PX-350 dead key - How do I fix ?

[SixStringer]

My cat urinated around the keys (5th F#, G) and now after letting it dry for several days I noticed two keys are dead. I opened up the unit, cleaned out the key,  rubber contacts and the PCB with alcohol and no luck. The keys to either of their sides work perfectly fine. So I opened up the PCB that lies beneath the rubber contacts and cleaned it as well. I cant seem to find any component burned out or corrosion damage from the cat urine so far. What could be the problem? ... Is there a way to run a diagnostics through the USB port to check if they are working? Unfortunately the ASC in India is quoting and initial estimate of $300 (and that too no guarantees on time or success as they are unsure they will get parts for a 7 year old keyboard) .. I don't want to thrash the unit as it has served me well and I can probably live with it for some more time until I save to buy a new one. But getting it fixed will be awesome. I am hands on opening assemblies so any help is appreciated. 

[IanB]

It may be that the cat's urine, which is a highly concentrated corrosive, has taken off the conductivity of the rubber domes in the keyswitch assembly. Do you have a multimeter?

A diagnostic won't tell us much since we already know the keys aren't working.

[SixStringer]

I removed the rubber domes above the non functional keys and tried in on the other keys and it works. I used the rubber domes aligned above working keys on the faulty ones and it doesn't work.  I have ruled out the following (1) Rubber domes (2) Conductive striping under them (3) Any corrosion around the striping that could affect the etched circuit. What I cannot ascertain is if the little black transistors / diodes underneath have conked off. I don't have a multimeter at the moment.

[IanB]

Can we have a picture of the little black things? They're probably diodes. They would be easy to test with a cheap multimeter that has a diode test range on it. Replacement will require some soldering.

[SixStringer]

The black square marks the area underneath the two key contact surface.

[IanB]

Hmm, Q343 (a transistor) and D42 (a diode) look a bit crusty from here. But to go any further you're going to need some kind of at least basic test gear like a multimeter, or else a technician to look at it. SMD (surface mount) components like these are rather fiddly to work with particularly if you're not experienced. I would suggest trying to find an electronic repairer. It's certainly fixable though.

[Jokeyman123]

IanB and 6-stringer-in my experience ,  once these carbon contacts become contaminated, it is very hard to restore these-and I have not had luck with alcohol-which I discovered through much trial and error can leave contamination of its own. As you said Ian this is a corrosive acid-I would try plain water and a small delicate bristle brush-I use an old toothbrush and gently try to get whatever remaining residue may be on the solder contacts. There is a possibility the acid may have corroded the solder joints enough to lose conductivity. chances are pretty good the components are fine, but the solder joints might be shaky. During multimeter testing hundreds of diodes in keyboard IC boards over the years-surprisingly I have never found a defective one, even in boards worse than this. And try to decontaminate the carbon contacts-don't use a brush on those-just the solder joints. You might also try a little baking soda solution with water on the solder joints which might neutralize whatever acid contamination could still be there. If the problem is loss of conductivity, this "may" restore that problem. and the damp plain water on the carbon contacts might remove the alcohol or other contamination from the carbon. But you might, after all this, still need to replace the entire circuit board. the problem is probably not-in the connecting bus to the keyboard, since this usually knocks quite a few keys out, and usually jumps around to different keys, which is a good thing-that is even harder to restore. hopefully that's not the case here.