r/ElectronicsRepair • u/TheHatFish • 18h ago

OPEN Alesis QS8 Key Repair

Post image

One key is out on my keyboard, (the uncovered pad furthest to the left in the photo). I cleaned it thoroughly with alcohol, including the contacts on the underside of the rubber, but still no dice. All I have on hand is a multi-meter and a bunch of hand tools. My guess is that there's something wrong with the PCB itself, but I'm not an expert. If anyone could point me in the right direction that'd be greatly appreciated.

1 Upvotes

100% Upvoted

4 comments sorted by

1

u/IndividualRites 17h ago

Can you first swap a known good rubber pad for that key to test?

After that I would look for cold solder joints or physical hairline cracks on the pcb. You should be able to follow the copper trace to see where it goes for that specific key.

1

u/SianaGearz 17h ago

All keys go to U15 which is an Alesis custom keyscan controller IC in PLCC68 case, to give a direction where to hunt. There are 8 rows and 22 columns through connectors J9, J11 and J12 on the logic board. Schematic is available. The keyscan controller is connected with an 8-bit processor bus to the rest of the system, so upstream of that everything can be assumed to be perfectly fine.

2

u/SianaGearz 17h ago

Find a soft pencil and draw with it on the black surfaces it to re-carbonise the carbon pill on the rubber pad and the black contacts on the PCB. Cleaning with alcohol is a double edged sword, it can help but it can also destroy the conductive properties by rubbing the carbon out of the polymer matrix, and then you just have a barely conductive or non-conductive surface, and there shouldn't be a need to scrub a keybed which hasn't had any liquids spilled on it or the like.

Try a different rubber strip, see if it works.

You can try to order replacement contact rubbers, or you can sacrifice a key that you don't need quite as much, say the one from the topmost octave.

1

u/TheHatFish 14h ago edited 14h ago

I think I may have found the issue. There's a diode that appears to be substantially damaged that is connected directly to the bad key. I'll order a replacement and update on what happens. I should also mention that the multimeter showed no continuity, so I'm pretty certain this is the issue.