Yamaha Clavinova keyboard distortion - CVP-83S - Page 1
Forum section: electronics / repair

author: thmjpr
author_rank: Regular Contributor
timestamp: August 01, 2020, 07:25:17 pm
content: Issue:- Distortion/crackling when key is pressed, seems worse at lower frequencies.Boards:- White board = main power amp and power supply- Green board = digital processingInitially I saw a number of leaking SMD caps on the digital board, that actually shorted out the board power rails and burned the PCB. Caps measured as close to 0uF.These bad caps were replaced, carbon was scraped away, but the problem was the same. Kind of a lesson to not pepper a bunch of cheapo useless caps around (there is plenty of capacitance on the power supply board).The power supply board was checked, all caps are good.Power amp pins were re-soldered. Pushing on any area of the power amp or digital board doesn't affect the issue.Clues:- distortion heard more when certain keys are pressed (frequencies)- same distortion heard in headphone jack- distortion present in recorded/demo sounds, so not caused by keys themselves- distortion seems to mostly go away after 10-15min of warm upIf the main amplifier chip is at fault, its not worth replacing. But if anyone has any other ideas, please post.What it sounds like:https://youtu.be/YuqCoRGCiMgSimilar thread here:https://www.eevblog.com/forum/beginners/fixing-a-cvp-85-piano-unknown-schematic-symbols/(possibly need to replace more caps)

author: magic
author_rank: Super Contributor
timestamp: August 01, 2020, 07:50:19 pm
content: So you enabled 'split and 'dual' and added the 'gunshot' voice to the upper half of the keyboard, nice prank.If this is for real then I would seriously consider the possibility that it's haunted by a ghost.Other than that, I think it's more likely to be some DSP gone wrong than the power amp.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: August 01, 2020, 08:10:35 pm
content: It may have been better to replace the caps with SMD tantalums.Soldering big radial electrolytics onto SMD pads with no means of supporting the weight of the electrolytics is just asking for vibration problems at present or later on, IMHO.It does sound like the sound is digitally corrupted, not distorted, this is not a power amp problem.Since there was/is a serious problems with the caps leaking, which damaged the PCB, I would guess this problem hasn't yet been fully addressed.Are all these replacement caps actually connected where they need to be? i.e. do the pads actually connect where they ought to?Are there any vias that are no longer vias due to corrosion?I think it unlikely the present sound problem is unrelated to the leaking capacitor problem.Edit: Oops, I put in a double negative.That also means: "I think it likely the present sound problem is related to the leaking capacitor problem"

author: fzabkar
author_rank: Super Contributor
timestamp: August 01, 2020, 08:26:22 pm
content: Service manual and circuit diagrams:https://elektrotanya.com/yamaha_clavinova_cvp-83s_sm.zip/download.html

author: thmjpr
author_rank: Regular Contributor
timestamp: August 01, 2020, 09:31:49 pm
content: Quote from: magic on August 01, 2020, 07:50:19 pmDefinitely checked the settings about 10 times because it does have those wild space reverb effects, etc.Quote from: Audiorepair on August 01, 2020, 08:10:35 pmThe caps were placed where the SMD used to, or jumpered to the appropriate area.In the burned out area I think there was one trace that was completely destroyed, otherwise the vias were just power and still intact enough.Good points on the DSP though, I had not considered that at all.There is a DAC near those caps that may still have some damage (NECD63200). I'm going to clean that again. If necessary it looks like it can be ordered and replaced (ebay).edit: no change after cleaning/re-soldering the DAC, but it still could be damaged.

author: magic
author_rank: Super Contributor
timestamp: August 02, 2020, 07:24:08 am
content: That crap doesn't sound like any "distortion". I doesn't seem to be harmonically related to the signal very much. It sounds almost like bursts of pink noise or something like that? Maybe it's your recording, but it doesn't even sound white (which could be explained by random bit flips in the digital domain AFAIK).Not sure if a broken DAC could do that.

author: KevinA
author_rank: Regular Contributor
timestamp: August 02, 2020, 07:28:03 pm
content: Rather that guess, put it into self test mode (page 38 of the service manual) and see what this tells you.

author: 2N3055
author_rank: Super Contributor
timestamp: August 03, 2020, 07:44:43 am
content: Don't desolder random bits so you don't damage something further.After you cleaned up elko damage, you must figure out what connections were broken.Look for vias that are eaten up, they trap electrolyte and get eaten up.. On surface look for broken traces..Do self test..This sounds like magic says, a wrongly read samples from sample memory either because of error on data or address buss or memory corruption...Study schematic. It's a detective work, so slow, smart and steady.. Eliminate possible problems one by one, until you get to the cause..Good luck, that is a beautiful instrument, it would be shame to go to waste..

author: mikerj
author_rank: Super Contributor
timestamp: August 03, 2020, 08:16:41 am
content: Quote from: thmjpr on August 01, 2020, 07:25:17 pmHaving lots of capacitance on the PSU board doesn't mean you can do without local decoupling, on a digital audio board you typical need plenty of decoupling. I take your point on the crap capacitors though.