optical knob encoder: HP/Agilent 33120A freq generator, tuning-knob failure

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Alpha type 4D3-11 pot , footprint 9.6x 11.2mm. 2 wiper arcs about 7 and 9 mm long. Wiper metal 0.1mm thick x 0.3mm. Could not measure contact force in-situ. With wiper removed from recess, 10 gm would visibly move one wiper relative to the other. No visible track scoring under a x30 magnification. Of course , those old enough, would have come across the effect of hardening grease in cassette tape mechanisms then VCR. Where an arm pivots on an axle and return action is just a light torsion spring.

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Lots of video editing gear uses optical shaft encoders. Typical failure is bushing wearout that alters the alignment of the rotary vs fixed disk. You'll find excess axial 'play' and often side-side play as well. Some decent lubricant early on sold have increased the life.

G=B2

FWIW, the acrylic "body" of manu LEDs can be resized.. and leaving the emitting surface area untouched generally won't reduce the output.

I've reduced the diameter of common LEDs to fit where they normally wouldn't. The tiny emitting chip is very small compared to the size of the outer diameter of the acrylic. A pin vise can be used to hold the leads of a common (thru-hole) LED.

There are some applications where the tiny chips are used without acrylic bodies, and the very fine gage gold leads are attached directly to gold plated circuit board pads. A home bathroom scale had what looked like a 3-digit 7-segment display, but the separate LED chips were mounted to the board, and a plastic housing was placed over the LED chips (with colored film) which made it appear to be a normal 3-digit module.

-- Cheers, WB .............

Have you ever tried the Griffin Powermate? It has a lot better feel that the old Panasonic jog wheels I used to use to edit video.

NYE also sells laser printer fuser grease. After several aborted attempts at finding a cheaper substitute, I've resigned myself to using the overpriced real thing.

In a past life, I designed marine radios. Pots were always a problem. If "sealed", they would eventually condense some water out of the air, and rot. If vented, salt encrustation and corrosion would become a problem. Sealing the shaft was a big help, but re-lubrication was tricky.

However, ignoring all these mechanical problems, we did have problems with the grease on the resistance material. It would develop dead spots, where the wiper would not make contact, usually where the volume and squelch controls spent most of their time. It was obviously a lump of grease that the wiper was riding on top of, but what was the cause?

Basically, silicon grease (PDMS) will absorb small amounts of water and aromatic solvents. These bring with it salt from the marine atmosphere. The salt crystallizes out of solution, the grease encapsulates it, and we have a lump. I played around with various microscope filters for hours until I could see the tiny salt crystals imbedded in the grease. Nye sent us some sample greases, which were a big improvement and which became standard for re-lubrication.

You won't appreciate proper pot lube until after you try to operate a mobile radio or HT when it's really cold, and find all the controls stuck in place due to thickening of the lubricant.

I've never seen this wedging. I have seen salt lumps formed when the pot is left in one position for long periods, in a hostile atmosphere.

Easily dissimilar metals , Al and brass and sliding fit , then the naval saying. Cold enough to freeze the (iron canon) balls off a brass monkey (trivet)

Hey, Win:-

We had a mechanical encoder failure on a 33220A arb function generator. It is a known issue with these encoders and Agilent sent a repair kit gratis (or we could have sent it in). It's an easy fix, so I elected to do it myself.

Best regards, Spehro Pefhany

Here's the service note: