HOw to clean a mechanical encoder

[Aussie Susan]

I have a Rigol DS1102D that has a mechanical encoder (from what I gather from the service manual and some other youtube videos) for several of the controls. Most of these are working well but two (one for the menu selection, cursor positioning etc. and the other for the horizontal trace position) cause the trace or controlled item to jump about - sometimes working well but other times not working at all or moving in a jerky back and forth manner.
I suspect that they need to be cleaned. I am reluctant to pull the scope apart just to clean these controls (but I can if that has to be done!).
Is there a (safe) way to clean these encoders - such as using compressed air, WD40, flooding with alcohol etc.?
Susan

 

[D.A.(Tony)Stewart]

Rigol has really annoying , really low quality rotary switches and is the side effect of a low budget. You are not alone.
Dust can be a problem but normally it is the lack of gold plating for friction contact surfaces that is mandatory for I<2A since there is no wetting (deoxiding) current. All good switch contacts <=2A must have flash gold plated contacts, which can range from 5~25 um thick I recall. Cost reductions affect this.

When infrequently used, it oxidizes. WD40 can lubricate the cutting action and connect with surface roughness which wears down plating, but that might need to be repeated every year or so.

 

[Aussie Susan]

Thanks Tony.
I've tried the WD40 and it seems to have helped one of the encoders but the 'trigger position' encoder is still a little jumpy - not as bad as before but I may need to look into replacing it if it continues to 'annoy' me.
Susan

 

[dick_freebird]

Can you get spray to the contacts? QD contact cleaner supposed to leave no residue (but where is the crud to go?) might help.

 

[Aussie Susan]

@dick - thanks for the suggestion. I;ve not heard of 'QD COntact Cleaner' (I'm in Australia - the clue is in my alias) but I see that there are a few places that sell it here.
Anyway, the more I used my scope yesterday the smoother the 'trigger position' encoder worked to the point where it is usable without constantly bugging me.
Thanks all
Susan

 

[D.A.(Tony)Stewart]

Along with WD40 is smooth dithering of the rotor end to end back and forth to remove the oxide.

 

[std_match]

Dust can be a problem but normally it is the lack of gold plating for friction contact surfaces that is mandatory for I<2A since there is no wetting (deoxiding) current. All good switch contacts <=2A must have flash gold plated contacts, which can range from 5~25 um thick I recall. Cost reductions affect this.

From where did you get the 2A minimum current for other contacts than gold? Do you mean 2 mA?
From my time in the automotive industry, I remember that at least one manufacturer had minimum 4V open circuit voltage and minimum 10 mA current for tin-plated connectors.

 

[KlausST]

From my time in the automotive industry, I remember that at least one manufacturer had minimum 4V open circuit voltage and minimum 10 mA current for tin-plated connectors.

For very reliable long life ... I see both values as the absolute minimum.

So for really reliable operation I use the higher DC voltage that is available. Maybe 12V or 24V (I´m doing many industrial applications)
And then I sometimes add an RC to cause a bit of a "controlled" inrush current. 50mA or so.

In many applications this may be overkill ... but when you want to run it on bad conditions like
* humidity
* dust / dirt
* or contacts that are meant for switching power

Klaus

 

[D.A.(Tony)Stewart]

Tin plated reduces oxidation but increase contact Rs vs silver alloy relay and mech. switches. Thus suitable for sensor switches. So tin plating is an exception for cheap low current contacts. Otherwise you will find telecom always used gold plated contact for long life signal relays up to 2A. Often automotive designs use low ESR cap loads in circuits or high L loads to provide the arc for low current sensor wetting action (deoxidize contacts)

Notice I said all “good” (quality) contacts <=2A are Au plated yet some are inadequate with only a few microns of Au plating. Witness all Apple lightning plugs with a black stripe on either side from burn thru the plating on connecting the USB 1st and surge low ESR currents connecting a charge source. This was a fatal iOS device design flaw that had a plug failure rate of only a few hundred connections.