Vintage Synth Explorer Forums

This is not really a request for help but maybe for moral support. I am working on an SY-77, had a broken mod wheel mount, and a key that had gotten unmounted. I decided to replace the screen and upgrade the floppy to a usb drive. I think I have now had to completely disassemble thing about 10 times now! It's like one massive monolith. Removing the keybed requires removing all three top boards (16 screws!), two metal mounting brackets with a total of maybe 16 more screws, and 4 MORE screws for the keybed to top case fit. There are just a huge ratsnest of cables to route that love to be in the wrong place...

Replaced the battery, 5000 cables removed to do this. put it all back together to test.

Replace screen... full on disassemble wire up, reassemble, pray to the lord baby jesus i dont have to do it again and test Viola

Remounted the key. full on disassembly to remove the keybed again! Put it all back together to test. Another key had apparently busted its pivot post. ordered another one... wait days.

Put that key in. Reassemble. Viola?? No. No a bunch of keys are not sounding... disassemble the whole thing again. Dont see anything wrong. Is it a circuit problem? Spare time spent for days combing manual, nothing useful.. Refit some keys, reassemble.

Different keys are now not sounding. No pattern, it isnt a bad trace which usually has a pattern to it...

Finally I notice that there a little metal leafs under each key that get pressed when the key goes down and every bad key's leaf head has been folded in by my clumsy key insertion. I had no idea that could happen! After some practice I finally figured out how to insert a key upside down so I can see the leaf head and ensure it doesnt get folded. What a pain in the neck!

Now I finally got every key sounding and one of the $#%^&* keys is $#&^*(#$ squeaking. SQUEAKING!

I have to take the whole mfing thing apart again. This is my declaration to the world of why I went insane.


OMG. Who makes a synthesizer so that ALL of the screws and connectors have to come out to take the MF'ing keybed out!

Took keybed out again today, squeak went away after reseating the key. She’s all back together now and passed all the built in tests. Finally got to have a little play on it, sounds great. Thank the lord that parts over haha.

Btw does anyone happen to know what the pots on the small board attached to the keybed aftertouch strip do? Next to the psu. They are labeled B10K and B100K, it says “gain adjust” next the 100k pot. I don’t anything in the service manual about adjusting these tho. Aftertouch seems to work great, passes the built in test fine.

Hi and good work meener
I have no idea about this specific model, but usually one trimmer controls how much pressure is needed for the aftertouch to kick in and the other trimmer controls the active range of the aftertouch.
Korg Triton uses a similar aftetouch circuit, for more info you can check the schematics in the service manual

Holy cr#p

That's a lot of mucking around....

I've always wanted either a SY77 or 99 but now I'm not so sure.... but to own an old synth means you have to be prepared to put it on the operating table every now and then... I've opened up my M1 so many times that I can do it blindfolded and my JD800 is still in bits all over my workbench...

why do we do it to ourselves?????????

Oh well... If I ever found a SY77/99 going cheap I suppose I'd buy it even knowing what I know now... a glutton for punishment is poor old me

Definitely a cool synth, just a pita to work on! It has a very cool "rompler" engine that has a ton of sweet, sweet '80s sounds and flavor, but that AFM engine is the real gem imo. DX7 on steroids, very cool. I really want a Korg M1, I remember when that came out and my friend had one (probably '88 or something) and I thought it had to be the coolest piece of tech I'd ever seen. Until I saw the JD-800! I just finished restoring a JD-800 myself. Much, much nicer to work on that the SY-77! Red glue is a b*#% tho, that was a very labor intensive restoration. That is another awesome sounding digital synth. Love the controls on it.

@Yekuku thank you for the info. I figured gain must be scaling the output from the aftertouch sensor but I hadnt thought of a cutoff/activation control - this makes a lot of sense! I found the schematic (it isnt included in the pdf service manual that is floating around) and it looks like these are part of a circuit with an NJM4558 dual opamp. Makes sense for the gain control! Other pot could be the threshold control you are talking about? One thing that is interesting is that the service manual and schematics dont match my unit in a couple ways that ive noticed. e.g. here the second pot is labelled B10k on my board, but B50k on the schematic. Probably some revisions throughout production. I still havent found a calibration procedure anywhere in the docs that ive read so far, even the aftertouch self-test documentation there is no mention of how to proceed if the test fails.

In any case the aftertouch seems to work fine, this is just my OCD wanting to make sure everything is as it should be.

It should be :
VR1: Offset adjustment ( adjusts the pressure sensitivity for the aftertouch to operate)
VR2: Gain ( sets the active aftertouch range)
If you wanna mess with them, firstly read the trimmers resistance with a multimeter and if sth goes wrong, you can readjust them to the original resistance value.

Edit: check this
https://blog.sector101.co.uk/2019/07/04 ... djustment/

**perfect** thank you!

Hola here!
At least the battery replacement can be done quick and dirty from the top...



Best!, Ready