For reference a major component of Servisol 'switch cleaner' is petroleum distillate, a major component of WD40 is...petroleum distillate. Of course petroleum distillate can cover a whole range of products but you get the idea :)
Yup, the can I have in front of me says switch cleaner and lubricant...
I think the issue with WD40 is that over time it wears away but leaves a sticky residue behind - and that residue is what attracts crud. I assume that other lubricants, designed to also be cleaners, are formulated so that they don't do this.
As an update, I tried some IPA, and that gave a huge improvement - in fact, it was perfect for a few days. As of this morning I'm suddenly getting signal drop-out on the left channel, but I suspect this isn't related to switch/pot contacts. Time to have a nose around inside and probably re-route some things to determine where exactly the fault's happening. Wish I had my 'scope and ESR meter with me :-(
(I'm also thinking I might prod the car parts place in town this weekend
- maybe they carry some form of switch cleaner)
cheers
Jules
Lubes differ of course, what's in wd40 is a sticky oil better suited to cars.
I have occasionally seen a volume pot carrying dc, but not wired up correctly, ie arranged so that any slight poor connection produces a lot of noise. These can typically be silenced just by connceting the unconnected pot end to the wiper, or if that cant be done fitting a fixed R to the wiper and ground or one of the other terminals.
NT
What do you mean by 'not wired up correctly'?
Carbon pots carrying DC are much more prone to be noisy.
The change from valves to transistors, with their lower impedance circuitry and leaky electrolytic coupling capacitors, considerably increased the incidence of noisy volume controls.
Some can be cleaned easily and give long service before more attention is required, whereas, if the track is badly worn, relief, if any, is only temporary, no matter what you use.
In such cases, the only remedy is replacement.
There shouldn't be an unconnected end! The pot will typically be connected between signal and ground with the output being between the wiper and ground.
Carbon pots carrying DC are much more prone to be noisy.
The change from valves to transistors, with their lower impedance circuitry and 'leaky' electrolytic coupling capacitors, considerably increased the incidence of noisy volume controls.
Some can be cleaned easily and give long service before more attention is required, whereas, if the track is badly worn, relief, if any, is only temporary, no matter what you use.
In such cases, the only remedy is replacement.
That will modify the 'law' of the pot and change the wiper position for most settings. If the track is worn in the area that is most usually used (not surprising!) moving the operating point to a relatively unused section can work.
Fine as a diy work around but not worthwhile if a replacement is to hand as that will give a better guarantee of a long term solution.
And do check that the electrolytic cap thats supplying the pot or goes from the wiper onto the next stage is connected the right way around as I've come across them connected arse about face sometimes;!...
I wasnt quite clear was I. Sometimes the pot is wired such that if the wiper goes oc, the output, which connects to the wiper, is o/c. Adding a fixed R across the pot's output prevents this, ie from wiper to ground end. It can be high enough value to have only a trivial effect on the 'law' of the pot, which is a fairly trivial matter anyhow.
NT
I wouldn't have thought that made the slightest bit of difference. If the wiper's o/c, a resistor between the wiper and the ground end of the pot still won't provide any output.
However, if the earthy end of the track has become disconnected from the earthy connection pin, but is otherwise intact, the top of the pot and the wiper is still a variable resistor. The volume will probably be maximum, and more-or-less uncontrollable. Adding a resistor between the slider and the earthy end will give you of degree of control.
The same is true if the top end of the track becomes detached from the connection, except that the volume will be zero. Adding a resistor will restore some output (albeit less than maximum), and a degree of control.
When the wiper connection goes o/c, you often get a dc offset showing up on the output wire, creating major noise. Adding a resistor prevents this, and can turn a very noisy pot into a silent well behaved one, some of the time.
NT
Erme - anyone else abandoned the insulator element and the switch cleaner element and gone straight over the the main ingredient, petroleum distillate?
I'd run out of switch cleaner and rather than run out for switch cleaner, I squirted some lighter fuel into some scratchy pots instead. All the usual gunge dissolved out and the pots worked fine afterwards.
Nick
The school is about to throw away its 1970s Russian stereo microscope [1] and I perused the instructions. To degrease it on delivery you are instructed to wash it with "High grade aviation gasoline". Can't see that going down well with the insurers these days.
[1] I'll rescue it and repair it, but it'll have to go to another home since I already have a much better one. All that's happened is the M2 screws that hold the binocular body onto the focussing slide have pulled out. Drill and tap to M2.5 and fit new screws should fix it.In message , Skipweasel writes
Hold it for me then
I'll be passing through shropshire next weekend
If it isn't the BM-51-2 shown about half way down here...
It's really nothing to write home about - but I hate to see things thrown out when a few minutes work would fix them.
Yup, here it is...same box, too.
You are implying that you have understood my reference to changing the law of the pot to be derogatory. This is not so - if you read it carefully, you will see that I was simply pointing out that changing the law of the pot (within reasonable limits, of course!) is the reason that your idea can successfully move the normal operating point away from the worn area of the track.
However, if the wiper goes o/c *after* you've made your modification - and that is the way I interpret your post - then the pot is useless: the only solution is replacement.
"When the wiper connection goes o/c ..." the pot no longer works, noise or no noise, so replace the bloody thing!
Better than nothing, which is what I have ATM
I should be in Shrewsbury next sunday, drop me some details
Not at all, its common for pots to go momentarily o/c while rotating them, and as long as its very brief its not normally noticed. If it gets to the point where it is noticeable, then yes, its replacement time.
NT
Oh, and the other channel followed it some 30 mins or so later. Strange that they didn't fail at the same time. It might be an age-related component failure and it's just coincidence that both channels died within a narrow space of time - or a single component failure has had some kind of knock-on effect that's killed something in both channels (and it took one side longer to go bad than the other).
I might get a chance later today to do some more in-depth digging. Ignoring the tuner stages, I don't think this thing is particularly complex, so it shouldn't take long to trace a schematic out.
cheers
Jules
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