Yellow Magic - no resonance/low volume

Just finished putting the boards together and having a couple of issues - low volume and no resonance on the filter. Everything else seems to work fine. Any help would be most grateful.

Do you have an oscilloscope?

If not:

  • Do you get acceptable signal level at point 1 (raw oscillators signal)?
  • At point 2 (filter output)?
  • At point 3 (VCA output)?

Unfortunately not.

How do I test these points?

Will I have to check signal levels by doing this…

You can “probe” the circuit with an audio jack connected to a mixer/amp. The tip of the audio jack should be connected to the point you want to probe ; the sleeve should be connected to any point of the ground at ground potential (points marked “GND”).

…excuse my ignorance!

yes, you need to look with a probe

Presuming that I’ve done this right, I get no sound at points 1,2 and 3. At points 4,5 and 6 I get a strong high pitch noise?

Any more thoughts on this please?

Do you get sound at the “OSC>” pin on the control board?

No nothing here either.

But do you still get sound (that follows what you play on the keyboard, not noise) on the audio output?

I’m thinking that you are not performing the test correctly.

I think you are right. When everything is set up with audio out and midi in, the unit plays ok, just very quiet and with no resonance. I haven’t done this test before…I tried to modify an audio jack to test and not sure how successful it was. Is there any other tests I could do. I appreciate the help :slight_smile:

Maybe you could sacrifice an audio cable for this task. Keep the jack on one end of the cable; cut the other end to get access to the two cables. Find out which one is the ground (sleeve) and which one is the tip (you could use your multimeter is continuity testing mode for that).

Connect the “sleeve” cable to the GND pad on the control board; and the “tip” cable to the point you want to probe.

One thing I might not have been clear about: when probing the points described above (starting at 1.), you need to have the control board connected to the filter board, and receiving MIDI notes.

Ah. I think that the cable I made was correct but didn’t have the control board connected. I will try again…thanks

Ok, test complete. OSC> pin gives a good strong signal. Point 1also gives a good signal. Point 2 and 3 are much quieter. Still no resonance at any point.

Remove IC3. Set your multimeter to current measuring mode (AC, I, 200mA or 20mA range). What is the current flowing between pin 1 of IC3 and pin6 (measured on the socket, chip removed)?

I get a zero reading from these points on IC3 socket (filter board)

Can you post a photo showing how you take the measurement?

Settings and testing?