Synthesizer Patel

July 13, 2007 7:43 AM

How do I clean a circuit board that appears to suffer from oxidation?

I recently acquired a synthesizer that runs perfectly except one setting switches sporadically. I decided to open up the synth and look inside and it had obviously suffered from some oxidation or something to that effect. The circuit board which contains the setting that is messed up appears to be in a state of disarray. There are little specks of brownness that plague one side of the board. Yesterday, I attempted to use contact cleaner and it couldn't lift the gunk from the circuit board. Does anyone know a method that will remove the gunk but not destroy the board?

Google search was not too fruitful.

posted by cloeburner to technology (11 comments total)

The brown stuff sounds more like what happens when a capacitor cooks off. Look for a capacitor that appears bulged or split. Take a picture and post it if possible.

Is it near the battery compartment? Is it possible that a battery leaked onto the board at one point? If so, the usual method is to use a toothbrush and vinegar to neutalize the acid, and the carefully rinse with distilled water. Let it dry THOROUGHLY before applying any sort of power.
Battery corrosions is usually whitish or light green though.
posted by cosmicbandito at 7:47 AM on July 13, 2007

I had a imac g4 logic board that someone spilled coke (cola) on, what we did was removed everything we could from it, took a low flat dish, added water and Efferdent (yes the same stuff people use for dentures) let it sit in that over night. let it dry out for about a week, put it back together and it has been running flawlessly for almost a year now. but of course, YMMV.
posted by ShawnString at 8:13 AM on July 13, 2007

We used to clean the flux off the PCBs rolling off the solder flow by scrubbing it with a toothbrush and deionized water - or was it distilled? Yeah, deionized - I think. Actually, both would probably work, and neither will hurt anything.
posted by DandyRandy at 8:29 AM on July 13, 2007

Isopropyl alcohol, aka rubbing alcohol, with a small brush will take it off if the gunk is flux. Let dry before use.
posted by strangememes at 8:43 AM on July 13, 2007

I tried taking pictures but right now I am unable to upload them due to a great variety of circumstances involving the computer. As a result, does anyone have a picture of flux so I could compare what it looks like?

I tried GIS but I only got super hot Aeon Flux pixxx.
posted by cloeburner at 8:51 AM on July 13, 2007

Burned-out capacitors is indeed a common problem with old synths. Comb the analogue-heaven or synth-diy mailing lists for tips on replacement or to find a good repair person.
posted by rhizome at 9:46 AM on July 13, 2007

"runs perfectly except one setting switches sporadically"

... More detail please. What setting, and how does it change? Is this setting controlled by a switch or a pot, or by a menu setting?

If the problem setting is set by a switch or a pot, I would look at the switch or pot first. Those are most likely to go intermittent with age.

I wouldn't get hung up on a little discolouration on the PCB. Corrosion damage to the PCB traces is usually pretty obvious - the copper is eaten away. Do look for other physical problems - burnt or toasty resistors, puffed-out or exploded capacitors, wires that are weak or disconnected, components with broken leads.

If there's no such obvious problem, you may need to get a service manual and do some serious testing and probing.
posted by Artful Codger at 11:05 AM on July 13, 2007

Flux looks like amber... somewhat darker. It is normal and non-conductive, usually.

Most should be on the solder side (bottom) of the board as opposed to the component (top) side.

If it's flux, don't bother removing it. If you REALLY want to get it off with easily procured material, PVC pipe cleaner with MEK works, but will rearrange your chromosomes, so wear gloves and use in a supremely ventilated area.

Concentrate on areas on the board where there are connections... usually gold plated areas. Make sure they are dust and crud free. Use gentle abrasion with a pencil eraser.

Good for you for trying to fix it!
posted by FauxScot at 1:15 PM on July 13, 2007

The circuit board can be cleaned with clean water or isopropyl alcohol and a toothbrush. But: some components don't like this treatment, including pots (knobs, sliders), piezo beepers, and sometimes switches. A synth is likely to have some of those on it.

I second cosmicbandito's and rhizome's suggesion that this might be residue from a capacitor that blew up (electrolytic capacitors are one of the few non-moving-parts components that still fail much, and they sometimes spray foul-smelling goo all over when they burst). And again, an analog synth will have many of these. In this case you'll need to find and replace the dead capacitor.
posted by hattifattener at 2:47 PM on July 13, 2007

Well, to elaborate... The hold function automatically triggers, I can temporarily disable it by pushing the load button [all of these are buttons to the right of the power button]. But after a while of playing the hold button will reactivate. When I opened the synth the circuit board that has the inputs for hold and cv/gate among others was looking a bit fluxxed, so I'm thinking maybe the problem stems from there. But maybe not, I have not noticed any exploded capacitors.

I've come across the service manual but I am having some difficulty deciphering it. Here is a link to it.
posted by cloeburner at 5:26 PM on July 13, 2007

Ah.

If I'm reading the schematic right, the hold switch (S9) is scanned by an input port of the CPU IC (IC 6). Note that the pin on IC 6 (pin 32), that the HOLD switch connects to thru a diode, ALSO connects to the keyboard, and also to the OCT UP pin of the Bender Board.

I would suspect the HOLD switch itself first, but there's also a less-likely possibility that there's a problem with the keyboard or the bender board.

The first thing I would try is to temporarily disconnect the HOLD switch somehow... either by removing the HOLD switch from the PC board or unsoldering the wire that connects the HOLD switch to the CPU (at the SW BOARD: pin 113).

If the problem disappears, the HOLD switch is the problem.

(I love old synths too. Paia synths mostly)
posted by Artful Codger at 6:37 PM on July 13, 2007