Alto L12 mixer, only 2007

[Eeyore]

Eeyore wrote:

N_Cook wrote:

And the master slider pot has failed (Chinese so assume unavailable).

Why ? They use standard parts and you can contact Phonic.
http://www.phonic.com/

Sorry, it was Alto.
http://www.altopa.com/default.asp
http://www.altopa.com/default.asp?p1=5&p2=32&p_id=35

Graham

 

[N_Cook]

All foregoing is now digression.

End-snipping and then grinding off the tinplate tangs before desoldering the
active pins is the way to deal with these , without colateral damage.
Getting inside, the non-resistive tracks are only 1mm wide and one pair of
single wiper "wires" must have been right on the edge of one such track so
intermittant contact, 1/2mm transverse bend and repaired.
Will resolder the remnant tinplate tangs for earthing and add hot-melt
around the housing where there is spaces.
All 9 of these sliders are the same, but no problem with a channel one going
U/S unless someone uses all channels, problem was of course, Murphy's law,
on the critical one..

Only info on the side is rather self evident 10KDx2.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[N_Cook]

For future reference I had a go at adapting one of the linear 250K ohm
slider pots. I doubt if the following could be used for the narrow tracks
inside the Chinese one, but if space allows for a more conventional one as I
had anticipated doing.

With 2 narrow pieces of "masking tape" I laid one, leaving just the outside
edge of the 250K track exposed and another one on the paxolin, leaving a 2mm
strip un-masked .
Squirted out some "RFI/EMI" spray into a pot and then with a toothpick laid
down a thin line of aquadag, or whatever it is, along about 40 percent of
the track (for comparison purposes) . Silver paint would have done instead,
but just a prooving exercise.
When dried that measured 23 ohm , over its length, and about the same for
that portion of the pot track via the 2 relevant terminals.
With a razor made 3 cuts, so divided the aquadag track into quarters. Then
some nail varnish just over the aquadag and onto the remaining paxolin just
to confirm no adverse reaction and a suitable fixative and rassembled.
I suspect the characteristic would be a bit wavy rather than linear, if
properly plotted out, but results
5 percent 10 ohm
10 % 400 ohm
20% 1.8K
30% 8K
40% 42K
50% 66K
and then much as the original 120K to 250K of course

I didn't bother with the following, but
For the upper section, for a log characteristic, then lay down a full length
aquadag track and make more , closer spaced cuts, and also a 1K and 20K
resistors or whatever , to fit, external to the pot.
Other non-linear characteristics , other than log could be so fashioned. And
as the thickness of the aquadag track is not critical then rotational pots
could be so converted almost as easily. The only criteria are higher ohmic
value to start with than final requirement, low wattage and enough space to
lay down these extra tracks.
Another one for my tips files. The internet timewasters can continue their
predilictions and buy 1000 off from Hong Kong or whatever they have to do.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[N_Cook]

The "aquadag" I used contains nickel and air drying acrylic resin

Closer checking with vernier calipers and DVM there was an abrupt jump at
23%,
from 1.5K to 3.4K, so not a perfect solution


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

 

[Eeyore]

N_Cook wrote:

I just thought of a possible way round the surface roughness.
Lay the resistive dust in place. Reaassemble the pot with the wiper at one
end and run the 3 wire fingers,of each wiper, along the track and then undo
the pot again. Then fuse the toner/graphite hopefully to something like
20Kohm and then add 1K and 20K (actual on test) resistors each side, .
Rather than 2 differing mixes of resistive dust on each track.

For CHRIST'S SAKE buy the proper replacement part !

You STILL haven't answered the question about what the travel is in mm. 60mm
most likely IME. Dual 10kA sliders are available widely that'll fit. I think
there are only 2 popular footprints.

http://www3.alps.com/WebObjects/catalog.woa/E/HTML/Potentiometer/SlideMixers/SlideMixers_list1.html

Look at those 'low profile master types'. Soundcraft use them in the Spirit
range, so they can be obtained as spares from them.

Graham

 

[Eeyore]

N_Cook wrote:

The "aquadag" I used contains nickel and air drying acrylic resin

Closer checking with vernier calipers and DVM there was an abrupt jump at
23%,
from 1.5K to 3.4K, so not a perfect solution

How much are you going to charge this poor customer for an incompetent repair
?

Graham

 

[Eeyore]

N_Cook wrote:

Only info on the side is rather self evident 10KDx2.

ALPS D taper is 10% resistance at the centre (-20dB) as opposed to the more
popular A taper which is 15% (-17dB).

A virtual certainty it's an Alps part. Is the base also white plastic ?

Graham

 

[Eeyore]

N_Cook wrote:

And the master slider pot has failed

Does it look a bit like this ? Wrong length in the pic and only mono but this is
basically the kind of part.

http://cgi.ebay.co.uk/Slide-Potentiometer-10K-100K-or-500K-1-49p-ea_W0QQitemZ220339258157QQihZ012QQcategoryZ48618QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Graham