TDK-Lambda Nemic-Lambda Dodgy Knob

[gigavolt]

The labs I work for really likes to use these TDK-Lambda power supplies.  They're the little 2"x4"x18" units with a few buttons and a single knob on the front.  They seem nice, but I swear a solid 25% of them (like five at this point) have an issue where the knob on the front goes bad and only decrements the values on the screen.  IE you turn the knob clockwise on the voltage setpoint menu and it just decreases the voltage to zero (it's noisy and sometimes the voltage does go up a bit, but generally just decreases).  It makes them impossible to use except for remote control (fortunately how we mostly talk to them anyways, but still annoying).

Given how common this is in our lab it seems like a dodgy design and I thought I'd check here if anyone knows more / how to fix it.  A brief search revealed nothing.

[gigavolt]

OK, so I opened it up and the knob is a quadrature encoder.  Seems like both phases work fine enough but are a bit noisy if I watch them with a DMM.  Don't have anything nicer to look at it for the moment however.  Might try contact cleaner tomorrow.

Edit: And if I spend some time turning the knob back and forth quickly I can sort of make it work.  Probably wiping some dirt out of the encoder.  Crazy that this is a thing that happens regularly with these units.

[Jay_Diddy_B]

Hi,

I have had similar experience with four ZUP 60-7 power supplies.

I had to take the encoders apart. I cleaned the contacts with DeoxIT.

At the time I ordered EN16-H20AF15 from Digikey (987-1199-ND) as a spare part. I haven't tried these in a power supply. These are very reasonably priced.

Regards,
Jay_Diddy_B