Aion shreadmaster volume stuck at one value?

[zenless]

So i'm a little stumped. I built out a Aion shreadmaster, tested it out and seemed fine (though obviously missed something!)

After i boxed it i discovered the volume pot didn't seem to adjust.. used an ohm meter and found the resistance didn't change. So replaced it (100kA), but same problem. And outside the box the resistance did change! So I reflowed all the solder for the connections near by, but no change. My only thought is in the pictures there are a couple of small (though bought as 1/4 watt still) resistors from diyguitarpedals.
Should also note everything else seems to work fine, able to adjust gain, contour,etc without a problem from what i can tell.

Any tips on what to check? Here are pics!

[mgwhit]

After i boxed it i discovered the volume pot didn't seem to adjust.. used an ohm meter and found the resistance didn't change. So replaced it (100kA), but same problem. And outside the box the resistance did change! So I reflowed all the solder for the connections near by, but no change.

So what resistance do you measure between pins 3-2 and between pins 2-1 when it is in the box?  Is the volume always zeroed, flat out or somewhere in between?  Be aware that resistance is tricky to measure in circuit -- particularly when in the presence of capacitors and/or paths to ground.  I'm just interested to see what you get.

And please test continuity between the volume pot pins and their nearest components on the schematic.  I would recommend testing between pin 1 of the volume pot and pin 7 of IC2, between pin 2 and the near side of C17, and between pin 1 and the positive leg of C19.  Good luck!

[zenless]

After i boxed it i discovered the volume pot didn't seem to adjust.. used an ohm meter and found the resistance didn't change. So replaced it (100kA), but same problem. And outside the box the resistance did change! So I reflowed all the solder for the connections near by, but no change.

So what resistance do you measure between pins 3-2 and between pins 2-1 when it is in the box?  Is the volume always zeroed, flat out or somewhere in between?  Be aware that resistance is tricky to measure in circuit -- particularly when in the presence of capacitors and/or paths to ground.  I'm just interested to see what you get.

And please test continuity between the volume pot pins and their nearest components on the schematic.  I would recommend testing between pin 1 of the volume pot and pin 7 of IC2, between pin 2 and the near side of C17, and between pin 1 and the positive leg of C19.  Good luck!

So i must be crazy, now the values on the pot pin to pin do adjust. Volume does not actually change when adjusting the pot though. The resistance to c17 stays at 2.5 ohms, to ic2 pin 7 shows 740-900 k when adjusting. To c19 stays at 3.4ohm.

So C17 bad?

[mgwhit]

So i must be crazy, now the values on the pot pin to pin do adjust. Volume does not actually change when adjusting the pot though. The resistance to c17 stays at 2.5 ohms, to ic2 pin 7 shows 740-900 k when adjusting. To c19 stays at 3.4ohm.

So C17 bad?

No reason to suspect C17 of anything.  I was really just asking you to check continuity between the pot pins and those components, not resistance.

Test resistance between pins 1 and 2 and between pins 2 and 3.  Test those at maximum counterclockwise, twelve o'clock and maximum clockwise settings on the volume knob.  Also, what setting does the volume seem to be stuck on?  Somewhere in the middle or either extreme?

[zenless]

Those seem to adjust from approx 0 to 100k. The volume seems a little on the high side

[mgwhit]

Those seem to adjust from approx 0 to 100k. The volume seems a little on the high side

I should have added, is the resistance between pins 1 and 2 always approximately 100K minus the resistance between pins 2 and 3.  Apologies if that sounds obvious, but if the pot is adjusting resistance on the wiper now, and if pin 3 is connected to VA, there's not much left to check there.

Oh, and is this malfunctioning both inside and outside the enclosure now?

If the pot really appears to be functioning correctly, please go ahead and post the voltages from all of your IC pins.  I'd like to at least confirm that your VA is correct since that is what your volume pot uses as a virtual ground.

[zenless]

Those seem to adjust from approx 0 to 100k. The volume seems a little on the high side

I should have added, is the resistance between pins 1 and 2 always approximately 100K minus the resistance between pins 2 and 3.  Apologies if that sounds obvious, but if the pot is adjusting resistance on the wiper now, and if pin 3 is connected to VA, there's not much left to check there.

Oh, and is this malfunctioning both inside and outside the enclosure now?

If the pot really appears to be functioning correctly, please go ahead and post the voltages from all of your IC pins.  I'd like to at least confirm that your VA is correct since that is what your volume pot uses as a virtual ground.

1 to 2 and 2 to 3 seem to add up to 100. The volume seems to behave the same either way. Where should i connect the other connection to from the IC? BTW Thanks for the help 

[mgwhit]

Where should i connect the other connection to from the IC?

Not sure what you mean here.  Are you asking how to measure voltage on the ICs?  If so, set your multimeter to around 20V DC, clip the black lead of your multimeter to a ground point in the circuit (right on the power jack is perfect as long as you don't short out to the power lug, or to the enclosure if it's connected and grounded) and then probe the IC pins with your red lead.  Start to the left of the notch and move around the pins counter-clockwise.  Apologies if that's not what you meant.

[zenless]

Where should i connect the other connection to from the IC?

Not sure what you mean here.  Are you asking how to measure voltage on the ICs?  If so, set your multimeter to around 20V DC, clip the black lead of your multimeter to a ground point in the circuit (right on the power jack is perfect as long as you don't short out to the power lug, or to the enclosure if it's connected and grounded) and then probe the IC pins with your red lead.  Start to the left of the notch and move around the pins counter-clockwise.  Apologies if that's not what you meant.

Ohhhh, ok that makes sense, thanks! For some reason my morning brain was reading that as looking for resistance originally. I'll check it out this evening. Thanks again!

[mgwhit]

Just so you know where I'm going here, you've confirmed that the potentiometer is functioning correctly, but it doesn't appear to be functioning as a proper voltage divider like a volume pot should.  If the connection to lower potential through the reference voltage rail (i.e. VA) is wonky, the potentiometer could just be functioning as a variable resistor, in which case it's affect on volume would be minimal.

[zenless]

Just so you know where I'm going here, you've confirmed that the potentiometer is functioning correctly, but it doesn't appear to be functioning as a proper voltage divider like a volume pot should.  If the connection to lower potential through the reference voltage rail (i.e. VA) is wonky, the potentiometer could just be functioning as a variable resistor, in which case it's affect on volume would be minimal.

Meant to do this sooner, anyway, here's the ic voltages
ic1
4.7
4.7
4.6
0
2.32
4.7
4.7
9.4

ic2
4.7
4.7
4.69
0
4.59
4.7
4.7
9.4

[mgwhit]

Well, there goes my theory....  Those all look good.

[zenless]

Hmm, maybe remove RPD2? Though if that was grounding it out too much it'd just fail completely wouldn't it? Maybe those smaller resistors aren't holding up ?

[mgwhit]

Hmm, maybe remove RPD2? Though if that was grounding it out too much it'd just fail completely wouldn't it? Maybe those smaller resistors aren't holding up ?

Double check the value of your RPD2 before you desolder it -- it should be Brown - Black - Black - Yellow - Brown and you can probably measure it easily, too.  I couldn't see it in your photos.  A smaller value there could mess with your output.

And while 1/8W resistors wouldn't be the first components I would choose for the power section of a circuit, those should be fine there.  If they had problems, they would fry themselves (usually visually obvious) and your VA voltage would be hosed.

[zenless]

Hmm, maybe remove RPD2? Though if that was grounding it out too much it'd just fail completely wouldn't it? Maybe those smaller resistors aren't holding up ?

Double check the value of your RPD2 before you desolder it -- it should be Brown - Black - Black - Yellow - Brown and you can probably measure it easily, too.  I couldn't see it in your photos.  A smaller value there could mess with your output.

And while 1/8W resistors wouldn't be the first components I would choose for the power section of a circuit, those should be fine there.  If they had problems, they would fry themselves (usually visually obvious) and your VA voltage would be hosed.

Thanks again. They're supposed to still be 1/4 watt, but making a guess of what if they were 1/8th. I'll double check RPD2 tonight.