Mixer channel at full volume, fader has no effect

[stoneattic]

I know I'm going to catch crap for even trying to fix this POS but I have an Alesis 1622 mixer that had a bunch of problems so I just pulled apart and cleaned everything. Nw everything works except one channel which is at full volume as if the fader were all the way up. This channel was acting this way before so I didn't don it with my cleaning. The pre-trim will control the level and everything else in the channel (EQs, etc) appears to work except the fader.

I'm used to passive volumes, like guitars, so it seems to me that would indicate that the fader is shorted (zero resistance) but I guess the fader's function could be different though. Any ideas besides setting it on fire?

Thanks in advance.

[jrfrond]

Sounds like either an open ground or wiper, depending on how it was "wired" (I don't remember). The problem is that the 1622 was made with totally integrated PCB construction and the fader carbon tracks are screened on the PC board, with the fader and pot wipers as separate assemblies. Sorry to say, but these things were born to fail. I've worked on a bunch of them, and the outcome was NEVER good.

[stoneattic]

No doubt the design, or at least the implementation is awful. But since the only issue is channel 6 I figured I should give repairing it a shot. Based on what you mentioned regarding a possible open ground I took it back apart and did some measuring.

One of the attached pics shows the carbon tracks for each fader and the other pic shows all the channels sliders with 2 pairs of fingers each. Sorry for the crappy pics. There's a thicker carbon track in the middle and a thinner track on each side. It looks like each pair of fingers connects the middle track with and outer track. So on all the other channels if I measure the connection at the bottom of the track to ground I get zero. If I measure channel 6 I get infinity. If I measure from one end of the track to the other I get 12.5K on all channels except 6, which I get 25K. I also get 12.5K to ground on all channels except 6, with give infinity. This is confusing to me. If I got the same 12.5K on the channel 6 tracks it would seem that adding a jumper from the tracks to ground would solve the problem, but the difference in resistance leads me to believe there's something else going on here.

Any ideas? Thanks again.

[Steve Conner]

Sounds like the bottom end of the thick carbon track has come disconnected from the PCB. Might be worth trying that conductive silver paint used to repair rear windscreen defrosters.

[stoneattic]

I was initially thinking the same thing, but 2 things got me wondering.
What are the chances that both of the channel 6 carbon track became disconnected but none of the others?
Why am I reading twice the resistance on channel 6 than the others?

Thanks!

[Steve Conner]

The difference in resistance means that a track is broken somewhere. The question is just where. I don't understand the exact reason for the readings you're seeing, but I'm sure I could fix the thing without needing to.

How did just those two tracks get busted? Maybe the knob for channel 6 got a real good whack and put a hairline crack in the PCB. Inspect carefully with a bright light and magnifying lens.

[J M Fahey]

Agree with above posts and add:
1) don't worry about the 25 K measurement vs. half that in others.
It's normal in certain pot configuration ... if properly grounded which this one is not.
Since you have 3 carbon tracks per pot, try to make each bottom end measure the same to ground (almost 0) as the others; conductive paint may work, but will be peeled by the sliding contacts , so maybe you will need to add something (a drop of epoxy, a small piece of plastic) to avoid it reaching "0", stopping just when reaching the repaired spot but not going over it.
2) If the repair does not work, maybe you can Dremel cut a somewhat wider slot in the PCB, forget the klunky printed pot, and mount a regular slider pot there.
Better than nothing.
3) I still can't believe the planed obsolescence mentality that was used in that design.
They guaranteed you have to drop the mixer in the dumpster after "x" hours of use.
Oh well.

[jrfrond]

The Pros and Cons of the Alesis 1622:

Pros: One of the first truly affordable racktop-mount mixers available.

Cons: Good idea, poor execution, born to fail, nearly unserviceable.

Alesis just NEVER got their mixer act together. The large-format X2 eventually amassed a looseleaf binder full of mods. Again, an affordable 8-bus mixer (pre-Mackie) that was just a design nightmare. The later Studio 32 was ANOTHER service nightmare! WTF?

The old Alesis Corp. was one of those companies that had some really cool products, but didn't quite think it all through, as evidenced by the number of mods and software updates needed for many products out of the chute. They were quick to push stuff into the market. One day it was vaporware, or an AES/NAMM mockup, and the next week, it was shipping. The ADAT, for which we were the first service center in NYC, was a real nightmare and moneymaker at the same time, because there were seemingly countless software and hardware updates between v1.00 and the final (for the Classic aka "Blackface") v4.03.

[km6xz]

Nowadays there is not much excuse for keeping a 1622 alive or using valuable desk space but in its day, musicians could afford it. The next higher step was 2-3 times as much.
The biggest paid was regular trouble shooting was impossible since getting to anything meant splitting the face panel from the IC board, which meant every pot, slide switch and fader immediately became an open circuit. If any defect is found, the only way to verify it was to reassemble the whole thing just to be able to run a signal through it. The circuit itself, except for faders, pots and slide switches was pretty reliable and not horrible. The painted-on faders, pots and switches however combined to put the whole mixer firmly in the category of horrible.
Ah, yes, the frequent field mods of Alesis products, a godsend for service shops. We got a plaque for the 5,000th ADAT Blackface we reworked...in the first 2 years, before we really got a lot of Alesis products. The last year or more of the old company, they fired all their techs, 23 of them, and sent all their factory work to us. That worked ok until they stiffed me for several hundred thousand in unpaid invoices, and the upper management bought the company out of bankruptcy for a song without any of the debt they personally amassed and started right back in business. I will never recommend any new Alesis product to even my worst enemy as a result of that fraudulent maneuverer. All customers were stiffed since they could not get their products fixed under warranty, nor get parts. As far as I know they are still crooks.

[jrfrond]

Nowadays there is not much excuse for keeping a 1622 alive or using valuable desk space but in its day, musicians could afford it. The next higher step was 2-3 times as much.
The biggest paid was regular trouble shooting was impossible since getting to anything meant splitting the face panel from the IC board, which meant every pot, slide switch and fader immediately became an open circuit. If any defect is found, the only way to verify it was to reassemble the whole thing just to be able to run a signal through it. The circuit itself, except for faders, pots and slide switches was pretty reliable and not horrible. The painted-on faders, pots and switches however combined to put the whole mixer firmly in the category of horrible.
Ah, yes, the frequent field mods of Alesis products, a godsend for service shops. We got a plaque for the 5,000th ADAT Blackface we reworked...in the first 2 years, before we really got a lot of Alesis products. The last year or more of the old company, they fired all their techs, 23 of them, and sent all their factory work to us. That worked ok until they stiffed me for several hundred thousand in unpaid invoices, and the upper management bought the company out of bankruptcy for a song without any of the debt they personally amassed and started right back in business. I will never recommend any new Alesis product to even my worst enemy as a result of that fraudulent maneuverer. All customers were stiffed since they could not get their products fixed under warranty, nor get parts. As far as I know they are still crooks.

Yeah Stan, but think of the good ol' days of training sessions with John and Angela, and all of us hangin' out eating those fabulous Alesis home-made lunches.

Doesn't kill the pain of getting ripped-off though.