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Lexicon PCM81 ENCODERS Replacement Special Ef­fects Plugins
Old 19th September 2016
  #1
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italo de angelis's Avatar
 

Lexicon PCM81 ENCODERS Replacement

Hi fellows

my 81 ADJUST encoder went crazy. Turning it clockwise or counter-C-W takes the displayed parameter to its max. value only and locks there.
I tried Lexicon Customer Support but they have no more parts for these units.
So I opened it up. There is a small board with the 2 ADJUST and SELECT encoders mounted on. Removing this small board is pure madness. You can get it loose from the front panel but not off it as it requires removing the whole motherboard. So much for being the 81 "more friendly serviceable" than the PCM80.
I was able to spray some contact cleaner thru it and there was some slightly better behavior but I'm sure it won't last. It needs more love than that.


My question is:
have you ever got a chance to change these encoders yourself?
Hard? Doable?
Do you happen to know which brand and model the encoders are?

The only way to fix these issues at this point in time is DIY job. So... once done, the info will be available to everybody for future reference.

THANK YOU!!!

Attached Thumbnails
Lexicon PCM81 ENCODERS Replacement-encoders-board.jpg  
Old 19th September 2016
  #2
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Radardoug's Avatar
 

I think you will find if you take the front panel off, you can get the encoder board out.
If you look on the Lexicon FTP site you will find the service manual. Lexicon usually had good parts lists in their manuals.
Try this listing, find one that works for you.
http://nz.mouser.com/Passive-Compone...ncoder&FS=True
Old 20th September 2016
  #3
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italo de angelis's Avatar
 

Quote:
Originally Posted by Radardoug View Post
I think you will find if you take the front panel off, you can get the encoder board out.
If you look on the Lexicon FTP site you will find the service manual. Lexicon usually had good parts lists in their manuals.
Try this listing, find one that works for you.
http://nz.mouser.com/Passive-Compone...ncoder&FS=True

Thanks.
I already checked all PCMs service manuals. Not really clear what it says about the encoders:

pcm81 encoder board

202-00514 RES,CF,5%,1/4W,100 OHM 4 R202-205
245-03610 CAP,CER,.01uF,100V,Z5U,AX 4 C200-203
452-09762 SW,RTY,ENCODER,36 POS,VERT MNT 2 SW14,15
680-09764 CABLE,079,SCKT/SCKTRA,6C,2.0" 1 J103
710-09837 PC BD,ENC,PCM80&1/90&1 1

I guess... SW=?, Rotary, 36 positions, vertical mounting SW14,15=???
Attached Thumbnails
Lexicon PCM81 ENCODERS Replacement-encoders-board.png  
Old 20th September 2016
  #4
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Look through that Mouser page I gave you. Its a 36 position mechanical decoder. You want to try and find a mechanical equivalent. It will take some time.
Old 20th September 2016
  #5
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italo de angelis's Avatar
 

Quote:
Originally Posted by Radardoug View Post
Look through that Mouser page I gave you. Its a 36 position mechanical decoder. You want to try and find a mechanical equivalent. It will take some time.
I did and selected MECHANICAL/PCB MOUNT/36 DETENT.
These are the ones that come up:
http://www2.mouser.com/Passive-Compo...ncoder&FS=True

Below is the drawing from the schematics manual.
Attached Thumbnails
Lexicon PCM81 ENCODERS Replacement-encoders.jpg  
Old 20th September 2016
  #6
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JoaT's Avatar
Looks quite similar as the layout in 91. You can get it off by taking the front enclosure off. There's screws you beed to undo from below, so you have to take the bottom cover off as well. After that it should be relatively easy. Don't forget to remove the knobs and loosen the retaining bolts so it comes off.
In my 91 the encoder board wes disassembled when I got the unit. I just soldered it back together and put it back in it's place.
Old 20th September 2016
  #7
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italo de angelis's Avatar
 

Quote:
Originally Posted by JoaT View Post
Looks quite similar as the layout in 91. You can get it off by taking the front enclosure off. There's screws you beed to undo from below, so you have to take the bottom cover off as well. After that it should be relatively easy. Don't forget to remove the knobs and loosen the retaining bolts so it comes off.
In my 91 the encoder board wes disassembled when I got the unit. I just soldered it back together and put it back in it's place.

The encoders board is the same for all PCMs 90/80/91/81.
What do you mean your unit's encoder board was disassembled? It was maybe have been not in place. It doesn't require soldering, unless you mean components were not in place.
Old 20th September 2016
  #8
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Quote:
Originally Posted by italo de angelis View Post
The encoders board is the same for all PCMs 90/80/91/81.
What do you mean your unit's encoder board was disassembled? It was maybe have been not in place. It doesn't require soldering, unless you mean components were not in place.
The previous owner had desoldered the encoder panel on intention of using one encoder as a spare part for something else. He didn't have it in him to put it back together, so I did.

The said unit has a checksum error and I think it is the reason it ended up as a spare parts source.
Old 20th September 2016
  #9
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italo de angelis's Avatar
 

Quote:
Originally Posted by JoaT View Post
The previous owner had desoldered the encoder panel on intention of using one encoder as a spare part for something else. He didn't have it in him to put it back together, so I did.

The said unit has a checksum error and I think it is the reason it ended up as a spare parts source.
Wow!
So you added the missing encoder?
Do you remember what that is?
thanks
Old 20th September 2016
  #10
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sadly, no. Both of them were still available, just needed to solder them back to the board.

As far as I can understand, there's nothing so special about an encoder.
Old 20th September 2016
  #11
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I was able to disassemble the front panel and spray some good contat cleaner into the encoder.
It doesn't expose brand/model. It needs to be desoldered for that.
Anyway... it works fine now.

And...
my PCM80 which had developed a "watery" display... was also fixed. We were able to change the 2 capacitors on the FUTABA display board and it's not working nicely.

Love the PCMs.
Old 20th September 2016
  #12
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As far as I could tell, there was no markings of any kind under the encoder. Best bet would be to use the manual page quoted above to hunt the encoder. Great it started working with just the spray cleaning!
Old 20th September 2016
  #13
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Quote:
Originally Posted by JoaT View Post
As far as I could tell, there was no markings of any kind under the encoder. Best bet would be to use the manual page quoted above to hunt the encoder. Great it started working with just the spray cleaning!
Unfortunately the manual doesn't say WHICH brand/part# is that. Nonsense.
It needs to be desoldered and the back of the encoder will show the info.
Hopefully this will be all it needs....
Looks like an Alps encoder though.
Old 4th January 2018
  #14
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I have contacted the original manufacturer for the Lexicon PCM80 encoder and am contemplating having some manufactured. Would anyone be interested in have a need for some?
Old 4th January 2018
  #15
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italo de angelis's Avatar
 

Quote:
Originally Posted by Hitechavs View Post
I have contacted the original manufacturer for the Lexicon PCM80 encoder and am contemplating having some manufactured. Would anyone be interested in have a need for some?
Who is the manufacturer?

thanks.
Old 4th January 2018
  #16
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Since nobody else has said anything, I guess I'll go ahead and say it; how do we know that it is, in fact, the encoder that is defective and not the chip(s) that are respocible for translating the encoder's signals? Everybody in this thread just simply assumes that the OP's diagnosis is correct - it could be, but it may not be. I never trust anybody who is not a technician with experience in such matters. I've seen many threads run wild with everybody just guessing as to what the problem could be. You should make sure that the encoder is indeed the problem before you order any because the minimum order is probably a couple of thousand.
Old 4th January 2018
  #17
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italo de angelis's Avatar
 

It is the encoder. Definitely...
I swapped a board from another PCM and it worked fine.
Old 4th January 2018
  #18
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What I do on hard to find and unique parts is just go to EBay and try to find a dead unit for spare parts and scrounge them off there.
made out very well on many hard to find parts fixes like that plus there are often knobs and switches and boards perfectly find that can be cannibalized to make one great working unit. if course you have to know what the problem is so you aren't buying a second unit with the same issues.
Old 4th January 2018
  #19
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SP2016's Avatar
Quote:
Originally Posted by italo de angelis View Post
Who is the manufacturer?

thanks.
Lexicon first has used 50 position encoders which were made by ALPS.
These went out of production and Lexicon then used 36 position encoders made by NOBLE.
There has been an official LEXICON service bulletin about that, but I cannot find that anymore.
I only had a note and no further information.
But maybe it is of any help to you.
Old 5th January 2018
  #20
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Couldn't find a service manual WITH the schematics pages.

Is it a basic rotary encoder with single-ended A and B pulses (electrically shifted by 90° to allow CW/CCW discrimination)?

If the encoder is only used as pulse source when turning the button the exact number of pulses per rotation is not critical. There are many manufacturers of small panel-mount rotary encoders for Human Machine Interface uses. It becomes more difficult to find a replacement part if pins are soldered on the PCB. Of course electrical signal compatibility must be checked.
Old 5th January 2018
  #21
PCM 80 Value knob

Ok I can fix a human spine, but not electronics. PCM 80 the value knob just spins. Haven't looked yet but is that likely just a mechanical detent problem? Fixable by me only if minor soldering. All else works fine.
Old 6th January 2018
  #22
Here for the gear
Here's the schematic...an easy replacement if you're handy with some desoldering wick and an iron. Good luck sifting through the many layers of Mouser catalog tho. Easy to get lost in there!

Crazydave, I'll gladly repair your PCM if you repair my spine !!!!!

/Rithma
Attached Thumbnails
Lexicon PCM81 ENCODERS Replacement-lex_pcm_encoder.jpg  
Old 6th January 2018
  #23
Quote:
Originally Posted by rithma View Post
Here's the schematic...an easy replacement if you're handy with some desoldering wick and an iron. Good luck sifting through the many layers of Mouser catalog tho. Easy to get lost in there!

Crazydave, I'll gladly repair your PCM if you repair my spine !!!!!

/Rithma
Thanks rithma I really appreciate it. I'd love to do that barter and would if I could!
Old 18th February 2018
  #24
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researchtriangle's Avatar
 

Quote:
Originally Posted by italo de angelis View Post
I was able to disassemble the front panel and spray some good contat cleaner into the encoder.
It doesn't expose brand/model. It needs to be desoldered for that.
Anyway... it works fine now.

I have the same issue with my encoder! How were you able to correctly spray contact cleaner into the encoder without desoldering from the board? On my PCM81, the encoder clips are soldered to the board. Contact cleaner should be sprayed underneath and insider the encoder, no?
Old 18th February 2018
  #25
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italo de angelis's Avatar
 

Quote:
Originally Posted by researchtriangle View Post
I have the same issue with my encoder! How were you able to correctly spray contact cleaner into the encoder without desoldering from the board? On my PCM81, the encoder clips are soldered to the board. Contact cleaner should be sprayed underneath and insider the encoder, no?
Anywhere you see holes in the encoder assembly. Spray there.
Old 18th February 2018
  #26
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researchtriangle's Avatar
 

Yep, ended up just doing that. Encoder works perfectly now! Awesome. Thanks for this tip.
Old 4 days ago
  #27
Gear Head
Does anyone here have the PCM-81 service manual? Would really appreciate it if someone could upload it here. It seems like only the user manuals are available here: ftp://ftp.lexiconpro.com/pub/PDFs/manuals/PCM81/
Old 4 days ago
  #28
Nobles offices are in the Midwest. Their minimums are 500 pieces per line item.
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