Yet another DX7 No Sound post

I’m pretty new to using an oscilloscope, but I have it set to 10x mode, 5v, 10us and DC. On the distorted DX7 I’ve been able to watch the scope clearly show when I’m playing keys when I probe a few things (it’s been a while so I can’t remember what I probed). I’ll check it again tomorrow when I have more time. Side note-I’m totally bummed about the distorted DX7 because that one is in beautiful shape otherwise and DID work for a while. No idea if it’s something I can replace or not but that’s for another thread and another time. I am hopeful I can get at least ONE of the two motherboards working so I can maybe Frankenstein one good DX7 out of it.

What we are working on now looks pretty good at this stage. As a next step I would suggest to attach something to the output, set the volume to about 1/2-way and play a key …

Sorry to not get back sooner, I’m juggling a million projects in my spare time so this one gets set aside at times. So far still no go. The volume fader DOES change the level of hiss, which I feel is much louder than it should be, but still no sound. I’m still thinking it’s farther back up the chain. Hopefully if it is, it’s before the proprietary chips.

… either I am or you are confused now. Is that the unit that had NO sound or did you accidentally now check the other one that has continually noise !!!

While I do switch them back and forth at times to test things, this is the one that makes no sounds/tone. It makes a hiss, which did get louder at some point after I replaced a component (before you got involved I believe). I just failed to mention it. But no tone at all so far, just hiss/noise bed.

The one that DOES make tones is not hissy, just distorted like a very aggressive synth lead on every patch. I stopped mentioning that one at the point where you said to focus on the one that doesn’t make tones so as not to cause confusion.

Thanks - was just a little unsure.

Can you take meter and check the voltages on the following points:

IC43 - pins 3, 2 and 1
IC42 - pins 14 and 15

That’s to see what the reference voltage on the DAC looks like.

Sorry it took me so long to get back to this

Pin 1: 10.2
Pin 2: 5.2
Pin 3: 4.9

Pin 14: 0
Pin 15: 0

Pretty sure IC42 shouldn’t be zero?