SCI PRO-ONE REPLACEMENT POTS AND KNOBS

Post Reply
FuRRbaLL
Site Admin
Posts: 12
Joined: Thu Mar 20, 2014 10:05 pm

SCI PRO-ONE REPLACEMENT POTS AND KNOBS

Post by FuRRbaLL » Sat Apr 14, 2018 12:20 pm

For many years ive been wondering why SCI made such a cool synth with such crappy parts. My guess is that they needed to keep cost down on the pro-one to be competitive. The bad factory keybeds and the crappy potentiometers make this synth feel much cheaper than it looks. And now being nearly 40 years old,its feels even worse! Ive had nights when a made an amazing patch to use in a song,then the next day it doesnt sound the same.Finding those sweet spots again were often difficult.

The original pots are wobbly,dont feel good,and usually wont hold their values very well. Many Pro-one owners had pots that get difficult to turn then snap off the ends of the shaft. If you really look at one,they use a cheap plastic shaft on a cheap wafer board. No wonder they wear out so easily. Ive seen guys spraying crap inside the pots to get them to free up,or stop them from being crackly. Spraying stuff inside them eventually makes them worse! There are even some people that can rebuild them or swap pieces from other bad ones to make one useable pot. Prices for these cheap pots are insane and seriously not worth it.

So i had the idea to replace the pots with something else,something more modern. The SCI pots are very difficult to obtain since they are not an average type of pot. I was on a mission to find something comparable that will work in my synth.
the main issue with finding a replacement pot,is that the pot is mounted directly to the synths PCB. They also have a bit longer shaft than most pots and use a D shaped end for the knob. My idea was to keep the synth looking like it was all original.
Since my synth is mint,this was needed. My thought was,even if i cannot find exact replacement pots,i can always modify the knobs to fit the shafts so it still looks original. I hate the idea of using parts that really butch up a synth and look bad,such as using different knobs. I think the Pro-One just wont look the same with totally different knobs.

After a while of buying different pots and matching up the specs and measurements. I came to the conclusion that the one pot I received will have to do. It came the closest to the original pot,and met my specs as far as: size,height,turning radius,feel,wobbleness (a term i made up),pin out,and ease to buy. There may be better pots or ones that match the original P1 pots,I felt that those may be limited on how many i could get for the future and the price i was going to pay. Remember,youll need about 23 of these pots to do a full restore on a P1. If they cost $10 each,that gets very expensive very quickly!
However,there is some bad with the good. The pots are not EXACT. they wont be a complete drop in replacement. It may take a bit of modification to get them to be perfect....and they do. I was willing to deal with the bad just as long as it didnt turn into a huge hack job or make things worse in the future. MY goal was to keep the synth looking totally stock on the outside,under the hood is a different story just as long as it out performs what was in it to begin with!
There are some people that get all nervous and crazy when you mention putting any different part into a synth that wasnt officially designed for. And i can understand,but as the synth ages,these parts are almost impossible to find and in some cases near impossible to fix! Sometimes its better to go a different route and fix it right with something different. And i can tell you,that everyone that has played my Pro-One LOVES the new pots,they way they feel and everything about them!
I have done a few of these mods on a few P1s and these people love their synths again and ask themselves why they left those old crappy pots in for so long. I had pots laying around and people asking to buy them for spares or whatever,usually i giggle cause the original pots are made so crappy why would someone pay $20 for an old outdated piece of junk,when you can replace it with a wayyy better pot for UNDER $2.

IF you are up to replacing your pots there are a few things you need to be BEFORE taking your synth apart.
Read-up and research BEFORE doing anything! ....NO one wants a messed up pro one!

The pots and knobs are from Mouser
POTS -858-P231QC20BR100K
KNOBS-450-AE186

:!: ***PLEASE NOTE***: the factory knobs will NOT fit the new pots! :!:
:!: ***ALSO NOTE***: the new knobs will NOT fit the old pots! :!:
So try to order as many knobs as many pots you plan to replace!
:!: ###ALSO NOTE###: The octave switches and knobs are different part numbers, the new knobs will NOT fit the octave switches. :!:
IF you need new octave switches,you can still buy new ones from Ebay or other sources. You will have to use a Factory SCI knob on the octave switches.

PICTURE-A :The bottom of the pots will look like this:
Image
Please note a few differences than the original SCI pots. There is not mounting brackets for the pot,and the pot isnt a PCB pin type. but dont worry...

PICTURE-B: top of the Pots will look like this:
Image
Please note a few differences than the original SCI pots. There is a different shaft type and a threaded mid part. but dont worry....

PICTURE-C : pro-one pots:
Image

PICTURE-D :
Image

The new knobs look almost exactly like the original SCI pro-one knobs,BUT its not made for the D-type shafts! So these knobs will fit our new pots perfectly!

After you ordered your parts,you are ready for step 1.

:idea: I WILL NOTE,THIS IS NOT AN EASY MOD TO REPLACE THE POTS. THE MORE POTS YOU DO,THE HARDER AND MORE TIME CONSUMING IT GETS!
THERE ARE A FEW MODIFICATIONS THAT NEED TO BE DONE TO MAKE IT COMPLETE AND WORK PERFECT! TRY TO FOLLOW MY GUIDE AS BEST YOU CAN.

::::::::::::Things you will need to do this project::::::::::::
-a piece of posterboard or something you can make a decent sized template. or something to make a few templates.
-a fine tipped marker. we will need this to help make the template and to mark the PCB if we need to. a few different colors may help too.
-a soldering workstation with a good iron! with good solder and solder remover and possibly some solder wick. the more experienced you are at soldering the better this will turn out!
this requires a good soldering technique and some skill.
-good lighting! you will need to see what you are doing! we will be measuring,using templates,and removing things from the PCB and cleaning it up. It needs to be near perfect,so you need to see everything!
-solid core wire
-some basic handtools -pliars,wire cutters,wire strippers,screwdrivers,ect...
-small file or light sandpaper.
-nylon washers for PCB AND STANDOFFS (OPTIONAL,UNLESS YOU HAVE FITMENT ISSUES)
-drill and drill bits (most times this is not needed,but just incase)
-a mechanics depth gauge
it looks like this:
PICTURE-E :
Image


:!: BE SURE THE SYNTH IS UNPLUGGED BEFORE TAKING IT APART! :!:
---STEP 1- REMOVE ALL THE KNOBS OFF OF THE PRO ONE. BEING CAREFUL AS YOU TAKE THEM OFF NOT TO DO ANY DAMAGE.

---STEP 2- REMOVE ALL OF THE 7 SCREWS HOLDING THE CASE ONTO THE METAL CHASSIS. BE CAREFUL WHEN TAKING OFF THE PLASTIC COVER,THERE ARE WIRES YOU WILL NEED TO DISCONNECT.
DISCONNECT THE MODULATION/PITCH CONTROLLER ,KEYBOARD RIBBON CABLE,AND POWER TO PCB WIRES. *NOTE*- BE SURE TO MARK THE RIBBON CABLE SO IT CANNOT BE PUT ON BACKWARDS. I WOULD STRONGLY SUGGEST DO THIS TO ALL THE CONNECTORS JUST TO AVOID ANY CONFUSION LATER ON.

---STEP3- ONCE ALL THE WIRES ARE DISCONNECTED FROM THE PCB,UNSCREW THE PCB FROM THE TOP CHASSIS. DO NOT BEND THE PCB FOR ANY REASON! BE VERY CAREFUL!

---STEP4- PLACE THE PCB ON A FLAT NON-STATIC SURFACE WITH THE POTS FACING UP AT YOU. DO NOT TOUCH ANY IC FOR ANY REASON!
:idea: IMPORTANT!-- FLIP ALL OSC SWITCHES (OSC-A AND OSC-B) UP. FLIP ALL OTHER SWITCHES DOWN! :idea:

---STEP 5- CUT OUT A PIECE OF POSTER BOARD ABOUT THE SIZE OF THE SCI CONTROL PANEL. PRETEND YOUR TEMPLATE IS GOING TO BE YOUR SCI CONTROL PANEL.
I WOULD SUGGEST MAKING A FEW DIFFERENT TEMPLATES TO HELP YOU. THE REASON WE NEED TO MAKE A TEMPLATE IS BECAUSE THE NEW POTS DO NOT HAVE THE LOCATION BRACKETS TO SNAP INTO THE PCB.
WITHOUT A TEMPLATE,YOU WILL BE UNSURE IF THE POTS ARE LINED UP PROPERLY AND IT WILL BE VERY DIFFICULT TO PUT THE PCB INTO THE TOP CHASSIS OR WILL LOOK LIKE CRAP. THE BETTER YOUR TEMPLATES=THE BETTER YOUR FINAL RESULTS!
WHEN I DID A FEW PRO-ONES,I MADE SEVERAL TEMPLATES FOR EACH ONE. TAKE YOUR TIME AND MAKE GREAT TEMPLATES,BECAUSE IF YOU DO NOT,THE REST OF THIS PROCESS IS VERY VERY DIFFICULT!!!

TO MAKE A PROPER TEMPLATE.ITS EASIEST TO LAY THE CUT OUT PIECE OF POSTER BOARD ON TOP OF THE CONTROL PANEL.I USED A BIT OF TAPE TO HOLD IT ON, THEN I FLIPPED THE CONTROL PANEL OVER AND USED A FINE TIPPED MARKER TO MARK OUT ALL THE HOLES AND SWITCH AREAS. I DID THIS SEVERAL TIMES SO I HAD A FEW KNOWN BACK-UPS INCASE SOMETHING WASNT WORKING OUT.
IT MAY TAKE A FEW POSTER BOARDS TO GET TEMPLATES THAT ARE PERFECTLY ACCURATE AND ONES THAT YOU ARE SATISFIED WITH. TO GET THE HOLES IN YOUR TEMPLATE,I TAPED THE TEMPLATE DOWN TO A SHOP TABLE AND DRILLED OUT THE HOLES ONE BY ONE WITH A DRILL BIT EXACTLY THE SAME SIZE AS THE HOLE IN THE CONTROL PANEL. YOU CAN ALSO USE A RAZOR BLADE TO CUT THEM OUT TOO IF THE DRILL IS RIPPING UP YOUR POSTER BOARD. NOT ALL POSTER BOARD IS CREATED EQUAL. USE A RAZOR TO CUT OUT THE SQUARE HOLES FOR THE SWITCHES. MAKE AS MANY TEMPLATES AS YOU CAN. BE SURE THE HOLES ARE THE SAME SIZE AS THE CONTROL PANEL! ...IF THEY ARE TOO MUCH BIGGER,THIS WILL INCREASE THE ODDS OF THE POTS BEING OFF CENTER. IF THEY ARE TOO SMALL,THE POTS MAY NOT GO THROUGH THE HOLE AND WILL BE DIFFICULT TO WORK WITH.
THE TRICK IS TO GET A HOLE ALMOST EXACT SAME SIZE AS THE CONTROL PANEL HOLES.

--STEP 6-CHECK ALL OF YOUR TEMPLATES ON THE OLD POTS! YOUR TEMPLATES SHOULD SLIDE DOWN OVER THE OLD POTS AND LINE UP PERFECTLY JUST LIKE THE PANAL COVER DOES! IF NOT,YOU CAN MAKE NEW ONES OR USE TAPE IN AREAS TO PATCH UP THE HOLES.
THE TEMPLATES WILL NEED TO BE AS PERFECT AS IT CAN BE. IF YOU WANT YOUR SYNTH TO BE PERFECT,YOUR TEMPLATE MUST BE NEAR PERFECT TOO!
IVE BEEN ASKED IF YOU CAN USE THE PRO ONES CONTROL PANEL INSTEAD OF MAKING A TEMPLATE. AND YES YOU CAN! BUT...IT WILL MOST LIKELY NEED TO BE REMOVED FROM THE TOP UPPER CHASSIS AND THERE IS A CHANCE YOU COULD SCRATCH OR DAMAGE IT BY ACCIDENT.
IF YOU FEEL YOU CAN DO THIS,THEN IT WILL SAVE YOU TIME FROM MAKING TEMPLATES. ITS UP TO YOU. BUT ID STILL MAKE A TEMPLATE JUST INCASE YOU ARE IN THE MIDDLE OF THIS PROJECT AND YOU NEED TO CUT OUT A SECTION TO LINE STUFF UP BETTER.

---STEP 7- TAKE ONE OF THE NEW POTS REMOVE ALL THE HARDWARE (NUTS AND WASHERS) AND BE SURE IT GOES THROUGH YOUR TEMPLATE HOLES! IF IT DOES NOT OR SEEMS WAY TOO TIGHT, OPEN UP YOUR TEMPLATE HOLES SLIGHTLY BY DRILLING OR BY USING A RAZOR.
DOUBLE CHECK YOUR TEMPLATE ON THE OLD POTS AGAIN AND BE SURE NOTHING LOOKS FUNKY. ALWAYS BEST TO DOUBLE CHECK THINGS.
ALSO CHECK TO SEE IF THE NEW POTS GO THROUGH THE SCI CONTROL PANEL EASILY. IF NOT,THIS IS WHERE YOU MAY NEED TO DO SOME DRILLING. BUT DONT DO IT NOW! WAIT UNTIL LATER. (USUALLY THIS DOESNT NEED TO BE DONE)

---STEP 8- REMOVING THE OLD POTS. BEFORE YOU GO CRAZY,ONLY REMOVE ONE POT AT A TIME!!! THE MORE POTS YOU REMOVE,THE MORE DIFFICULT IT IS TO LINE THEM UP. UNSOLDER JUST ONE OF THE POTS AT A TIME. THE POTS ARE SOLDERED BY THE THREE TERMINALS AND ALSO BY THE BRACKETS ON THE PCB. IT IS A BIT OF A CHALLENGE TO GET THEM OFF SOMETIMES. YOU WILL NEED A HOT SOLDERING IRON FOR THIS. ONCE YOU REMOVED ONE POT. TRY TO CLEAN UP ALL THE SOLDER ON THE PCB BOARD WHERE THE OLD POT WAS SITTING. GET OFF AS MUCH SOLDER AS YOU CAN IN THAT AREA AS YOU CAN. THE PCB ARE WHERE THE POT BODY SITS MUST BE VERY FLAT WHEN YOU ARE READY TO SOLDER IN THE NEW POTS!

---STEP 9- TAKE YOUR NEW POT AND LIGHTLY TIN (SOLDER) THE 3 TERMINALS AND THE BOTTOM EDGE OF THE BODY WHERE THE BRACKET WAS FOR THE OLD POTS. THE REASON FOR THIS,IS WHEN WE MOUNT THE NEW POTS,WE WILL SOLDER THE BOTTOM BODY OF THE POT TO THE PCB TO PREVENT IT FROM MOVING OR BRAKING LOOSE. THERE IS NO OTHER WAY TO SECURE IT TO THE PCB. YOUR SOLDERING SKILLS WILL BE VERY VALUABLE WHEN WE SOLDER THE POT BODY TO THE PCB. YOU MUST DO THIS WITHOUT MOVING THE NEW POT ONCE IT IS LINED UP AND ALSO AVOID TOO MUCH POOLING OF SOLDER UNDER THE POT. IF YOU GET TOO MUCH POOLING OF SOLDER UNDER THE POT,IT WILL LEAN TO ONE SIDE OR STICK UP. THIS IS WHY I SAY TIM THE BOTTOM EDGES CAUSE IT WILL SOLDER MUCH QUICKER TO THE PCB THIS WAY AND SOLDERING THE TERMINALS HELPS PREVENT SOLDER MESSES ON THE PCB LATER.
ONCE YOU TIN THE BOTTOM SIDE EDGES WHERE THEY WILL MOUNT TO THE PCB,LIGHTLY FILE OR SAND THE SOLDER ON THE BOTTOM OF THE POT. BE SURE IT IS VERY FLAT!
PICTURE A SHOWS WHAT IT LOOKS LIKE WHEN YOU FIRST TIN THE ONE EDGE. FROM THIS PIC,YOU CAN SEE THE SOLDER GLOB AND IT NEEDS TO BE FILED FLAT. DO THIS TO BOTH SIDE OF THE POT,OR WHERE YOU NEED TO MOUNT THE POT WHERE IT MOUNTS ON THE PCB.
THE MORE YOU SOLDER THE POT TO THE PCB,THE STRONGER THE HOLD IT WILL HAVE. I HAVE YET (3-4 YEARS LATER) HAVE HAD A POT SNAP OFF THE PCB BOARD! THIS IS WHY GOOD SOLDERING WILL YEILD BETTER RESULTS!

---STEP 9- PLACE THE POT ON THE PCB WHRE THE OLD ONE WAS REMOVED. USE YOUR TEMPLATE TO LINE IT UP WITH THE OTHER POTS ON THE PCB. ONCE YOU THINK YOU GOT IT IN THE PERFECT SPOT,LIGHTLY SOLDER THE POT TO THE PCB ON ONLY ONE SIDE!
LET IT COOL DOWN AND RECHECK YOUR WORK. CHECK IT WITH OTHER TEMPLATES IF NEEDED. DOES IT LOOK ALIGNED WITH THE OTHER POTS? IS IT LEANING COMPARED TO THE OTHER POTS?
:!: ***IMPORTANT** - -IS THE POT SHORTING OUT ON ANY TRACES IT SHOULDNT BE??? YOU MUST BE VERY AWARE OF THIS AT ALL TIMES!!! :!:
IF FOR SOME REASON IT DOESNT TURN OUT GOOD, UNSOLDER THE POT AND START OVER FROM STEP 8. CLEAN UP THE PCB AND THE POT AND BE SURE THE POT SURFACE IS FLAT AGAIN. BE SURE THERE ISNT GOING TO BE SHORTED TRACES ON THE PCB! BE SURE YOU ARE SOLDERING THE POT BODY TO GROUND POINTS!

IF ALL LOOKS GOOD,THEN YOU ARE READY TO MOVE ON. NOW SOLDER THE OTHER SIDE OF THE POT TO THE PCB. ONCE IT COOLS,SOLDER THE OTHER SIDE BETTER SO ITS STRONGER. SOLDER AS MUCH OF THE POT BODY AS YOU CAN SO ITS VERY STRONG. RECHECK YOUR WORK WITH YOUR TEMPLATE WHEN YOUR DONE!
:!: ...AGAIN,BE SURE THERE ISNT GOING TO BE SHORTED TRACES ON THE PCB! :!:

---STEP 10- TAKE YOUR MECHANICS DEPTH GAUGE (PICTURE E) AND COMPARE THE HEIGHT OF THE POT BODY TO THE OTHER POTS. BE SURE THE HEIGHT IS SIMILAR. THERE IS AN ALLOWABLE DIFFERENCE SO DONT FREAK OUT IF YOU ARE A SMALL FEW MILLIMETERS HIGHER (IM A METRIC GUY,BUT IN USA THIS WILL BE 32ND OF AN INCH). CHANCES ARE,YOU WILL BE A BIT HIGHER,BUT DONT FEAR...THERE IS ROOM FOR THIS. BE SURE IT IS PRETTY EVEN ALL THE WAY AROUND THE POT. THIS STEP IS NOT SUPER IMPORTANT IF YOUR POTS ARE STRAIGHT AND NOT LEANING. ITS MORE OF A SUGGESTION INCASE THERES A HUGE DIFFERENCE IN PARTS TOLERANCES. IF SO,YOU MAY NEED TO SHIM THE MAIN PCB BEFORE YOU INSTALL IT. I HAVENT HAD ONE YET,BUT THE IDEA IS THERE JUST INCASE IT NEEDS TO BE DONE. YOU CAN SHIM THE PCB WITH NYLON WASHERS BETWEEN THE PCB AND THE UPPER CHASSIS CASE.
YOU CAN FIND THESE NYLON WASHERS AT MANY HARDWARE STORES IF NEEDED.

---STEP 11- USING THE SOLID CORE WIRE, CONNECT YOUR POT TERMINAL PINS TO THE CORRECT PCB HOLES. SOLDER THE WIRE TO THE CORRECT PIN. IT SHOULD ALL LINE UP PRETTY EASILY. CUT OFF ANY EXTRA WIRE STICKING OUT. MAKE IT LOOK NICE AND PRO.

it should start looking kinda like this after you complete a few pots! HIGH DEF PIC!
Image


---STEP 12- REPEAT THIS PROCESS FOR AS MANY POTS AS YOU NEED TO REPLACE. BE SURE TO USE THAT TEMPLATE ANY CHANCE YOU CAN. SOME AREAS ARE TRICKY TO GET INTO AND SOME COMPONENTS MAY NEED TO BE MOVED AROUND A BIT. SO BE VERY CAREFUL! :!: ALWAYS BE SURE TO CHECK FOR SHORTS! A SHORT COULD CAUSE DESTRUCTION TO MANY COMPONENTS INSTANTLY! :!:

---STEP 13- ONCE YOU FINISH UP SOLDERING ALL YOUR POTS. TRY FITTING THE PCB BACK INTO THE UPPER CHASSIS CASE. IT SHOULD JUST POP RIGHT IN.
CHECK TO BE SURE THE POTS FIT THE HOLES PROPERLY WITHOUT HAVING TO FORCE THEM TROUGH. BE SURE TO DO THIS WITH ALL THE POT HARDWARE REMOVED! (NO NUTS OR WASHERS). IF IT ALL FITS GOOD, CHECK TO BE SURE THE PCB WILL MOUNT TO THE UPPER CHASSIS STAND OFFS. IF THERE IS ONLY ABOUT 1MM HIGHER HEIGHT,YOU SHOULD BE OK TO SCREW IT IN. IF ITS MORE THAN THAT OR YOU THINK THE PCB COULD CRACK IF YOU SCREW IT DOWN. YOU WILL NEED TO INSTALL NYLON WASHERS BETWEEN THE PCB AND THE STANDOFFS. DONT TIGHTEN THE SCREWS TOO TIGHT,ITS EASY TO BREAK OFF STANDOFFS! IF YOU HAVE BROKEN STANDOFFS,IT COULD COMPLICATE THE INTEGRITY OF THIS REPAIR. IVE USED A TWO PART EPOXY TO FIX STANDOFFS IN THE PAST WITH GOOD SUCCESS.

---STEP 14- ONCE YOUR PCB IS SCREWED IN. TURN ALL THE POTS TO THE LEFT. NOW GET YOUR KNOBS AND CAREFULLY INSTALL THEM. THEY ARE TIGHT TO INSTALL,SO YOU WILL NEED TO HOLD UNDER THE POT ON THE PCB WITH ONE HAND AND USE YOUR OTHER HAND THE PUT THE KNOB ON. KINDA USE YOUR HANDS AS A CLAMP. FAILURE TO DO IT THIS WAY MAY CRACK THE PCB!!!

---STEP15- PUT THE SYNTH TOGETHER AND TRY HER OUT. YOU MAY NEED SOME TUNING IF YOU REPLACED ANY OTHER INTERNAL COMPONENTS. I USUALLY REPLACE THE CAPS WHEN IM IN THE PRO-ONE,MANY OF THEM CAN USE IT. EVEN A NEW FATAR KEYBED AND A FEW MODS HERE AND THERE WILL HELP TOO. ONCE ITS TOGETHER,YOU CAN PUT THE HARDWARE ON THE POTS FOR MORE STRENGTH! LIGHTLY TIGHTEN THEM UP,NO NEED TO GO CRAZY!

YOU SHOULD BE DONE AT THIS POINT! I WISH YOU ALL GOOD LUCK WITH THIS. TAKE YOUR TIME AND DO IT RIGHT!
YOUR PRO ONE WILL LOVE YOU FOR DOING THIS REPAIR AND YOU WILL LOVE IT MORE...TRUST ME!






.

Post Reply