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Yamaha SY77 wierd glitching/ random sounds PLEASE HELP
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Author Yamaha SY77 wierd glitching/ random sounds PLEASE HELP
alfredobean2
I recently bought a Yamaha SY77 off eBay which was described as having sound issues. I went to look at the unit and when played it was sometimes making very random and glitchy sounds when the keys were pressed (strange pops, white noise, etc), and was sometimes working fine (when you hit the key in a certain way or were using a certain voice). When I first saw it I thought this was an issue with the internal battery, as I knew this was a common issue with these units, and it sounded similar to a toy keyboard that was running out of battery. So I bought it, thinking it would just need a simple battery replacement. d'oh!

I brought it home and immediately opened it up and replaced the battery. I then booted it up and restored the factory defaults using the voice + bank B + 8 trick. Sadly, this did not change or improve the sounds whatsoever, and it is exactly the same as when I bought it. sad banana

Here is the link to a YouTube video I posted to demonstrate the issues:
https://m.youtube.com/watch?v=Qvjh5An8ExQ

It looks like other people may have experienced these issues too, here is a link to a different eBay listing from a while ago which seems to describe the same issues:
https://www.ebay.co.uk/itm/Yamaha-SY77- ... SwIYtdYU54

If anyone has any advice or ideas about what may be wrong with this unit, and how to fix these issues, I would greatly appreciate your input in this thread. I am also going to post this to the Yamaha SY77 forums to see if they have any ideas.
Thanks for any help thumbs up
Rigo
Maybe you find some information here:

Yamaha SY77 Forum
alfredobean2
Rigo wrote:
Maybe you find some information here:

Yamaha SY77 Forum


I looked around on the Yamaha SY77 forums before making this post and I couldn’t see any threads that were talking about any similar problems. I have also posted this info to a new thread on the Yamaha SY77 forums, to see if anyone there can help. Ta.
NS4W
Sounds circuit bent - maybe something is shorting on the PCM chip?
alfredobean2
NS4W wrote:
Sounds circuit bent - maybe something is shorting on the PCM chip?


You might be right- that’s certainly the kind of sounds it is making (although they’re not controllable in any way so I don’t think it’s circuit bent on purpose)

Do you know what the name of the pcm chip might be so I can locate it on the board? Ive never fixed a big synth like this so I’m pretty inexperienced with chip names etc.

Should I try reflowing the solder or checking for shorts on my meter if I can locate the chip?

Thanks for the help thumbs up
OIP
i had a similar issue, my SY77 which i got for super cheap and did the screen replacement on started just playing random waveforms and would cycle through them. was 3 years ago so i honestly can't remember all the troubleshooting i did but i ended up just buying a replacement DM2 board as one came up on ebay.

there's a similar thread here: https://yamahamusicians.com/forum/viewtopic.php?f=54&t=4291&start=45

the issue is with addressing the AWM storage, and i think it's caused by multiplexer or other logic type ICs rather than the memory chip itself. i bought some replacement chips but didn't try them before getting the new board.

the good (?) news is you can still make FM patches just fine. i'd suggest a good look at the DM2 board for any continuity issues as mentioned in the linked thread.. personally i think i damaged something with static or physically loosened an old solder connection when putting the synth all back together.
alfredobean2
OIP wrote:
i had a similar issue, my SY77 which i got for super cheap and did the screen replacement on started just playing random waveforms and would cycle through them. was 3 years ago so i honestly can't remember all the troubleshooting i did but i ended up just buying a replacement DM2 board as one came up on ebay.

there's a similar thread here: https://yamahamusicians.com/forum/viewtopic.php?f=54&t=4291&start=45

the issue is with addressing the AWM storage, and i think it's caused by multiplexer or other logic type ICs rather than the memory chip itself. i bought some replacement chips but didn't try them before getting the new board.

the good (?) news is you can still make FM patches just fine. i'd suggest a good look at the DM2 board for any continuity issues as mentioned in the linked thread.. personally i think i damaged something with static or physically loosened an old solder connection when putting the synth all back together.


Thanks for the link! I couldn’t seem to find any forums describing similar issues, so the info on there is really useful. I tried the test which one of the users said fixed his, by testing the continuity on the rom chip pins ( I tested the 62304s which I think are the rom chips as those were the ones he seemed to be testing in his photos) although I couldn’t seem to find any shorts on any of the chips. As I said earlier in this thread this is my first big synth fix so I may have done it wrong.

I also tried a method a different user suggested, which was to tap with a chopstick on the DM2 board to try and fix any possible cold joints, sadly this also didn’t work.

I’m going to have a good look through the whole forum this weekend to see if there are any other ideas I can try out.

Thanks for the help smile
OIP
no probs, yeah i was on a similar path. the schematics are available but it's a pretty dense design. i think it's possible to isolate the RAM chip which is being addressed and then backtrack to find the logic chips that send the address pins telling it which sample to play, but it's quite a task.

i'm not sure if my problem was the exact same as yours, if i remember right it would play a different sample with each keypress sometimes. but it was definitely the same kind of thing, crazy random samples and only affecting the AWM.

it's a great synth, definitely worth some work and even just using for FM. the screen replacement is almost essential as well, as the backlights seems to have a finite lifespan.
alfredobean2
OIP wrote:
no probs, yeah i was on a similar path. the schematics are available but it's a pretty dense design. i think it's possible to isolate the RAM chip which is being addressed and then backtrack to find the logic chips that send the address pins telling it which sample to play, but it's quite a task.

i'm not sure if my problem was the exact same as yours, if i remember right it would play a different sample with each keypress sometimes. but it was definitely the same kind of thing, crazy random samples and only affecting the AWM.

it's a great synth, definitely worth some work and even just using for FM. the screen replacement is almost essential as well, as the backlights seems to have a finite lifespan.


Yeah, it seems like is going to take some time to fix. My current plan is to ask some questions to some more experienced friends I know, and see if they have any ideas.

It’s interesting what you say about the issue being AWM, as when I try editing any of the samples, the AWM operators seem to work most of the time, unless I use 4 AWM, which seems to cause some small issues. On mine it seems that the AFM generators are the ones which produce the really harsh, noisy, glitchy sounds, as when I edit a sound and switch it to AFM it has a serious meltdown with any amount of AFM operators.

Does this mean I should be looking at a different chipset or maybe even a completely different board when looking for shorts? I’m pretty uneducated about how the layout of the pcbs relates to the sound generation, so I maybe completely wrong, but if you or anyone else has any ideas about how this might allow me to narrow down my search for the issue slightly, that would be great.

Thanks again for the help smile
OIP
oh if it's the FM that has the issue then yeah it's different.. but the troubleshooting ideas are i guess the same. i don't know why it seems to affect the keyboard version and never the TG77, it might be that stuff shifts inside when moving them around as they are such bulky units.

if it's at all possible i'd suggest trying to find a working version and swap out the boards, at least then you narrow the problem down to one board and can replace if necessary.
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