Spurious LEDs on dimly. Damp? Dust?

[jazzystu]

Hello Folks.

I have a stage EX which resides at my parents house. It is exceedingly low milage.

It has spent ages and ages in a cold room which may not be 100% dry on reflection. It also had a light coating of dust. (I know, I know). I give it a play when I'm here, as I am today and I noticed that when I have the Piano section on, the lowest of the split keyboard lights lights dimly. If I de-select the piano so nothing is on, the top drawbar lights 1 and 3 come on dimly, as does the overdrive light.

Everything works 100%, including these LEDs when they are meant to. There just seems to be some "funnies" regarding the leds. I assume this is not a unique occurence.

I have given it a bloody good clean and a gentle vacuum and things are the same. I've moved it into the dry and warm living room, so that it can dry out.

I suppose the next step is to start stripping it down. However, it is more of an iPhone than a Rhodes.

[jazzystu]

Surface contamination on the circuit board could cause this. In which case a careful cleaning could help. If you do this yourself take care to discharge static electricity by touching something large and metal (like the Nord's chassis) before touching the electronics.

Given the damp environment, "dendrite" or "whisker" growth on the circuit board are another possible cause for this (google "pcb dendrite growth" for images). These are metal paths that can grow on the circuit board (often in damp environments). Early lead-free solders were very susceptible to this.

A surface cleaning might not remedy the problem as the dendrite could grow underneath the solder mask (the green coating on the outer surface of the circuit board).

[jazzystu]

Thanks for that.

Looks like I need to get the screwdrivers out.

[jazzystu]

Giving it some thought, it's probably dust. I should be shot for letting it get so dusty.

[jazzystu]

Right. I have dehumidified the piano and the fault was still there, so I cracked out the anglepoise lamp, got a bottle of Old Speckled Hen open and set about taking it to bits.

It was easy to dismantle. All the screws along the back, all the screws on the end cheeks and the line of about 3 under the circuits. The top lifted off and I disconnected the 2 ribbon connectors and put the top panel to one side.

It was surprisingly dusty and I can see how the slightest moisture could cause problems. I got an artists paint brush and a vacuum cleaner and set about painting the dust off into the cleaner. This worked perfectly and the dust came off leaving what looked like a new circuit board. I vacuumed the interior and put the keyboard assembly to one side.

I got the top panel, pulled all the knobs off NOT INCLUDING THE PROGRAM WHEEL!!!!! and then flipped it over, using 2 books to keep the potentiometer stalks off the table. I whipped off the screws holding the circuit boards following giving the back of the boards some cleaning love. The top side of the boards were quite clean, but dust had got in around the program control knob and some of the buttons. I got my paintbrush out and carefully dusted it off. Again, everything came off fine and I set about putting it back together. It flew back together, I plugged it in and problem solved.

In my estimation, the program knob is a problematic ingress point for dust and crap.

GET A DUST COVER AND USE IT.

If you are having problems with things around the program knob, or spurious led lights coming on dimly, it is due to crap in this area.

DO NOT USE A CLEANING FLUID.

DO NOT USE ANYTHING MORE THAN A VERY CLEAN BRUSH TO MOBILISE THE DUST!!!!

Hopefully this thread will serve people on the interweb.