Aion VH Drive issues

P

punchy712

Active member
Hey everyone, I'm a little stumped with this issue and I'm hoping to get some help. First time building an Aion pedal, the VH drive (https://aionfx.com/app/files/docs/vh_drive_channel_documentation.pdf) and it worked for a few minutes, but then it got noisier and noisier until after a couple of minutes where now it's all noise that's coming out of it even with nothing plugged in.

The one thing that's obvious that I screwed up is that I mounted the foot switch on the wrong side of the board. I'll have to fix it before I box it, but I don't think it would cause any issues while I'm testing it (please let me know if I'm wrong).

The voltage coming out of the power board look good, +/- 15v and going to each IC as expected in pins 4 and 8. The one odd thing I see is that pins 1, 2, and 3 of IC 1 have some negative voltage (-8v to -12v) and I can't explain that but I'm also not sure it would cause the issue here.

In the screenshot, IC1 is removed while I was testing some voltages only.
 

Attachments

  • IMG_2046.jpeg
    IMG_2046.jpeg
    730.3 KB · Views: 15
  • IMG_2045.jpeg
    IMG_2045.jpeg
    757.6 KB · Views: 15
Sort by date Sort by votes
That's really odd. Does it make that noise in the bypassed position as well? With IC1 pulled?

The fact that there's noise on your input, and there are negative voltages on the first input half of IC1 makes me think that something has gone wrong very early in the signal chain, maybe even on the daughterboard. Do the negative voltages on IC1 happen with the chip in or out? If it's out, do you get any negative voltages there? That might be a clue that there's a short/low impedance path between something in the input chain and the negative supply. (Bad cap somewhere in the power section?)

My SWAG is that the noise you hear is the switching noise from the DC-DC converter.
 
Upvote 0 Downvote
When bypassed, the clean signal at the output is all good. When IC1 is pulled there is no noise present at the input where I was probing in the audio clip.

The voltage of IC1 (pin 1-8) with the chip in: -7v, -6v, -8.5, -15v, 0v, 0.1v, 0v, 15v. With the chip out: -8v, -7.5v, -6v, -15v, 0v, -0.01v, -0.01v, 14.95v. The voltages at pins 1 to 3 always fluctuate, especially with the chip out where the voltage drops until it settles a bit (like a capacitor being drained and then filled).

My guess on the noise is the same as you that it's the big DC-DC converter. With the issues starting very early in the chain it seems like it shouldn't be that hard to narrow down the issue but I'm not fully understanding what's going on.

In case this may be a clue to others because it doesn't make sense to me. I measure the resistance of a few of the resistors in the circuit (with it powered off) and the values don't make sense as I thought they should measure okay since they're just connected to ground. RPD is 61k (should be 2.2M), R2 is 180k (should be 270k). I pulled them out just to make sure they're okay and they measure correctly. The value of R1, which is not connected to ground, measure as expected in the circuit.
 
Upvote 0 Downvote
You must log in or register to reply here.
Back
Top