Encoder [for dial knobs] polarity

[EugenioN]

Hi all!

I'm servicing a pro audio mixer (this one: https://www.soundcraft.com/en/products/si-impact), and I need a bunch of replacement rotary encoder. The genuine spares are quite an unobtainium stuff in small quantities, so I'm looking for a same specs, pin to pin compatible part.

I've come across this Bourns encoder: https://www.mouser.it/ProductDetail/Bourns/PEC11L-4015F-N0020?qs=sGAEpiMZZMvy8cVzszrmR8xmhWWclkAFml9Qhvp67z0%3D
They are the exact same size, same pulses per rev and same pinout, but I really can't understand this quadrature output table (from datasheet):
[ Specified attachment is not available ]

The measured signals are shown here:


It looks like A and B are swapped: when rotating CW I got rising edges of A (yellow) when B=HIGH (green) and viceversa during CCW rotation. The inversion occurs about at 200ms after trigger position. This is the opposite of every single quadrature encoder I've ever encountered, as per my experience.
The actual circuit is exactly the same as the one depicted in the datasheet: one common tied to gnd, the A and B switches connect to positive rail via a couple of pullup resistors.

Can those encoders be custom made for this specific product, with the only purpose of pissing off the service guy after discovering that 27 of those new little knobs turns the opposite direction than the old ones?
Am I missing something?

[Audiorepair]

It's possible the originals are reversed but unlikely.

More likely something got lost in translation with the data sheet/interpretation.

I have had a total of one rotary encoder replacement where the original was backwards, and one recently in a Sony Minidisk where the common was where one of the outputs normally are.


You are going to have to do this anyway, so just fit one in the desk and see which way round it goes.

[EugenioN]

Hi, I've just tested one brand new encoder and I can confirm: the original ones definitely have swapped A and B signals 

They're manufactured by AeTna (never heard of): rotational feedback torque is good and "smooth", and they seem of overall good quality, albeit the all failed in a short run.

These ones from Bourns are dimensionally identical, but with a less appealing and cheapish torque feedback: PEC11L-4015F-N0020 (datasheet here:https://www.mouser.it/datasheet/2/54/pec11l-777793.pdf)

Cheers!

[Audiorepair]

I have to say thats a pretty shitty trick from Soundcraft.

Or maybe they got conned.