General Tips for synthesizer repairs


1) Cleaning potentiometers/Sliders
2) Cleaning Interconnects/Switches
3) Cleaning/restoring rubber cup key contacts
4) Cleaning battery spills
5) Replacing batteries and battery types
6) Reversing yellowing in keys and other abs plastic parts.
7) Wall wart and damper switch polarities










Welcome to the general troubleshooter guide. Sound Doctorin's latest attempt to help all of us techs move on to doing more useful things. :-) Please note that in order to use this guide you should know that * you should never work on anything when it's plugged in to live voltages unless you absolutely know all the parameters and if you are wrong and get killed you have nobody to blame but yourself! * Some equipment has capacitors which retain electrical energy even after the device is unplugged. While this is not the case with synthesizers generally..at least not enough to hurt you badly unless you jammed the think into your heart or something maybe... I mention this for the possibility that someone may try to use the advice given here in on a TV set or some device that does contain dangerous voltages when unplugged. In these cases you must discharge preferrably using an insulated probe pair with a resistance capable of sustaining the maximum power that the voltages in the set or whatever could deliver. To be safe 1000 ohms at 10W rating is recommended for all but very high energy gear found in physics laboratories possibly etc. * Soldering irons can burn you. I've found this out the hard way. If you are looking for a part on the floor and hook the cord on your iron and it falls and stabs you in the hand....and as you shriek in pain and flick it out it swings and comes right back and burns you even worse...think of me will you? * You should use adequate ventilation (whatever that is..) when soldering or melting plastic insulation probably worse yet :-)









Cleaning Potentiometers

       First let me warn you that a few other problems occur in potentiometers that may *seem* to be dirty. 1) People overheat the leads while soldering in pots that have conductive plastic technology in them. You can totally ruin these pots by overheating leads and there is no cure but to get a new one that I know of. 2) There are times I've been able to recrime leads on pots that were just not adequately crimped there to make contact. Wiggle the leads with a meter and see if you see any jumping around. You may have to alligator clip between the leads and the pot lead to do this. 3) Sometimes they just get moved so much (or vibrated!) that a groove wears right in the conductive trace that forms the potentiometer! At this point you need to replace it. In some cases pots or sliders can be taken apart and you may be able for instance to combine the broken part with other parts if you save your old broken pot parts like I do! :) 5) Parts inside get so rusty that they cannot be cleaned.

      Anyway barring any of the above, I've had good success using GC "Jiffy Bath" or Caig "Cailube" in the past. Both of these products have been upgraded and Caig now has 'faderlube" which is recommended for fader products. Prior to this all I used left sliders still feeling sticky but most of the time that product will work on both rotating pots and faders ok. Any good contact cleaner with some lube for rotating pots is good but these are the professionally recommended products I've had good experience with and I have NOT seen any signs of metals detereorating from use of these things etc. as has been rumored from old useages of a cleaner that apparently did damage metals. Cramlon or whatever it was called.





Cleaning switches and interconnects

      Somtimes a contact can be reached and cleaned with light abrasive if it's a homogenous material (ie. not coated on the surface with contact material that you will wear away). But I often use Caig "Deoxit" because it seems to improve contacts and protect them for some time. This product has no lube so it's great for non-moving contact situations or rarely moved things that even without lube won't wear out in a million years :-) NOTE: the tactile switches commonly used in data entry on synths (eg. Roland JX10) are prone to becoming dirty over the years. You can, rather than replacing them which often is a huge ordeal, hose some deoxit right into the junction of the part you press and the body of the things. This will get the cleaner into the switch. Then begin press press pressing it with a hard tap. Often you can shatter the dirt right off inside and hosing again and again flush it out. Sometimes takes a few minutes per switch but HEY...sure beats pulling the whole thing apart and putting a new one in there. This has saved me many hours. Most often when I do this the switches work perfectly for years. (Eg. my memorymoog which had almost all of them fouled when I got it.)









Cleaning/Restoring Keyboard contacts

      I'll preface my previous article on this to note that I began to see some polysix units that I simply could not get to respond to the treatments described below. This spurred me to develop a much better solution and I recommend all technicians stock some of these contacts so that when you run into a keyboard with tough ones you can simply re-face them! This self-adhesing material is remarkable. I believe it actually has better characteristics than the original contacts though we of course have only been testing it a few months. But it's a material used by NASA and it looks extremely stable. It measures a couple hundred ohms when you lay probes near each other on it just like the new contacts measured from the factory! I've completely outfitted a couple 61 key units and it works fantastic! Plus saves a lot of time scrubbing the contacts as recommended below. One should still clean the contacts so that the adhesive will stick good with ethanol or acetone as needed. But you don't have to sit there measuring with the probes and then hope that it works when you get it back in! Sometimes they seem to measure fine even and they still don't work when you get the whole board back in! So these little contact disks take all the trouble out of it. Here are the details and ordering instructions for the contact disks!.

      They can be a little tricky to place. I put them on the edge of a sharp knife blade and carefully lay them precisely over the original contact then press down with a clean thumbnail etc. And that's it! You've got a brand new contact!

      While some contacts are cleaned with switch contact cleaners described above or scraping/scaling carefully on metal contacts, other times you will find these silicon rubber cups with black conductive impregnated 'disks' inside that press against a couple contacts on the boards. These are commonly used in synthesizer products beginning with the Korg PolySix, Roland Junos, SCI synths after T8 but including P600, Oberheim OB8, Akai synths, Fender Chroma Polaris etc. Often you will notice that a note becomes intermittent or has to be pressed hard. Or they can totally drop out altogether. On concentric ring or dual types (ie. velocity sensing) they can cause variations in senseitivity. Eg. a soft touch can give a loud note.

      FIRST do NOT use contact cleaners! They cause the rubber to swell some and just make things worse and it's tough to get out! While sometimes 99% ethanol will work quite nicely, here is a summary of the proceedures I've used to cope with this problem when that doesn't do it, from an edited SDIY article: ------------------------------- These are the rubber cup switch arrangements. Sometimes they get actual dust/dirt under them. I just cleaned up an old AX73 of the same technology last night. WOrked great after getting all the crumbs out save one note that I had to pull the key off from and 'massage' it around with a blunt end probe. (You can actually kind of fine sand the surface some without even pulling the contact strips out) Other times (eg. my memorymoog) I've seen contacts be very persistently foul. I'd like to develop something that will really allow people to repair those contacts. Nickel print won't stick to silicon at all. Most other things won't either of course. I recently had a disaster trying to use BOTH the solution offered by oaktree that you mix AND the Caig contact repair product on a DX100. Bad. It worked for some days then refouled. Worthless. Don't bother. I don't understand it. THe material still looks integrable but it absolutely just loses conductivity over time. So until we find a real solution: 1) Sometimes acetone will eat a little of the surface rubber and leave the conductive impregnated material. Treat it, scale the surface with an exacto etc. and sometimes it's good. Measure with probes. You should have a conductivity of 500 ohms or less when you press them side by side on the surface of that stuff. If it's 1000 ohms they are going to be totally flaky usually. 700 might work ok in most apps I've seen. 2) Light abrasive can sometimes bring them back 3) Sometimes the contact just seem to have no conductive material left in it! :-) I have ones from a Mono/poly I did in my studio that simply can't be gotten back..like one or two per strip! Bad lot of them? I think so. That's my research on the matter. -Bob

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Cleaning up Battery spills on circuit boards.

       First please ESPECIALLY if you have a Siel DK600, Peavey DPM series, or Polysix, check your battery if you haven't recently. If it's leaking get it out of there asap. You may have to use sharp side cutting pliers to clip the leads on them, then clean the area with baking soda solution to neutralize the acid then clean it off. You can get water on most circuit boards for a short time if they are powered down. Just blow under chips with high pressure air to make sure it all gets dry in the area affected. THen you may need to use a small wire brush to clean up solder joints etc. Or even an xacto knife or the like. Often traces are gone and you may need a real tech to figure out which and where they go. When they find out they will cut the old trace so it isn't stray at both ends and solder a new wire around the trace or sometimes if it's a small area affected solder a wire between the two points scraping the surface of the trace to form a pre-tinned surface using flux as needed.



Replacing batteries and selecting the right type.

      Synthesizers will usually use one of two types. NiCad are common in earlier synths with memory (eg. polysix, Siel DK600). And as per note above these are likely to leak and cause horrible problems on the circuit boards. Some like the Kawai SX210/240 put the battery in a little better place at least. But see the cleanup note above if this has befallen your circuit board. Meanwhile these batteries should usually ride at 3.6Volts and they are charged continually when the synth is on provided all circuitry is in working order there. Often a few hundred ohms is placed between the 5V source and the battery so that it doesn't get current too fast from the supply. And when power is off then a diode prevents current from moving back to the 5V supply (except in Sequential multi-trak where a design flaw causes it to actually leak down in about a year). The battery is only supposed to power the nonvolatile RAM chip and keep it's chip enable line turned off so that larger current isn't needed to do that task.

      Anyway simpler circuits use the Lithium (Li) battery. These are usually about 3Volts and are found in many Roland and yamaha products; even earlier memory synths like the DX7 and JUNO-106. While it is usually possible to install a 3.6V nicad in these circuits, the problem is they tend to lose charge over long periods of time and fail much more quickly. Lithium cells I've seen last ohh..well... I've never done the one in my wavestation from '91 for instance that I can recall! I know many last 10 or 12 years routinely. HOWEVER you can NOT use the Li cell in an application that requires NiCad. Li batteries are not rechargeable and will get hot and maybe explode or something if you try. So never substitute when in doubt.

      Anyway removing batteries can be a pain and as I mention above in the battery spill situation, it may be best to use a sharp pair of side cutters to clip the leads and then desolder them. Why? Because the heat sink provided by the ground plane of the board and the battery together may create a situation where you will destroy the trace otherwise. Whereas if you get the battery off the trace first then you can much more easily apply heat to the area you need to apply it to. I also recommend for Li batteries, buying a cell holder for a dollar or whatever rather than just soldering another battery onto the board. You may want to wire these away from where it was originally mounted and use Goop automotive or equiv. to hold the back of the cell holder against something that it won't create problems with. You can have fairly long wires on these cells! It's not like they are a high frequency circuit or something! Enjoy. -Bob


It has been discovered that hydrogen peroxide can at least partially reverse the yellowing of ABS plastic parts used in many computer and synth products. Check out this link.



Power Adapter Polarity and damper switch polarity guide

      Often there is confusion resulting from differing standards across the industry historically. Yamaha and Roland for instance use Normally closed switches on their damper pedals. Causing a hung note if one is hooked to a machine set to use normally open switches. Some damper switches have a polarity switch. Anyway most other manufacturers use the normally open. As to why they did this I'm not sure. A closed contact is less likely to get dust between the contact points I guess. But perhaps it was from a convention of interfacing with circuitry where the designer preferred that the switch be closed when in active for a 0V reference. Who knows.

      Power adapters though are often responsible for destroying parts in keyboards and other devices. When they are used on the wrong device! One must be careful to see to it that the proper polarity is used. Often a diode is installed so that if a reversed supply is used, it will simply short out the supply to protect the other circuitry from catching a reversed power which could destroy other more expensive parts. Often the diode will be destroyed by this process and will often short circuit so that no matter what supply is used the device still will not work until the diode is replaced.

      Meanwhile, the likelihood of damaging the power supply is also high. A fuse or thermal fuse may blow during the process of shorting out the diode. Anyway here is a table, to my knowledge, of what types of supplies are used by various manufacturers. If you know of exceptions notify me, thank you. Note that *all* supplies of this type are referred to as AC adapters since the adapt household AC current to the voltages needed by your device! The device may require some other AC voltage (Eg. 9V for Alesis gear) or it may require a rectifier/filter circuit to produce DC voltage, or it my even require a voltage regulator to make sure the line is very stable. Also various types of jacks are used to connect this voltage to the unit. The most common ones are the 2.1mm and 2.5mm barrel jacks. The 2.1mm is far the most common. The polarities are listed below with the center of the jack being the 'tip'. Some other manufacturers use DIN or other connectors also in some cases. Eg. some older Alesis gear, Behringer, etc.

Polarities/type of AC adapters that use 'barrel' plugs ("type" is DC or AC out)

Alesis - AC output, usually 9V
Boss - Tip Negative, 9VDC REGULATED
Casio - Tip Negative, 7.5 to 12VDC depending on unit
Digitech - AC output, usually 9V
Kawai - Tip Negative 9 or 12VDC usually
Korg - Tip Negative 9 or 12VDC usually
Peavey - AC output, usually 16V
Roland - Tip Negative on EARLIER units, Positive on later ones!, usually 12VDC
Siel - Tip Positive, 12VDC
Yamaha - Tip Positive, 9 or 12VDC usually