And the master slider pot has failed (Chinese so assume unavailable). Long but tiny cross section stereo 2x 10K log pot. Found a larger one that there maybe enough space and can be screwed onto/under/through the top panel and wired into the pcb but it is 2x 250K lin of course.
10K and 1K resitors in parallel with each pot, will that be a work around or will the characteristic be too "lumpy" on the low end?
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I'd be surprised to see this as a suitable solution. Can you swipe a pot from the last channel or are they different? I've done this in the past when no alternative was available and the customer knew what to expect.
I'd thought of that but to safely remove the failed one I will be grinding off the mounting tangs, then desolder the active pins, as there is SM right up against the pots. They are all similarly crammed in , but there is space between the pcb mounted pots and the back face of the top panel.
I will plot out a 25:1 ratio fudged pot to see how removed it is from the original 10K at 100 percent and 1K at 50 percent travel.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Yep , graphing it out the characteristic is hopeless. Matter of opening up the pot and dabs of silver paint or a graphite compo along the tracks and a pair of resistors looks necessary to bring it back to something like functional equivalent.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I long since stopped wasting my time on such activities. Right electrical characteristic but totally wrong dimensions or vice versa or minimum order requirements, main agents only , etc etc always a total waste of time and/or money , I now always go for fudged work arounds.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Anyway sometimes you can find manufacturers that will sell you faders for their gear that are also found in other equipment. Like your Numarks, Kam, Mackie, Behringer, Soundcraft etc etc. Get a few spare and you can sometimes swap tracks or shafts where the fader isn't quite the same. Stereo versions sometimes have the same footprint but just don't use half the pins, so you can just get a few of those for all cases.
If there is really no way to replace a fader I tend to leave it at that, rather than attempt a Bodgitt and Scarper repair. I won't do anything I wouldn't want another tech to look at and go tch tch.
and see if any of them might offer a workable solution for you. I realize it will probably never be an exact match for the original taper, but sometimes it can be worked out really close. Good luck ==============
Dave M
Never take a laxative and a sleeping pill at the same time!!
" * I have heard that you can use copier toner dust to melt over a section of worn resistor material and repair it. "
probably referring to my tip for worn pots, fully detailed here
Dismantle the pot down to the carbon track clean/degrease. Make up resistive compound from photocopier toner and graphite powder obtainable from locksmiths for dry "lubrication". the following resistivity values are very approximate for .02 inch thick film. graphite:toner ratios
1:1 ,200 ohm per square inch
1:10, 100k ohm per square inch
1:30 10M ohm per square inch Mask off area surrounding carbon track,sprinkle on the powder,fuse the film in a low oven approx 150 degrees centigrade or hold the barrel of a soldering iron 1mm from the powder to heat .When fused lightly abraid with a nail file,and reassemble pot.High ohmic pots are a bit iffy,low ohmic are fine. p.s. I would be interested to hear of any suggestions for higher resistivity addmixture for higher ohmic pots (for more even distribution)
Which I will probably use for this Chinese pot. the main problem with it is not having a nice flat surface after "curing". Needs some sort of aqua process perhaps to give an initial flat surface. Aquadag or whatever EFI/EMI screening black (dries to slightly brown side of black) stuff is , may be useful for very low ohm but probably too brittle and does not adhere to impervious surfaces. My can of it is too old to get product details RS stock number "551-570" other than it contains MEK and xylene
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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