Yamaha digital keyboard.   Fixed one problem and created another - Page 1
Forum section: electronics / repair

author: gooseEL34
author_rank: Regular Contributor
timestamp: December 24, 2014, 04:26:04 am
content: Keyboard is a mid level Yamaha YGP-535.Lots of Youtube videos if you have a broken key, or one non-responsive key due to grime or obstruction.Had a broken solder joint on 12v dc IN connector so I fixed that.Put her together And now all the C# and G keys only play at max velocity (keyboard is touch sensitive)What might cause that?Fact: I had to remove the ribbon cable connecting the keyboard action to the main PCB. Maybe a damaged ribbon cable?UPDATE: I reversed the ribbon cable (which would have put the contacts opposite of their original position, and no change, so I do not suspect the ribbon cable from the action mini PCB to the main PCB.Doesn't seem to be a physical obstruction issue as it is ALL the c# and g notes.Help??!!??

author: amyk
author_rank: Super Contributor
timestamp: December 24, 2014, 06:08:39 am
content: You may want to get themanualfor it, it contains schematics and I can see that it is a multiplexed keyboard, but I don't know how it detects velocity (are the keys pressure-sensitive? Variable resistors?) so that is what you should look into.All the C# and G keys are on the same column/row, so the fault is common to them.

author: Shock
author_rank: Super Contributor
timestamp: December 24, 2014, 03:25:41 pm
content: Take it apart as you did and clean it fully then carefully assemble again. It will normally be a stuck key or an intermittent contact or a wire fell off, so check that while your putting it back together. Obviously when it's disassembled you can measure for voltage while manually manipulating some keys or contacts. IPA is a good cleaner just don't wipe away carbon contacts with it, don't use detergents.The most likely failure after that is an intermittent solder joint on the controller IC in which case you can manually trace tracks to see what they connect to.Please take and post clear photos of everything if you need more help.

author: gooseEL34
author_rank: Regular Contributor
timestamp: December 25, 2014, 01:51:19 am
content: Again, I am thinking that it CANNOT be a dirty contact on a key or keys.My rationale is that it is EVERY C# and G note. If there was gunk under one contact, I am unsure how that would make all other notes of the same pitch sound at max volume.This keyboard senses velocity by having two contacts under the key at different heights. The pressing of the key depresses one, then the other, and the processor determines velocity by the timing between the first and second contact hit.When the person above said the C# and G are on the same row, what did that mean?

author: amyk
author_rank: Super Contributor
timestamp: December 25, 2014, 02:05:42 am
content: Quote from: gooseEL34 on December 25, 2014, 01:51:19 amThat makes sense; the problem is probably a short between the two contact's signals for the C#/G row/column, causing it to detect both closing simultaneously and interpreting that as areallyfast press.The keyboard is a simple multiplexed type, with the switches arranged in a grid at the intersection of row/column signals:http://www.openmusiclabs.com/learning/digital/input-matrix-scanning/single-mux/Look at the schematics in the manual.

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: December 26, 2014, 12:45:44 pm
content: I have been in a few failed Yamaha Clavinovas, mainly due to the owners pouring Coca-Cola into the keyboard.They sense the key velocity with two different length plastic pins hitting a silicone band that has two conductive plastic 'lines' on the bottom side. These are pressed onto two standard membrane keypad type contacts. The OPs instrument sounds as if it uses the same method.Any repair that interferes with the silicone band can cause the problem of full volume on one or more keys. This will typically be a track repaired with a link wire in effect 'jacking up' the conductive plastic.This would be a starting point. The key decoding on the Clavinovas is in groups of 6 keys, with the conductive plastic 'broken' at the ends of the groups of 6 keys.

author: gooseEL34
author_rank: Regular Contributor
timestamp: December 27, 2014, 05:06:32 am
content: Thanks guys.Put it back together after taking off all the keys and resetting the plastic membranes andfor some reason....it works!!!