Behringer K900Fx disassembly

[svpribyl]

I need to replace the effects select knob but it’s not immediately obvious how to get to the electronics. Any hints on disassembly?

Thanks!

[Enzo]

What is your skill level?

From photos I see three chassis screws across the top. It is conceivable the handle also has to come off, but I doubt it. Then I also see three chassis screws along the bottom of the rear panel. And I see two chassis screws on either side panel along the rear edge.

Pull all those it ought to slide out the rear.

[svpribyl]

Hi Enzo,
The screws along the sides were the ones that I missed. It came apart just fine after that.
My brother is helping me with the electronics. He could replace the potentiometer if I can find a replacement. I was hoping there was a part number on the potentiometer, but none was visible. Do you have any idea how I might find the part number? I saw the schematic for the other Behringer amp on this forum, but it doesn't seem to have part numbers either.

Steve

[Delta362]

Take a photo or two of the pot. There should be some markings on the back and possibly near the terminals as another location that we can help decipher.

[svpribyl]

I'm not sure the best way to share photos. I uploaded them here:

https://ibb.co/mHnmPkK
https://ibb.co/wgCvQp9
https://ibb.co/dmDs5L7
https://ibb.co/72wZ68K

The rotary selector in question has a green housing. One of the photos is from the back.

Steve

[Delta362]

For some reason, I was thinking a pot on my brain, but looking at the photo, it's clearly marked as SW1. That's appears to be a 3 leg encoder. It could be absolute or incremental, I can't tell from your device. Something like the below to get you started. You'll need to check how many indentations to make a full rotation (PPR), does it have any stops, shaft length.

https://www.mouser.com/c/electromech...7C~Incremental

[Enzo]

It is more than a three-leg encoder, it is a three leg encoder with a push switch. It is incremental. You spin it to a number you like, then push to select.

I think I have a couple on a board to be pulled.

SOmething like this? https://www.mouser.com/ProductDetail...LwoVCNNg%3D%3D


How is the existing one bad?

[svpribyl]

The existing unit will rotate and the accompanying digital led display will change with the rotation, but the push-to-select feature isn't working. So it's stuck on selection #64! I wonder if the odd specks of dirt in the photos were caused by some kind of leakage. The amplifier still works, I just can't select a different effect.
The existing unit has 24 detents, the shaft is 3/4" long black plastic (for the knob to slide down on), and the housing is 1/2" square.
Enzo, yours looks very similar! Except the shaft is shorter than mine. I don't know if the existing knob that I pulled off would sit far enough down.

We are getting closer! You guys are great!

Steve

[Delta362]

The part number Enzo linked is PEC12R-4215F-S0024. The 15 in the number is their code for shaft length. Take a look at the datasheet attached to his part number and see which length of shaft matches yours. It could be 20mm as that's close to 3/4", but measure yours to be sure.

PEC12R-4220F-S0024 might be it.

https://www.mouser.com/c/electromech...~With%20Switch

[svpribyl]

I found this one, also. https://www.digikey.com/en/products/...22AF25/2620668
It's even green, like mine!

[g1]

I found this one, also. https://www.digikey.com/en/products/...22AF25/2620668
It's even green, like mine!

No switch in that one.
I think we have covered this issue before in a different thread, searching for 'behringer encoder' on this forum might find a sub someone has used.

[sugeda]

... P0381_service_RnD_Conf_GLOB_Overview_P0381_Service_Manual_2015-04-20_Rev.0.pdf

[Enzo]

I have two of them in my hand. Well. I set them down to type. They had been removed from a mixer panel from a Behringer PMH880 or similar.

[svpribyl]

I took the new component to meet with my brother. He just cleaned the existing one out with compressed air and it is working again. It's possible the shaft wasn't moving vertically far enough to engage the switch.
Thanks for all your help!

Steve

[Jazz P Bass]

Nice !