2024-12-28 - Fixing a Yamaha P-140 Electronic Piano --------------------------------------------------- I recently was asked to look at a Yamaha P-140 electronic piano[0] with a bad connection on the power supply. The power plug had to be pushed very hard for the piano to work, so it wasn't really possible to play it properly anymore. My first repair attempt consisted of checking if the plug was making proper contact, but after that didn't lead to any success, I decided to take the piano apart and look inside. Disassembly ----------- The disassembly process wasn't particularly difficult. On the bottom, all the screws around the edge[1] have to be unscrewed[2]. Note that there is a screw remaining at the top right. This is only because the plastic inside had already broken off[3]. Once the screws have been removed, the entire bottom (including the actual keyboard) can be removed, although there is a connector that has to be removed from its socket on one side[4]. The parts of the piano can be seen in [5] and [6]. I only took [5] after removing the board with the power socket, so I added a red arrow pointing to the place where the board is supposed to be. [7] shows the board when it is screwed in. The annoying part is that the screws holding the power board cannot be accessed without removing the entire metal frame it is attached to. In order to remove that, several screws have to be removed[8]. There is also a cable holder on the right side[9], as well as another cable holder and a grounding cable on the left side[10] which should be unscrewed so the metal frame with the power board can be moved more easily. Once everything has been unscrewed, it should be possible to move the frame enough to unscrew the power board from the bottom[11] (I took this picture after fixing the board, so my repair of the cracked connections is already visible). Of course, the ribbon cable shown in [7] also has to be unplugged from the larger board. If I remember correctly, the socket for the ribbon cable was of the type where you have to pull the sides (marked in [12]) away from the circuit board in order to release the cable (and push them back in later to fasten the cable again). I'm not sure anymore, though, because this was a while ago and the pictures I took are my only reference. Cracked Solder Joints --------------------- Once I had removed the power board, it quickly because apparent why the piano wasn't working correctly. There was a big crack in the solder connection for the power socket[13]. After removing the solder, it became even more apparent that part of the solder pad had ripped off completely[14]. I decided to lay a thick piece of wire down over the ripped and intact parts of the pad in order to fasten the power socket properly[15][16] (the wire was actually the lead from a capacitor I had used for something else). I noticed that there was a crack in the connection on the left as well, although that one wasn't nearly as bad, so I performed the same procedure there for good measure. Finally, I added some UV solder mask, although I'm pretty sure that was completely useless since the one I have isn't really good for mechanical strength, it's just good for protecting exposed traces[17]. Putting the piano together is fairly straight-forward, just remember to to put back all the screws, and take care to plug the cable between the top and bottom back in (the one that was shown in [4]). Wrong Power Supply ------------------ One final issue I noticed was that the power socket was clearly marked with "12V" on the outside[18], but the piano was being used with a third-party power supply which supplied 19.5V. I have no idea who thought that was a good idea, but it's good that it seemingly didn't do any damage. I do wonder if maybe the plug on the third-party power supply was too long, causing more force on the socket when plugging it in, leading to the cracks on the solder joints, although I don't know how realistic that theory is. It is an old piano, so I think it's just as realistic that the damage was natural after plugging in the power plug so often. I managed to find a matching 12V power supply in my collection of random stuff, so that issue was also fixed. There was no marking anywhere saying what amperage the power supply should have, but the label on the bottom did mention that the original power supply was a Yamaha PA-5D, which according to various sources on the internet appears to supply 1.5A, so I just took a 12V power supply with at least 1.5A. Do note that the symbol below "DC IN 12V" in [18] specifies that the inside of the plug should be the positive terminal and the outside should be the negative terminal. As far as I can tell, this seems to be the most common configuration, but do watch out for it when searching for a replacement power supply so you don't accidentally damage anything. Final Thoughts -------------- The piano has been working fine so far, although I can't really say how well the solder joints will hold up in the long term. If they do crack again, the next step would probably be to add a completely separate power socket that isn't directly soldered to the board. The idea would be to screw a power socket into the side of the piano, and connect it to the board with cables. That would be a much better design anyways since soldering a socket which is under a fair amount of stress directly to a circuit board is generally a recipe for disaster. [0] gopher://lumidify.org/I/phlog/2024-12-28-piano/piano.jpg [1] gopher://lumidify.org/I/phlog/2024-12-28-piano/bottom.jpg [2] gopher://lumidify.org/I/phlog/2024-12-28-piano/bottom_unscrewed.jpg [3] gopher://lumidify.org/I/phlog/2024-12-28-piano/plastic_broken.jpg [4] gopher://lumidify.org/I/phlog/2024-12-28-piano/bottom_connector.jpg [5] gopher://lumidify.org/I/phlog/2024-12-28-piano/piano_open1.jpg [6] gopher://lumidify.org/I/phlog/2024-12-28-piano/piano_open2.jpg [7] gopher://lumidify.org/I/phlog/2024-12-28-piano/power_board.jpg [8] gopher://lumidify.org/I/phlog/2024-12-28-piano/screws_inside.jpg [9] gopher://lumidify.org/I/phlog/2024-12-28-piano/cable_holder1.jpg [10] gopher://lumidify.org/I/phlog/2024-12-28-piano/cable_holder2.jpg [11] gopher://lumidify.org/I/phlog/2024-12-28-piano/power_board_bottom.jpg [12] gopher://lumidify.org/I/phlog/2024-12-28-piano/power_board_marked.jpg [13] gopher://lumidify.org/I/phlog/2024-12-28-piano/power_board_crack.jpg [14] gopher://lumidify.org/I/phlog/2024-12-28-piano/power_board_ripped_pad.jpg [15] gopher://lumidify.org/I/phlog/2024-12-28-piano/power_board_wire.jpg [16] gopher://lumidify.org/I/phlog/2024-12-28-piano/power_board_wire_soldered.jpg [17] gopher://lumidify.org/I/phlog/2024-12-28-piano/power_board_final.jpg [18] gopher://lumidify.org/I/phlog/2024-12-28-piano/power_socket.jpg