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Re: Yamaha CS-50 All Keys of E not working

PostPosted: Thu Jul 06, 2017 2:37 am
by wizardmix
Mooger5 wrote:Final post for today (yawn).

Part of the KAS PCB layout. Notice the C, C#, D, D# notes and so on. Also notice the multitude of Es! Which one is it? It´s the one that leads to pin 11 of IC1. Notice how all the other Es are linked by jumper wires. I think "E" here, apart the musical note, stands for Earth. They of course meant Ground points. The shields of the wires are soldered to them. The central conductor of the lime green wire is soldered to the relevant E note.
I speculate, but it´s possible during a previous service job some tech soldered the E green wire to one of the Earth points by mistake, if they are labeled in the PCB like they are in the service manual.

Cheers.


Good God Man!! I second Rasputin's comment, waaaay above and beyond brother but extremely appreciated nonetheless. The information has been forwarded, my friend just called me to say thank you so I forward that thanks to you. This will be put to immediate use -- as will the CS50 once it's up to snuff. He won't like that I said this but in the off chance you liked BMSR from the Dandelion Gum era, you helped one of the original members on his birthday no less.

Re: Yamaha CS-50 All Keys of E not working

PostPosted: Thu Jul 06, 2017 11:06 am
by madtheory
Awesome work Mooger5! So we have 3 possibilities:
1. Open circuit caused by dead diode or dry joint.
2. The last person in there confused the note "E" with "Earth" because Yamaha didn't translate the word for "signal ground" as opposed to "Earth" correctly.
3. Rotting CMOS Yamaha custom chip.

Re: Yamaha CS-50 All Keys of E not working

PostPosted: Thu Jul 06, 2017 10:40 pm
by Mooger5
Thanks for the kind words, guys :) Some of the compliments are highly exaggerated haha. Please keep in mind, until further notice, the synth is not fixed yet; the diagnostics may be wrong and if so, the effort was worthless.

By simply using a diode such as 1N4148 it´s possible to confirm right away. With the anode lead, touch one of the octave tabs in the KAS (U1 or U2 etc) and at the same time touch the E-keys tab (E-23 in the KAS PCB) with the cathode lead. The E line should finally trigger a sound. No need to press a key as this simple test bypasses the keyboard.

Image

Re: Yamaha CS-50 All Keys of E not working

PostPosted: Fri Jul 07, 2017 9:49 pm
by Mooger5
I just thought of an even easier test! This time you don´t need to mess inside the unit: just turn the glissando on and set the time to medium to slow. Hit one key that works (which means every key but the E notes), say C4; then hit one of the keys that don´t work, say E2. If my hunches are right, the glissando function will not aknowledge the second key was hit thus it should not work. Nothing will happen! Ha! Isn´t that great?
IF the glissando works, you should hear the downwards scrolling through every note but the E notes. This would mean everything from the keyboard matrix to the Keyboard coder and assigner is OK, including the famous green wire. It would also mean the problem lies ahead, in the D/A circuit. Let´s hope not...

Re: Yamaha CS-50 All Keys of E not working

PostPosted: Fri Jul 07, 2017 10:37 pm
by madtheory
Now that's clever. People pay good money for techs who are scientific y'know! :)

Re: Yamaha CS-50 All Keys of E not working

PostPosted: Mon Jul 10, 2017 9:17 pm
by Mooger5
I´m only in this for the passion for vintage synths and the education.

Re: Yamaha CS-50 All Keys of E not working

PostPosted: Tue Jul 11, 2017 12:51 pm
by madtheory
Ya, that was a compliment :)

Re: Yamaha CS-50 All Keys of E not working

PostPosted: Tue Jul 11, 2017 8:06 pm
by Mooger5
Thanks. Damn Catholic tradition. I´ll never be rich :D

Re: Yamaha CS-50 All Keys of E not working

PostPosted: Wed Oct 03, 2018 5:17 pm
by meatball
I wonder if i might ask to exploit that 'catholic tradition' further - i'd certainly be happy to forward the good deed ... :P

i have a related problem on my CS50 that has taken me to the brink of my troubleshooting skills :P

Re: Yamaha CS-50 All Keys of E not working

PostPosted: Wed Oct 03, 2018 9:27 pm
by Mooger5
This was a fun thread! Too bad the OP never reported back. It would be good to known if all that talk helped to fix the synth.

Re: Yamaha CS-50 All Keys of E not working

PostPosted: Thu Oct 04, 2018 5:13 am
by meatball
Mooger5 wrote:This was a fun thread! Too bad the OP never reported back. It would be good to known if all that talk helped to fix the synth.


yes i'd sure like to hear more about what went down etc