I had this board for about 2 weeks now, it's an Allen&Heath System 8, oldye from the eighties and
prior to my ownership the guy had in his studio and
used often for tracking/recording but probably
didn't get a lot of use for the past month or so.

I'm getting the scratchy noise on a lot of knobs and
switches [gain, eq, pan, mute, etc.] and i cleaned 2
channels by taking all the knobs and buttons and clean
the pots/switches by vacuuming then using isopropyl.
I have been using it on a daily basis hoping it'll get loose and stop making the noise but hasn't happen yet.

What would be the next thing to do? I know it can be opened and take each module out as it's semi-modular.
So is there a way of getting rid of the noise or will i have to replace those pots and switches?

Isopropyl won't take any of the oxidized crud off the metal contacts.

Assuming you have low current switches and pots, DeOXIT GOLD spray
can really help. I've used on my old Rhodes a bunch of times and it
always works. On the potentiometers, it will wear off after a while, and
you'll have to re-apply. If you have sealed pots, then it's sometimes
difficult or impossible to get the spray onto the resistive surface (which
can scratch or tear after a long time). In those cases, either spray
the sh*t out of them and hope the seal isn't too good .. or you'll have
to replace them.

If you have high-current switches, the DeOXIT contact conditioning spray
can clean all the gunk off...

I'd try those ... other than that, break out the soldering iron and replace them.

jeff

Well the guy before had these sprayed with DeOxit, in
fact there was a bunch of it still around the pots when i cleaned it and i can hear the gooey stuff inside the pots
when i wiggle them a bit so there's some in it.
I'm not sure how i feel about this DeOxxit stuff, i almost
think it attracts more dirt then it cleans especially with
this board which has plenty of room between the plastic
knobs and the board.

I am getting ready to open it up tonight to see how it looks. How do you know if the pots are sealed or not?
Is it obvious and if they're not i should be able to open them up and clean them, right?


b.

deoxit did wonders for my old board!thumbsup

Crackling pots are not always due to dirty contacts. This also happens if a coupling capacitor leaks and allows DC to get into the circuit. If you have a multimeter you can verify if this is the problem by measuring for DC voltage across the outer terminals of the pot.

--Ethan

I used to have an A&H System 8. Great affordable mixer. Built like a tank. Decent pre's and EQ.

Wash out the de-oxit with a non residue contact cleaner. Caig products leave a film behind, that attracts dirt and carbon dust. Switches can be filled with the same non-residue contact cleaner, exercised and then blow it out with compressed air.

Jim Williams
Audio Upgrades

@ james

i got your old system 8, man.heh
bought it from adam in cleveland, couple of weeks ago.


@ethan
i do have a multimeter and i just opened the board last night so i can do the DC test. What
am i looking for? Just for the readings to be the same?
There's a few things going on with this board and
i'm trying to see what needs to be repaired.
I've tested the caps by running an oscillator thru
the boards's inputs and the busses and master came out pretty good, everything under 0.5db
difference [i've run a 1k osc and set everything
at 0db then ran a 20hz, 50hz, and 15k osc] but
the channels were kinda off, some of them by
1.5db. I've looked inside and the caps looked fine though.

Another thing about the scratchy pots is that some of them, like the gain pots, are not putting
any signal through sometimes unless i turn the knob to about half way then the sound kicks in.
Some of them get kinda distorted also when pushed close to 10, and some of the eq pots give
some nasty pops when pushed close to the max.

Thinking this is a semi-modular design i figured
i can open it up and take some of these channels
out to either clean or replace the pots but it doesn't seem that easy, there are about 20 wires
that run from one end of the board to the other,
through every strip's board so i'd have to cut them in order to get the strips out. Not really wanting to deal with that

@jim

that's kinda what i'm leaning towards, i'm not so
sure about the deoxit stuff altough lots of people
like it.
It's true there's some lubby stuff inside the pots
from the last owner and i'd like to get rid of it.
I have isopropyl [i think is %90], would that do
and can i just pour it inside the pots and not worry about leaking on the board inside?
The bottom part is opened so i'm not worried about leaking other then the rest of the parts.
thx.

sorry i cant be of more help, but deoxit usually works for me...

anyway, where were you on the columbus ohio thread?

Columbus OH Sluts, declare yourselves!

The lube is on the shafts, don't remove it. Too much spray can wash it out, less is more when applying cleaners. Modern non residue spray cleaners with the red applicator tip are available from any electronics dealers like Fry's. A quick squirt into the slot at the side of the pot is usually enough. Don't worry about DC leakage, El caps rairly short out, they usually open up in failure, opposite of tantalums which can short out. Those are old, low quality caps, replacing them with low impedance types like Rubycon Z, Nichicon HE or Panasonic FM will help if you enlarge them a bit (220 uf instead of 47 uf).

Jim Williams
Audio Upgrades

@imnickb

yeah, i've had that thread opened about a week ago,
i thought i've replied to it, i guess i forgot. i'll get on it
though.......

@jim

thanks for the info.....
about the caps, i did the test with Mr. Goreski's help @http://www.AnalogRules.com
he mentioned that those readings weren't that bad but
i dont know it's seating well with me. i mean, i had the
faders on some channels as far as -2db in order to get a 0db reading @ 1k osc.
And the other frequencies readings going up and down
like that, i dont know i can be happy with it. Maybe i'm
spoiled by the digital accuracyheh

I probably will have to recap eventually.
What do you think about those 20 wires going through
all the boards? I will have to cut them, right? Then just
solder at the ends?

Easiest is to put the probes across the outer pot terminals, with the meter set to DC, and see what you get with no signal passing through. The DC voltage should be very small, down in the low millivolts.

--Ethan

Last night i did some cleaning on two channel using 2
different cleaners to see what results i get and so far i'm not too happy.

Here's what i did:

On the first channel i've used a radio shack brand cleaner, "Precision Electronics Cleaner", and the ingredients are Isohexane, Carbon Dioxide, and Ethanol.
It's supouse to be non-residual.

On the second channel i've used Isopropyl at %91 and
the rest water. I've used an eye droper to pour this in and i liked it better than the spray can which was a little messy.
Both channels were sprayed/poured 3 times with plenty
of twisting of each pot while it was wet and plenty of time in between applications.
I've noticed some improvements on some of the pots but there are still a few which have not improved at all.

The same radio shack i got the cleaner from has
the DeOxit brand in store and that'll be my next step.
However, i'm a bit skeptical. I feel some of these pots
are not gonna get any better.
I haven't tried testing the contacts with the multimeter yet due to the way things are setup [i have to twist everything around in order to able to have the board upside down and plugged in].

What do you guys think about all this so far?

Those 16 mm pots are rated at 15 k rotations, maybe they are past that. The last step to recover them is an ultrasonic wash. That requires you to de-solder the buss bars and romove the modules. A small washer can be used if you remove the pots via a desoldering tool like the Hakko 808. Once cleaned, you need to re-lube the pot shafts or they will seaze. I have seen hopelessly scratchy pots come back clean after that.

Jim Williams
AudioUpgrades

Jim, about the buss bars, are they all one long wire?
I'm assuming i'd have to desolder them on every
strip and pull them out if that's the case.
What about cutting them so i can do one strip at atime then resolder back togheter?


thx.