What is the purpose of "Recapping" a synth??

[chinchee]

Hello,
What is the purpose of "recapping" a synth? What does this mean? I always see people talking about this in forums, and threads on the net. They especially talk about "recapping" the power supply? I'm lost on this topic. How do I know if my synth needs "recapping", or if it needs it at all?

thanks

[tallowwaters]

Replacing capacitors, which go bad every 15 years or so.

Early sign is usually just a large amount of noise that can't be traced to any normal source...

[steveman]

Capacitors are components that dry out with age. In some cases this means they go short, cause damage to other components. On older vintage synths it's worth doing (or getting someone else to do it).

[chinchee]

Thanks for replying!!!
How do I know which capacitors need to be changed? For example, if there is some excess noise when I turn up the master volume on my synth, how do I know what capacitors this would correspond to inside?

[th0mas]

You usually start with the power supply as it has the most effect and also the most potential to damage the entire synth.

IE, a bad cap in the PS could short and run a higher voltage through the synth than what was supposed to.

I'm about to do this to my CS-20m as it blows fuses. hooray

[tallowwaters]

Just so you know, capacitors can carry enough juice to kill you, so I suggest you learn how to discharge them. Not to be an alarmist, as it is an easy procedure, but it is something you should know.

sometimes a visual inspection can suss out bad caps. Are they bowed out on the top or sides? are they leaking? etc. (don't be fooled by the odd resin that some manufacturers put on the cap/board points.

[piRoN]

(don't be fooled by the odd resin that some manufacturers put on the cap/board points.

Which for reasons unknown is usually made the same colour as the orangy-brown stuff that dying electrolytics spit out.

I had that problem fixing my Fireworx PSU. All the caps had brown stuff on them, I had to try and discern the one with the ever-so-slightly different shade.

[Hybrid88]

Just so you know, capacitors can carry enough juice to kill you, so I suggest you learn how to discharge them. Not to be an alarmist, as it is an easy procedure, but it is something you should know...

So how's it done?, thinking of doing some cap work on a power supply myself and it would be good info to know.

[Steve Jones]

Some synths sound dramatically better after a re-cap, the Minimoog for example. Others don't sound any different, I re-capped my SH-7 recently and it made no sonic difference, I had another SH-7 in the workshop to compare it with before and after.

If the bad caps are in the audio path, filters or EQ's, then they will make the synth sound thin. If the caps are used in timing circuits such as ADSR's then the time constants of the circuits will shift.

Lately I have been noticing that every Korg MS and PS series synth that comes in all have dried out and sometimes leaky caps. I have been seeing power ripple problems in a lot of MS-20's.

A point to note: Electrolytic capacitors need voltage across them to stay properly formed. If you want the electrolytic caps in your gear to die quickly, the best way to do it is to leave the machine turned off for long periods.

[xpander]

the value of the capacitors will change as they dry out, too.

[tallowwaters]

http://www.repairfaq.org/REPAIR/F_capte ... APTEST_009

[nathanscribe]

This relates to PCs, but the information still has relevance.

http://www.badcaps.net/pages.php?vid=31

[hfinn]

Lately I have been noticing that every Korg MS and PS series synth that comes in all have dried out and sometimes leaky caps. I have been seeing power ripple problems in a lot of MS-20's.

I can attest to this. After fully recapping a PS-3100 it sounded so much more full and robust. Took me forever though, I replaced over 130 or so caps!

[th0mas]

Just to mention this, as I spent many years doing electronics without such a device, you need to get a "solder sucker", or a "solder vacuum". If you don't use one you're doing it wrong.

looks like this:


I can't believe I went years without such a thing and only trying to use desoldering braid (which is good for doing SMT or for cleaning up excess, but not for removing solder in through-hole holes)

[cornutt]

So how's it done?, thinking of doing some cap work on a power supply myself and it would be good info to know.

I'd only worry about it for large electrolytics, but... The easiest way to discharge a cap is to put a voltmeter on it and wait for the voltage to drop to zero. The small amount of current that the voltmeter draws from the circuit being probed will gradually discharge the cap.