallel (opposing  polarities) connected to the pot wiper. The wire that was connected to the  pot wiper is then connected to other end of the diodes and this junction  also has a 100k resistor to GND.
>>>
>>>
>>>regards,
>>>rob.
>>>
>>>
>>>On 12 Nov 2013, at 12:27, 65 Lotus <Lotus@...> wrote:
>>>
>>>
>>>>>>>  I  recall seeing a dead band resistor mod for this issue on another board  when using a modern Honeywell/clarostat replacement  pot.
>>>>> 
>>>>>That was  me. I'll see if I can find my notes over the next day or  so.
>>>>>
>>>>>
>>>
>>>
>>>
>

Hi James:

If you don't mind, where did you find a NOS OB-Xa pitch bend pot?  Wouldn't mind having one to return mine to stock configuration.

And what I really need if anyone has one is a NOS Depth pot (just above and to the right of the pitch bend lever). It's got lots of problems with the wiper and the push/pull function. 

A new one of those and the old girl would be 100%!

Scott

  ----- Original Message ----- 
  From: James 
  To: oberheim@yahoogroups.com 
  Sent: Friday, November 22, 2013 10:06 AM
  Subject: Re: Re: [oberheim] Oberheim OBX-a pitch bend issue





  I resolved my pitch bend issue. It was just a glitchy pitch bend pot and cleaning the pot would not clear the dead-band sensitivity.  Sourced a NOS AB J type 10K and everything is perfect as taper can be slightly different on the modern replacements. I agree that the pot shaft collar and return spring mechanism needs to be setup tight but enough clearance to run as friction free as possible.  Dead band and tuning on both narrow and wide is spot on.

  James






  On Friday, November 22, 2013 7:09 AM, 65 Lotus <Lotus@...> wrote:

    
   
  And, it helps to tug on the pot shaft slightly when tightening in order to preload the wiper against the carbon trace. This got rid of the last little bit of "return to zero" slop in the new-manufacture replacement pot on my OB-Xa.
    ----- Original Message ----- 
    From: robiecurrier@... 
    To: oberheim@yahoogroups.com 
    Sent: Thursday, November 21, 2013 5:01 PM
    Subject: RE: Re: [oberheim] Oberheim OBX-a pitch bend issue


    The slop is really slight and it usually takes me a few tries to get it perfect. Did you replace the pot or clean it?  If it isn't a new one, there can be a spot where the carbon is worn away, which would point toward just replacing the pot.  If the pot is a replacement, the mechanism that attaches to the pot shaft has to be tightened at the exact right spot, at least that's how it is on the OBX.  On the OB8, I'd need to look at the schematic again to know for sure.  It sounds like the issue you are experiencing will take some experimentation to get right.  Before you get into that, it would be prudent to replace U2 (1458), D1, and D4 just to rule them out as causes.  If these don't fix it, then it's probably wise to check out the mechanicals.  
    -Rob


    ---In oberheim@yahoogroups.com, <robhukin@...> wrote:


    Hi Rob and All, 


    Indeed, I did end up removing the (extra) deadband mod. The existing deadband circuit works fine as long as U8 is trimmed for 0V. The problem is that any offset at the NARROW switch (U14) - noticeable by a slight change in pitch when it is engaged - is trimmed by the CENTRE LEVER trimmer, which inevitably moves the bender out of the deadband range. I didn’t find a way out of this problem, but it seemed I was the only one concerned (not the client). I had stripped, cleaned and relubed the pitch bend pot but I shall also pay attention the the spring mechanism next time - although there was no noticeable slop…


    rob.


    On 19 Nov 2013, at 17:16, robiecurrier@... wrote:




        I have fixed this issue on multiple Oberheims.  The deadband mod is not a good solution.  The real problem is mechanical and oftentimes is two fold.  The first issue is that the sealed pot used has got carbon powder built up inside on both sides of the wiper.  The pot needs to be opened and cleaned or simply replaced.  This will clean up most of the slop, however, the spring loaded pitch bender mechanism has two metal arms inside that are attached to a spring.   These arms are supposed to hold the lever perfectly snug in the center position, but many times, one arm is slightly bigger than the other and needs to be filed down slightly where the arm hits the detent.  You need to shave the arm very slightly so the detent can't wiggle between the two spring loaded arms.  When you get it right, there will be no slop and no need for the deadband circuit (which doesn't actually work properly anyway).  This has solved the problem in 100% of the oberheims I have fixed that suffered from the pitch bender not returning to exact center.  This takes me about 3 or 4 hours to do, and I have done it many times.  I would expect a first timer to take a couple of hpurs more.  Definitely not a quick and easy fix, but worth it when done right.  
        -Rob Currier


        www.NewEnglandAnalog.com
        207-703-2350




        ---In oberheim@yahoogroups.com, <robhukin@...> wrote:


        Hi All, 


        I have an OBXa in for repair that has that mod. It is two diodes (1N914 or similar) in parallel (opposing polarities) connected to the pot wiper. The wire that was connected to the pot wiper is then connected to other end of the diodes and this junction also has a 100k resistor to GND.


        regards,
        rob.


        On 12 Nov 2013, at 12:27, 65 Lotus <Lotus@...> wrote:


            
            >>  I recall seeing a dead band resistor mod for this issue on another board when using a modern Honeywell/clarostat replacement pot.

            That was me. I'll see if I can find my notes over the next day or so.

Scott, There is one on e-bay right now for $20. Both AB and clarostat marketed the identical pots. Problem solved! Search for 

JA1N200P103UA
Auction below. 

http://www.ebay.com/sch/i.html?_trksid=p2047675.m570.l1313.TR0.TRC0&_nkw=JA1N200P103UA&_sacat=0&_from=R40





On Friday, November 22, 2013 1:30 PM, 65 Lotus <Lotus@...> wrote:
 
  
 
Hi James:
 
If you don't mind, where did you find a NOS OB-Xa 
pitch bend pot?  Wouldn't mind having one to return mine to stock 
configuration.
 
And what I really need if anyone has one is a NOS 
Depth pot (just above and to the right of the pitch bend lever). It's got lots 
of problems with the wiper and the push/pull function. 
 
A new one of those and the old girl would be 
100%!
 
Scott
----- Original Message ----- 
>From: James 
>To: oberheim@yahoogroups.com 
>Sent: Friday, November 22, 2013 10:06  AM
>Subject: Re: Re: [oberheim] Oberheim  OBX-a pitch bend issue
>
>
>I  resolved my pitch bend issue. It was just a glitchy pitch bend pot and  cleaning the pot would not clear the dead-band sensitivity.  Sourced a  NOS AB J type 10K and everything is perfect as taper can be slightly different  on the modern replacements. I agree that the pot shaft collar and return  spring mechanism needs to be setup tight but enough clearance to run as  friction free as possible.  Dead band and tuning on both narrow and wide  is spot on.
>
>James
>
>
>
>
>
>
>On Friday, November 22, 2013 7:09 AM, 65  Lotus <Lotus@...> wrote:
>
>  
> 
>And, it helps to tug on the pot shaft slightly  when tightening in order to preload the wiper against the carbon trace. This  got rid of the last little bit of "return to zero" slop in  the new-manufacture replacement pot on my OB-Xa.
>----- Original Message ----- 
>>From: robiecurrier@... 
>>To: oberheim@yahoogroups.com 
>>Sent: Thursday, November 21, 2013 5:01  PM
>>Subject: RE: Re: [oberheim] Oberheim  OBX-a pitch bend issue
>>
>>
>>The slop is really slight and it usually takes me a few tries to get it  perfect. Did you replace the pot or clean it?  If it isn't a new one,  there can be a spot where the carbon is worn away, which would point toward  just replacing the pot.  If the pot is a replacement, the mechanism  that attaches to the pot shaft has to be tightened at the exact right spot,  at least that's how it is on the OBX.  On the OB8, I'd need to look at  the schematic again to know for sure.  It sounds like the issue you are  experiencing will take some experimentation to get right.  Before you  get into that, it would be prudent to replace U2 (1458), D1, and D4 just to  rule them out as causes.  If these don't fix it, then it's probably  wise to check out the mechanicals.  
>>-Rob
>>
>>
>>---In 
    oberheim@yahoogroups.com, <robhukin@...> wrote:
>>
>>
>>Hi Rob and All, 
>>
>>
>>Indeed, I did end up removing the (extra) deadband mod. The existing  deadband circuit works fine as long as U8 is trimmed for 0V. The problem is  that any offset at the NARROW switch (U14) - noticeable by a slight change  in pitch when it is engaged - is trimmed by the CENTRE LEVER trimmer, which  inevitably moves the bender out of the deadband range. I didn’t find a way  out of this problem, but it seemed I was the only one concerned (not the  client). I had stripped, cleaned and relubed the pitch bend pot but I shall  also pay attention the the spring mechanism next time - although there was  no noticeable slop…
>>
>>
>>rob.
>>
>>
>>On 19 Nov 2013, at 17:16, robiecurrier@... wrote:
>>
>> 
>>>
>>>>
>>>>I have fixed this issue on multiple Oberheims.  The deadband  mod is not a good solution.  The real problem is mechanical and  oftentimes is two fold.  The first issue is that the sealed pot  used has got carbon powder built up inside on both sides of the wiper.   The pot needs to be opened and cleaned or simply replaced.   This will clean up most of the slop, however, the spring loaded  pitch bender mechanism has two metal arms inside that are attached to a  spring.   These arms are supposed to hold the lever perfectly snug  in the center position, but many times, one arm is slightly bigger than  the other and needs to be filed down slightly where the arm hits the  detent.  You need to shave the arm very slightly so the detent  can't wiggle between the two spring loaded arms.  When you get it  right, there will be no slop and no need for the deadband circuit (which  doesn't actually work properly anyway).  This has solved the  problem in
 100% of the oberheims I have fixed that suffered from the  pitch bender not returning to exact center.  This takes me about 3  or 4 hours to do, and I have done it many times.  I would expect a  first timer to take a couple of hpurs more.  Definitely not a quick  and easy fix, but worth it when done right.  

>>>>-Rob Currier
>>>>
>>>>
>>>>www.NewEnglandAnalog.com
>>>>207-703-2350
>>>>
>>>>
>>>>
>>>>
>>>>---In oberheim@yahoogroups.com,  <robhukin@...> wrote:
>>>>
>>>>
>>>>Hi All, 
>>>>
>>>>
>>>>I have an OBXa in for repair that has that mod. It is two diodes  (1N914 or similar) in parallel (opposing polarities) connected to the  pot wiper. The wire that was connected to the pot wiper is then  connected to other end of the diodes and this junction also has a 100k  resistor to GND.
>>>>
>>>>
>>>>regards,
>>>>rob.
>>>>
>>>>
>>>>On 12 Nov 2013, at 12:27, 65 Lotus <Lotus@...> wrote:
>>>>
>>>> 
>>>>>
>>>>>>>>  I  recall seeing a dead band resistor mod for this issue on another  board when using a modern Honeywell/clarostat replacement  pot.
>>>>>> 
>>>>>>That was me. I'll see if I  can find my notes over the next day or so.
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