Whine from very old Arachnid board (the saga continues)

[p_wats]

Ever have one of those weeks where nothing you touch works?

After scrapping the last Arachnid board that had been working fine until I pushed it too far with more mods I decided to try again, taking what I learned to an even older Arachnid/Octagon board.

I carefully built it up and tested each stage before moving on, then when it came time to box it up I noticed that, while it worked, there was a persistent whine/high pitch sound with the wet signal. Trying to be more methodical this time, I've eliminated other variables (relay board, clock module, etc.) and am back to mostly just the old Arachnid PCB.

• The whine I'm noticing is not present on pin 1 of the FV-1, but can be heard in the circuit once it leaves the chip (Pin 28)
• It is present without anything plugged in to the input
• It does not go away when the circuit is boxed up and grounded to the enclosure
• It is still present with battery power

This circuit was boxed up and working fine for a long while before I took it out of the enclosure (maybe my first PedalPCB project)---I even recorded with it and don't ever recall this whine being there before.

Has anyone ever experienced anything similar? Thanks for any troubleshooting support for this or my last attempt!

(in the photo below the crystal and 15pf cap are not actually soldered, just there to test after I removed the clock module. The connection at R5 is to toggle internal programs. Also, the relay board is disconnected from power and I'm using gator clips on the main board to test in/out)

 

[p_wats]

Came back to this after a few days away.

This is the board version I'm working with: https://web.archive.org/web/20180417131331/http://www.pedalpcb.com/docs/Octagon.pdf

• I've checked all components and replaced a few, just to be sure (including the R5, where the toggle switch connects).
• I've also re-flowed all joints.
• Voltages look fine.

However, the more I grasp at straws the worse off the board ends up (I now need to replace a pot, as it hasn't handled being bent back and forth very well), so I'm hoping for more educated guesses.

 

[p_wats]

I've now compared this schematic to the more recent version and changed some values and amended where I could to match (aside from the mix pot and mode control changes). I've also swapped the ICs.

There's still a persistent high pitch whine underneath the wet signal.

I've got 2 working newer version Arachnids beside me that are perfectly quiet.

Starting to grasp at straws, so open to any suggestions!

 

[p_wats]

I had some time today, so I replaced every electrolytic capacitor (including subbing in MLCCs for all the 1uf coupling caps).

The whine is still there.

For some effects it wouldn't be that noticeable, as I could roll back the mix (the whine goes away as you decrease the wet signal), but half the fun of these weirder FV-1 patches is to go all out.

At this point, unless @PedalPCB or anyone else has run into something similar, I'm not sure what else to try, so I'll likely put this one away for a while and rebuild my self esteem with something simple. Last night I shot awake thinking I'd spilled molten solder everywhere, so I think I need a break from troubleshooting!

 

[p_wats]

What are the odds the whine could be coming from the FV-1? I've got some low-temp solder and am tempted to try removing the FV-1 from the board and replacing it with the one I removed from my other Arachnid (the one that wouldn't do anything but internal programs).

I don't expect that to actually help, but I've replaced almost every cap, ICs and checked voltages and continuity, and still a high pitch whine persists (even on battery power).

 

[p_wats]

After solving an issue with a different build, I decided to give this another once over. Here are more findings:

• The whine sound disappears when rolling back the mix pot (all pots seem to function fine)
• I've followed the schematic and traced continuity through the entire circuit, finding no issues
• I've temporarily added another 100uf cap from 9v to ground, VREF to ground and 3.3v to ground, but it never had an effect

 

[Robert]

It could be the FV-1, and it seems like you've eliminated a lot of other possible causes, but defective FV-1 ICs are pretty rare.

 

[p_wats]

It could be the FV-1, and it seems like you've eliminated a lot of other possible causes, but defective FV-1 ICs are pretty rare.

Yeah, I doubt it's actually the FV-1, as it would have to have become defective since this circuit was removed from the enclosure and modded, messed with etc.

I'm just not sure what else it could be at this point, as all other ICs were replaced, as well as all electrolytics and continuity between all points has been verified. I'll let it sit for a bit and see if there's a eureka moment later.

 

[zgrav]

you could try replacing the voltage regulator for the FV-1. possibly a noise source.

 

[p_wats]

you could try replacing the voltage regulator for the FV-1. possibly a noise source.

Worth a shot!

I've now socketed the regulator and tried a few different ones---seems to be no difference in noise.

I have noticed that the regulator gets much warmer than in my other Arachnid builds though, so I'm curious if that's a symptom worth investigating.

 

[zgrav]

At least eliminating other part issues is making progress. Not surprisingly, it makes sense to eliminate everything else before swapping out the FV-1.

 

[p_wats]

I was able to use the low-temp solder recommended in another thread by @zgrav to get the FV-1 off the board. After which I soldered in the one I took off a different recently failed build, in which I could only access internal FV-1 programs. Lo and behold, the whine was gone, but I could only access internal programs again!

Adding the other FV-1 back, I could access the EEPROM, but the whine was back.

My understanding is the FV-1 is pretty resilient, but is it possible I have somehow managed to damage two, in totally different ways?

Have you seen anything like this before @PedalPCB ?