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commodorejohn
August 8th, 2013, 06:30 AM
So this Casio keyboard I got at the beginning of the month has some issues with its keybed. I knew this beforehand, but I was unaware of the sheer extent of the problem. One is that basically every key has a different amount of tension and half of them will whack down right into the board, but that's just a matter of replacing springs. The bigger problem is a couple of the velocity sensors that barely work at all, the middle B in particular. The seller said he'd tried to repair a couple damaged traces and botched it because he wasn't very good at soldering.

Holy cow was that an understatement.

http://imageshack.us/a/img198/4715/dx7g.png
I was expecting to have to get out my solder-sucker and remove some glopped-on solder from the board. Instead, he basically burned off an entire contact pad. I don't even know how you would do that in the course of normal soldering, unless he had the iron down on the board and then had to go answer the phone or something...

So I'm looking at this and trying to figure out what I can do to fix it. Can you get some kind of contact-pad applique for this sort of thing? The surface is fairly uneven; should I try to sand/fill it and then repair over that? (It's a one-layer PCB, so it wouldn't be risking other layers.) Ultimately I can use this thing as a glorified MIDI module if nothing else, but it'd be nice to have it all up and running again...

SParent
August 8th, 2013, 07:01 AM
I did something like this in my first days of trial and error at SMD rework... using a butane minitorch!! Needless to say, I got myself a SMD rework station, as the minitorch is basically uncontrollable. Maybe he used one...

commodorejohn
August 8th, 2013, 10:07 AM
Additionally, anyone know a good place to find compression springs? I've got the dimensions for the ones I need (20mm free-14mm solid for black, 21mm-14mm for white x 7mm diameter x 1mm wire width, 15 coils,) but none of the sites I've turned up actually have those dimensions available...

(Additionally, anyone know a good way to estimate spring force without dedicated measuring equipment?)

arrow_runner
August 8th, 2013, 11:14 AM
Could you get a free sample pack or something with varying spring forces, then you could just compare them by 'feel'?

Old Thrashbarg
August 8th, 2013, 03:44 PM
Can you get some kind of contact-pad applique for this sort of thing? The surface is fairly uneven; should I try to sand/fill it and then repair over that?

If you can get the surface flat, then you can probably use a conductive ink/paint to draw new traces. It's usually not critical that it look exactly like the original, just as long as you make it so that the little pad on the key can create a bridge between the two sides.

Another (somewhat more ghetto) option would be to find a junk cell phone or remote or whatnot that uses a similar type of pad and has a thin PCB, cut one of the pads out of that, dremel out a recess in your keyboard PCB, glue in the new section of board, and connect up the traces with some thin wire.

Bungo Pony
August 10th, 2013, 06:18 AM
My first thought would be to mildly grind the area down and then use a fine wire (like wire-wrap) to make it functional again. Cover it with a small coat of epoxy and then sand it back down to the wire.

commodorejohn
August 10th, 2013, 07:52 AM
I've had adhesive copper tape suggested to me, so I ordered a roll of that and will give it a try...I probably will sand it down, though, since it's pretty uneven.

Craig4Hlp2
August 19th, 2013, 11:56 PM
Hi,
I am Craig form USA . I am new in this forum, i want some latest advice's regarding repairing system.Please help me.

Thanks...
Craig Davies...

commodorejohn
August 23rd, 2013, 11:31 PM
On a tangentially-related note, I'm repairing another keyboard, a Korg DW-8000 that I got at a lower-than-normal price because it wasn't working. I've managed to make a good bit of progress in getting it working; got it to boot into normal operating mode instead of insane gibberish mode this evening. I don't know what happened to this thing, but several legs on the system EPROM were black with corrosion, and when I attacked the assorted corrosion on the board with Q-tips and rubbing alcohol, I wound up wiping off layers of sticky brown residue. If the rust on the bottom of the case were more widespread, I'd think it had been sitting in an inch or two of standing water...

Anyway, one of the issues is a humming noise on the outputs that kicks in a second or so after power-up, then jumps about a fifth. I kind of suspect the transformer here, since it's visibly coated in that brown residue, but I'm curious - why would it only start making noise a bit after power-up, and why would it then make a sudden jump in frequency? Is the transformer a likely explanation, or are these behaviors evidence against it?

It's time like these I wish I had an oscilliscope...

SParent
August 25th, 2013, 03:30 AM
Another option would be to sand the burned area, expose the copper trace that remain on the board leadind to the sanded area, and reproduce some pattern using "surface mount component fix" (see http://www.ebay.com/itm/Surface-Mount-Component-Fix-No-Solder-Permanent-Repair-/290556125218) applied with a toothpick.
When it's cured, sand it to make it even, and it shoud be like new (almost...).

Chuck(G)
August 26th, 2013, 09:56 AM
On a tangentially-related note, I'm repairing another keyboard, a Korg DW-8000 that I got at a lower-than-normal price because it wasn't working.

I had to deal with a similar issue with an old Roland Juno 60 synth. Eventually, I went over the entire thing, resoldering every connection. No problems since. There, a 'scope was pretty much essential in getting everything lined up afterwards.

Right now, to my right, I have an old Casio WK-1200 keyboard that developed a range of issues, from no output to odd operation. Again, resoldering everything fixed it.

So that's where I'd start. The sticky brown goop is probably just leftover soldering flux--it's soluble in isoproanol, brown, and sticky.

commodorejohn
August 26th, 2013, 10:06 AM
Huh. I'm not sure why there'd be soldering flux all over the board and not just where there are soldered connections, but then I know very little about PCB production processes...anyway, I'll bear that in mind. I'd rather not have to resolder everything, but I'd certainly like a working synthesizer. (And I suppose if I do, it's a reasonable excuse to do a recapping while I'm at it; luckily the service manual has a BOM if I need it.)

(Man, the Juno 60. The guy I bought my Oberheim and JX-10 from has one, and he was initially suggesting he'd sell it to me, but he's decided to hang onto it...I'd just buy one myself, but they've absolutely shot up in price in recent years.)

Chuck(G)
August 26th, 2013, 10:45 AM
Well, if you do get a Juno 60, those DCO chips (multi-lead things covered in ceramic goop) are pretty quirky--and nailing down problems on an analog synth like that is pretty hard without a 'scope. Construction is pretty primitive, plywood and all.

marrkede
August 28th, 2013, 09:39 AM
I think using this option that you should go to sand the burned area, expose the copper trace that remain on the board leadind to the sanded area, and reproduce some pattern using "surface mount component fix is pretty good with no illegal things like the violation of patents and copyrights laws presreved.







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commodorejohn
August 28th, 2013, 11:53 PM
Well, the good news is that the DW-8000 is now up and running and making noises, after only two hours of trying to solder leads one of to those damn coin-cell holders they sell at Radio Shack that doesn't fit any boards with soldered-in coin cell batteries and has terminals about as long as a gnat's pecker >=| Set up a test patch, and it makes noise alright! Still needs work, though; sometimes notes don't trigger, and I'm not sure at this point if it's just dirty key contacts, or if some of the voices need adjusting. The hum on the outputs is gone, but it's still a bit noisy, and plugging or unplugging cables from the outputs seems to cause glitchy wild noises to be generated...

Still, progress!