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
IC43
Pin 1: 10.2
Pin 2: 5.2
Pin 3: 4.9
IC42
Pin 14: 0
Pin 15: 0
Pretty sure IC42 shouldn’t be zero?
Electronic Musician magazine May 1989:
“DX7: When you press buttons 16 and 32 simultaneously and then press the function button, the unit will ask you if you want to proceed with the test mode. Pressing Yes will begin the tests. To proceed with each test, the Yes button will increment to the next test, No will decrement. Note that some tests require a RAM cartridge or the performance pedals, the Yes button can skip those tests for which you may not have the necessary hardware. Voice data should not be affected.”
Hope this helps,