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#2842212 - 03/16/17 10:57 AM Open ARP Surgery
Markyboard Offline
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Registered: 02/10/01
Posts: 4327
Loc: Springfield, Virginia
Working on Dave Doerfler's String Ensemble this cold/blustery week on the East Coast. The lower 20 keys when assigned one of the mono bass tones (cello, contra-bass) would glide down to the lowest note upon release. Also the lowest key would not trigger its own bass tone which provided a helpful clue. Since all the other sounds worked across the entire keyboard it wasn't looking like a key contact issue. Bunch of intermittent crackling as well.

Guts laid upside down. These bottom boards (trace side showing) are the divider circuits (non-bass), master oscillator and power supply (closest). Also a couple of broken keys needing a little reconstructive surgery later on:


Rear panel boards - bass divider circuit board on the left with the bass circuit next board over:


Trying to trace signals from the key contacts I needed to "expose" more of the hidden boards. This product design is really cool allowing the frames on which the boards are mounted to swing up on hinges:




The frame holding the rear panel boards removed and flipped up for re-work. Contact boards with gold spring contacts ala minimoog now exposed:


The culprit - bad diode (at top) on the bass circuit board:


No problem- we keep many of these around in case of snow storm freak


Putting key back together. Replacements are unavailable thus far.






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KC Island
#2842213 - 03/16/17 10:58 AM Re: Open ARP Surgery [Re: Markyboard]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 4327
Loc: Springfield, Virginia
Back together and working. A little cosmetic tape on re-glued key and switched position to lowest C. Also cleaned switches which seems to have taken care of crackling problem.




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#2842216 - 03/16/17 11:12 AM Re: Open ARP Surgery [Re: Markyboard]
DanL Offline
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Registered: 09/22/05
Posts: 3702
Loc: DE
You are a geek in the most respected way. Dave needs to show up at the next meetup and bring this baby with him!
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#2842222 - 03/16/17 11:31 AM Re: Open ARP Surgery [Re: Markyboard]
Wastrel Offline
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Registered: 05/13/09
Posts: 2213
Loc: Los Angeles
Good for you for keeping the old beast alive. Those are some seriously old looking electronics by today's standards. Back when it was fun and feasible to work on your own stuff. Nice job.
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#2842224 - 03/16/17 11:39 AM Re: Open ARP Surgery [Re: DanL]
Outkaster Offline
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Registered: 02/25/06
Posts: 5393
Loc: Rochester, NY
Surprised replacement keys are not available anywhere?
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#2842227 - 03/16/17 11:54 AM Re: Open ARP Surgery [Re: Outkaster]
Joe Muscara Offline
Triple Secret Banninated
10k Club

Registered: 02/21/05
Posts: 18439
Loc: Heaven, Hell, or Houston
twothumbs

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#2842230 - 03/16/17 12:01 PM Re: Open ARP Surgery [Re: Joe Muscara]
davedoerfler Offline
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Registered: 12/27/12
Posts: 5515
Loc: thin ice
Wow. I'm at work and just saw this thread. I am stunned and humbled.
Have to go. More later. Mark is the man. twothumbs

PianoBanana cheers PianoBanana cheers PianoBanana
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"skating away on the thin ice of the New Day."

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#2842246 - 03/16/17 01:08 PM Re: Open ARP Surgery [Re: davedoerfler]
aronnelson Offline
Gold Member

Registered: 09/04/14
Posts: 573
Was the diode lifted like that or were you removing it?
Good catch!
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Minimoog, Micromoog, Arp Odyssey, Yamaha CS-01, Roland JP-8000, MS2000R, Yamaha VL1, unrealBook for iPad.

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#2842255 - 03/16/17 01:53 PM Re: Open ARP Surgery [Re: aronnelson]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 4327
Loc: Springfield, Virginia
No, that was my aha moment. When I lifted that leg of the diode the bottom key started working and I could see the tone frequency no longer being squelched by -18V or so. I subsequently removed a nearby transistor as it was kind of a 50/50 shot at this point as to which component failed.

OK - tbh I removed 2 transistors - the first one was the wrong one being upside down and all- but don't tell Dave. facepalm grin

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#2842256 - 03/16/17 01:55 PM Re: Open ARP Surgery [Re: Outkaster]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 4327
Loc: Springfield, Virginia
Originally Posted By: Outkaster
Surprised replacement keys are not available anywhere?


Nah - I came up empty. Syntaur shows "out of stock". I PM-ed a guy on gearslutz who was selling them in 2012 but I doubt that's going to come through.

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#2842257 - 03/16/17 01:57 PM Re: Open ARP Surgery [Re: DanL]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 4327
Loc: Springfield, Virginia
Originally Posted By: DanL
You are a geek in the most respected way.


It's a disease you know:



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#2842274 - 03/16/17 03:06 PM Re: Open ARP Surgery [Re: Markyboard]
aronnelson Offline
Gold Member

Registered: 09/04/14
Posts: 573
> When I lifted that leg of the diode the bottom key started working

I love reading about this stuff! GREAT!
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Minimoog, Micromoog, Arp Odyssey, Yamaha CS-01, Roland JP-8000, MS2000R, Yamaha VL1, unrealBook for iPad.

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#2842280 - 03/16/17 03:25 PM Re: Open ARP Surgery [Re: DanL]
davedoerfler Offline
MP Hall of Fame Member

Registered: 12/27/12
Posts: 5515
Loc: thin ice
Originally Posted By: DanL
Dave needs to show up at the next meetup and bring this baby with him!


The only reason I missed last summer as I wasn't on the Continental USA at the time. Depending when the next hang is it still might be where it is now, damn thing is heavy. laugh
_________________________
"skating away on the thin ice of the New Day."

Jethro Tull

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#2842283 - 03/16/17 03:27 PM Re: Open ARP Surgery [Re: Markyboard]
davedoerfler Offline
MP Hall of Fame Member

Registered: 12/27/12
Posts: 5515
Loc: thin ice
Originally Posted By: Markyboard
Originally Posted By: DanL
You are a geek in the most respected way.


It's a disease you know:

"The Knack".
I don't have it. In fact, in light of these photo's, I have whatever the opposite of "The Knack" is. facepalm
_________________________
"skating away on the thin ice of the New Day."

Jethro Tull

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#2842285 - 03/16/17 03:37 PM Re: Open ARP Surgery [Re: Markyboard]
ITGITC? Offline
Grand Poobah of Posting
10k Club

Registered: 12/18/02
Posts: 17397
Originally Posted By: Markyboard
No, that was my aha moment. When I lifted that leg of the diode the bottom key started working and I could see the tone frequency no longer being squelched by -18V or so. I subsequently removed a nearby transistor as it was kind of a 50/50 shot at this point as to which component failed.

OK - tbh I removed 2 transistors - the first one was the wrong one being upside down and all- but don't tell Dave. facepalm grin



markyboard you my heeeeeeerow cool

How 'bout a brewski?
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#2842287 - 03/16/17 03:49 PM Re: Open ARP Surgery [Re: ITGITC?]
davedoerfler Offline
MP Hall of Fame Member

Registered: 12/27/12
Posts: 5515
Loc: thin ice
Originally Posted By: ITGITC?


markyboard you my heeeeeeerow cool

How 'bout a brewski?



He likes IPA's. wink
Don't I know it. laugh
_________________________
"skating away on the thin ice of the New Day."

Jethro Tull

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#2842301 - 03/16/17 05:10 PM Re: Open ARP Surgery [Re: davedoerfler]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 4327
Loc: Springfield, Virginia
Gentlemen...


Oh, and as Dr Bryce enlightened me about toasting a couple of weeks ago....


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#2842305 - 03/16/17 05:18 PM Re: Open ARP Surgery [Re: Markyboard]
davedoerfler Offline
MP Hall of Fame Member

Registered: 12/27/12
Posts: 5515
Loc: thin ice
Originally Posted By: Markyboard

Oh, and as Dr Bryce enlightened me about toasting a couple of weeks ago....


This is true. I was there also. cool
_________________________
"skating away on the thin ice of the New Day."

Jethro Tull

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#2842307 - 03/16/17 05:23 PM Re: Open ARP Surgery [Re: Markyboard]
Michael Wright Offline
MP Hall of Fame Member

Registered: 01/05/12
Posts: 2487
Originally Posted By: Markyboard

Oh, and as Dr Bryce enlightened me about toasting a couple of weeks ago....
Not long.
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#2843220 - 03/20/17 05:12 PM Re: Open ARP Surgery [Re: Markyboard]
davedoerfler Offline
MP Hall of Fame Member

Registered: 12/27/12
Posts: 5515
Loc: thin ice
Originally Posted By: Markyboard
Back together and working. A little cosmetic tape on re-glued key and switched position to lowest C. Also cleaned switches which seems to have taken care of crackling problem.


Picked up my keyboard today. It has never sounded so good. Of course through Mark's speaker system it will never sound as good at my crib. Big shout out to brother Markyboard for keeping the old Moog's and ARP's alive. It's a labor of love and we at KC are lucky to have guys like this in our midst. cheers
_________________________
"skating away on the thin ice of the New Day."

Jethro Tull

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#2843235 - 03/20/17 06:39 PM Re: Open ARP Surgery [Re: davedoerfler]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 4327
Loc: Springfield, Virginia
Originally Posted By: davedoerfler
It's a labor of love and we at KC are lucky to have guys like this in our midst. cheers


Thanks Dave. Speaking of which... after telling you I may have heard the last from Heinz (a much respected tech/engineer) I just received this email from him.

After a long time being out of business I'm back in life again.
Mr. Murphy showed me his laws can come true, it's a long story.
Now I've a final solution for the MM supply.
So I need your adress again for sending you an additional print, which solves the overload problem of the +15V supply.


As small a group as we are on this forum I suspect the true vintage synth tech/engineers types on this planet are way smaller in numbers. And as also discussed we just lost 3 of the best over the last few years that I know about. Needless to say I'm ecstatic to find out it wasn't 4.

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#2843249 - 03/20/17 07:30 PM Re: Open ARP Surgery [Re: Markyboard]
davedoerfler Offline
MP Hall of Fame Member

Registered: 12/27/12
Posts: 5515
Loc: thin ice
Originally Posted By: Markyboard
as also discussed we just lost 3 of the best over the last few years that I know about. Needless to say I'm ecstatic to find out it wasn't 4.


Excellent news, indeed. twothumbs
_________________________
"skating away on the thin ice of the New Day."

Jethro Tull

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#2843312 - 03/20/17 11:23 PM Re: Open ARP Surgery [Re: davedoerfler]
Barryjam Offline
Senior Member

Registered: 10/03/05
Posts: 147
Loc: Auburn, Northern CA
One of my tech heros is slipping badly. He sorta knows it. I'll leave it at that.
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Barry

Home: Steinway L, Bob Schleicher A100 chop, 142 Leslie.

Gigs: Yamaha CP4, Nord Electro 4D 61, Ventilator II. Sound System: A&H QUsb mixer, Crown & QSC amps, JBL SRX-700 speakers

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#2843348 - 03/21/17 05:43 AM Re: Open ARP Surgery [Re: Barryjam]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 4327
Loc: Springfield, Virginia
Very sorry to hear that Barry.

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#2843356 - 03/21/17 06:22 AM Re: Open ARP Surgery [Re: Markyboard]
Mike Martin Offline
MP Hall of Fame Member

Registered: 01/10/01
Posts: 2972
Loc: Naperville, Ilinois
Wow Mark, I'm blown away! Great job!!!

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#2843363 - 03/21/17 06:41 AM Re: Open ARP Surgery [Re: Mike Martin]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 4327
Loc: Springfield, Virginia
Thank you Mike!

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