Yamaha PF85 has series of dead D and G# keys

[Charlesy]

Hey guys. I picked up an older 88 key digital piano, a Yamaha PF85, from a friend. It has 6 dead keys, specifically the three D keys on the right half and the three G# keys on the right half. I'll be opening it up to work on it shortly (I've done work on amps, pedals, etc but never on a keyboard), and was wondering if anyone has a good idea of the issue here since it's the same noted keys.) Thanks!

 

[Charlesy]

Bump.

 

[SeaGtGruff]

I don't know if these search results might help-- the service manual isn't available for free at ElektroTanya.com, and it looks like the sites that have it require you to buy it.

http://www.ioffer.com/i/yamaha-pf85-pf-85-technical-repair-service-manual-mau-514580881

http://www.manualsparadise.com/service-repair-manuals/Yamaha/PF85/RWSPFM-45949164-1

 

[Charlesy]

I have the service manual, but I'm not experienced with PCBs (or PCB schematics, for that matter). I've worked mostly with vintage tubes, caps, etc. Just hoping for some specific pointers on the trace/wire/connector that's suspect. And how to open the unit. It has three hinges on the back bottom so I assume I don't have to pull every screw. The service manual has an exploded view but no simple opening procedure listed.

 

[happyrat1]

Get your hands on a logic probe and check the ribbons leading from the multiplex drivers for the keyswitches.

Also remove and reseat the ribbon connectors after cleaning the contacts with some Deoxit Contact Cleaner.

The problem is probably a couple of dirty ribbon connectors from the multiplex drivers to the individual octave boards.

Gary

 

[Charlesy]

Thanks for the response. I got the top opened easily but I assume I have to pull the key assembly(s) to get at the AE board? Why is it two different semi-octaves dead? And can you identify the exact connection so I don't have to pull them all and reseat all? I can send along the service manual if that helps. Too big to send via forum.

 

[Charlesy]

Also, logic probe? Can I use a digi multi-meter?

 

[happyrat1]

The pulses happen too quickly for a DMM to pick up on them. A logic probe latches the signal so you can actually see it when it happens.

They cost between $20 and $30

Otherwise, I'm sorry I can't be much more help.

Look up keyboard multiplexers on google to get a better idea of how they work.

Gary

 

[Charlesy]

The videos don't seem to be similar to my unit which is older and has heavy weighted keys. I'm hesitant to approach this until I'm comfortable removing the keys. I've included a JPG from the service manual showing the exploded view of the keyboard. If anyone has any tips or caveats on approaching their removal so I can get at the PCBs, that would be great.

 

[Charlesy]

I'm also including an exploded view of the entire unit, if that helps. (See above post.)

 

[Charlesy]

From looking at other posts, I'm thinking its a broken data line on one of the PCBs. My only issue is getting out the keys so I can get access to the top of the PCBs to check them out.

 

[Charlesy]

Got it apart after studying the exploded view. The center PCB has two possible points of issue from what I can see, both from spills. I cleaned them with iso alcohol to no effect. Hard to tell if the traces nearby are intact or not, but I suspect one at least may be damaged. Can you do a simple continuity check on traces?

 

[happyrat1]

It could be the traces or it could be the connectors or it could be a cold solder joint or it could be a blown driver chip.

You can't really test these things without at least a logic probe...

Using an ohmmeter in circuit would just give you inconclusive results because of other components loading the circuit.

Gary

 

[Charlesy]

I'll see if anyone local has one I can borrow. I'll probably post some photos soon of the suspect spots on the suspect board.