Faders no longer fading? Tascam m-3500

[AnalogApples]

Am I going crazy? I meticulously and carefully cleaned each fader with d-100 DEOXIT. Dried them all with paper towel, then cleaned them again.

I’ve now noticed 2 faders that seem to do nothing to the volume. At the bottom, they turn off the signal, but everywhere else it’s the same volume.

I’ll have to tear apart the mixer again but I’m stressing. Maybe I plugged a couple wiring harnesses in reverse. Or what I really worry about is that there’s so much buildup on the moving part of the fader that it can’t contact the entire carbon track.

Live and learn I guess. Literally no change in volume which seems stuck at unity gain everywhere I move the fader, until it gets to the bottom and it goes silent. ?

 

[sweetbeats]

What kind of faders do you have? It sounds like you might have an issue where the wiper that progressively shunts signal to ground is not contacting. If you weren’t careful with your cleaning process you have have deflected a wiper set enough it no longer contacts the element…complete hypothesis.

 

[AnalogApples]

What kind of faders do you have? It sounds like you might have an issue where the wiper that progressively shunts signal to ground is not contacting. If you weren’t careful with your cleaning process you have have deflected a wiper set enough it no longer contacts the element…complete hypothesis.

These are those ALPS faders in a metal case. I’ll maybe post more details tonight after I get home and feed myself. I’d be surprised if I bent something. They seemed durable and I was being gentle. Thanks for the clue!

 

[AnalogApples]

Putting a multimeter on it reveals that I do not know how to test a fader with a multimeter ?

I do see some fuzz caught under the wiper part that bridges the two carbon tracks. I’ll clean this out and try it again.

2nd edit: there are finely broken solder joints where the fader wire harness clips into the PCB. I’m reflowing the solder to see if that fixes the problem. It appears that when I removed and reinstalled the fader wire clips, I broke a couple solder joints that were on their last leg. Let’s see if this fixes it!

3rd edit: this seems like it fixed the problem. I better check the other 120 solder points to make sure none of them cracked.

 

[sweetbeats]

Okay. Good job. Glad you found the issue.

 

[AnalogApples]

Okay. Good job. Glad you found the issue.

I was wrong, it didn’t fix it. I just tried putting a different fader on that same channel and it’s the same exact behavior. Fader goes from silence straight into unity gain…. I’m going to bed. I’ll dig into it more tomorrow. Thanks man!

 

[ecc83]

The only way that can happen is if the 'earthy end' of the fader is not in fact being tied to a ground. N.B. those faders might have two 'grounds'? One for attenuation to very low, -90dB say and then a 'gap' which gives a so called "infinite off". Check wiring carefully.
Duggey Self writes about this. I shall find me book.

Dave.

 

[AnalogApples]

The only way that can happen is if the 'earthy end' of the fader is not in fact being tied to a ground. N.B. those faders might have two 'grounds'? One for attenuation to very low, -90dB say and then a 'gap' which gives a so called "infinite off". Check wiring carefully.
Duggey Self writes about this. I shall find me book.

Dave.

Thanks Dave! At the end of the night I’d seen that it’s not my fader causing the problem. I did identify that the solder joints in these areas are super brittle, so, I suspect a broken solder joint that I haven’t found yet, one deeper in than the ones I already found. I’ll be home in 6-7 hours and will continue digging then. For whoever is reading this in 2034, the solder joints where the fader wires clip in are falling apart and it’s hard to notice. The majority of my problems with this mixer have been broken solder joints at fader or at the XLR input jack.

 

[ecc83]

Thanks Dave! At the end of the night I’d seen that it’s not my fader causing the problem. I did identify that the solder joints in these areas are super brittle, so, I suspect a broken solder joint that I haven’t found yet, one deeper in than the ones I already found. I’ll be home in 6-7 hours and will continue digging then. For whoever is reading this in 2034, the solder joints where the fader wires clip in are falling apart and it’s hard to notice. The majority of my problems with this mixer have been broken solder joints at fader or at the XLR input jack.

Rather than attempt to track down bad joints just link out the circuit?
Used to do that on tellies, early PCBs tech' was CRAP!

Dave.

 

[AnalogApples]

Rather than attempt to track down bad joints just link out the circuit?
Used to do that on tellies, early PCBs tech' was CRAP!

Dave.

It looks like the bad joints are all in one spot that’s been jostled a bunch over the years, so, it should be quick.

What is ‘linking out the circuit’? I’m just a lay person who pick up some tech skills out of necessity. Do you mean attach jumper wires from the fader directly to the channel strip?

 

[ecc83]

It looks like the bad joints are all in one spot that’s been jostled a bunch over the years, so, it should be quick.

What is ‘linking out the circuit’? I’m just a lay person who pick up some tech skills out of necessity. Do you mean attach jumper wires from the fader directly to the channel strip

Well I would need good close ups of the PCB but where I have had cracked print I don't necessarily repair it just trace where is comes from and goes and link it out. A neat job is done if you follow the line of print...didn't have it then but you could 'tack' the wires in place with superglue.

Dave

 

[AnalogApples]

Well I would need good close ups of the PCB but where I have had cracked print I don't necessarily repair it just trace where is comes from and goes and link it out. A neat job is done if you follow the line of print...didn't have it then but you could 'tack' the wires in place with superglue.

Dave

Oh! Now I understand. Yeah it isn’t the actual traces that are broken, it’s where the clip is soldered onto the PCB. I can see the wires protruding beyond the solder and they move with no solder. So I’ll just reflow that solder and do ‘em all.

I will repost here once I get all this done if this does not fix the issue. Thank you all for your support in helping me keep this mixer alive!

 

[Slouching Raymond]

Dry joints?

 

[AnalogApples]

Dry joints?

I’m learning new terms here!

 

[ecc83]

I’m learning new terms here!

Ray is a "Limey" like me and I suspect "of a certain age"? "Dry" joints was a common term 'in the trade' for poor soldering. "Cold joint" is another.

I would do more than simply remelt the solder, best to clean of as much as you can, I use solder wick, and then fix with fresh solder.

Dave.

 

[AnalogApples]

Ray is a "Limey" like me and I suspect "of a certain age"? "Dry" joints was a common term 'in the trade' for poor soldering. "Cold joint" is another.

I would do more than simply remelt the solder, best to clean of as much as you can, I use solder wick, and then fix with fresh solder.

Dave.

My mother always said, “if you’re going to take the time to do a job, take the time to do it right.”

Thanks for the correct way to repair a dry joint. I will do it this way. Cheers from Wisconsin in the USA!

 

[AnalogApples]

I pulled up each channel strip to inspect the solder joints connected to the other failing joints. I discovered that many of the wires were reversed during manufacturing.

From looking at the fader, is it ok to swap wires for 2 and 3? Like, can wire 2 go in 3’s spot on the fader? And vice versa? I’ll correct them all since I’ve got it apart but if it doesn’t matter then I’ll leave it alone.

 

[RFR]

I pulled up each channel strip to inspect the solder joints connected to the other failing joints. I discovered that many of the wires were reversed during manufacturing.

From looking at the fader, is it ok to swap wires for 2 and 3? Like, can wire 2 go in 3’s spot on the fader? And vice versa? I’ll correct them all since I’ve got it apart but if it doesn’t matter then I’ll leave it alone.

I’d say leave it alone if it came like that from the factory. Keep in mind however they wired it up, it worked.
Your task is to restore it back to its original state of functionality.

 

[AnalogApples]

I’d say leave it alone if it came like that from the factory. Keep in mind however they wired it up, it worked.
Your task is to restore it back to its original state of functionality.

Thanks for your input! I will leave it alone. My only concern that if the signal is balanced by the time it gets to the faders. Then I worry that inverts the phase. This happens on 10 out of 40 faders, so, I’ll assume the manufacturer was not as ignorant as I am, and the wiring is fine. Thanks y’alll!

 

[AnalogApples]

Update: after repairing dry joints, I still had the issue in 7 (seven) channels. The fader goes from “off” to 20db gain, no in between. Out of curiosity I reversed the red and blue wires on the faulty channel. Literally unsoldered the fader wires from the channel PCB and flipped them around. So far this has repaired 2 of 2 attempted faulty channels. WHAT A RELIEF!! These things must’ve come wired incorrectly from the factory! Wow!