Accent and decay not working, please help

[MMM]

But the Cutoff knob works fine?

[bryeng]

Yeah the cutoff works just fine. Like I say just the decay and accent not doing anything.

By the way, you do want these tests to be done with IC12 in place, as that's what I'm doing.

[MMM]

This will work fine without IC12. My guess right now is that either the filter envelope isn't even generated or that it doesn't reach the filter - probably the former.

With IC 12 removed and Decay at max measure the voltage on Pin 1 (where IC12 would go) while playing a note.

[bryeng]

With IC12 removed I get 0.025V at pin 1 both when a note is played and not.

[MMM]

This means the filter envelope isn't generated.

Check if D37 has the correct polarity. Then measure the voltage on both sides of it when playing a note.

(I'll check in again tomorrow.)

[bryeng]

OK,

D37 is the correct way round. There's ~1V at the cathode (marked side) and ~0V at th anode when a note is played. They are also around these values when no note is played. When the note is played they may fluctuate up by ~0.2V but then return to their orignial voltage. This fluctuation only happens sometimes though?!

Thanks again for your help so far with this; its very much appreciated.

[MMM]

This is getting a bit difficult to debug without an oscilloscope.

The "fluctuation" on the anode side of D37 should be a very short pulse (about 1ms) of about 0.8v when a note is played (this is the "trigger" for the envelope). Naturally measuring this with a multimeter may not result in a meaningful display, even if that pulse is ok. Since there actually is something happening on that side I'll guess the trigger is there.

On the cathode you should get the envelope portion: On pressing a note it should jump to about 12v and then fall again. My guess now is that the problem is somewhere around Q39 to Q41. Please inspect them visually (if they are the right types and correctly positioned). You can also check if 12v are present at the middle pins of Q40 and Q41.
Perhaps you may want to check before if R152 and R138 have to correct values.

[bryeng]

It's fixed! I took R152 out to measure its resistance and when I put it back everything works fine! It must have had one hell of a dry joint on it.
Anyway its all working as it should and sounds fantastic. Thanks so much for your help with this, without your help I would have been aimlessly poking aroud inside the x0xb0x.

Thanks again!

[MMM]

Congrats! Have fun with your xoxbox!