Controls

Before checking any knobs and switches with your hands, use your eyes. Controls can be delicate, and abuse can not only cause them to misfunction, but can also damage the circuitry on which they are mounted. Therefore, look for bent or badly scuffed knobs. You should also check to see whether any potentiometers - rotary or linear - are unusually stiff. This is sometimes a consequence of someone using an inappropriate switch cleaner, and it may indicate that the vital lubricants within the component have been washed away. If so, a previous owner has traded short-term functionality for long-term destruction, and it's quite possible that you will have to replace these pots at some point in the future.

Now check that none of the knobs or faders are stuck in one position. Freeing these can be hazardous, and you should take care to ensure that no damage occurs. Unfortunately, you may not be the first potential purchaser to inspect the instrument, and who knows what damage the previous idiot did? So check the operation of all the knobs, faders, wheels and joysticks. They should be smooth and continuous in action. Most can be replaced, but why take risks?

Checking moving buttons and switches should be easy, unless they have become intermittent. However, be aware that membrane switches can be more fragile than large, moving switches. Furthermore, any dents in the surfaces of these can create strange problems that you may not immediately attribute to a damaged switch. So inspect all membrane switches carefully. If they appear scruffy, or if the legends have become illegible, they may have been abused, and that can lead to very expensive repairs. The membranes switches for synths such as the Moog Source, ARP Quadra, and ARP/Rhodes Chroma are no longer available, and any repair (if possible) can therefore mean a bespoke job.

Fortunately, some synths that appear to use membrane switches - the Yamaha DX7 Mk1 and Oberheim Matrix 6 are common examples - do not. On these, the upper membranes cover sets of 'micro' switches that are more easily replaced.

If you are considering buying an instrument with one or more dead or intermittent switches, it might be best if you knew how much the repair will cost. Some units - such as the Clavia Nord Lead and the Oberheim 'OB' series - offer quick and easy access to the controls, whereas others - the Kurzweil K2000, K2500, and K2600, the Roland D70 and the Korg Trinity - require almost complete disassembly of the instrument. This can take hours, so the repair might be more expensive than you expect.