Roland D-50 D50 keyboard repair forum..

[Riva Stereokromatik]

When I just turn on the keyboard, the characters appear crazy. But after 1 minute, everything is normal. There is data loss when I turn off. And the battery is new, changed recently when the problem began to appear. Maybe this battery is not good, I'll try to exchange it for another. Thanks to reply

[Jazz P Bass]

Or you could actually measure the voltage on it.
Most new batteries come in at a little over 3 volts dc.
I would give a real good look at the soldering job that the factory did.
It may need a reflow.

[loachparty]

Ok another D50 problem.

I'm about to lose my mind. I have one key that makes no sound. No other issues. It was purchased this way about a year ago.

Cleaned contacts - check. nope.
Tested diodes in both directions - check (and repeated a thousand times). all fine.
Done readings across the surfaces of all contacts in question - check. consistent & normal.
Rubbed a little graphite on the contacts - check, no luck.
tried a different, known-working section of the rubber contacts over the PCB contacts - check, no luck.

Then, finally, getting creative for testing purposes: used some wire to hit all PCB contacts at once for that key: the key fires, sound, but a little more fidgety than the other keys.

Aaaaaaaargh.

The thing is and was immaculately clean inside.

Any thoughts? I'm guessing it's the contacts on the PCB, even though they look fine, and when I make the connection with the wire it's hitting a section of the PCB contact that the rubber contact doesn't reach. Is there anything I can paint on to re-enforce them or do?

[Jazz P Bass]

Ever so lightly, rub the pcb with a pencil eraser.

[loachparty]

Still no luck.

[loachparty]

It makes me wonder if there's something goofy with the PCB that isn't visible. A crack underneath the surface of the contact?

Or even some slight irregularity in the circuit where the resistance of the rubber contacts is too severe to allow the connection to be significantly made?

Ugh.

[Enzo]

You are just going to have to trace every inch of that particular crossing in the key matrix. The diodes and contacts may be fine, but without a complete circuit, nothing will happen.

Keys are grouped, there are strobe lines and return lines. Each note has its own crossing of a strobe to a return. If a strobe line or a return line went bad, then you would have a lot of dead notes, like every eight notes would be a dead one, or something like that. But with just one, then I doubt there is some system level problem, you have a fault in the traqces for that specific key.

You can test whether key closures are completing the contact with an ohm meter. Beyond that, check continuity from contact to diode, and from diode to ribbon cable or whatever connects the keybed to the rest of the world.

And remember that velocity keyboards have two contacts for each key, so for example if the second contact never closes, the thing infers no complete keypress. Or if a solder bridge or something has a key as constantly closed, then striking it does nothing, because the system is still waiting for the key to "come up."

[loachparty]

Yeah, every other key is perfectly fine.

I don't think I've tested contact to diode yet, but since I can get the key to trigger by making the contact with another conductive surface (wire, foil on a fingertip) most of the variables you noted seem like a longshot. Using that method I can produce both soft and full-velocity notes depending on the circuit I complete. When I do the correct note is triggered, for what it's worth.

Perplexing.

Unsure how to easily test the key closures w/ rubber in place since it covers the exposed contacts and the traces are coated.

Guess I'll have a beer and meter the heck out of everything pertinent you suggested, of course the key in question is on the opposite end of the board as the ribbon cable. Hopefully my leads reach.

You can test whether key closures are completing the contact with an ohm meter. Beyond that, check continuity from contact to diode, and from diode to ribbon cable or whatever connects the keybed to the rest of the world.

And remember that velocity keyboards have two contacts for each key, so for example if the second contact never closes, the thing infers no complete keypress. Or if a solder bridge or something has a key as constantly closed, then striking it does nothing, because the system is still waiting for the key to "come up."

[loachparty]

The plot thickens. I tested around the board within about a six-key range in relationship to the contacts in question and everything seemed fine, then I did some gymnastics (now I know what those little superfluous circular contact points are for) and it seems like contact is in fact being made via the rubber contacts being depressed, though I'm averaging about 950+/- on the iffy key vs 850+/- on the other keys. There are a lot of variables there though. Sort of a three-hand job and hard to keep steady.

Couldn't get anything on any key via the ribbon but the postion was awkward so I may not have been making good contact.

All very frustrating. If it weren't just one key it'd make more sense.

[loachparty]

which begs the questions: why am I able to trigger the key with another conductive material and why do other pairs of rubber contacts also not work, since the obvious answer, given the testing, would have been debris stuck to or loss of conductivity on said rubber contacts.

[loachparty]

I also tested across the four PCB contacts btw, no shorts between them.

[Enzo]

Oh, I guess I didn't understand you could in fact trigger the note with wires.

You jumper other points on the traces and trigger the note, but not the contact surfaces themselves? SO then proces of elimination. The actual contact points on the board, jumper wire right on them doesn;t work? Hold one end of your jumper on a contact surface, then the free ende work back from the other contact surface towards traces that work. See if you can find a point where it works on this side but not the other side of some point. Then look for a crack in the trace or other gap. And if that side doesn;t do it, then hold your jumper on the other contact surface and do the same thing out the other trace.

It is only one key, so it has to be specific to that key, local. SOmewhere you are losing continuity

[loachparty]

Yeah, I would think but I tried everywhere local, even between points that, if broken, should've caused faults in other keys. I checked everything at least 2-3 times but it's still possible I made an error.

I'd forgotten about the PCB attached the back of the keyboard, there are four sets of (functionally, ribbon though only one is a ribbon literally) cables running to the keyboard's PCB... for a total of 33 contact points, short of the total # of keys. I hadn't taken off the keys directly on the other side of the section the smaller PCB is connected to; I overlooked that part of the board. Hopefully prodding in that vicinity will yield results. Still seems like a longshot since I can get the note to trigger by other means, in both full and low velocity.

[Enzo]

Well, there is some difference between triggering it by wire and by rubber contact, you just have to determine what that difference is. I know I know, sounds simpler than it is, but that is the bottom line. You SHOULD be able to set a machine screw nut or some other bit of metal on the contact surface where the rubber hits and trigger the note. I sometimes use the butt end of one of my pin punches, not that it matters.

There will be a strobe bus serving multiple keys, and a return bus service other groupings of the keys. Each key (not forgetting there are two sets of contacts for velocity) represents placing a diode between the two buses. I don't think your ribbons are involved, since that would take out multiple keys. Somewhere along the traces between those two buses, you have an open or some other reason contact cannot be made.

I know I am stating the obvious and it may not be all that helpful, but there are only so many places this could be. If you can touch metal across the contact surface and trigger the note, then the problem is getting the rubber guy to do it too. If touching there does not trigger the note, then it is a matter of working back from the contact surface to determine where the break occurs.

[Jazz P Bass]

That 'rubber contact' can be a real PITA.
The 'carbon dot' is very finicky.
I have seen references to 'do not touch the carbon'.
My digital scope uses such a contact as an on/off switch.
Intermittant as all get out.
I ended up scarfing a 'carbon dot' from one of my son's broken toys & glued it on top of the other one.
It now works perfect.
Not saying this can be applied to the Roland.
Just thought I would throw it in the mix.